U.S. patent application number 12/841289 was filed with the patent office on 2011-07-14 for gunshot detection system and method.
This patent application is currently assigned to ELTA SYSTEMS LTD.. Invention is credited to Gil Tidhar.
Application Number | 20110170798 12/841289 |
Document ID | / |
Family ID | 39768978 |
Filed Date | 2011-07-14 |
United States Patent
Application |
20110170798 |
Kind Code |
A1 |
Tidhar; Gil |
July 14, 2011 |
GUNSHOT DETECTION SYSTEM AND METHOD
Abstract
A device and a method for use in detection of a muzzle flash
event is described. The device can include a Photo Detector Array
(PDA), sensitive in at least a portion of the NIR and SWIR
spectrum, and a filter of electromagnetic radiation selectively
passing in this portion a spectral range of low atmospheric
transmission, the PDA has an integration time shorter than a
duration of the muzzle flash event.
Inventors: |
Tidhar; Gil; (Modiin,
IL) |
Assignee: |
ELTA SYSTEMS LTD.
Ashdod
IL
OPTIGO SYSTEMS LTD.
Lod
IL
|
Family ID: |
39768978 |
Appl. No.: |
12/841289 |
Filed: |
July 22, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/IL2008/000105 |
Jan 23, 2008 |
|
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12841289 |
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Current U.S.
Class: |
382/276 ;
250/338.4 |
Current CPC
Class: |
G01J 1/42 20130101; H04N
5/332 20130101; G01J 3/2803 20130101; H04N 5/33 20130101 |
Class at
Publication: |
382/276 ;
250/338.4 |
International
Class: |
G06K 9/36 20060101
G06K009/36; H01L 27/14 20060101 H01L027/14 |
Claims
1. A method for use in detection of a muzzle flash event, the
method comprising sensing electromagnetic radiation by a Photo
Detector Array (PDA), sensitive in at least a portion of the NIR
and SWIR spectrum, wherein said electromagnetic radiation passed
through a filter of electromagnetic radiation configured and
operable for selectively passing, in said at least portion of the
NIR and SWIR spectrum, a spectral range of low atmospheric
transmission, said sensing having an integration time shorter than
a duration of the muzzle flash event.
2. The method of claim 1, wherein said time is shorter than
10.sup.-2 s.
3-62. (canceled)
63. The method of claim 1, the utilized sensing at least for a part
being performed within the NIR spectrum.
64. The method of claim 1, the utilized sensing at least for a part
being performed within the SWIR spectrum.
65. The method of claim 1, the PDA having a sensitivity maximum at
a wavelength longer than 3 microns and a sensitivity cut-off at a
wavelength shorter than 5 microns.
66. The method of claim 1, the PDA having a sensitivity maximum at
a wavelength shorter than 3 microns.
67. The method of claim 66, the PDA having a sensitivity cut-off at
a wavelength shorter than 5 microns.
68. The method of claim 66, the PDA having a sensitivity cut-off at
a wavelength between 1.4 .mu.m and 1.65 .mu.m.
69. The method of claim 66, the PDA having a sensitivity cut-off at
a wavelength 1.65 .mu.m and 1.8 .mu.m.
70. The method of claim 66, the PDA having a sensitivity cut-off at
a wavelength between 1.8 .mu.m and 2.5 .mu.m.
71. The method of claim 1, the PDA having a sensitivity maximum at
a wavelength longer than 0.75 microns.
72. The method of claim 1, the PDA having a region of a predominant
sensitivity fully within the NIR/SWIR range, said region being a
region where the sensitivity is higher than 20% of a maximum PDA's
sensitivity.
73. The method of claim 72, wherein the predominant sensitivity is
higher than 35% of a maximum PDA's sensitivity.
74. The method of claim 72, wherein the predominant sensitivity is
higher than 50% of the maximum PDA's sensitivity.
75. The method of claim 72, wherein the predominant sensitivity is
higher than 70% of a maximum PDA's sensitivity.
76-85. (canceled)
86. The method of claim 1, the sensing being substantially within a
range of low atmospheric light transmission at least partially
including the trough situated around 1.15 .mu.m (micron).
87. The method of claim 1, the sensing being substantially within a
range of low atmospheric light transmission at least partially
including a trough extending from 1.34 .mu.m to 1.50 .mu.m.
88. The method of claim 1, the sensing being substantially within a
range of low atmospheric light transmission at least partially
including a trough extending from 1.80 .mu.m to 2.00 .mu.m.
89. The method of claim 1, the sensing being substantially within a
range of low atmospheric light transmission at least partially
including a trough extending from 2.50 .mu.m to 2.90 .mu.m.
90. The method of claim 1, the PDA being a CMOS PDA.
91. The method of claim 1, the PDA being an intracavity PDA.
92. The method of claim 1, an integration time of the sensing being
between 10.sup.-2 s and 5.010.sup.-3 s.
93. The method of claim 1, an integration time of the sensing being
between 5.010.sup.-3 s and 2.010.sup.-3 s.
94. The method of claim 1, an integration time of the sensing being
between 2.010.sup.-3 s and 5.010.sup.-4 s.
95. The method of 1, an integration time of the sensing being
between 5.010.sup.-4 s and 10.sup.-4 s.
96. (canceled)
97. A device for use in detection of a muzzle flash event, the
device comprising a Photo Detector Array (PDA), sensitive in at
least a portion of the NIR and SWIR spectrum, and a filter of
electromagnetic radiation selectively passing in said portion a
spectral range of low atmospheric transmission, the PDA having an
integration time shorter than a duration of the muzzle flash
event.
98. The of claim 7, wherein said integration time is shorter than
10.sup.-2 s.
99-163. (canceled)
164. The device of claim 97, the PDA at least partially being
sensitive within the NIR spectrum.
165. The device of any one of claim 97, the PDA at least partially
being sensitive within the SWIR spectrum.
166. The device of any one of claim 97, the PDA having a
sensitivity maximum at a wavelength longer than 3 microns and a
sensitivity cut-off at a wavelength shorter than 5 microns.
167. The device of claim 97, the PDA having a sensitivity maximum
at a wavelength shorter than 3 microns.
168. The device of claim 167, the PDA having a sensitivity cut-off
at a wavelength shorter than 5 microns.
169. The device of claim 168, the PDA having a sensitivity cut-off
at a wavelength between 1.4 .mu.m and 1.65 .mu.m.
170. The device of claim 168, the PDA having a sensitivity cut-off
at a wavelength 1.65 .mu.m and 1.8 .mu.m.
171. The device of claim 168, the PDA having a sensitivity cut-off
at a wavelength between 1.8 .mu.m and 2.5 .mu.m.
172. The device of any one of claim 97, the PDA having a
sensitivity maximum at a wavelength longer than 0.75 microns.
173. The device of claim 97, the PDA having a region of a
predominant sensitivity fully within the NIR/SWIR range, said
region being a region where the sensitivity is higher than 20% of a
maximum PDA's sensitivity.
174. The device of claim 173, wherein the predominant sensitivity
is higher than 35% of a maximum PDA's sensitivity.
175. The device of claim 173, wherein the predominant sensitivity
is higher than 50% of the maximum PDA's sensitivity.
176. The device of claim 173, wherein the predominant sensitivity
is higher than 70% of a maximum PDA's sensitivity.
177-186. (canceled)
187. The device of claim 97, the device adapted to sense
electromagnetic radiation substantially within a range of low
atmospheric light transmission at least partially including the
trough situated around 1.15 .mu.m (micron).
188. The device of claim 97, the device adapted to sense
electromagnetic radiation substantially within a range of low
atmospheric light transmission at least partially including a
trough extending from 1.34 .mu.m to 1.50 .mu.m.
189. The device of claim 97, the device adapted to sense
electromagnetic radiation substantially within a range of low
atmospheric light transmission at least partially including a
trough extending from 1.80 .mu.m to 2.00 .mu.m.
190. The device of claim 97, the device adapted to sense
electromagnetic radiation substantially within a range of low
atmospheric light transmission at least partially including a
trough extending from 2.50 .mu.m to 2.90 .mu.m.
191. The device of claim 97, the PDA being a CMOS PDA.
192. The device of claim 97, the PDA being an intracavity PDA.
193. The device of claim 97, an integration time of the PDA sensing
being between 10.sup.-2 s and 5.010.sup.-3 s.
194. The device of claim 97, an integration time of the PDA sensing
being between 5.010.sup.-3 s and 2.010.sup.-3 s.
195. The device of claim 97, an integration time of the PDA sensing
being between 2.010.sup.-3 s and 5.010.sup.-4 s.
196. The device of claim 97, an integration time of the PDA sensing
being between 5.010.sup.-4 s and 10.sup.-4 s.
197. (canceled)
198. (canceled)
199. (canceled)
200. The device of claim 97, wherein said filter passes less than
50% of energy of wavelengths being outside said spectral range of
low atmospheric transmission and sensed by the PDA.
201. The device of claim 97, wherein said filter passes less than
25% of energy of wavelengths being outside said spectral range of
low atmospheric transmission and sensed by the PDA.
202. The device of claim 97, wherein said filter passes less than
10% of energy of wavelengths being outside said spectral range of
low atmospheric transmission and sensed by the PDA.
203. The device of claim 97, wherein said filter passes less than
2% of energy of wavelengths being outside said spectral range of
low atmospheric transmission and sensed by the PDA.
204. The device of claim 200 having for at least one wavelength of
said spectral range a sensitivity between 50% and 75% of the
sensitivity of the PDA.
205. The device of claim 200 having for at least one wavelength of
said spectral range a sensitivity larger than 75% of the
sensitivity of the PDA.
206. A processing unit for use in detection of a muzzle flash
event, said processing unit being adapted to process pixel signals
originating from a PDA and to generate substantially likelihoods of
muzzle flash detection for pixels of the PDA, the processing unit
comprising a multiplexer dividing the pixel signals between at
least two branches.
207-209. (canceled)
Description
RELATED APPLICATIONS
[0001] This application is a Continuation of International
Application No. PCT/IL2008/000105 filed on Jan. 23, 2008, which is
incorporated herein in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to the field of detection and
location of high speed photon emitting events, of firearms
gunshots, and particularly of muzzle flashes.
BACKGROUND OF THE INVENTION
[0003] There are various methods that can be used for snipers
detection and locating weapon fire, including small arms. The
phenomena utilized by these methods include the so-called muzzle
blast and flash; the shock wave, vortex, and thermal signature of
the bullet in flight; and retro-reflection from the sniper's
optical sight. Other phenomena, for instance disturbances of the
refractive index of atmosphere caused by vortices shed by the
bullet in flight, can potentially be utilized for snipers
detection.
[0004] One of the optical signals caused by weapon firing is the
muzzle flash, which is the incandescent flash at the weapons muzzle
caused by the ignition of oxygen, the expulsion of burning powder
grains and the expansion of powder gasses. The phenomenon of muzzle
flash is more clearly pronounced in various assault rifles, short
barrel infantry weapons, and "cut down" weapons. For instance, in a
short barrel, the bullet can leave the barrel before the powder is
completely burnt. In this case, the unburnt powder ignites in the
air, giving off a bright flash. For a shooter, muzzle flash
presents a serious problem: it increases the shooter visibility to
the enemy and obscures the target view. As a result, the shooter
using a weapon generating muzzle flash must move quickly after
firing to avoid return fire.
[0005] Although muzzle flash can be partially hidden by flash
suppressors or partially reduced by using cartridges with a
faster-burning gunpowder, so that the propellant gases will already
have begun to cool by the time they exit the barrel, this is not
always convenient for the shooter. For example, the size of a
device necessary to hide the muzzle flash from an enemy can be too
large.
[0006] For the side opposite to a shooter, a problem consists in a
muzzle flash detection, which can be considered as one of high
speed imaging applications. For purposes of study, such detection
can be done in the laboratory.
[0007] At the present time, a few muzzle flash detecting systems
can be used in the battle field. Examples of such systems include
Radiance Technologies' WeaponWatch.TM., RAFAEL's SPOTLITE, Maryland
Advanced Development Lab's VIPER. The VIPER equipment, for example,
consists of a mid-wave infrared (MWIR) camera, together with
real-time signal processing, magnetic compass, and user display and
alarm. It is advertised as providing gun detection within 70 msec
after gunfire and geolocation of the firing event. Using
MWIR-camera also allows concurrently performing forward looking
infrared imaging (FUR) of a region of interest.
[0008] The known snipers detection methods also suffer from various
problems. One of the problems associated with MWIR cameras, is that
these cameras are expensive and bulky. Most of them are based on
cryogenically cooled fast refresh-rate detectors.
[0009] Uncooled infrared sensors for an integrated sniper location
system were studied in [8]. The system of [8] had a focal plan
array size of 320.times.240 pixels allowing a field of view of 20
(H).times.15 (V) degrees with an accuracy of 2 mrad. The system's
weight was 5 pounds, frame rate 60 Hz, size 12.2 (L).times.5.0
(W).times.4.1 (H) inches, noise equivalent input 5.6.times.10-12
W/cm2, and power consumption 9V. The projected price of the device
was about $10,000. The uncooled bolometric detectors are typically
significantly slower than the muzzle flash, and thus the signal is
smeared over a long time harming the signal to noise ratio (SNR).
These detectors are mostly sensitive to the 8-12 um range, where
the signature is relatively low.
[0010] Other countersniper systems, such as relying on acoustic
signals (e.g. muzzle blast and bullet shock wave), may be lighter
and lower in cost than systems based on cooled detectors. However,
the acoustic countersniper systems typically have low angular
accuracy and performance which is reduced in urban terrain, due to
sound reflections.
[0011] Also, detection of rifle, sniper and small arm shooting or
firing can be in principle done by the solar blind UV (SBUV)
imaging technology and used for force protection and snipers
detection. The UV signature of the firing is due to the secondary
burning of the residual gun powder, ejected from the barrel.
Nevertheless, this signature is also relatively small and may not
provide usable detection range and acceptable false alarm rate.
Some design and manufacturing of SBUV imaging systems is done, for
example, by Ofil LTD (http://www.sbuv.com).
[0012] In principle, various detection methods can be combined with
each other. Also, a muzzle flash detected by any method can be
shown on a scenery image obtained by imaging with visible light.
For example, technology of the Ofil LTD utilizes a bi-spectral
visible-UV DayCor.RTM. camera and is aimed and presenting such
combined images.
SUMMARY OF THE INVENTION
[0013] There is a need in the art in facilitating detection and
location of high speed photon emitting events, of firearms
gunshots, and of muzzle flashes by providing a novel fast event
detection technique allowing effective detection. A presented here
novel technique, constructed by the inventors, has adaptations
(versions and embodiments) useful for such detection.
