U.S. patent application number 10/166224 was filed with the patent office on 2003-12-11 for sonar display system and method.
Invention is credited to Carter, G. Clifford, Struzinski, William A..
Application Number | 20030227823 10/166224 |
Document ID | / |
Family ID | 29583731 |
Filed Date | 2003-12-11 |
United States Patent
Application |
20030227823 |
Kind Code |
A1 |
Carter, G. Clifford ; et
al. |
December 11, 2003 |
SONAR DISPLAY SYSTEM AND METHOD
Abstract
A system and method for displaying sonar data are disclosed. In
a presently preferred embodiment, each of N channels from a
beamformer are separately processed utilizing a pair of passive
broadband detection processors such as SCOT processors and SPED
processors. The output of each SCOT processor and each SPED
processor are scaled, aligned, and then compared. The maximum
scaled and aligned output from each pair of processors is selected
for input to a bearing time history display.
Inventors: |
Carter, G. Clifford;
(Waterford, CT) ; Struzinski, William A.; (New
London, CT) |
Correspondence
Address: |
Office Of Counsel, Bldg 112T
Naval Undersea Warfare Center
Division, Newport
1176 Howell Street
Newport
RI
02841-1708
US
|
Family ID: |
29583731 |
Appl. No.: |
10/166224 |
Filed: |
June 5, 2002 |
Current U.S.
Class: |
367/107 |
Current CPC
Class: |
G01S 3/8083 20130101;
G01S 7/5273 20130101 |
Class at
Publication: |
367/107 |
International
Class: |
G01S 015/89 |
Goverment Interests
[0001] The invention described herein may be manufactured and used
by or for the Government of the United States of America for
Governmental purposes without the payment of any royalties thereon
or therefore.
Claims
What is claimed is:
1. A system for displaying sonar data from a plurality of
beamformer output channels, comprising: a plurality of first
detectors, each having a first detector input and a first detector
output, and each first detector input being joined to one channel
of said plurality of beamformer output channels; a plurality of
second detectors, each having a second detector input and a second
detector output, and each second detector input being joined to one
channel of said plurality of beamformer output channels; a
plurality of comparators, each having comparator inputs joined to
one first detector output and one second detector output, and a
comparator output for providing a selected output from said
comparator inputs; and a display joined to said plurality of
comparator outputs.
2. The system of claim 1, wherein said plurality of comparators
each utilize a binary OR operation for selecting the comparator
output from said first detector output and said second detector
output.
3. The system of claim 1, wherein said plurality of comparators are
each operable for selecting a maximum value as the comparator
output from said first detector output and said second detector
output.
4. The system of claim 1, wherein said first detectors and said
second detectors utilize different types of broadband detection
schemes.
5. The system of claim 4, wherein: said first detectors utilize a
generalized cross correlation detection scheme; and said second
detectors utilize a display adapted energy detection scheme.
6. The system of claim 5 wherein said generalized cross correlation
detection scheme comprises a smoothed coherence transform detection
scheme.
7. The system of claim 5 wherein said display adapted energy
detection scheme comprises a scheme selected from a sub-band
extrema energy detection scheme and a sub-band peak energy
detection scheme.
8. The system of claim 1, wherein said display provides a bearing
versus time history display.
9. A method for displaying beamformed sonar data from a plurality
of channels, comprising the steps of: splitting each of said
plurality of beamformed sonar data channels; processing each split
data channel in at least two different detection processors;
recombining each of said split processed data channel into a
plurality of recombined data channels; and displaying said
plurality of recombined data channels.
10. The method of claim 9, wherein said processing comprises
simultaneously processing said split data channel in each
processor.
11. The method of claim 10, wherein said step of recombining
comprises performing a binary OR operation among said split
processed data channels to produce a plurality of recombined data
channels.
12. The method of claim 11, further comprising scaling each said
split processed data channel prior to said step of recombining.
13. The method of claim 10, wherein said step of processing each
data channel comprises: performing generalized cross correlation
processing on one part of each split data channel; and performing
display adapted energy detection processing on another part of each
split data channel.