[0014] The main idea of the technique of the inventors applied for
example for gunshot detection, is to utilize imaging of light in
spectra of relatively short-living and low power muzzle flash
components, which though allow achieving a relatively high useful
detector signal. The technique may utilize one or more of the
following: filtering electromagnetic radiation for acquiring
substantially a spectral range corresponding to relatively low
light transmission in atmosphere; collecting and sensing
electromagnetic radiation in near infrared (NIR) and/or short wave
infrared (SWIR) ranges; acquiring pixel images with a relatively
small integration (exposure) time or high imaging frame rate;
acquiring sequential images with a relatively small dead time
between them; acquiring images with a relatively wide field of view
(FOV) for a pixel or for a given number of pixels at the light
detector; acquiring multipixel images of a scenery; processing
outputs of the photodetector (imager) pixels for detection of a
flash-type signal portion in the detected light. For example, the
processing may select, for any pixel, a signal portion indicative
of muzzle flash type intensity variation in time. For another
example, the processing may estimate, for any pixel, a likelihood
of occurrence of a muzzle flash event, e.g. by comparing a signal
obtained from the pixel with the time signature of muzzle flash.
The processing may be organized in layers (stages), consecutively
processing a smaller number of pixels. For example, the layers may
be organized to consecutively reestimate the likelihoods of
occurrence of muzzle flash events for a smaller number of pixels at
each layer. Processing may be parallel at some layer; however the
technique of the inventors may as well utilize non-parallel layers
of processing for reducing data bandwidth. For example, the
processing may have a layer at which a signal obtained from a pixel
is compared to signals obtained from adjacent or close pixels, and
if time signatures of a group of such pixels are similar, a
possible muzzle flash alarm is suppressed. The processing layers
may be connected by pixel selection units, decreasing number of
"candidate" pixels processed at the later stage. Each pixel
selection unit transmits a list of the "candidate" pixels from an
earlier layer to a later layer. For example, a pixel selection
layer may be adapted to transmit a limited or a constant number of
"candidate" pixels from each frame, by selecting pixels with the
highest likelihoods of occurrence of muzzle flash. If output of a
processing layer is not the likelihoods, but for example a signal
portion indicative of muzzle flash type intensity variation in time
(as mentioned above), the consecutive pixel selection layer
generates pixels likelihoods. In this sense, a pixel selection
layer is complementary to its preceding processing layer. However,
the inventors do not require always having a pixel selection layer
for each processing layer: outputs of the latter may be for example
directed to a memory rather than to the former. In addition to the
list of the "candidate" pixels, a processing layer will need
additional data for (re)estimating muzzle flash likelihoods. For
example, temporal and/or spatial information on outputs of various
processing stages and/or of the Photo Detector Array (PDA, e.g.
photo diode array) may be needed. The needed data may be stored in
a memory unit configured for access by the layer. Before data are
stored, they may be compressed or sampled with a reduced sampling
rate (relatively to the output of the corresponding data source
stage). The compression can be performed in a compressing module.
The processing may have analog and digital layers, where the first
of digital layers is preceded by an analog-to-digital converter
(ADC).
[0015] The technique of the inventors can be used for detection and
location of strobe light sources, pulsed lasers, lightnings, as
well as antitank missile launches and shell firings.
[0016] With regards to the wavelengths useful for detection of
muzzle flash, the inventors have considered that the detection can
be facilitated in some of its aspects by using imagers (e.g. based
on PDAs), predominantly sensitive in near-infrared (NIR) and/or
short-wave infrared (SWIR) region: in contrast to MWIR/LWIR
imagers, NIR/SWIR imagers typically need not be cooled. Partially
due to this fact, partially due to other reasons, NIR/SWIR imagers
also may be lighter, less expensive, and less power-consuming than
MWIR/LWIR imagers, especially when the MWIR/LWIR imagers are
considered together with their respective coolers and portable
power supplies. NIR/SWIR imagers (particularly, NIR/SWIR PDAs)
include many types of silicon imagers, which typically are
sensitive up to about 1050 nm, and many types of InGaAs imagers
(i.e. PDAs), which typically are predominantly sensitive in a band
starting from around 950 nm and ending somewhere between 1700 and
2500 nm (NIR/SWIR), depending on the specific InGaAs composition.
SWIR imagers include some types of Mercury Cadmium Telluride (MCT)
imagers. Imagers' sensitivity bands depend not only on their
materials, but also on their structures (e.g. quantum structures).
A typical sensitivity band has a sharp decline after a sensitivity
maximum and ends with a long-wavelength cutoff. In some
embodiments, an imager or imager arrangement of the technique of
the inventors has a long-wavelength cutoff longer than 3 .mu.m
(i.e. the SWIR region edge) while this imager is used for NIR/SWIR
imaging; such a long-wavelength cutoff can be useful for example
when the imaging is to be done in a broad region within the
NIR/SWIR range. In some other embodiments the imager has a cutoff
shorter than 3 .mu.m (this relates to those qualities of the
typical shorter wavelength imagers that have been discussed above).
In some embodiments the cutoff is between 0.75 and 1 .mu.m, in
others it is 1 .mu.m and 1.4 .mu.m, in some others it is between
1.4 .mu.m and 1.65 .mu.m, in yet others it is between 1.65 .mu.m
and 1.8 .mu.m, in yet some others it is between 1.8 .mu.m and 2.5
.mu.m. In some embodiments, it is the sensitivity maximum that is
at a wavelength shorter than 3 .mu.m or alternatively constrained
within the specified ranges. Also, in some adaptations, the imager
has a sensitivity maximum being at a wavelength longer than 3
.mu.m, so as to utilize a relatively flat region of growth of the
sensitivity band, but has a cutoff shorter than about 5 .mu.m, so
as to utilize this region of growth not too far away from the
band's maximum, i.e. while the sensitivity is already relatively
high.
[0017] The selection of the photodetector material and sensitivity
band parameters can depend for example on type of event or muzzle
flash to be detected and on the presence/absence of clutter and the
low light atmosphere transmission optical filter. In particular, in
some embodiments the wavelength of the sensitivity band maximum is
close to or is aligned with one of the atmospheric absorption
peaks, so that the imager is utilized efficiently. The imager
operation is efficient if it occurs in a range where the imager's
sensitivity is more than 20% (or, according to alternative
definitions, 35%, 50%, and 70%) than the imager's sensitivity
maximum. Thus defined range (i.e. defined according to one of the
alternatives) constitutes a predominant range of the imager
sensitivity. However, it should be noted, that the efficient use of
imager is not a requirement: the sensitivity of the PDA may be
sacrificed for other factors, such as response time. Also, a not so
efficiently used imager of one type may still be more sensitive
than an efficiently used imager of another type. Any imager can be
used as long as it is suitably sensitive.
[0018] Additionally, for NIR/SWIR imaging, the sensitivity maximum
of the imager may be kept at a wavelength longer than 0.75 .mu.m
for achieving higher efficiency. Although some NIR/SWIR imaging may
be performed if the sensitivity maximum is shorter than 0.75 .mu.m
and the cutoff is longer than 0.75 .mu.m.
[0019] It should be understood that the above sensitivity
considerations are relevant for the sensitivity as measured in
circumstances of the imager operation. The sensitivity is dependent
on temperature. The operation temperature of the PDA may be lower
than -30.degree. C., or between -30.degree. C. and 0.degree. C., or
between 0.degree. C. and a PDA's ambient temperature (while it is
higher than 0.degree. C.), or higher than the PDA's ambient
temperature. The latter option for the PDA selection (i.e. for the
PDA operation temperature selection) is used in some of the
adaptations in which the portability is a goal; it would require no
cooler or would require only a weak cooler. The ambient temperature
is the temperature which the PDA would have had the device be not
turned on. If there is anything external to the device (e.g.
support) or anyone else (e.g. the user) that heats the imager, this
would affect the ambient temperature, which by default would be a
weather temperature. For the operation temperature to be in the
desired range, cooling, when necessary, may be provided by
cryogenic coolers in the coolest of these ranges or, for example,
by thermoelectric coolers in hotter ranges. Cooling may be or may
not be necessary in the hottest of the ranges. For the above
temperature ranging it was considered that weather/ambient
temperature is often above 0.degree. C.; it is understood, however,
that the device may be used at the ambient temperature which is
below 0.degree. C. and, possibly, even -30.degree. C.: in this case
the device may be configured or adapted to have not to have a
cooler or have only a weak cooler. If cooling is used, then
focusing optics (and/or filter) may also be mounted within the
respective cooled region.
[0020] For the purposes of the present application, the limits of
infrared ranges are defined here: NIR 0.75-1.0 .mu.m; SWIR 1.0-3
.mu.m; MWIR 3-8 .mu.m; LWIR 8-14 .mu.m. Thus defined ranges
correspond to commonly accepted infrared nomenclatures. For
example, within the SWIR range there are several absorption peaks
of water and carbon dioxide: at approximately 1.15 .mu.m, 1.39
.mu.m, 1.9 .mu.m, and 2.7 .mu.m. The absorption peaks are commonly
known and some of them are shown on some of the figures referenced
below.
[0021] The technique of the inventors may utilize a detector unit
configured to have, inter alia, a narrow spectral band filter
corresponding to low light transmission in the atmosphere. Such a
filter may increase, in some scenarios, signal to clutter and
signal to shot noise ratios. In typical muzzle flash detection
systems, the spectral band utilized for detection is wide and
corresponds to the highest transmission atmospheric windows. In
some embodiments of the invention, detection may be performed in
the narrow range(s) of the least atmospheric transmission, because
though a large portion of the muzzle flash signal would be lost
with the introduction of the narrow filter, the reduction of
sunlight clutter and the shot noise would be more drastic and would
overcompensate the reduction in the informative optical signal, if
only the remaining portion of the latter is above the sensitivity
threshold.
[0022] The technique of the inventors may utilize acquiring images
with a relatively small integration (exposure) time and/or high
frame rate. In particular, in some adaptations of the technique,
the integration time is selected to be substantially equal or
smaller than the duration of existence of the muzzle flash
components which to be detected (this duration can be defined as a
time interval between the moments at which the detected radiation
intensity equals half of the maximum detected radiation intensity).
The integration time can be defined as a time between resetting a
pixel and subsequent reading a pixel or a duration of a time period
during which photons collected by a pixel are transformed to
electrons of a single signal reading from a pixel. The rationale
behind the choice of the integration time is in that imaging for a
time longer than the duration of the detection muzzle flash portion
would collect rather clutter and noise than a useful signal. The
technique may use integration time between The PDA integration time
may be between 10-2 s and 5.010-3 s, or between 5.010-3 s and
2.010-3 s, or between 2.010-3 s and 5.010-4 s, or between 5.010-4 s
and 10-4 s, or it might be less than 10-4 s.
[0023] The desired integration time can be set by an appropriate
shutter, particularly an electronic shutter. It should be noted
that the technique of the inventors may utilize acquiring images
with a relatively long integration time, for example longer than
the pulse duration. Nevertheless, in the case of integration time
longer than the pulse duration, the smaller is the integration
time, the better is the signal to noise ratio and signal to clutter
ratio. Moreover, better signal to noise and signal to clutter
margins allows enlarging the Instantaneous Field Of View (IFOV)
(e.g. by decreasing the focal length of the imaging lens) and thus,
for a given pixel count, allows increasing the entire Field Of View
(FOV). With integration time shorter than the pulse duration, the
inventors' technique can also benefit from analyzing the time
signature of the detected signal.
[0024] The technique of the inventors may utilize acquiring
sequential images with a relatively small dead time between them.
The dead time can be defined as a time between reading a pixel and
subsequent resetting a pixel. The signal (e.g. charge) generated at
the pixel during the dead time gets lost. In some adaptations of
the technique the dead time is selected to be less than the
detected muzzle flash duration (or a predetermined part of the
detected muzzle flash duration, such as one tenth). In particular,
the technique may be adapted to use dead time under a millisecond.
The desired dead time can be set by an appropriate shutter scheme,
for example by a rolling shutter.
[0025] The technique of the inventors allows detection of muzzle
flashes in a relatively wide PDA field of view or per pixel field
of view. Consider, for example, a muzzle flash occurring at a
certain distance that gets projected on a pixel. The same muzzle
flash occurring further from the imager will then be projected on a
spot smaller than a pixel; and the pixel then will generally
collect more clutter and less signal (in particular because a
smaller portion of signal will propagate towards the imager and
because this smaller portion will undergo more absorption in the
atmosphere). This will result in a lower signal to clutter ratio
and a lower chance of successful muzzle flash detection. Thus, for
a desired distance of detection a pixel should not collect light
from a too broad region. Though, it can be concluded that the
projection spot for a muzzle flash may be smaller than a pixel (in
one or two dimensions) and yet allow detection, if optical
resolution allows.
[0026] It should be noted, that the useful number of pixels is tied
with various factors such as the photodetector architecture and the
complexity of processing used for detection. Thus, the useful field
of view of an exemplary PDA's pixel and the field of view of the
photodetector itself depend on a type of detection being
implemented. The field of view of a single pixel may be selected to
be relatively wide, so as to correspond, for example, to the size
of a muzzle flash occurring at a distance smaller than a few tens
of meters. Typically, muzzle flash would occur at a distance larger
than that, and would cover area smaller than a pixel. In accordance
with the above, when muzzle flash occurs, the pixel signal would be
a sum of a signal due to the background and of a signal due to the
muzzle flash. The background typically changes slowly, so if a fast
change in the total pixel signal is detected, this makes the pixel
a candidate for the processing aimed at checking muzzle flash
occurrence. The wider the pixel's field of view, the smaller the
relative part of the muzzle flash signal in the total pixel signal,
for the desired range of detection. Therefore, there is a trade-off
between the achievable range and pixel field of view. While the
desired range is achieved, the total field of view can be increased
by increasing a number of pixels in the detector. The increased
total field of view is preferred when it is desired to detect shots
from as many directions as possible. However, using a too large
pixel count might require too expensive optical and computational
hardware, and too much power for operation. In some adaptations of
the technique of the inventors the divergence angle of the field of
view of a single pixel is selected to be between 0.1 and 0.2
degrees, or between 0.2 and 0.5 degrees, or larger than 0.5
degrees. In some adaptations of the technique the field of view of
the photodetector is selected to be between 30 and 50 degrees, or
between 50 and 90 degrees, or larger than 90 degrees, in at least
one dimension. The desired field of view may be created by
appropriate optics with a focal length selected to project the
filed of view on the detector surface.
[0027] The technique of the inventors may advantageously utilize
acquiring multipixel images of scenery. In some adaptations of the
technique the imager is selected to have between 10,000 and 100,000
pixels, or between 100,000 and 1,000,000 pixels, or it may be
suitably more than 1,000,000 pixels. Using the multipixel imaging,
muzzle flash locating may be performed relatively accurately and
precisely. The muzzle flash lateral location is, to a large degree,
determined by the imaged direction of a pixel or group of pixels
which detected the muzzle flash. The muzzle flash longitudinal
location is, to a large degree, determined by the intensity of the
received signal and shape of the pixel group which detected the
muzzle flash.
[0028] The muzzle flash detecting processing, which particular
example is parallel processing, may be performed by a unit
configured to apply such operations to the pixels outputs as single
or multiple (in particular double) signal differentiating, peak
detecting, bandpass filtering, match filtering and/or other
operations aimed at selecting or detecting muzzle flash type
signal(s) from the detected signals. An output signal obtained as a
result of a single pixel processing (e.g. an output signal of
obtained from a pixel of the parallel processing unit) may be
interpreted for estimating likelihood that the corresponding PDA
pixel has detected a muzzle flash. For example, the likelihood may
be contained in the output of the match filter. If the likelihood
is larger than a certain threshold, the event may be interpreted as
a muzzle flash or a candidate muzzle flash, and a signal (alarm)
intended to inform an operator or a user about the shot may be
produced, or a candidate alarm may be transferred to a next layer
or stage of processing.