14. The method of claim 13 wherein said generalized cross
correlation processing comprises SCOT processing.
15. The method of claim 13 wherein said display adapted energy
detection processing comprises processing by a method selected from
sub-band extrema energy detection and sub-band peak energy
detection.
Description
CROSS REFERENCE TO RELATED PATENT APPLICATIONS
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] (1) Field of the Invention
[0004] The present invention relates generally to sonar displays
and, more particularly, to a system and method suitable for
displaying the outputs of multiple broadband processors with
different detection algorithms whereby each multiple broadband
processor operates on N-channels of sonar data from a towed
array.
[0005] (2) Description of the Prior Art
[0006] It is well known that submarines and other vessels may
utilize different types of towed arrays of sonar sensors for
receiving sonar data. The towed array may typically have some
number, N, of channels wherein the number of channels is typically
related to the number of sonar detectors in the array. For
instance, there may be one channel output for each acoustic sensor
input to provide for conservation of energy with respect to each
sensor. Each channel output may typically be considered as a beam
"pointed to" a particular listening direction. With fewer beam
outputs, information is lost. With more beams, the outputs are
merely interpolated values of the input set. So if, for example,
there are N=10 sensor inputs, then there may be N=10 independent
beam outputs steered in N=10 different directions.
[0007] The information is processed to determine various attributes
of targets. For instance, bearing is a measure (as a function of
time) of the angle to the target (or acoustic source) relative to
true North or relative to the direction of the ship's heading.
Bearing rate is the rate of change of the bearing with respect to
time. High bearing rate contacts are close to the array and tend to
be relatively easy to spot. With respect to relative bearings, low
bearing rate contacts tend to fall into one of three categories:
opening away, running on parallel velocity, or on a collision
course.
[0008] For processing the data received by the particular type of
towed sonar array, different types of broadband detection
processing schemes may be used. Each type of broadband detection
processing scheme will typically have different advantages and
disadvantages depending on the particular type of scenario of use.
However, in the past, the output of each broadband detection
processing scheme has required a separate display format. Due to
the difficulty of viewing two different displays concurrently or
one at a time, it would be desirable to provide a single display,
such as a single bearing versus time history display, whereby the
relative advantages of each type of detection scheme are built into
a single display format.
[0009] Patents that show attempts to solve the above and other
related problems are as follows:
[0010] U.S. Pat. No. 5,481,505, issued Jan. 2, 1996, to Donald et
al., discloses a method and apparatus for detecting, processing and
tracking sonar signals to provide bearing, range and depth
information that locates an object in three-dimensional underwater
space. An inverse beamformer utilizes signals from a towed
horizontal array of hydrophones to estimate a bearing to a possible
object. A matched field processor receives measured covariance
matrix data based upon signals from the hydrophones and signals
from a propagation model. An eight nearest neighbor peak picker
provides plane wave peaks in response to output beam levels from
the matched processor. A five-dimensional M of N tracker identifies
peaks within the specified limit of frequency, bearing change over
time, range and depth to specify an object as a target and to
display its relative range and depth with respect to the array of
hydrophones.
[0011] U.S. Pat. No. 5,251,185, issued Oct. 5, 1993, to P. M.
Baggenstoss, discloses an improved sonar signal processor and
display combining the use of both coherent and incoherent signal
processors. In addition to a conventionally used matched filter
detection processor, an incoherent signal processor comprising a
cross-range energy filter and a down-range energy filter is used.
The cross-range energy filter detects objects characterized by a
narrow bearing response; whereas the downrange energy filter
detects objects characterized by a narrow range response. The
detection events resulting from the incoherent signal processor are
displayed in a subdued color to prevent distraction from the
primary display events and to reduce the false alarm rate by
allowing the sonar operator to view events in the context of
natural boundaries.