[0029] As it has been mentioned above, the processing unit can be
organized in layers or stages. The filtering performed by one stage
of the muzzle flash selecting processing unit can effectively
reduce an amount of data for processing to be performed at further
stages, thus allowing to apply to the reduced amount of data a more
complex processing and to reduce requirements for the technical
characteristics needed at a particular stage of the muzzle flash
detector. In some embodiments of the technique of the inventors,
the processing is performed in stages, with a parallel stage aimed
at analyzing time-dependences of pixels outputs being the first or
one of the first stages. The parallel layer of processing can be
combined with a module for selection of pixels which most likely
detected muzzle flash. A further (e.g. the second) stage thus can
receive a list of candidate pixels from the module. This further
layer of processing then may process this pixel list, by obtaining
from a corresponding memory unit data needed for reestimation of
likelihoods of muzzle flash event for pixels from the list. The
data needed for reestimation may include historical data of pixels
from the list and historical data of pixels situated close to the
pixels from the list. The historical data may include previously
generated outputs of various processing stages, pixel selection
modules, and of the PDA. The historical data, before they are
stored in the memory, may be compressed. For example, PDA outputs
may be divided so that one replica will follow to the first layer
of processing and another replica(s) will follow to a compression
module(s) and then to a memory unit(s). Thus, the memory unit can
be used to store historical data for all pixels.
[0030] Likewise, the data to be used for reestimation may be or
include data obtained after a candidate event, in addition to the
historical data, as the processing does not have to be immediate,
and in fact may benefit from taking into account information
gathered after the candidate event had occurred. In this case, to
obtain the same quality of detection, the memory unit may be used
to store only a portion of volume of the historical data, because
the data may be gathered more intelligently when the candidate
pixels are known.
[0031] The staged (layered) processing allows decreasing power
consumption of the detector and weight of the needed power supply
and increases a maximum allowed input data bandwidth (e.g. number
of pixels in the PDA and the breadth of the field of view) and the
portability of the detector.
[0032] Layer(s) of processing may be combined by such pixel
selection utilities, as Constant False Alarm Rate module(s) (CFAR
modules), which confirm/suppress the candidate alarms for the same
number of suspicious pixels per frame (or a certain number of
pixels of the PDA) or time interval. The use of CFAR technique
allows not to jam a next processing stage of the detection system,
but to keep maximal probability of muzzle flash detection. The CFAR
module is one of possible pixel selection modules.
[0033] The parallel processing can include parallel analog in-pixel
signal processing done by a corresponding processing (sub)unit. The
parallel analog processing unit can be based, for example, on the
hybrid detector technology not requiring compromising in-pixel
processing power or array fill factor. In some embodiments the fill
factor of the PDA is between 60% and 75%, in some others it is
between 75% and 90%; in some other embodiments it is higher than
90%. The fill factor may be also outside of the specified regions,
however, typically, the higher the fill factor, the higher the
chance of muzzle flash detection for remote muzzle flashes. In
particular, close to 100% fill factor almost eliminates the chance
that the remote muzzle flash will be projected on the dead area
(where the PDA is not sensitive). In addition, even for not so
remote muzzle flashes, the higher is the fill factor, the higher is
the collectable signal. The hybrid detector can be fabricated as a
Read Out Integrated Circuit (ROIC) with in-pixel signal processing
flip-chip bonded to photodiode or other photodetector array.
[0034] The parallel in-pixel signal processing may also be done in
a separate electronics module (not in the ROIC). The parallel
processing of the PDA pixels' outputs can include analog-to-digital
conversion and processing of the digital data by a field
programmable gate array (FPGA). The term parallel should be
distinguished from simultaneous in the context of the present
application: the parallel processing can be either simultaneous or
not. If pixels' outputs are processed independently of each other,
such processing is parallel, independently on order in which their
processing is performed. The parallel processing is parallel to an
extent allowed by cross-talk.
[0035] After the first, time-dependence analyzing and possibly
parallel, layer or stage of processing, there may be other layers
of processing, further testing pixels for presence of gunshot
events. For example, a second (or further) layer of processing may
be configured to operate in the following way. It may select and
analyze one or several candidate or suspicious events, i.e. signals
coming from pixels which have been determined by the first layer
processing, for example including a CFAR module, to have high
likelihood of detecting muzzle flash events. For each of the
suspicious pixels (candidate pixels) the second layer of processing
reestimates the likelihood that this pixel detected a muzzle flash.
Since the second layer analyzes a smaller dataset that the first
layer, it may use more sophisticated algorithms or processing,
requiring higher computing time and power per pixel, to better
distinguish between muzzle flash, noise and clutter. For this
purpose, the second layer of processing may use signals obtained
from neighboring or close pixels and/or signals obtained at close
time moments. For example, the second layer may be configured to
check whether an event is repeated for several adjacent or close
pixels and propagates along a straight line on the PDA. If the case
is such, the source of the moving event (i.e. of a sequence of
events) may be identified as a moving object rather than a muzzle
flash. Thus the invented detection system eliminates events lasting
too long time or passing too long distance: for example, level-1
may eliminate most of the events lasting too long within one pixel
over time, while level-2 may eliminate events lasting too long in
the entire frame, though lasting for a relatively short time in
each of the involved pixels. The closeness or relative location in
space of the involved pixels allows inferring that the sequence of
events is not a sequence of the independent events, but a single
moving event.
[0036] The second layer of processing may be fed with data in the
Constant False Alarm Rate regime and confirm/suppress the candidate
events/alarms for a constant predetermined number of suspicious
pixels without jamming the detection system. The confirmed alarms
can be passed to an operator or a user of the detection system
(e.g. by an optical signal or a sound).
[0037] The reasons why some of the preferred embodiments of the
invented technique use at least two layers of signal processing can
be illustrated by the following consideration. The system of the
invention may need to make for example of decisions per second.
This number is obtained assuming a frame rate of 500 per second and
a PDA of 200,000 pixels. The inventors assumed that a final false
alarm rate (FAR) of not less than approximately 1/3 hours is
desired. Then, only one false alarm is allowed in every decisions.
In such a case, if one would apply the most sophisticated algorithm
or processing to each of the pixels all the time (at the PDA frame
rate), the algorithm would use a lot of computing power. Thus, to
save the power, the inventors in some cases choose to split the
processing into layers, to utilize more efficient computing power
scheme.
[0038] In some of the embodiments the reduction of data bandwidth
is 3-9 orders of magnitude per layer. The reduction of data
bandwidth can be understood as a reduction of number of potential
alarms: the layers reduce their number from the original pixel rate
(number of pixels in PDA times the sampling rate) to the maximum
allowed FAR. The layers may eliminate also true events, however the
probability of detection (Pd) is kept high. For example, detection
with a probability of success of over 80% and allowed FAR of not
more than 1 per 3 hours (i.e. approximately 1 per 104 seconds) may
be considered. By utilizing a PDA with 2.times.105 pixels and frame
rate of 500 per second, a designed detection system obtained
2.times.105.times.500=108 samples per second. Accordingly, the
specified FAR corresponded to 1 false alarm per 1012 sampled
pixels. The first layer detected at least 90% of true events, and
falsely detected muzzle flash in average in 1 case per 105 sampled
pixels (i.e. defined some pixel as a candidate while that pixel did
not correspond to the muzzle flash). The designed second layer
detected at least 90% of true events, and falsely detected muzzle
flash in average in 1 case per 107 sampled pixels. The combined
performance of the system therefore was characterized by the
probability of detection of 81% (90% times 90%) and the FAR of 10-4
s-1 (10-5.times.10-7.times.(2.times.105).times.500 s-1).
[0039] In accordance with the above, in some embodiments, the
second layer receives data from the first layer through a CFAR
utility, structurally included either into the first layer or the
second layer and selecting a constant number of the most suspicious
events for processing in the rest of the second layer. Selecting
more suspicious events than the second layer can handle would
create an overflow, e.g. a fail of a cycle. Selecting too few
events would increase the FAR. Operating in its normal mode, the
second layer further reduces the FAR, to the maximal allowed level.
For example, the first layer may reduce the data rate from the
pixel rate of about /sec to about /sec and the second layer may
reduce the FAR to a desired /sec, which is 7 additional orders of
magnitude. In some preferred embodiments the decrease in the number
of candidate events due to the first, in particular parallel, layer
is smaller than the decrease in the number of candidate events due
to a further layer (e.g. the second layer).
[0040] In this connection it should be understood, that the layered
architecture can facilitate detection of very short events, such as
muzzle flashes, while it the technique of the inventors is aimed at
operation with a high rate (decision-making rate) and an efficient
power use scheme.
[0041] The technique of the inventors may combine detection in
different spectrums, such as SBUV or visible, by using one or more
PDAs sensitive to one or more wavelengths. For example, the
detection of the flash intensities corresponding to different
wavelengths can be done with one detector using time and/or pixel
multiplexing. In particular, a secondary visible light or NIR
imaging can serve for independent detecting of muzzle flashes and
for reducing the false alarm rate (FAR) of a prime (in this example
SWIR) imaging by confirming or suppressing suspicious events. In
other words, the results of the prime imaging may be verified by
the results of secondary imaging.
[0042] Also, visible light or NIR imaging can serve for deduction
of the background by subtraction of images, because, for example,
in daylight the muzzle flash is stronger in the SWIR range, while
the background is stronger in NIR or Visible light.
[0043] The muzzle flash detector may be incorporated into a gunshot
detection system also including an acoustic or any other gunshot
detector. Such a system can perform concurrent detection of the
muzzle flash and of some other (e.g. acoustic or SBUV) signal
associated with the gunshot, e.g. of muzzle blast and/or bullet
shock wave. This double (e.g. optic/acoustic) detection scheme is
aimed at decreasing the FAR and increasing the ratio of probability
of gunshot detection (PD) to the FAR. The user is notified about
the gunshot only if both optical detector and the acoustic detector
identify a gunshot (i.e. if the optical detector "suspicion" or
alarm is confirmed by the acoustic detector within a short period
of time needed for sound to cover the distance to the user).
[0044] In some of the preferred embodiments the inventors' system
includes or is associated with a control unit configured for at
least one of the following: for processing the output signals of
the parallel processing unit for confirming/suppressing the
possible alarms by construing information contained in spatial
and/or temporal features of the detected optical signal(s); for
processing signals obtained from multiple detectors (e.g. optical,
such as PDA, or acoustic, or two optical for different wavelength
ranges) for confirming/suppressing the possible alarms and/or for
determining a distance to the flash; for defining the PDA working
parameters and/or parallel processing parameters based on external
conditions (e.g. weather, lighting); for determining a weapon used
by the shooter (e.g. by comparing the detected data with reference
indicative of different muzzle flashes signatures, or by measuring
the time between muzzle flashes in case of bursting fire). In
accordance with the above, the control unit may be configured to
implement the second and/or further layers of processing. Thus, the
control unit facilitates the detection of a muzzle flash event.
[0045] The technique of the inventors may be aimed at a high
capability of use by a human having a restricted immediate access
to various carrying equipments, for example a soldier or a
policeman. To this end, weight of some of the embodiments may be
selected to be between 1 kg to 3 kg, or between 0.3 to 1 kg, or
lighter than 0.3 kg. Such selection is facilitated, when the PDA
does not require a cooler, in particular a cryogenic cooler (e.g.
Stirling cooler), and a relatively heavy portable power source for
feeding the cooler (consequently, the system may need only a
relatively portable light power source). This relates to the above
references to the range of the PDA working temperatures. In fact,
some of the inventors' technique's adaptations are configured to
employ a working temperature as of natural environment (or slightly
larger, due to heat dissipation in the device). However, it should
be understood, that the high portability is not a requirement; the
system may be heavy, especially when it becomes necessary due to
other reasons, for example when the system needs to be shielded
and/or when the system needs to stay operative for long periods of
time and thus requires a highly capacitive power source. For
another example, the system may be stationary mounted for
constantly observing a desired scenery, which may be a subway
station, or a street with governmental offices, or any place where
a terrorist or bandit attack might be expected, and therefore it
may not need portability. Likewise, the inventors' system may be
mounted on a tank, or a car, or a bus, etc. The system may be fed
with a constant power supply, similarly to a home lamp or a desktop
computer, and it may be configured to utilize a MWIR/LWIR imager
and a cooler and benefit from a stronger muzzle flash MWIR signal.
However, the inventors have realized that the latter MWIR/LWIR
imager and a cooler are not necessary, and do not have to be
utilized when the relatively high portability is desired.
Contemplating on the latter case, the inventors have found that the
portability may be increased, when the system of the invention is
more specifically configured for a specific mission. The inventors
have considered that for some missions, the mission duration is
typically between 6-12 hours, while for some other missions the
duration may be between 1 and 6 hours, or between 12 and 24 hours,
or longer than 24 hours. In fact, the expected mission duration
depends on a scenario, which caused the need to use the inventors'
system, on the scenery, the length of the day in the season, the
capabilities of the system's user to stay in engagement or to
replace or recharge the portable power supply. Thus, as the
inventors have found, the capacity of the portable power supply may
be selected so as to provide the system a desired operative
duration, for example in one of the ranges of the mission duration
above. The power supply, if it is light, may provide enough
electricity even for a larger number of hours. In particular, the
capacity of the portable power supply (e.g. an accumulator or a
battery) may be less than 0.1 W, or between 0.1-1 W and between
1-10 W or larger than 10 W. It should be understood, that modern
muzzle flash detecting devices are typically equipped with power
supplies of more than a 50 W capacity and therefore have a reduced
portability, if at all.
[0046] Additionally, it should be noted, that the allowed weight of
the system may be a decreasing function of the expected mission
duration, because the user may need to carry additional supplies
(e.g. food, water, bullets) with him or her to the mission, and the
total weight may be limited. Therefore, for some embodiments the
inventors select the capacity of the power supply and the system
weight not independently, but in combination. This way, a
relatively high portability and a relatively high usability of the
device of the inventors can be achieved.
[0047] In this connection, it is reiterated, that in accordance
with the features of the invention herein presented, the technique
of the inventors can be effectively utilized for detection not only
of muzzle flashes, but also for detection of other flashes and
short events, for example of strobe light sources, pulsed lasers,
lightnings, antitank missile launches, and shell firings.