[0012] U.S. Pat. No. 5,216,640, issued Jun. 1, 1993, to Donald et
al., discloses an apparatus and method for detecting, processing,
and tracking sonar signals. Plane wave energy from the sonar signal
source is measured at multiple points using an array of plane wave
energy receptors. These measurements are processed using an inverse
beamformer to generate output beam levels. These output beam levels
are then processed using the spectrum normalizer to yield spatially
and spectrally normalized output beam levels. The normalized beam
levels are then processed using an eight nearest-neighbor
peak-picker to provide plane wave peaks. Finally, the plane wave
peaks are processed by a three-dimensioned M of N tracker to
identify peaks within a specified limit of frequency and angle
change over time. The identified peaks may be displaced or recorded
for further analysis.
[0013] U.S. Pat. No. 5,058,081, issued Oct. 15, 1991, to Gulli et
al., discloses a method of formation of channels for a sonar after
being sampled at a frequency T=1/4f.sub.0 (where f.sub.0 is the
receiving center frequency of the sonar) the signals from the
hydrophones of the sonar and having translated them to baseband,
the signals thus translated are subsampled with a period
T.sub.SE=kT (wherein k is an integer) substantially equal to 1.25
B, where B is the reception bandwidth of the sonar. A first set of
signals is subsampled at identical times to form a frontal sector.
Two further sets of signals are subsampled with delays between the
signals from two adjacent hydrophones equal to T, which determines
two side sectors adjacent to the frontal sector. The subsampled
signals are then transmitted serially by the towing cable of the
sonar device towed array and are processed in FFT circuits which
allow to form in each sector a set of channels covering the sector.
This allows to considerably reduce the data transmission rate
between the towed portion of the sonar and the portion located in
the towing ship.
[0014] U.S. Pat. No. 4,935,748, issued Jun. 19, 1990, to Schmidt et
al., discloses a blast recorder and method for monitoring and
processing vibrations from blasts, and for displaying the results
in a nearly real time basis and in a manner which is easily
interpreted by a relatively unskilled field worker and corresponds
to a form which closely correspond to the real damage causing
aspect of the blast than heretofore. The invention operates by
receiving seismic energy signals from a blast sensor, processing
the energy signals to obtain velocity signals relating to said
blast, filtering either the energy signals prior to, or the
velocity signals following said processing step, into high and low
frequency bands, to obtain high and low band velocity signals,
integrating over the period of the blast the high and low band
velocity signals to obtain high and low band displacement signals,
determining the peak velocity signal in each band, over the period
of the blast, and displaying one or all of the peak of the velocity
signal determined in the high frequency band, the peak of the
velocity signal determined in the low frequency band, and the
displacement signal related to the low frequency band.
[0015] U.S. Pat. No. 3,713,087, issued Jan. 23, 1973, to Bauer et
al., discloses an acoustical detection apparatus for determining
the direction of origin of sounds. A first acoustic receiving
system having a relatively high uniform sensitivity in a
predetermined plane and a relatively low sensitivity in and about
the direction perpendicular to the plane is provided. A second
acoustic receiving system having a spherical sensitivity pattern is
also provided. The sensitivity of the second system is set
substantially equal to the sensitivity of the first system in the
predetermined plane. Means are provided for comparing the outputs
of the first and second systems, the ratio of these outputs
indicating the direction from which received sounds are arriving.
In a preferred embodiment, of the invention, the first acoustic
receiving system has a donut-shaped reception characteristic.
[0016] The above cited prior art which does not show a suitable
means for combining the results of multiple broadband detection
processing schemes to thereby produce a single display wherein the
advantages of each type of broadband detection scheme are
incorporated without the need for viewing multiple displays
concurrently or consecutively. Those skilled in the art will
appreciate the present invention that addresses the above and other
problems.
SUMMARY OF THE INVENTION
[0017] Accordingly, it is an object of the present invention to
provide an improved sonar system and method.
[0018] It is another object of the present invention to provide a
system with one or more processes for combining the outputs from
multiple broadband detection schemes.
[0019] It is yet another object of the present invention to provide
a sonar operator with a single bearing versus time history display
which is based on the outputs of two passive broadband
detectors.
[0020] An advantage of a system in accord with the present
invention is that it is less likely to miss an acoustic
contact.
[0021] A feature of the present invention, in one embodiment, is
the use of at least two detectors operating on data supplied
through each sonar data channel to effectively split the data path
whereby the data is processed in several ways simultaneously and
subsequently recombined into one data path.