[0048] According to a broad aspect of the invention, there is
provided a method for use in detection of a muzzle flash event. The
method may include one or more of the following:
[0049] (a) focusing on a Photo Detector Array (PDA) electromagnetic
radiation, being at least partially within the near infrared (NIR)
and short wave infrared (SWIR) spectrum;
[0050] (b) focusing on a pixel of a PDA electromagnetic radiation
from a relatively large pixel field of view (FOV);
[0051] (c) acquiring multipixel images of a scenery by a PDA,
comprising a relatively large number of pixels;
[0052] (d) focusing on a PDA electromagnetic radiation from a
relatively large field of view;
[0053] (e) filtering electromagnetic radiation so as to allow
sensing by a PDA of substantially a spectral range corresponding to
relatively low light transmission in atmosphere;
[0054] (f) sensing by a PDA electromagnetic radiation, being at
least partially within the near infrared (NIR) and the short wave
infrared (SWIR) spectrum;
[0055] (g) using a relatively small integration time for sensing
electromagnetic radiation by a PDA;
[0056] (h) using a relatively small dead time for sensing
electromagnetic radiation by a PDA;
[0057] (i) multiplexing pixel signals originating from a PDA into
at least two replicas;
[0058] (j) recording a replica of pixel signals originating from a
PDA into a memory;
[0059] (k) applying a processing to pixel signals originating from
a PDA, the processing being adapted for use in selection of
candidate pixels, whose signals are substantially similar to the
temporal-spatial signature (i.e. temporal and/or spatial) of muzzle
flash;
[0060] (l) utilizing a relatively portable system for the
detection;
[0061] (m) utilizing a relatively low capacity portable power
supply for the detection;
[0062] (n) using a PDA at a temperature equal to or higher than a
temperature of natural environment for the detection;
[0063] (o) not utilizing a cooler for a PDA being used for the
detection;
[0064] (p) focusing on a Photo Detector Array (PDA) electromagnetic
radiation wherein the focusing is optimized for an object distance
less than 50 meters;
[0065] (q) using a Photo Detector Array (PDA) with a fill factor
larger than 60%.
[0066] According to a broad aspect of the invention, the processing
for the detection of a muzzle flash event may include at least one
of the following:
[0067] (a) eliminating spatial background portion from the pixel
signals;
[0068] (b) eliminating relatively slowly changing portions from the
pixel signals;
[0069] (c) selecting pixel signals' portions substantially similar
to the temporal signature of muzzle flash;
[0070] (d) an analog processing of time dependence of the pixel
signals, the processing being adapted to generate substantially an
estimate of likelihood that a pixel detected muzzle flash;
[0071] (e) a parallel processing of time dependence of the pixel
signals, the processing being adapted to generate substantially an
estimate of likelihood that a pixel detected muzzle flash;
[0072] (f) a digital processing of a time dependence of the pixel
signals, the processing being adapted to generate substantially an
estimate of likelihood that a pixel detected muzzle flash;
[0073] (g) selecting the candidate pixels by comparing a
substantial estimate of likelihood that a pixel detected muzzle
flash with a threshold common for a plurality of operating
pixels;
[0074] (h) selecting the candidate pixels by comparing an estimate
of likelihood that a pixel detected muzzle flash with a threshold
obtained using replicas of the pixel signals;
[0075] (i) selecting substantially the same number of the candidate
pixels from subsequent frames;
[0076] (j) at least two processing stages, a later of the stages
applying a processing for the selection of the candidate pixels to
a smaller number of the pixels than an earlier of the stages;
[0077] (k) at least two processing stages, a later of the stages
applying, to the pixels, a processing for the selection of the
candidate pixels, using more processing time per pixel than an
earlier of the stages;
[0078] (l) selecting, as the candidate pixels, those of the pixels,
whose signals together with their vicinity pixels' signals present
substantially the spatial signature of muzzle flash;
[0079] (m) eliminating from the selection those of the pixels,
whose signals together with their vicinity pixels' signals present
substantially the temporal-spatial signature of a moving light
source;
[0080] (n) confirming, as the candidate pixels, those of the
pixels, whose signals together with their vicinity pixels' signals,
obtained after their initial selection of the candidate pixels,
increase an estimate of likelihood that a pixel detected muzzle
flash;
[0081] (o) eliminating from the selection those of the pixels,
whose signals are not accompanied by an acoustic signal with a
signature substantially similar to the signature of a shot.
[0082] The electromagnetic radiation being focused on the Photo
Detector Array (PDA) may in part or in whole be within the NIR
spectrum. In particular, it can be fully within the NIR spectrum.
It can also be at least partially within the SWIR spectrum. In
particular, it can be fully within the SWIR spectrum.
[0083] In some embodiments, the focusing is optimized for an object
distance larger than 50 meters (i.e. the distance from the muzzle
flash to the detection device). In some embodiments, the focusing
is optimized for an object distance less than 50 meters.
[0084] The relatively large pixel field of view (FOV) may be
between 0.1 and 0.2 degrees, or between 0.2 and 0.5 degrees, or it
may be larger than 0.5 degrees.
[0085] The device's PDA may include a relatively large number of
pixels. The relatively large number of pixels may be between 10,000
and 100,000 pixels, or between 100,000 and 1,000,000 pixels, or it
may be more than 1,000,000 pixels.
[0086] The relatively large field of view may be between 30 and 50
degrees, or between 50 and 90 degrees, or it may be larger than 90
degrees.
[0087] The filtering may be performed in the spectral range at
least partially including the trough of low atmospheric light
transmission situated around 1.15 .mu.m. Additionally or
alternatively, it may be performed in the spectral range at least
partially including the trough of low atmospheric light
transmission situated around 1.39 .mu.m; the trough of low
atmospheric light transmission situated around 1.9 .mu.m; the
trough of low atmospheric light transmission situated around 2.7
.mu.m.
[0088] The sensed by the PDA electromagnetic radiation may be at
least partially within the NIR spectrum. In particular it may be
fully within the NIR spectrum. It may be at least partially within
the SWIR spectrum. It may be fully within the SWIR spectrum.
[0089] The PDA may be a CMOS PDA. Also, it may be an intracavity
PDA.
[0090] The PDA integration time may be between 10-2 s and 5.010-3
s, or between 5.010-3 s and 2.010-3 s, or between 2.010-3 s and
5.010-4 s, or between 5.010-4 s and 10-4 s, or it might be less
than 10-4 s.
[0091] The PDA dead time may be shorter than 1 millisecond.
[0092] The replicated pixel signals may be compressed before the
recording.
[0093] The processing for the detection of a muzzle flash, while
including eliminating relatively slowly changing portions from the
pixel signals, may include at least one differencing the pixel
signals. In particular it may include the second order differencing
of the pixel signals.
[0094] The processing may include selecting pixel signals' portions
substantially similar to the temporal signature of muzzle flash.
Such portions for selection may be pulses in the form of a peak.
The peak to be selected may be of a predetermined duration.
[0095] The analog processing adapted to generate substantially an
estimate of likelihood that a pixel detected muzzle flash may
include at least one differencing of the pixel signals. In
particular, it may include the second order differencing of the
pixel signals. It may include passing the pixels signals through a
matched filter, adapted to match the temporal signature of muzzle
flash. The substantial estimate may be a voltage potential at an
output of an analog circuit performing the analog processing.
[0096] The selecting candidate pixels by comparing an estimate of
likelihood that a pixel detected muzzle flash with a threshold may
use common threshold within at least two groups of adjacent pixels,
while threshold may be varying between the groups.
[0097] According to a broad aspect of the invention, there is
provided a device for use in detection of a muzzle flash event. The
device may include a PDA and one of the following features:
[0098] (a) optics adapted to focus on the PDA electromagnetic
radiation being at least partially within the near infrared (NIR)
and short wave infrared (SWIR) spectrum;
[0099] (b) optics adapted to focus on a pixel of the PDA
electromagnetic radiation from a relatively large pixel field of
view (FOV);
[0100] (c) optics adapted to focus on the PDA electromagnetic
radiation from a relatively large field of view;
[0101] (d) a filter of electromagnetic radiation accommodated so as
to allow sensing by said PDA of substantially a spectral range
corresponding to relatively low light transmission in
atmosphere;
[0102] (e) a shutter, allowing to use a relatively small
integration time for sensing electromagnetic radiation by the
PDA;
[0103] (f) a shutter controller, adapted to define a relatively
small dead time for sensing electromagnetic radiation by the
PDA;
[0104] (g) a multiplexer, adapted to divide pixel signals
originating from the PDA into at least two replicas;
[0105] (h) a memory, storing a replica of pixel signals originating
from the PDA;
[0106] (i) a processing unit adapted to process pixel signals
originating from the PDA, the unit being adapted for use in
selection of candidate pixels, whose signals are substantially
similar to the temporal-spatial (i.e. temporal and/or spatial)
signature of muzzle flash;
[0107] (l) a portable power supply, configured to provide the
device with electricity for a relatively short time of the device
operation.
[0108] The device's shutter may be an electronic shutter. The
shutter controller may utilize a rolling shutter scheme for
operating the shutter.
[0109] The device's PDA may be sensitive within a part or the whole
of the NIR and SWIR spectrum, or of the NIR spectrum, or of the
SWIR spectrum.
[0110] The device's relatively large pixel field of view (FOV) may
be between 0.1 and 0.2 degrees, or between 0.2 and 0.5 degrees, or
larger than 0.5 degrees.
[0111] The device's relatively large number of pixels may be
between 10,000 and 100,000 pixels, or between 100,000 and 1,000,000
pixels, or more than 1,000,000 pixels.
[0112] The device's relatively large field of view may be between
30 and 50 degrees, or between 50 and 90 degrees, or larger than 90
degrees.
[0113] The device's spectral range may include a part or the whole
of the trough of low atmospheric light transmission situated around
1.15 .mu.m. As well, it may include a part or the whole of the
trough of low atmospheric light transmission situated around 1.39
.mu.m, and/or the trough of low atmospheric light transmission
situated around 1.9 .mu.m, and/or the trough of low atmospheric
light transmission situated around 2.7 .mu.m.
[0114] The device's PDA may be at least partially sensitive within
the NIR spectrum. The PDA may be sensitive only within the NIR
spectrum. The PDA may be at least partially sensitive within the
SWIR spectrum. The PDA may be sensitive only within the SWIR
spectrum.
[0115] The device's PDA may be a CMOS PDA. The PDA may be an
intracavity PDA.
[0116] The PDA integration time may be between 10-2 s and 5.010-3
s, or between 5.010-3 s and 2.010-3 s, or between 2.010-3 s and
5.010-4 s, or between 5.010-4 s and 10-4 s, or it might be less
than 10-4 s.
[0117] The device's PDA dead time may be lower than a
millisecond.
[0118] The processing unit may be in-pixel.
[0119] The device may include a compressing unit accommodated to
compress a replica of the pixel signals.
[0120] The device may be configured to have a relatively low
weight.
[0121] According to another broad aspect of the invention, there is
provided a processing unit for use in detection of a muzzle flash
event. The processing unit may be adapted to process pixel signals
originating from a PDA, and adapted for use in selection of
candidate pixels, whose signals are substantially similar to the
temporal-spatial signature of muzzle flash. The processing unit may
be also adapted to perform at least one of the following:
[0122] (a) eliminating spatial background portion from the pixel
signals;
[0123] (b) eliminating relatively slowly changing portions from the
pixel signals;
[0124] (c) selecting pixel signals' portions substantially similar
to the temporal signature of muzzle flash;
[0125] (d) selecting the candidate pixels by comparing a
substantial estimate of likelihood that a pixel detected muzzle
flash with a threshold common for a plurality of operating
pixels;
[0126] (e) selecting the candidate pixels by comparing an estimate
of likelihood that a pixel detected muzzle flash with a threshold
obtained using replicas of the pixel signals;
[0127] (f) selecting substantially the same number of the candidate
pixels from subsequent frames;
[0128] (g) selecting, as the candidate pixels, those of the pixels,
whose signals together with their vicinity pixels' signals present
substantially the spatial signature of muzzle flash;
[0129] (h) eliminating from the selection those of the pixels,
whose signals together with their vicinity pixels' signals present
substantially the temporal-spatial signature of a moving light
source;
[0130] (i) confirming, as the candidate pixels, those of the
pixels, whose signals together with their vicinity pixels' signals,
obtained after their initial selection of the candidate pixels,
increase an estimate of likelihood that a pixel detected muzzle
flash.
[0131] (j) eliminating from the selection those of the pixels,
whose signals are not accompanied by an acoustic signal with a
signature substantially similar to the signature of a shot.
[0132] The processing unit for use in detection of a muzzle flash
event may include at least one of:
[0133] (a) an analog processing unit, adapted to apply analog
processing to time dependence of the pixel signals, so as to
generate substantially an estimate of likelihood that a pixel
detected muzzle flash;
[0134] (b) a parallel processing unit, adapted to apply parallel
processing to time dependence of the pixel signals, so as to
generate substantially an estimate of likelihood that a pixel
detected muzzle flash;
[0135] (c) a digital processing unit, adapted to apply digital
processing to time dependence of the pixel signals, so as to
generate substantially an estimate of likelihood that a pixel
detected muzzle flash;
[0136] (d) at least two processing stages, a later of the stages
applying a processing for the selection of the candidate pixels to
a smaller number of the pixels than an earlier of the stages;
[0137] (e) at least two processing stages, a later of the stages
applying, to the pixels, a processing for the selection of the
candidate pixels, using more processing time per pixel than an
earlier of the stages.
[0138] In the processing unit, the eliminating of background
portions may include determining scene motion vectors.
[0139] In the processing unit, the eliminating relatively slowly
changing portions from the pixel signals may include at least one
differencing of the pixel signals. The differencing may be second
order differencing of the pixel signals.
[0140] In the processing unit, selecting candidate pixels by
comparing an estimate of likelihood that a pixel detected muzzle
flash with a threshold may include selecting a pulse in the form of
a peak. The peak may be of a predetermined duration.
[0141] The analog processing unit may include a circuit configured
for performing at least one differencing of the pixel signals. The
circuit may be configured for performing the second order
differencing of the pixel signals.
[0142] The analog processing unit may include a matched filter,
accommodated on a pass of the pixels signals, the matched filter
being adapted to match the temporal signature of muzzle flash.
[0143] The analog processing unit, adapted to apply analog
processing to time dependence of the pixel signals so as to
generate substantially an estimate of likelihood that a pixel
detected muzzle flash may be adapted to generate the substantial
estimate as a voltage potential at an output of the analog
processing unit.
[0144] The processing unit may use common thresholds within at
least two groups of adjacent pixels, the thresholds differing
between the groups.
[0145] According to a broad aspect of the invention, there is
provided a device for use in detection of a muzzle flash event, the
device including a PDA, relatively highly sensitive in at least a
portion of the NIR and SWIR spectrum, and a filter of
electromagnetic radiation, selectively passing substantially a
spectral range corresponding to relatively low light transmission
in atmosphere.
[0146] According to a broad aspect of the invention, there is
provided a device for use in detection of a muzzle flash event, the
device including a PDA, having a cutoff wavelength lower than 3
microns, and a readout circuit for the PDA, the circuit being
configured and operable to sample each operating pixel of the PDA
more than 500 times per second.
[0147] According to a broad aspect of the invention, there is
provided a device for use in detection of a muzzle flash event, the
device including a PDA, having a cutoff wavelength shorter than 3
microns, and a processing unit adapted to detect muzzle flash
events in an output of said imaging arrangement.
[0148] According to a broad aspect of the invention, there is
provided a device for use in detection of a muzzle flash event, the
device including a PDA, sensitive in at least a portion of the NIR
and SWIR spectrum; a filter of electromagnetic radiation
selectively passing substantially a spectral range corresponding to
relatively low light transmission in atmosphere; the PDA being
configured to operate with a relatively small integration time for
sensing electromagnetic radiation. The device may include a
processing unit adapted to process pixel signals originating from
the PDA, the unit being adapted for use in selection of candidate
pixels, whose signals are substantially similar to the
temporal-spatial signature of muzzle flash.
[0149] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing, by a Photo Detector Array (PDA) which is
sensitive in at least a portion of the NIR and SWIR spectrum,
electromagnetic radiation, passed through a filter of
electromagnetic radiation selectively passing in the portion a
spectral range of low atmospheric transmission, the sensing having
an integration time shorter than a duration of the muzzle flash
event.
[0150] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing, by a Photo Detector Array (PDA),
sensitive in at least a portion of the NIR and SWIR spectrum,
electromagnetic radiation, passed through a filter of
electromagnetic radiation selectively passing in the portion a
spectral range of low atmospheric transmission, the sensing having
an integration time shorter than 10-2 s.
[0151] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing by a Photo Detector Array (PDA)
electromagnetic radiation, passed through a filter of
electromagnetic radiation selectively passing a spectral range of
low atmospheric transmission and focused on the PDA, a per pixel
field of view (FOV) of the PDA being larger at the focusing
distance than the muzzle flash.
[0152] The focusing distance may be larger than 50 m.
[0153] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing by a Photo Detector Array electromagnetic
radiation, passed through a filter of electromagnetic radiation
selectively passing a spectral range of low atmospheric
transmission and focused on the PDA, a per pixel field of view
(FOV) of the PDA being larger than 0.1 degrees.
[0154] The Photo Detector Array may be sensitive in at least a
portion of the NIR and SWIR spectrum.
[0155] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing electromagnetic radiation by a Photo
Detector Array (PDA) sensitive in at least a portion of the NIR and
SWIR spectrum, the sensing recurring with a dead time shorter than
a duration of the muzzle flash.
[0156] The dead time may be shorter than the one tenth of the
duration.
[0157] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing electromagnetic radiation by a Photo
Detector Array (PDA) sensitive in at least a portion of the NIR and
SWIR spectrum, the sensing recurring with a dead time shorter than
one millisecond.
[0158] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing electromagnetic radiation by a Photo
Detector Array (PDA) sensitive in at least a portion of the NIR and
SWIR spectrum and multiplexing pixel signals of the PDA into at
least two replicas.
[0159] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing, by a Photo Detector Array (PDA),
electromagnetic radiation, passed through a filter of
electromagnetic radiation selectively passing a spectral range of
low atmospheric transmission, and multiplexing pixel signals of the
PDA into at least two replicas. The method may include recording a
replica of the pixel signals into a memory.
[0160] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing, by a Photo Detector Array (PDA) sensitive
in at least a portion of the NIR and SWIR spectrum, electromagnetic
radiation, passed through a filter of electromagnetic radiation
selectively passing in the portion a spectral range of low
atmospheric transmission, the PDA having a fill factor larger than
60%. The fill factor may be between 60% and 75%. The fill factor
may be between 75% and 90%. The fill factor may be higher than
90%.
[0161] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing electromagnetic radiation by a Photo
Detector Array (PDA) sensitive in at least a portion of the NIR and
SWIR spectrum, and detecting the muzzle flash in output of the PDA
by applying a signal processing to pixel signals of the PDA.
[0162] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing by a Photo Detector Array (PDA)
electromagnetic radiation passed through a filter of
electromagnetic radiation selectively passing a spectral range of
low atmospheric transmission, and detecting the muzzle flash in
output of the PDA by applying a signal processing to pixel signals
of the PDA.
[0163] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing electromagnetic radiation by a Photo
Detector Array (PDA) sensitive in at least a portion of the NIR and
SWIR spectrum, and selecting candidate pixels by applying a stage
of processing to pixel signals of the PDA, the stage being
configured to provide a stage data rate decrease factor smaller
than a data rate decrease factor between an initial data rate of
the PDA and an alarm rate benchmark of 100 alarms/s. The benchmark
is an estimate of a maximum shooting rate that may be caused by a
single shooter. This estimate is not limiting for embodiments which
are not specifically adjusted in view of this benchmark.
[0164] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing by a Photo Detector Array (PDA)
electromagnetic radiation passed through a filter of
electromagnetic radiation selectively passing a spectral range of
low atmospheric transmission, and selecting candidate pixels by
applying a stage of processing to pixel signals of the PDA, the
stage being configured to provide a stage data rate decrease factor
smaller than a data rate decrease factor between an initial data
rate of the PDA and an alarm rate benchmark of 100 alarms/s.
[0165] The stage data rate decrease factor may be smaller than 20
multiplied by a square root of the data rate decrease factor
between the initial data rate of the PDA and the alarm rate
benchmark.
[0166] The processing may include comparing pixel signals of the
PDA with a temporal-spatial signature of the muzzle flash.
[0167] The processing may include eliminating spatial background
portion from the pixel signals. The processing may include
eliminating substantially slowly changing portions from the pixel
signals. The eliminating may include at least one differencing of
the pixel signals. The eliminating may include second order
differencing of the pixel signals.
[0168] The processing may include selecting pixel signals' portions
substantially similar to a temporal signature of the muzzle flash.
The selecting may include selecting a pulse having a form of a
peak. The peak may be of a predetermined duration.
[0169] The processing may include an analog processing of time
dependence of the pixel signals. The analog processing may include
at least one differencing of the pixel signals. The analog
processing may include second order differencing of the pixel
signals. The analog processing may include passing the pixels
signals through a matched filter, adapted to match the temporal
signature of muzzle flash. The analog processing may provide a
voltage potential at an output, the voltage potential being
indicative of an estimate of likelihood of a detection of the
muzzle flash.
[0170] The processing may include a parallel processing of time
dependence of the pixel signals.
[0171] The analog processing may be adapted to generate
substantially estimates of likelihood that a respective to the
estimate pixel has detected the muzzle flash.
[0172] The parallel processing may be adapted to generate
substantially estimates of likelihood that a respective to the
estimate pixel has detected the muzzle flash.
[0173] The processing may include a digital processing of time
dependence of the pixel signals.
[0174] The digital processing may be adapted to generate
substantially estimates of likelihood that a respective to the
estimate pixel has detected the muzzle flash.
[0175] The processing may include selecting candidate pixels by
comparing, for a plurality of pixels, substantial estimates of
likelihood that a respective to the estimate pixel has detected the
muzzle flash with a likelihood threshold being common for a
plurality of pixels. The threshold may be the same within each of
two or more groups of adjacent pixels and different between the
groups.
[0176] The processing may include selecting candidate pixels by
comparing, for at least one pixel, an estimate of likelihood that
the pixel has detected the muzzle flash with a likelihood
threshold, obtained using a replica of the pixel signals.
[0177] The method may include selecting substantially the same
number of candidate pixels from subsequent PDA frames.
[0178] The method may include utilizing at least two processing
stages, a later of the stages applying a processing selecting
candidate pixels to a smaller number of the PDA pixels than an
earlier of the stages.
[0179] The method may include using at least two processing stages,
a later of the stages selecting candidate pixels by utilizing more
processing time per its candidate pixel than an earlier of the
stages.
[0180] The method may include selecting into candidate pixels of
pixels whose signals together with their vicinity pixels' signals
present substantially a spatial signature of the muzzle flash.
[0181] The processing may include suppressing selection into
candidate pixels of a pixel whose signal together with its vicinity
pixels' signals present substantially a temporal-spatial signature
of a substantially moving light source.
[0182] The processing may include at least two stages, the
processing at a later stage including confirming selection into
candidate pixels of a candidate pixel whose likelihood estimate of
having detected the muzzle flash has increased at the later stage
of the processing. The later stage of processing may utilize the
candidate pixel's signal and candidate pixel's vicinity pixels'
signals.
[0183] The processing may include suppressing selection into
candidate pixels of a pixel whose signal is not accompanied by a
detection of an acoustic signal with an acoustic signature
substantially similar to the acoustic signature of the muzzle
flash-causing event.
[0184] The method may include cooling of the PDA. The sensing may
be performed at a temperature between -30.degree. C. and a PDA
ambient temperature. The sensing may be performed at a temperature
higher than a PDA ambient temperature.
[0185] The sensing may be performed without cooling the PDA.
[0186] The method may include utilizing for the detection a power
supply allowing more than 1 hour of the detection.
[0187] According to a broad aspect of the invention there is
provided a method for use in detection of a muzzle flash event, the
method including sensing, by a Photo Detector Array (PDA),
sensitive in at least a portion of the NIR and SWIR spectrum,
electromagnetic radiation, passed through a filter of
electromagnetic radiation selectively passing in the portion a
spectral range of low atmospheric transmission, the method
including utilizing for the detection a power supply allowing from
1 to 24 hours of the detection.
[0188] The power supply may allow more than 6 hours of the
detection.
[0189] The power supply may allow less than 12 hours of the
detection.
[0190] The method may include utilizing for the detection a power
supply of less than 10 Watts output power.
[0191] The method may include utilizing for the detection only
equipment portable by a human during the detection. A weight of the
equipment may be less than 3 kg.
[0192] The power supply may allow more than 6 hours of the
detection.
[0193] The utilized sensing at least for a part may be performed
within the NIR spectrum. The utilized sensing at least for a part
may be performed within the SWIR spectrum. The PDA may have a
sensitivity maximum at a wavelength longer than 3 microns and a
sensitivity cut-off at a wavelength shorter than 5 microns. The PDA
may have a sensitivity maximum at a wavelength shorter than 3
microns. The PDA may have a sensitivity cut-off at a wavelength
shorter than 5 microns. The PDA may have a sensitivity cut-off at a
wavelength between 1.4 .mu.m and 1.65 .mu.m. The PDA may have a
sensitivity cut-off at a wavelength 1.65 .mu.m and 1.8 .mu.m. The
PDA may have a sensitivity cut-off at a wavelength between 1.8
.mu.m and 2.5 .mu.m. The PDA may have a sensitivity maximum at a
wavelength longer than 0.75 microns.
[0194] The PDA may have a region of a predominant sensitivity fully
within the NIR/SWIR range, the region being a region where the
sensitivity is higher than 20% of a maximum PDA's sensitivity. The
predominant sensitivity may be defined as higher than 35% of a
maximum PDA's sensitivity. The predominant sensitivity may be
defined as higher than 50% of the maximum PDA's sensitivity. The
predominant sensitivity may be defined as higher than 70% of a
maximum PDA's sensitivity.
[0195] The sensing may be substantially within a range of low
atmospheric light transmission at least partially including the
trough situated around 1.15 .mu.m (micron). The sensing may be
substantially within a range of low atmospheric light transmission
at least partially including a trough extending from 1.34 .mu.m to
1.50 .mu.m. The sensing may be substantially within a range of low
atmospheric light transmission at least partially including a
trough extending from 1.80 .mu.m to 2.00 .mu.m. The sensing may be
substantially within a range of low atmospheric light transmission
at least partially including a trough extending from 2.50 .mu.m to
2.90 .mu.m.
[0196] The method may include compressing a replica of pixel
signals of the PDA before the recording.
[0197] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA), sensitive in at
least a portion of the NIR and SWIR spectrum, and a filter of
electromagnetic radiation selectively passing in the portion a
spectral range of low atmospheric transmission, the PDA having an
integration time shorter than a duration of the muzzle flash
event.
[0198] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA), sensitive in at
least a portion of the NIR and SWIR spectrum, and a filter of
electromagnetic radiation selectively passing in the portion a
spectral range of low atmospheric transmission, the sensing having
an integration time shorter than 10-2 s.
[0199] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA), a filter of
electromagnetic radiation selectively passing a spectral range of
low atmospheric transmission, and optics adapted to focus at least
the spectral range on the PDA, a per pixel field of view (FOV) of
the PDA being larger at the focusing distance than the muzzle
flash.
[0200] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array, a filter of
electromagnetic radiation selectively passing a spectral range of
low atmospheric transmission, and optics adapted to focus at least
the spectral range on the PDA, a per pixel field of view (FOV) of
the PDA being larger than 0.1 degrees.
[0201] A device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA) sensitive in at least
a portion of the NIR and SWIR spectrum, the device adapted to
operate with a dead time shorter than a duration of the muzzle
flash.
[0202] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA) sensitive in at least
a portion of the NIR and SWIR spectrum, the device adapted to
operate with a dead time shorter than one millisecond.
[0203] The device may include a shutter, which may be an electronic
shutter.
[0204] The device may include a shutter controller for operating a
shutter with the selected dead time.
[0205] The shutter controller may utilize a rolling shutter scheme
for operating the shutter.
[0206] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA) sensitive in at least
a portion of the NIR and SWIR spectrum and a multiplexer, adapted
to divide pixel signals originating from the PDA into at least two
replicas.
[0207] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA), a filter of
electromagnetic radiation selectively passing a spectral range of
low atmospheric transmission, and a multiplexer, adapted to divide
pixel signals originating from the PDA into at least two
replicas.
[0208] The device may include a memory for storing a replica of the
pixel signals.
[0209] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA) sensitive in at least
a portion of the NIR and SWIR spectrum, a filter of electromagnetic
radiation selectively passing in the portion a spectral range of
low atmospheric transmission, the PDA having a fill factor larger
than 60%.
[0210] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA) sensitive in at least
a portion of the NIR and SWIR spectrum, and a processing unit
adapted to detect the muzzle flash in output of the PDA by applying
a signal processing to pixel signals of the PDA.
[0211] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA), a filter of
electromagnetic radiation selectively passing a spectral range of
low atmospheric transmission, and a processing unit adapted to
detect the muzzle flash in output of the PDA.
[0212] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA), sensitive in at
least a portion of the NIR and SWIR spectrum, and a processing unit
including at least one stage of processing adapted to select
candidate pixels by applying the stage to pixel signals of the PDA,
the stage being configured to provide a stage data rate decrease
factor smaller than a data rate decrease factor between an initial
data rate of the PDA and an alarm rate benchmark of 100
alarms/s.
[0213] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA), a filter of
electromagnetic radiation selectively passing a spectral range of
low atmospheric transmission, and a processing unit including at
least one stage of processing adapted to select candidate pixels by
applying the stage to pixel signals of the PDA, the stage being
configured to provide a stage data rate decrease factor smaller
than a data rate decrease factor between an initial data rate of
the PDA and an alarm rate benchmark of 100 alarms/s.
[0214] The stage data rate decrease factor may be smaller than 20
multiplied by a square root of the data rate decrease factor
between the initial data rate of the PDA and the alarm rate
benchmark.
[0215] The processing unit may be adapted to compare pixel signals
of the PDA with a temporal-spatial signature of the muzzle
flash.
[0216] The processing unit may be adapted to eliminate a spatial
background portion from the pixel signals.
[0217] The processing unit may be adapted to generate scene motion
vectors.
[0218] The processing unit may be adapted to eliminate
substantially slowly changing portions from the pixel signals. The
processing unit may be configured to perform the elimination using
at least one differencing of the pixel signals. The processing unit
may be configured to perform the elimination using a second order
differencing of the pixel signals.
[0219] The processing unit may be adapted to select pixel signals'
portions substantially similar to a temporal signature of the
muzzle flash.