[0022] These and other objects, features, and advantages of the
present invention will become apparent from the drawings, the
descriptions given herein, and the appended claims. It will be
understood that above listed objects and advantages of the
invention are intended only as an aid in understanding aspects of
the invention, are not intended to limit the invention in any way,
and do not form a comprehensive list of objects, features, and
advantages.
[0023] In accordance with the present invention, a system for
displaying sonar data is provided which can comprise elements such
as a sonar array with a plurality of sonar sensors and a plurality
of data channels. The plurality of data channels can be split to
form a plurality of first detector channels and a plurality of
second detector channels. A plurality of comparators may be
utilized for selecting an output from each of the first detector
channels and each of the second detectors. A display can be
provided for displaying a comparator output for each of the
plurality of comparators. The plurality of comparators can in one
embodiment each utilize a binary OR operation selecting from the
first detector channel and the second detector channels. The OR
operation can be of the type which selects a maximum value from
each of the first detector channels as compared with each of the
second detector channels when the outputs of the detector channels
are not strictly binary.
[0024] The system can further comprise a plurality of first
normalizers for the plurality of first detector channels, and a
plurality of second normalizers for the plurality of second
detector channels. The comparators can be used select a maximum
output from the first normalizers as compared to the second
normalizers. Preferably, the first detector channels and the second
detector channels utilize different types of broadband detection
schemes. In a preferred embodiment, each of the first detector
channels utilizes a Smooth Coherence Transform (SCOT) processor and
each of the second detector channels utilize a Sub-band Peak Energy
Detection (SPED) processor. In one embodiment, the display is a
bearing versus time history display.
[0025] A method is also provided for displaying the sonar data
which may comprise one or more of the following steps such as
processing sonar data through a plurality of data channels,
splitting each of the plurality of data channels for processing by
at least two different detection processors, recombining each of
the split data channels to form a plurality of recombined data
channels, and utilizing data from each of the plurality of
recombined data channels for a display. The processing may comprise
simultaneously utilizing a first detector and a second detector.
The step of recombining may further comprise executing a binary OR
operation on an output related to the first detector and the second
detector to produce a plurality of OR outputs. Other steps may
include displaying the plurality of OR outputs on the display
and/or scaling the outputs of the first detector and the second
detector prior to the step of executing the OR operation.
[0026] In one particular embodiment of the invention, a SCOT OR
SPED (SOS) method is provided for displaying sonar data which may
comprise one or more steps such as providing N channels of sonar
data, detecting each of the N channels of sonar data with a
plurality of SPED detectors, detecting each of the N channels of
sonar data with a plurality of SCOT detectors, and producing
channels of data for display by performing a binary OR operation
between a SPED output for each respective SPED detector and a SCOT
output for each respective SCOT detector for each of the N channels
of sonar data. Other steps may include scaling and aligning each
SPED detector output and each SCOT detector output prior to the
step of performing the OR operation. The OR operation may comprise
selecting a maximum of the SPED output as compared to the SCOT
output. Other steps may include displaying the N channels of data
for display in a bearing versus time history display format.
Additional or alternative steps may include producing the
N-channels of sonar data with a beamformer and applying data from a
towed array with a plurality of sonar sensors to the
beamformer.
BRIEF DESCRIPTION OF THE DRAWING
[0027] A more complete understanding of the invention and many of
the attendant advantages thereto will be readily appreciated as the
same becomes better understood by reference to the following
detailed description when considered in conjunction with the
accompanying drawing wherein corresponding reference characters
indicate corresponding parts and wherein the FIGURE is a block
diagram of a sonar processor system that may be used for processing
sonar data to provide a sonar display in accord with the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0028] Presently, two types of passive broadband detection
processing schemes are frequently favored for concurrent use in
analyzing data from towed sonar arrays. One group of prior art
detection processing techniques is referred to as Generalized Cross
Correlation (GCC) methods. One type of GCC broadband detection
processing is the Smoothed Coherence Transform (SCOT) cross
correlation method; however, other types also exist in the prior
art. Another group of prior art detection processing techniques are
energy detection methods having frequency and time normalizations
for display. These methods include the Sub-band Peak Energy
Detection (SPED) method and the Sub-band Extrema Energy Detection
(SEED) method. These two types of processing, as may presently be
used with the invention, are discussed hereinafter in some detail
for reference although other types of detectors such as, for
instance, other types of broadband detection processing schemes,
could also be used. Therefore, the present invention is not limited
to use of SCOT processing and SPED processing.