[0220] The processing unit may have a part that is in-pixel.
[0221] The processing unit may include an analog processing unit
adapted to process time dependence of the pixel signals. The analog
processing unit may include a circuit adapted to perform at least
one differencing of the pixel signals. The analog processing unit
may include a circuit adapted to perform second order differencing
of the pixel signals.
[0222] The analog processing unit may include a matched filter,
adapted to match the temporal signature of muzzle flash.
[0223] The analog processing unit may be adapted to provide a
voltage potential at outputs, the voltage potential being
indicative of an estimate of likelihood of a detection of the
muzzle flash.
[0224] The processing unit may include a parallel processing unit
for processing time dependence of the pixel signals.
[0225] The analog processing unit may be adapted to generate
substantially estimates of likelihood that a respective to the
estimate pixel has detected the muzzle flash.
[0226] The parallel processing unit may be adapted to generate
substantially estimates of likelihood that a respective to the
estimate pixel has detected the muzzle flash.
[0227] The processing unit may include a digital processing unit
processing time dependence of the pixel signals.
[0228] The digital processing unit may be adapted to generate
substantially estimates of likelihood that a respective to the
estimate pixel has detected the muzzle flash.
[0229] The processing unit may be adapted to select candidate
pixels by comparing, for a plurality of pixels, substantial
estimates of likelihood that a respective to the estimate pixel has
detected the muzzle flash with a likelihood threshold being common
for a plurality of pixels.
[0230] The threshold may be the same within each of two or more
groups of adjacent pixels and different between these groups.
[0231] The processing unit may be adapted to select candidate
pixels by comparing, for at least one pixel, an estimate of
likelihood that the pixel has detected the muzzle flash with a
likelihood threshold, obtained using a replica of the pixel
signals.
[0232] The processing unit may be adapted to select substantially
the same number of candidate pixels from subsequent PDA frames.
[0233] The device may include at least two processing stages, a
later of the stages configured to apply a processing selecting
candidate pixels to a smaller number of the PDA pixels than an
earlier of the stages.
[0234] The device may include at least two processing stages, a
later of the stages configured to select candidate pixels by
utilizing more processing time per its candidate pixel than an
earlier of the stages.
[0235] The processing unit may be adapted to selecting into
candidate pixels those pixels whose signals together with their
vicinity pixels' signals present substantially a spatial signature
of the muzzle flash.
[0236] The processing unit may be adapted to suppress selection
into candidate pixels of a pixel whose signal together with its
vicinity pixels' signals present substantially a temporal-spatial
signature of an unsuitably moving light source.
[0237] The processing unit may include at least two processing
stages, a later stage of the stages adapted to confirm selection
into candidate pixels of a candidate pixel whose likelihood
estimate of having detected the muzzle flash has increased at the
later stage of the processing.
[0238] The later stage of processing may utilize the candidate
pixel's signal and candidate pixel's vicinity pixels' signals.
[0239] The processing unit may be adapted to suppress selection
into candidate pixels of a pixel whose signal is not accompanied by
a detection of an acoustic signal with an acoustic signature
substantially similar to the acoustic signature of the muzzle
flash-causing event.
[0240] The device may include a cooler for the PDA. The cooler may
be of a kind enabling sensing at a temperature lower than a PDA
ambient temperature.
[0241] The device may be configured without a cooler for the
PDA.
[0242] The device may include a power supply allowing more than 1
hour of the detection.
[0243] According to a broad aspect of the invention there is
provided a device for use in detection of a muzzle flash event, the
device including a Photo Detector Array (PDA), sensitive in at
least a portion of the NIR and SWIR spectrum, and a filter of
electromagnetic radiation selectively passing in the portion a
spectral range of low atmospheric transmission, the device
including a power supply allowing from 1 to 24 hours of the
detection.
[0244] The power supply may allow more than 6 hours of the
detection.
[0245] The power supply may allow less than 12 hours of the
detection.
[0246] The device may include a power supply of less than 10 Watts
output power.
[0247] The device may be portable by a human during the
detection.
[0248] The PDA may be a CMOS PDA. The PDA may be an intracavity
PDA.
[0249] The device may include a compressing unit adapted to
compress a replica of pixel signals of the PDA before the recording
them into a memory.
[0250] According to a broad aspect of the invention there is
provided a device for use in muzzle flash detection, the device
including a Photo Detector Array (PDA), having a cutoff wavelength
shorter than 3 microns, and a processing unit adapted to detect
muzzle flash events in an output of the PDA.
[0251] The device may include a filter of electromagnetic radiation
selectively passing in the PDA's sensitivity band a spectral range
of low atmospheric transmission.
[0252] The filter may pass less than 50% of energy of wavelengths
being outside the spectral range of low atmospheric transmission
and sensed by the PDA.
[0253] The filter may pass less than 25% of energy of wavelengths
being outside the spectral range of low atmospheric transmission
and sensed by the PDA.
[0254] The filter may pass less than 10% of energy of wavelengths
being outside the spectral range of low atmospheric transmission
and sensed by the PDA.
[0255] The filter may pass less than 2% of energy of wavelengths
being outside the spectral range of low atmospheric transmission
and sensed by the PDA.
[0256] The device may have at least one wavelength of the spectral
range a sensitivity being between 50% and 75% of the sensitivity of
the PDA.
[0257] The device may have at least one wavelength of the spectral
range a sensitivity larger than 75% of the sensitivity of the
PDA.
[0258] According to a broad aspect of the invention there is
provided a processing unit for use in detection of a muzzle flash
event, the processing unit being adapted to process pixel signals
originating from a PDA and to generate substantially likelihoods of
muzzle flash detection for pixels of the PDA, the processing unit
including a multiplexer dividing the pixel 222 signals between at
least two branches.
[0259] According to a broad aspect of the invention, there is
provided a device for use in detection of a muzzle flash event, the
device being substantially as described in the patent application
with reference to the specification.
[0260] According to a broad aspect of the invention, there is
provided a processing unit for use in detection of a muzzle flash
event, the processing unit being substantially as described in the
patent application with reference to the specification.
[0261] According to a broad aspect of the invention, there is
provided a method being substantially as described in the patent
application with reference to the specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0262] To further clarify the above and other advantages and
features of the present invention, and to further show how it may
be carried out in practice, an additional, at times more
particular, description of the invention and invention features
will be rendered in the below detailed description, at times with
reference to the appended drawings. It is appreciated that these
drawings, when depict only particular embodiments of the invention,
are not to be considered limiting of its scope. Hence, the
invention will continued to be described and explained with
additional specificity and detail through the use of the
accompanying drawings in which:
[0263] FIG. 1A is an example flow chart of the detection method,
according to the to the inventors' technique;
[0264] FIG. 1B is an example of a possible organization of a
detection system according to the inventors' technique;
[0265] FIGS. 2A and 2B schematically illustrate two examples of a
detection system, according to the inventors' technique;
[0266] FIG. 2C shows the sensitivity curves of various exemplary
materials used in photodetectors;
[0267] FIGS. 3A-3D exemplify some possible configurations of the
processing system, according to the inventors' technique, capable
of use in the detection system, according to the inventors'
technique;
[0268] FIGS. 4A and 4B exemplify the operation of the analog
processing unit, according to the inventors' technique;
[0269] FIGS. 5A-5C illustrate the principles underlying the use of
an optical filter in the technique of the inventors; and
[0270] FIG. 6 schematically illustrates an example of a
weapons-firing detection system organized according to the
inventors' technique.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0271] The present invention provides a novel technique for use in
detection of short events, for example of a gunshot event including
a muzzle flash event.
[0272] FIG. 1A shows a flow chart of the main steps in an example
of the detection method of the invention. As shown, near infrared
(NIR) and/or short wave infrared (SWIR) electromagnetic radiation,
possibly including radiation emitted by an occurred muzzle flash,
is collected from a field of view (FOV). The radiation is
spectrally filtered for detection of substantially a spectral range
corresponding to relatively low light transmission in atmosphere.
As it has been found by the inventors, the muzzle flash radiation
components being in such spectral range can provide a relatively
high useful signal and signal-to-noise ratio, though they carry
only a portion of overall muzzle flash intensity and are relatively
short-existing. Also, it should be understood that only a portion
of the collected light can be due to the muzzle flash event, i.e.
can be useful. The radiation of the chosen spectral range is
detected with an appropriate photodetector array (PDA). The PDA
integration time may be between 10-2 s and 5.010-3 s, or between
5.010-3 s and 2.010-3 s, or between 2.010-3 s and 5.010-4 s, or
between 5.010-4 s and 10-4 s, or it might be less than 10-4 s. As a
result, outputs of the PDA provide electrical signals, some of
which are indicative of the muzzle flash, if it has occurred.
[0273] The example of the detection method optionally includes also
other steps some of which are shown in FIG. 1A. In particular, a
detection of those signals portions, which are due to the muzzle
flash, may be carried out, with a certain detection probability and
false alarm rate. In the present example, the detection includes a
parallel processing, filtering signal portions varying as
flash-type intensity (in the selected wavelength range) with time.
This parallel processing may constitute a first layer of processing
in the inventors' technique.
[0274] The inventors' technique may have a stage at which it
determines an estimate of likelihood that an arbitrary pixel (e.g.
each of the pixels) has detected a muzzle flash event. This
estimate actually can be the output of the parallel processing.
[0275] The inventors' technique may determine a "suspicious" pixel
(or pixels) for which the estimated likelihood of detection of a
muzzle flash is higher than for others (this can be done by a pixel
selection unit, such as CFAR). The method may also have a step at
which it determines a pixel (or pixels) which likelihood is higher
than a certain threshold. An alarm signal intended to inform an
operator (or operating utility) or a user about the possible muzzle
flash event may then be produced. The alarm signal may be a simple
signal, e.g. a sound tone or a light flash, or it may be a
composite signal carrying such data as for example pixel position,
PDA orientation, determined likelihood, direction to the flash. The
data can be presented in a form perceived by another device or by
humans. The alarm signal may be recorded on a memory carrier.
[0276] The inventors' technique may include processing aimed at
reestimation of the likelihoods for a portion of pixels. The
likelihoods may be reestimated by a second layer processing using
signals obtained from pixels being close to the suspicious pixels
and/or signals obtained at times being relatively close to the
moment for which the reestimation is done.
[0277] In particular, the second layer of processing may perform
the following. For each of the suspicious pixels the second layer
of processing may reestimate the likelihood that this pixel has
detected a muzzle flash. To this end the second layer of processing
may, for example, check whether the suspicious pixel belongs to a
two-dimensional (2D) projection of trajectory of an object crossing
the field of view and generating a strong light signal. In such
case the likelihood corresponding to this pixel may be decreased,
because the signal could be produced by a strong sunlight reflector
or artificial light source, e.g. by a bird crossing the field of
view or a car light or a sun glint. A tracking test aimed at
discriminating pixels grouping in trajectories may be based for
example on the Hough Transform. For another example of the
operation of the second level processing, the likelihood
corresponding to a suspicious pixel may be increased if this pixel
has neighboring pixels which signals or likelihoods are indicative
of an existence of a pixel group having a muzzle flash
characteristic shape. For example, this characteristic shape can be
similar to the infinity sign. For yet another example of the
operations performable by the second level processing, the
likelihood corresponding to a suspicious pixel may be adjusted
according to the spatial and temporal characteristic of the pixels
signals. Such adjustment may account for the possibility of fire
bursts. If the second layer of processing receives two or more
suspicious flashes separated by a certain characteristic time
period and possibly by few pixels, it can increase the likelihoods
of these events being muzzled flashes, because they could be
produced by e.g. a machine gun. On the contrary, detection of
aperiodic suspicious events separated by small time periods may be
indicative of the absence of muzzle flashes, because there would be
no enough time for weapon recharge. The above-described processing
is facilitated if signals produced by the PDA and/or first layer of
processing are stored in a memory for a time period in which they
may be useful for the second and other layers of processing. The
data from the PDA and/or first layer when they are prepared for
further use can be sampled or transformed, e.g. partially averaged,
into less broadband data. The data also can be compressed (without
loss of information) and stored in the memory in the compressed
form.
[0278] The first layer of processing thus may work with the second
layer of processing in a Constant False Alarm Rate regime (CFAR
regime): a constant stream of suspicious (candidate) events from
the first layer may be selected and processed by the second layer.
The second layer is designed to handle a predetermined constant
flow of suspicious events (e.g. 10 or 20 per frame). Due to the
significant data reduction performed by the first layer (e.g. from
.about.100,000 pixels per frame to .about.10 suspicious pixels per
frame), the second layer has significantly more time per pixel to
analyze the suspicious events. A suspicious event is confirmed and
an actual alarm is produced if the reestimated likelihood of that
the corresponding suspicious pixel has detected a muzzle flash
event is larger than a certain threshold.
[0279] FIG. 1B schematically illustrates an example of a system 50
configured in accordance with the technique of the inventors.
System 50 includes one or more of the following: collecting optics
5; an optical filter 10; a photodetector pixel array 20; a shutter
21, a processing system 22. Collecting optics 5 may be configured
to define a certain chosen FOV in a certain chosen wavelength
(sub)region (e.g in a broader NIR/SWIR region). Optical filter 10
may be configured to pass light corresponding to bands of low
atmospheric transmission, particularly in the chosen NIR/SWIR
wavelength region. PDA 20 is sensitive in the corresponding
NIR/SWIR bands. Shutter 21 may be an electronic shutter defining
the small PDA integration time, as specified above. Additionally or
alternatively, shutter 21 may be configured to define a small dead
time. Shutter 21 may be a rolling shutter. Subsystem 22 performs
the processing of electric signals (i.e. of a video stream)
produced by PDA 20 operated by shutter 21.
[0280] In the present example, subsystem 22 includes a level-0
processing unit 25, a calibration utility 24, a level-1 processing
unit 35 performing parallel processing, a pixel selection unit 40,
a level-2 processing unit 45, a compression utility 44, and a
memory utility 46.
[0281] Level-0 processing unit 25 may apply a non-uniformity
correction (i.e. correction for the non-linearity of PDA response)
to the raw signal from the pixels. Calibration utility 24 may store
a bad pixels map for photodetector 20 (the bad pixels can be found
during calibration of the photodetector). During operation of the
inventors' gunshot detection system, calibration utility 24 can
eliminate the bad pixels from the data which are input to level-1
processing unit 35. Level-0 may be configured to find motion
vectors.
[0282] Level-1 processing unit 35 performs, as described above and,
more specifically, below, while referring to the examples of FIGS.
2A-2B and 3A-3D, the data reducing processing aimed at detection of
muzzle flash, particularly through selection of muzzle-flash
time-dependency in the received signals. The level-1 may use
relatively simple algorithms (such as second order derivative) to
identify signals which resemble a muzzle flash time signature. In
the parallel implementations, the layer-1 analyzes the time
dependent signal from each pixel independently of other pixels, in
order to reduce computing power. The level-1 processing typically
allows achieving effective data reduction of 3-6 orders of
magnitude for level-2 processing or for alarm rate (the data
reduction for level-1 can be defined as a number of pixels divided
by a number of suspicious pixels in a frame). The level-1 and
level-2 may utilize for connection a pixel selecting utility 40,
such as the CFAR utility, so that a number of suspicious events
does not overflow layer-2 processing capacity. For each of the
suspicious pixels the layer-2 processing may need to obtain the
values of its neighboring pixels, several frames before and after
the suspicious event occurred. To this end outputs of the PDA or
any level (level-0, level-1 and/or level-2) processing unit may be
stored in memory utility 46.
[0283] The pixel-selecting utility 40 can prepare a list of
candidate pixels for the layer-2. To this end, this utility can
compare the likelihoods calculated by the layer-1 or it can
generate the likelihoods based on the outputs of the layer-1. It
also may be configured to connect with level-0 and/or memory (these
connections are not shown on FIG. 1B), because it may use
historical or spatial data to calculate temporal and spatial
statistics for pixels, for example statistics on luminance level in
the vicinity of the pixel of the candidate event and/or before
and/or after the occurrence of the candidate event in order to
evaluate the spatial statistical significance of the event. Indeed,
the utility may benefit from taking into account information
gathered after the candidate event had occurred, if it is
configured to use for reestimation data obtained after a candidate
event, in addition to or instead of the historical data. To this
end, a delay of several tens to hundreds of frames between data
processed in the second stage and in the first stage may be
utilized.
[0284] Level-2 processing unit 45 implements the above-mentioned
second layer of processing aimed at determining suspicious pixel(s)
and reestimating the likelihood(s) that the system has detected a
muzzle flash. For this purpose, the second layer of processing may
use signals obtained from neighboring (close) pixels and/or signals
obtained at close time moments. Hence, level-2 processing unit
combines signals received from level-1 processing unit 35 through
pixel selection unit 40 and/or uses signals stored in level-1
memory utility 46. It also may store data that it produces (e.g.
likelihood estimates) in memory utility 46 and may access the data
earlier recorded in this memory. The processing implemented by
level-1 and level-2 processing unit may be in accordance with the
bad pixel map.
[0285] In particular, level-2 unit may be configured to reestimate
the muzzle flash likelihood in view of a possibility of the
splitting of the muzzle flash projection to several close or
adjacent pixels (e.g. 2 or 4 pixels), which together represent the
same event. In this connection, it should be noted, that a muzzle
flash projection may not lose its specific shape, such as heart
shape, balloon shape, droplet shape round shape. At short
distances, the details of the shape may be imaged, analyzed by the
level-2 unit, and used for confirmation or rejection of muzzle
flash event and for localization of the respective muzzle
flash.
[0286] Level-2 unit may also be configured to reestimate the muzzle
flash likelihood in view of a possibility of various timings of the
muzzle flash relatively to the samplings, in order to take into
account the variability of the sampled muzzle flash waveform.
Indeed, a muzzle flash does not have to occur within a single
integration interval, it can begin in one frame and end in a
different frame.
[0287] Turning back to the level-0 processing, it may also be
configured to analyze the motion in the pictures, and generate
frame to frame motion vectors for blocks of m times n pixels, so
that clutter and background can be accurately deducted at the
further layer(s). The frame to frame motion vectors may be
generated by using a block matching algorithm proved useful for
motion compensation. As in MPEG applications, the generation of
motion vectors may be implemented in software or in hardware, in
FPGA or ASIC. In some of the preferred adaptations (embodiments),
the generation of motion vectors is performed by a programmed FPGA.
In another option the generation of motion vectors is performed at
layer 2 and only for suspicious (i.e. candidate) events.
[0288] Referring to FIGS. 2A and 2B, there are schematically
illustrated two examples, respectively, of a gunshot and muzzle
flash detection system of the present invention. The detection
system is configured to receive radiation from a certain field of
view and detect whether the received radiation contains a portion
emitted by a muzzle flash.
[0289] In the example of FIG. 2A, a detection system 100 includes a
light collecting and focusing optics 5 (e.g. a lens assembly formed
by one or more lenses) in front of a photodetector pixel array unit
20A, a parallel processing unit 30, and a control unit 38.
[0290] Lens assembly 5 collects light Lin from a region of interest
and may have a wide field of view of tens of degrees in each
lateral direction. It focuses light Lin onto photodetector array
20A. The region of interest can include a range of distances up to
several hundred meters, e.g. a range up to 500 m from the lens
assembly. The light focusing is applied to a predetermined
wavelength range. It should be understood that the lens assembly
may be operable by the control unit or manually by a user to focus
light from a different field of view and/or to focus light of a
different wavelength range. Though in the present example the lens
assembly is a constructional part of the detection system,
generally this is not a requirement.
[0291] Photodetector array 20A can be of any known type sensitive
to a subrange of ultraviolet/visible/infrared spectra.
Photodetector array 20A may be based, for example, on PbS, InAs,
GaAs, InGaAs, MCT, PbSe, or InSb for relatively fast and low cost
NIR, SWIR or MWIR detection. In some preferred embodiments the PDA
is light, fast, sensitive, inexpensive, and does not require
cooling and much power for operation. Also, in some preferred
embodiments the photodetector array has a large pixel count
detection array and allows accurate determination of a muzzle flash
event location. The sensitivity of various materials used in
photodetectors is shown on FIG. 2C, as a dependent of wavelength.
The technique of the inventors may utilize for example InSb (Indium
Antimonides) and MCT (HgCdTe) at 77K for MWIR imaging, and InGaAs
(300K) and Ex InGaAs (253K) for SWIR imaging.
[0292] The inventors have found that the NIR/SWIR detection of
muzzle flash can be utilized in the in-field muzzle flash detection
applications. This is because in addition to energy in the
MWIR/LWIR, the hot gasses of the muzzle-flash emit blackbody
radiation energy in the NIR/SWIR range.
[0293] Nevertheless, the inventors have chosen to use
photodetectors sensitive to NIR and/or SWIR light for the purposes
of muzzle flash detection in some embodiments of their technique.
This is because the inventors have considered that photodetectors
having the desired characteristics for their application are more
easily available in NIR/SWIR than in MWIR/LWIR and possible losses
in optical signal may be overcompensated by gains from a higher
sampling rate (smaller integration and dead time) and frame rate of
NIR/SWIR detectors; from the use of the solar blind filters which
reduce clutter and enhance signal to clutter ratio; from the
increased availability of higher resolution in the NIR/SWIR
detectors due to the higher maturity and lower cost of PDA
materials in this range; and from the relaxed need or lack of need
for cooling the PDA for achieving high performance. (Already the
relaxed need is beneficial, because cryogenic coolers become
smaller, lighter, less power-consuming, and costly with the
decrease of the PDA size and heat dissipation). For example, a
combination of NIR/SWIR optics and photodetector is typically
smaller than a similar combination of MWIR/LWIR optics and
photodetectors, because diffraction effect is smaller in NIR/SWIR,
a larger variety of optical materials and manufacturing techniques
is available, and NIR/SWIR detectors are faster and do not require
cryogenic cooling to provide fast and sensitive detection. The
technique of the inventors typically involves photodetectors having
a quantum efficiency of more than 20% in NIR/SWIR range used for
detection.
[0294] In connection with the above, it should be noted, that many
features of the invention are not restricted to the NIR/SWIR range.
In particular, the inventors have considered that detection systems
utilizing other wavelength ranges can also utilize the layered
architecture, the filtering of light of the low transmission in
atmosphere, the suppression of candidate events produced by an
inappropriate group of pixels, the shutting scheme providing the
small dead time, the light collecting scheme providing relatively
large field of view per pixel.
[0295] Parallel processing unit 30, capable for example of
implementing level-1 processing unit 35 of FIG. 1B, is configured
and operable according to the invention for filtering the
electrical output of the pixel array for detecting or selecting a
muzzle flash-type signal portion (e.g. for suppressing all signal
portions except for possibly present flash-type signal). The
processing unit may include an array of analog processors. These
processors may be configured for simultaneous operation. In some
other embodiments processing unit 30 is configured to perform
analog-to-digital conversion and process the digital data. The
operation in the digital configuration may be partially sequential.
The analog-to-digital conversion may be done before the level-1
processing unit, for example already at the PDA output.
[0296] Detector device 100 is associated with a control unit 38,
which may or may not be a constructional part of the system. The
control unit is connected to the output of the first level, for
example parallel, processing (sub)unit (via wires or wirelessly)
and may perform the second layer of processing. The level-2
processing unit 45 and memory utility 46 of FIG. 1B may be
implemented in control unit 38.
[0297] Control unit 38 is typically a computer system including
inter alia a digital signal processor 42, a memory 46, and
input/output utilities, generally at 48. The control unit is
configured for receiving and further processing data from analog or
digital, parallel, processing unit 30; and possibly also for
controlling at least some of the elements of the detector device.
For example it may perform the second layer of processing and/or
control the lens assembly, filter(s), PDA settings (i.e. settings
of the level-0 processing e.g. those input into level-0 processing
unit from level-0 processing utility), parallel processing unit
settings (threshold for pixel selection). It also may be configured
for receiving and/or providing signals to an operator. Input
utility 48 of control unit 38 may be configured to pass a limited
number of candidate pixels to the second layer of processing, for
example it may be configured to work in the CFAR regime.
[0298] In the example of FIG. 2B, showing another preferred
embodiment of the muzzle flash detection system of inventors,
detection system 100 includes a photodetector unit 20B associated
with a light collecting and focusing optics 5, an optical filter 10
accommodated in the optical path of light propagating towards the
pixel array 20, and an analog (in this case analog parallel)
processing unit 30 at the output of the pixel array. Filter 10 is
configured and operable to enable detection of relatively
short-living muzzle flash components, as will be more specifically
described further below with reference to FIGS. 5A-5C. Filter 10
may be a stand alone unit or may be integrated within an
intracavity detector. Photodetector unit 20B with filter 10 is
sensitive to substantially a spectral range corresponding to
relatively low light transmission in atmosphere. To this end, the
sensitivity of such arrangement to at least one wavelength of the
utilized low atmospheric transmission spectral range may be between
10% and 30%, or between 30% and 50%, or between 50% and 75%, or
larger than 75%. An average sensitivity of such arrangement to
wavelengths outside such range and present in daylight and to which
the photodetector (i.e. the imager) is fundamentally sensitive, may
be smaller than 10% (or 5%, or 1%).
[0299] Also device 100 may include a phase mask 8. The phase mask
may perform signal processing in the optical domain, for example,
subtraction of signals of two different wavelengths.
[0300] Further in FIGS. 3A-3D there are exemplified some possible
configurations of the processing (sub)system carrying out the
layer-1 in-pixel processing and, in case of FIG. 3D, also the
layer-2 processing. It should be understood that the layer-1
processing unit may be formed by an array of operating in parallel
individual processors, each of which is associated with the
detector pixel, and that the design of the parallel processing unit
is aimed at filtering muzzle flash time domain features in the
received signal, for example at amplifying the possibly present
signal portion having a time-dependence of a type producible by a
muzzle flash while removing other signal portions. The features to
be suppressed or removed from the photodetector signal are those
caused by noises and clutter. Hence, a pulse to be filtered by the
level-1 processing utility is that which has a well defined peak, a
muzzle flash type duration (for most firearms this duration is up
to about a few milliseconds) and an asymmetric form typical to the
muzzle flash. Other signal portions in the photodetector detector
pixel output are considered as associated with clutter or
noise.
[0301] The processing unit (e.g. 35 in FIG. 1B or 30 in FIGS.
2A-2B), in particular the parallel processing unit, may be an array
of matched filters. In this connection, FIG. 2A shows a pulse P
created at the photodetector output in response to a muzzle flash
and a time response characteristics TR of the matched filter
processing unit. Pulse P presents only the portion of a
photodetector output (SPD in FIGS. 2A-2B); however other portions
of the photodetector output are filtered out by the match filter.
One of the uniquenesses of pulse P lies in its asymmetric variation
with time. Pulse P grows from zero to a maximum in a first
predetermined time interval, and falls back to zero in a second,
typically longer, predetermined time interval. The second time
interval may be about two times longer than the first time
interval. The matched filter is adapted to detect the uniqueness of
the muzzle flash signal. Various matched filter physical
implementations, either analog or digital, are known per se and
therefore need not be described in detail. It should be noted,
however, that in some preferred embodiments the muzzle flash
features are filtered by in-pixel analog processing, such as
parallel in-pixel analog processing, or by separate digital
processing following an analog-to-digital converter (ADC). The
in-pixel processing can achieve very high speed, while keeping the
bandwidth of the output signal low (after the use of
pixel-selecting unit). This allows the next level of processing to
operate on a reduced input rate of suspicious events. It also
allows using the specific time-dependency or shape of signal for
better distinguishing between true events and other short but
different events. In some embodiments, the processing speed of the
first level of processing is selected to match the PDA sampling
speed, which is selected to produce at least several samples within
the time of the muzzle flash.
[0302] FIGS. 3B and 3C show specific but not limiting examples of
an analog in-pixel processing unit 30P adapted to filter in the
output of a photodetector pixel a muzzle flash type signal portion.
This portion has light intensity behaving as an asymmetric pulse of
a muzzle flash duration i.e. it has a characteristic muzzle flash
time variation.
[0303] In the example of FIG. 3B, analog processing unit 30P
processes a signal SPD from a pixel 22 of the photodetector array.
Unit 30P includes an integrating circuit 32, a delay utility 34, a
subtraction circuit 36, and a switch 33. Signal SPD is integrated
by a circuit 32. Switch 33 is clocked with a predetermined time T
(i.e. is shifted for a short time into its ON state with increments
of time T). Time T is substantially equal to a delay time of delay
utility 34 and is smaller than a pre-estimated time-width
(duration) of a muzzle flash pulse at the photodetector output
(e.g. pulse P shown in FIG. 3A). Since the integrated signal is
output to one input of subtraction circuit 36 and also, through
delay utility 34, to the other input of subtraction circuit 36, the
time change of the pixel output is determined. The result of
subtraction forms an analog signal SA, which then may be directed
to the memory utility and/or the pixel selection utility (and then
to the level-2 processing unit) and/or to the control unit.
[0304] In the example of FIG. 3C, analog processing unit 30P
includes a band pass filter 31, a peak detector 35, and two
switches 33A and 33B. A signal SPD from a pixel 22 of the
photodetector array is passed through band filter 31 to peak
detector 35. The band of filter 31 is selected so as to allow
passage of frequencies corresponding to Fourier transform of a
pre-estimated muzzle flash pulse at the photodetector output (e.g.
pulse P shown in FIG. 2A). Peak detector 35 outputs a peak value of
this pulse at its output node 35out. Switch 33A is a reset switch
for resetting a peak detector output 35out to zero once during a
certain time interval T1. Switch 33B is an output switch for
outputting the peaks to a control unit 38 (which is not shown in
this figure). This output is done right before the reset of the
peak detector. A sequence of the peak values forms an analog signal
SA. So designed analog processing unit 30P can select a signal
portion corresponding to a pulse of the flash-type intensity
variation with time in signal SPD. Peak detector 35 enables the
detection of the muzzle flash peaks in case of reset time T1 being
shorter or longer than the time-width of a muzzle flash pulse.