[0029] Referring now to the FIGURE, where sonar system 10 in accord
with the present invention is shown in a block diagram schematic
for receiving signals received typically by reflection from objects
in response to a transmitted sonar signal. The received signals are
used to provide events or pings for display with such events
corresponding to detected objects and providing data related to a
range and a bearing of the detected object. Sonar system 10
includes sonar transducer array 12 for receiving the sonar signals.
The present invention may be used with different types of sonar
transducer arrays which can be towed by vessels such as a
submarines and ships. Transducer array 12 is coupled via signal
line 14 to beamformer 14. Beamformer 14 provides a plurality of
outputs such as outputs 18, 20, and N. Beamformer 14 is a well
known specialized electronic system that delays or adds the signals
from individual hydrophone and provides these converted signals as
outputs, such as outputs 18, 20, and N, that are electronically
steered to a particular "look" direction. Outputs 18, 20, and N
comprise streams of digital data taken at an initial sampling rate.
Each output may typically correspond to a beam or lobe
characterized by a predetermined interval of ranges and a given
bearing.
[0030] In a preferred embodiment of the present invention, each
output or channel, such as channel 18, is split as shown into two
paths, such as paths 22 and 24, respectively. The particular inputs
used by processors 26 and 28, discussed hereinafter, can be time
domain complex full beam data, time domain complex half beam data
or the like, if desired. Thus, in the present invention, each
channel is processed separately utilizing two different processing
schemes. In a preferred embodiment, the combination of SCOT
processing and SPED processing is used for processing data from
each channel as indicated at 26 and 28. Thus, in the embodiment
shown in the FIGURE, each channel is processed at least twice in a
parallel fashion prior to a subsequent recombination as discussed
hereinafter. However, it will be understood that additional or
different broadband processing schemes can be used such that the
present invention can accommodate multiple parallel processing
schemes whereby the outputs are then further processed as discussed
hereinafter.
[0031] As indicated above, at least two detection algorithms are
normally required because the performance of each algorithm is
scenario dependent. For instance, SPED outperforms SCOT for static
and low bearing rate targets, but SCOT outperforms SPED for high
dynamic targets and two closely spaced targets in bearing. "Low
bearing rate" may considered to be a bearing rate at most 6
degrees/minute or otherwise defined. "High bearing rate" may be
considered to be a bearing rate at least 12 degrees/minute unless
otherwise defined. Two targets might be considered closely spaced,
as used herein, if they have a bearing separation of no more than
two beams. For instance, suppose there are M=10 beams over 180
degrees then each beam width is nominally 18 degrees. In this case
it may be desirable to resolve targets or acoustic contacts less
than, say, for M=10, 180/M=18 degrees.
[0032] The SCOT detection scheme and the SPED detection scheme are
each preferably displayed in the form of a bearing versus time
display. Since the SCOT detector and SPED detector react
differently in different scenarios, it is desirable to utilize
information from both types of detectors. Therefore, two displays
are required in the prior art, one for SCOT and one for SPED.
Previously, the sonar operator would need to view either the SCOT
display or the SPED display one at a time or both concurrently to
determine if targets of interest are present.
[0033] The particular embodiment of the SCOT processing preferably
used with the present invention provides for an input to the SCOT
processing which is time domain complex half beam data. The SCOT
processing consists, in a preferred embodiment, of eight
subfunctions: 1) Fast Fourier Transform (FFT) processing, 2) Power
Spectrum Estimation, 3) Weight, 4) Cross Spectrum, 5) Time
Integration, 6) Complex Multiple, 7) Complex-to-Real Inverse FFT,
and 8) Display Cell Interpolation. A description of each
subfunction is given.