However, in some preferred configurations, the reset time T1 is
selected to be shorter than the pre-estimated time-width of muzzle
flash pulse, because such a selection allows for comparing a
time-width of a received pulse with the pre-estimated time-width of
the muzzle flash and also because such a selection allows for
resolving signals from consecutive muzzle flashes.
[0305] Moreover, when time T1 is selected so as to be several times
(e.g. 10) shorter than the time-width of a muzzle flash pulse, the
analog processing unit can detect an asymmetry of a signal portion
corresponding to a pulse of the flash-type intensity variation with
time.
[0306] It should be understood that the technique of the inventors
is not limited to the above examples of the analog processing unit.
Other configurations of analog processing unit 30P may include
various circuits, including such known per se circuits as a
differencing circuit, a sample-and-hold circuit, a comparator, a
low pass filter, a high pass filter, an envelope detector. In some
preferred embodiments, the analog sampling is carried out with a
sampling rate less than a tenth of the duration of the selected
signal.
[0307] Thus, the analog processing unit may be configured to have a
time response allowing identification of the above-described
asymmetric pulse P. The analog processing may be useful for
facilitating a further digital processing (sampling, layer-2
digital processing) if it follows.
[0308] Another example of the processing system of the invention is
shown in FIG. 3D. This in pixel signal processing subsystem has a
first stage, in which signals obtained from different pixels are
not combined, and a second stage in which these signals are
combined. In the first stage a sensing element SE (i.e. a pixel)
sends a detected signal to a charge integrating transimpedance
amplifier (CTIA) circuit integrating the signal. Signal then
propagates to a variable signal detection, which deducts a Low Pass
Filter (LPF) averaged signal from the current signal. The result is
then input to a fast shift register, where the signal is processed
by a programmable logic, e.g. by a programmable logic implementing
the matched filter. The output of the register determines a
likelihood that an event has occurred within a given time frame.
The first parallel stage of processing finishes here. The signal
then is input into a slow shift register. The values in the slow
shift registers are co-processed with values in slow shift
registers of adjacent pixels. This co-processing is performed using
a mask bit latch or other logic, filtering the signals for portions
having a spatial signature of the event to be detected typically
for the event taking place in the middle of the mask. The mask
scans the entire image area in order to check for an event in each
of the pixels. This architecture may be used for other algorithms,
such as video motion detection, video tracking, Automatic Target
Recognition.
[0309] In another example, the system of the invention can be
organized as follows. The system uses a typical PDA and digital
processing. The PDA sends signals to a processing board, where they
are sampled and transformed into digital signal, containing the
signal level detected at each of the pixel. This digital signal may
be parallel. The digital signal is input into the layer-1
processing unit. For example, the interface between the PDA with
the processing board can be a digital communication link such as
the "Camera Link" standard. A possible bit-stream of the digital
signal can be estimated: for a 200,000 pixel detector working at
500 frame/sec rate and using 12 bit encoding of the analog signal,
the bit stream needs to be as high as 1 Gbps. The system therefore
uses the layered processing scheme, which can allow sampling at the
selected frame rate (e.g. 500 frames/sec). The processing at low
rates may be configured without a matched filter; it may be rather
configured to find at the second layer short events that appear in
1-2 frames and then vanish, where the suspicious events reaching
the second layer are those which prevail over a threshold,
established by the second layer's pixel selection utility (e.g.
CFAR utility), applied to the digital first layer. Such digital
layered processing may be performed in an ASIC or a field
programmable gate array (FPGA), for example of the Xilinx Vertex
family. Layer-1 can be hard coded into the FPGA, while the layer 2
algorithm (all or part) can be exercised in software, either based
on a processor core implemented in the FPGA, or on a separate
processor, such as control unit's processor. The algorithm can be
partially simultaneous and partially sequential--i.e. not all, but
several, pixels are processed simultaneously.
[0310] Referring to FIGS. 4A and 4B, the operations performed by
the analog or digital parallel processing unit are more
specifically described. FIG. 4A exemplifies a photodetector signal
SPD to be processed by the analog processing unit. Signal SPD is
composed of clutter and various noise portions, and has a muzzle
flash peak P1.
[0311] FIG. 4B exemplifies a signal SPD', a derivative of signal
SPD of FIG. 4A. The derivation can be performed by means of a
differencing circuit or subtracting circuit (36 in FIG. 3B).
Additionally, before the derivation, a low pass filter can be
utilized to remove from signal SPD the features corresponding to
very short events, i.e. events much shorter than the time width of
pulse at the photodetector output. Thus received signal SPD' has a
portion P1' corresponding to the muzzle flash and carries reduced
noise and clutter.
[0312] Signal P1' can be output directly from the parallel
processing unit or through an absolute value peak detector (not
shown), clocked with time that in some preferred embodiments is
shorter than the time between positive and negative extremes of
signal P1'. If the absolute peak value detector is used, then the
extremes of signal P1' are not lost from a sample of output signal
used by a digital processor 42 of control unit 40.
[0313] Considering the above mentioned uniqueness of the muzzle
flash pulse (P in FIG. 3A), this results in a uniqueness of pulse
P1': the magnitude of the positive peak of pulse P1' is
approximately two times larger than the magnitude of the negative
peak, but the duration of the positive part of pulse is two times
shorter than of the negative part. Thus, if pulse P1' is sampled
three times by the peak detector, the following sequence of values
will be generated: 0, +x, -x/2, -x/y, 0 (this sequence presents a
not limiting example). Here, x is a magnitude of the positive peak
of pulse P1', it depends on the shooter-detector distance; y is
some number greater than 2.
[0314] In addition to the processing unit reducing some noise and
clutter, the system of the invention may use other means to perform
muzzle flash detection with high probability and low false alarm
rate. For example, a filter, processing received light before its
detection by the pixel array (e.g. filter 10 in FIG. 2B), can be
used to increase the SNR/signal to clutter ratio.
[0315] Reference is made to FIGS. 5A-5C exemplifying the principles
underlying the filter selection. FIGS. 5A and 5B show a wavelength
dependence of the atmospheric transmission in the NIR and SWIR in
short ranges of 100, 200, and 300 m. It is seen that the
transmission is very low for example in a range around a wavelength
of 1.4 .mu.m. According to the invention, the ranges of the low
atmospheric transmission may be used to facilitate the muzzle flash
detection. Here are some of these ranges: 1.34 to 1.50 microns,
1.80 to 2.00 microns, 2.50 to 2.90 microns, 4.1 to 4.4 microns, 5.5
to 7.3 microns. In some preferred embodiments the first and/or the
second of these ranges are used. In some preferred embodiments, the
filter allows passage of not more than 50% of incident energy for
wavelengths being outside the low atmospheric transmission ranges
and sensed by the pixel array. In some other preferred embodiments,
the filter passes not more than 25%, 10%, and 2% of this
energy.
[0316] FIG. 5C illustrates an effect of increased signal to clutter
ratio in the ranges of low atmosphere transmission. Graph G1 shows
the sun irradiance, i.e. the intensity of sun radiation, on a clear
day at the sea level. Graphs G2, G3, G4 show ratios of the
intensity of light produced by an exemplary muzzle flash
respectively at distances of 100, 200 and 300 m. from the detector,
to the sun irradiance of graph G1. Graphs G2, G3, G4 have evident
peaks corresponding to the ranges of low atmospheric transmission.
These peaks correspond to the increased signal to clutter
ratio.
[0317] It should be noted, that peaks in graphs G2, G3, G4 can
decrease with an increase in the atmosphere humidity level. In this
case the spectral range may be widened to include wavelengths of
smaller atmospheric absorption.
[0318] The effect of the clutter can be considered in more detail.
The clutter is composed of several components. The first component
is the sun radiation and reflections of sun radiation from various
objects (e.g. from vegetation such as grass and leaves); the
maximum of this radiation is within the visible range. This sun (or
solar) clutter is non-uniform and impedes the muzzle flash
detection. This is because its illumination power and power
variation may be similar to the muzzle flash; for example its
non-uniformities might cause signal glitches that might be wrongly
interpreted as a muzzle flash when the detector is moved.
[0319] The second clutter component (the so-called "blackbody
clutter" is a black- or gray-body radiation of the detector
environment (e.g. air, building walls, etc.). The detector
environment has a relatively low temperature (when compared to the
temperature of the Sun); it emits light, which wavelength
distribution has a maximum intensity in LWIR (e.g. 10 micron). It
should be noted that the detector environment temperature is
distributed non-uniformly; in some cases these non-uniformities
present a useful signal.
[0320] The technique of the inventors can treat the above clutter
components differently. According to the invention, the
photodetector array may be of a type insensitive to the MWIR and
LWIR ranges. Thus, the second clutter component (the blackbody
clutter) does not generate a significant signal at the detector
output. The solar clutter can be detrimental during the day or the
night, if moonlight is present; but it can be almost totally
prevented by the narrowing of the imaged spectrum to the
wavelengths in the region(s) of low atmospheric transmission,
because at these wavelengths solar or moon light reaching the earth
surface is attenuated to essentially zero intensity.
[0321] The case when both clutter components are eliminated from
the photodetector array signal may be preferred also because it
provides for significantly reducing the shot noise associated with
the signal. The shot noise is proportional to the square of the
total signal: thus, if clutter is not eliminated, it causes a shot
noise that could be comparable with the muzzle flash portion of the
signal. Moreover, this noise might occasionally produce glitches
having temporal and spatial features somewhat similar to those of
the muzzle flash because the shot noise would be non-uniform even
if the clutter causing it would be uniform.
[0322] It should be noted that, as it follows from the blackbody
clutter wavelength distribution, the clutter and the shot noise can
be eliminated for the larger portions in the NIR rather than the
SWIR range.
[0323] Also, it should be noted, that the invented technique of
maximizing the signal to noise ratio (SNR) is different from a
common technique. While the latter would suggest filtering a signal
in a frequency range around the signal's peak(s), the technique of
the inventors can utilize imaging in the wavelength regions being
remote from the muzzle flash signal peak.
[0324] The narrowing of the imaged spectrum to the band(s) of low
atmospheric transmission is done by means of the optical filter
(which may be of any known type), which may be an external filter
or may be integrated with the photodetector array; e.g. by
introducing a narrow band cavity within the photodetector
array.
[0325] It should be understood that the use of the band filter is
beneficial when the solar clutter is the limiting factor. At night,
the solar clutter is orders of magnitude lower and the detector
noise becomes the limiting factor. Thus, at night, the filter can
be removed or not operated. This would improve the gunshot
probability of detection to false alarm count ratio, as well as
would allow for night vision, when SWIR is used. Hence, the filter,
if being present in the device, is configured in some of the
device's preferred embodiments to be shiftable between its
operative and inoperative states.
[0326] Although the narrowing of the imaged spectrum to the low
atmospheric transmission regions can increase the SNR at daylight
or moonlight, it should be done so as to allow propagation of
sufficiently wide wavelength range(s) to the photodetector. If the
signal arriving to the photodetector is too small, the detection
will be compromised by the internal (e.g. dark) noise of the
detector and the shot noise of the signal. It also should be noted
that before arriving to the photodetector the signal is attenuated
by the atmospheric absorption and the absorption of the filter.
Thus, the exact edges of the filtered wavelength range(s) can vary,
so as to maximize the total SNR ratio, in which both clutter and
noise are taken into account.
[0327] It should be noted that the control unit (or the layer-2
processing unit) can be configured to implement several processing
tasks. First, in accordance with the above, it may be configured to
determine whether one or a group of the digital or analog layer-1
output signals corresponds to a muzzle flash signal. This may be
done by processing the temporal and spatial features of the digital
or analog signals, e.g. by comparing the intensity of the analog
signals with a certain threshold, or by comparing the received
analog signals with various muzzle flash signatures stored in a
database in the memory utility. For instance, if an analog
processing unit differentiates the photodetector output or
subtracts sequential readings of the photodetector output, the
analog signals corresponding to a muzzle flash event will have a
"positive peak followed by negative peak" signature, e.g. a
signature as in FIG. 4B. Also, the muzzle flash radiation can be
focused on more than one pixel of the photodetector array (e.g. if
the center of the muzzle flash focuses on a line separating the
pixels). The control unit can take into account the division of the
optical signal between several adjacent pixels.
[0328] Second, the control unit may be configured to determine the
wavelength range(s) being optimal for detection (i.e. maximizing
the SNR ratio). It can facilitate operating the optical filter
(e.g. filter 10) and/or the collecting optics so at to achieve this
high SNR and/or output these data for the operator's review. Also,
the control unit may estimate a distance between the detector and
the muzzle flash, for example from the detected intensity of the
optical signal; as well as to determine the type of weapon that was
shot, etc.
[0329] The control unit can be configured to tune the optical
filter so as to periodically change its passing band to define a
time multiplexing scheme for the muzzle flash detection in more
than one wavelength range. For example, the photodetector may be
sensitive to two different subbands in the NIR/SWIR ranges, or to a
region of ultraviolet/visible range and a region of NIR/SWIR range;
etc. Thus various time-multiplexing schemes can be realized. It
should be understood that the relative intensities of signals of
various wavelength bands carry additional information, for example
about the distance to the muzzle flash, in particular due to the
difference between atmospheric absorption coefficient being
pertinent to the various wavelengths.
[0330] It should also be noted, that the time-widths (durations) of
muzzle flash pulses corresponding to different bands are generally
different. For example, ultraviolet radiation is emitted as a
result of the electron transitions between different molecular
levels during the chemical reaction of oxygen and burning powder,
thus the time-width of the ultraviolet pulse is small; the NIR/SWIR
radiation pulse is a result of the thermal radiation of the hottest
gas; and the MWIR/LWIR is a result of the thermal radiation of a
cooler gas, thus the time-width of the MWIR/LWIR signal is longer.
Within the time multiplexing scheme framework, the control unit
changes the pass band of the optical filter with a rate of change
selected to allow detection of signals of the shortest time
width.
[0331] The control unit can be configured to operate digital or
analog, typically parallel, layer-1 processing unit. For the analog
layer-1 processing unit this can be done, for example, by applying
voltage to switches in this unit, so as to selectively direct the
photodetector output to the circuits designed for processing
signals corresponding to input light of different wavelength
ranges, as in the time-multiplexing scheme.
[0332] Referring to FIG. 6, there is schematically shown an example
of a weapons-firing detection system 200 of the present invention.
System 200 includes a muzzle flash detector 100 (similar to either
one of FIG. 2A or 2B), an acoustic detector 70, and a control unit
210. Control unit 210 is configured similar to the above-described
control unit and also is adapted to receive and process the output
of the acoustic detector so as to compare the detection results of
both detectors. This way, most of the false alarms of each of the
acoustic and the muzzle flash detector can be avoided: control unit
210 will generate an alarm only when each of the optical and the
acoustic detector identifies a gunshot, and a delay between these
identifications is within some meaningful limit. The delay between
the identifications events at optical and acoustic detectors
depends on the distance to the shooter and the speed of sound at
frequency sensed by the acoustic detector. Therefore, this delay
can be used for determination of the distance to the shooter.
[0333] Those skilled in the art will readily appreciate that
various modifications and changes can be applied to the embodiments
of the invention as hereinbefore described without departing from
its scope defined in and by the appended claims.
* * * * *
References