[0034] The FFT processing subfunction converts the complex half
beam data to the frequency domain. The FFT operation is preferably
performed four times for the shortest time update interval, as
discussed below.
[0035] The Power Spectrum Estimation subfunction consists of four
steps: 1) Hanning Windowing, 2) Square Law Detector, 3)
Sum-and-Dump Integration, and RC Integration. Each of these steps
will now be described. A Hanning window is applied to the forward
and aft FFT data blocks that were generated in the FFT processing
subfunction. The window used is a modified Hanning window that is
normalized in power and to compensate for the complex-to-real
inverse FFT. A square law detector is then applied to the Hanning
windowed FFT data and followed by a sum-and-dump integrator. The
square law detector takes the magnitude squared of the data. The
data is time averaged (sum-and-dump integrator) to three time
update intervals, IT2, IT3, and IT4. These time update intervals
are chosen based on the frequencies or frequency range of interest.
The RC Integration step is performed only when the sum-and-dump
integrated data matures. A recursively smoothed average is
calculated using the RC integrator.
[0036] The next subfunction performed after Power Spectrum
Estimation is Weight. This subfunction computes weights using the
power spectrum estimates and the low and full band filters. The
weights are computed for the IT2, IT3, and IT4 integration times.
The Cross Spectrum subfunction performs the conjugate
multiplication of the forward and aft half beam pairs. The Time
integration subfunction time averages the normalized cross spectrum
estimates to the IT2, IT3, and IT4 data rates. The Complex Multiple
subfunction applies the weights calculated in the Weight
subfunction to the cross spectrum data from the Cross Spectrum
subfunction. The next subfunction is Complex-to-Real Inverse FFT,
which converts the normalized complex cross spectrum back to the
lag domain for display cell interpolation processing. The final
subfunction is Display Cell Interpolation. Time delays
corresponding to each of the display cells are computed based upon
the speed and sound and phase center displacement values. Then
interpolation in beam space and lag domain is performed. The output
of the SCOT processing 26 is applied to scale and align element 30
as discussed subsequently. The output may comprise some discrete
number of bearing cells, say for instance 401.
[0037] The particular embodiment of the SPED processing as used in
accord with the present invention preferably has inputs at 24
comprised of time domain full beam data. The SPED processing as
preferably used herein may consist of nine subfunctions: 1) Time
Domain Weighting such as Hanning (or Hamming, triangular, etc.), 2)
Fast Fourier Transform (FFT) Processing, 3) Frequency Bin
Selection, 4) Magnitude Squared Detection, 5) Time Integration, 6)
Noise Power Estimation, 7) Azimuthal Peak Detection and Fine
Bearing Calculation, 8) Peak Integration, and 9) Azimuthal
Smoothing. Describing each subfunction in more detail, a Hanning
window may be applied to the 50% (or variable depending on
processing power available and weighting/window selected)
overlapped complex time series beam data. FFTs are performed at the
IT2 data rate using the Hanning windowed data. A total of N beams
by some number of frequency bins (.about.1024) are produced. In
order to decrease the number of computations through the rest of
the processing, frequencies outside a selected frequency range of
interest are dropped from processing. The output of Frequency Bin
selection subfunction is N beams by some number of bins (.about.720
IT2 FFT data). Each beam's frequency spectrum is then
magnitude-squared bin by bin for IT2 truncation frequency spectra.
The IT2 squared magnitude data are time averaged to the IT3
(IT3=4*IT2) and IT4 (IT4=3*IT3) data rates. The integrators are
sum-and-dump integrators. The next subfunction performed is Noise
Power Estimation. This subfunction consists of three steps: 1) Time
Smoothing, 2) Tone Removal, and 3) Quiet Beam Selection. The Time
Smoothing step obtains a mean for each beam and bin by computing a
running average of the most recent 12 IT2 samples. If the current
time cycle is IT4, the IT4 data is used as the time average. The
Tone Removal step obtains a noise mean estimate for each beam by
using the split two pass mean normalizer algorithm. At each
frequency, the second quietest beam within a specified azimuthal
sector is selected as representative of the noise at the center of
the sector. The next subfunction performed after Noise Power
Estimation is Peak Detection and Fine Bearing Calculation. For each
frequency bin, if the amplitude is greater than the corresponding
bin in each of the adjacent beams, then that frequency bin is
considered the peak. The bearing is then computed for each peak
using a parabolic fit. The subfunction is performed for the IT2,
IT3, and IT4 data. The Peak Integration subfunction takes the IT2,
IT3, and IT4 data from the Peak Detection and fine Bearing
Calculation subfunction and integrates it across the frequency.
Prior to integration, the data are normalized by the squared of the
noise value from the second quietest beam. The last subfunction is
Azimuthal (i.e., bearing) Smoothing. This subfunction is performed
on the integrated data by sliding an averaging window over the
azimuthal cells. The output of the SPED processing is estimated
power as a function bearing for some discrete number of bearing
cells, say for instance 401, of smoothed data. This process is
repeated as time progresses.
[0038] Output from SPED processing 30 is also applied to a scale
and align section such section 32. The outputs of the SCOT 32 (or
other Generalized Cross Correlation, GCC, function) are a function
of delay and have a wide range of amplitudes. Unlike the normalized
cross correlation function which goes between minus unity and plus
unity, the GCC functions like the SCOT can have larger extremes. On
the other hand the SPED (and its variant the SEED) can have
different extremes. Also the SPED (or SEED) are a function of
bearing (which is related to delay by a cosine trigonometric
function). Scale and align 30 converts the SCOT processing output
to the same abscissa as the SPED. Then both outputs are delay or
both outputs are bearing. Scaling as indicated at 30 and 32, is an
attempt to have a common or consistent amplitude normalization. One
possible method for achieving this purpose, for example only, might
be to normalize each scan so that the maximum was unity and the
minimum was zero. However, it will be understood that there are a
variety of possible methods of normalizing, including single pass
and multi-pass sector space averagers.
[0039] Outputs 36 and 38 for Scale and Align elements 30 and 32 are
applied to select element 34 which preferably performs a comparing
and selecting function. In select element 34, a selection is made
from outputs 36 and 38 to determine how data from outputs 36 and 38
will be displayed. In a preferred embodiment, the desired scaled
and aligned output 36 of SCOT 26 and the scaled and aligned output
38 of SPED 28 are selected through the process of being OR-ed
together for each channel. OR-ing, as used herein, is preferably
the process of selecting the maximum in select 34 for each of the
channels. In this example, the maximum will be the maximum of
outputs 36 and 38 for each channel. The Boolean Algebra
mathematical function called "OR-ing," as presently used herein,
can be designed to capture a maximum of output one or output two
(or other detector outputs, if used). Thus, if either sub-system of
the total system makes a detection, the system will declare an
object present. In this way, one is guaranteed the best of
performance of either of the two sub-systems. A significant
advantage of such a system is that it is less likely to miss an
acoustic contact. While OR-ing is the presently preferred comparing
or selection means, other Boolean operators (NOR, NAND, AND) or
combinations of Boolean operators, as well as other types of
comparators and/or mathematical operators could also conceivably be
utilized. Scenario dependent feedback could also be supplied to
select element 34 or other means for controlling select element 34
could be utilized.
[0040] Thus, each channel 18, 20, . . . N, will now have an output
and be applied to section 40 for display. The display will be
produced in accord with principles previously used in displaying
data such as the SCOT or SPED. Therefore the presently preferred
output from select module 34 is SCOT or SPED which is herein
referred to as SOS. The SOS system, method, or algorithm eliminates
the need for two different displays to be viewed either
concurrently or consecutively by a sonar operator. Therefore, sonar
operator overload is reduced. Furthermore, since the sonar operator
needs to view only one display, the time required to determine if
targets of interest are present is reduced.
[0041] It will be understood that many additional changes in the
details, materials, steps and arrangement of parts, which have been
herein described and illustrated in order to explain the nature of
the invention, may be made by those skilled in the art within the
principle and scope of the invention as expressed in the appended
claims.
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