U.S. patent application number 13/022104 was filed with the patent office on 2014-08-21 for multi-mode seekers including focal plane array assemblies operable in semi-active laser and image guidance modes.
This patent application is currently assigned to RAYTHEON COMPANY. The applicant listed for this patent is Robert Rinker. Invention is credited to Robert Rinker.
Application Number | 20140231576 13/022104 |
Document ID | / |
Family ID | 44947173 |
Filed Date | 2014-08-21 |
United States Patent
Application |
20140231576 |
Kind Code |
A1 |
Rinker; Robert |
August 21, 2014 |
MULTI-MODE SEEKERS INCLUDING FOCAL PLANE ARRAY ASSEMBLIES OPERABLE
IN SEMI-ACTIVE LASER AND IMAGE GUIDANCE MODES
Abstract
Embodiments of a multi-mode seeker are provided for use in
conjunction with a predetermined laser designator. In one
embodiment, the multi-mode seeker includes a focal plane array and
a bi-modal processing system. The focal plane array includes a
detector array and a Read-Out Integrated Circuit (ROIC) operatively
coupled to the detector array. The bi-modal processing system is
operatively coupled to ROIC and is switchable between: (i) an
imaging mode wherein the bi-modal processing system generates video
data as a function of signals received from ROIC indicative of
irradiance across the detector array, and (ii) a semi-active laser
guidance mode wherein the bi-modal processing system generates
line-of-sight data as a function of signals received from ROIC
indicative of laser pulses detected by the detector array and
qualified as corresponding to the predetermined laser
designator.
Inventors: |
Rinker; Robert; (Tucson,
AZ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rinker; Robert |
Tucson |
AZ |
US |
|
|
Assignee: |
RAYTHEON COMPANY
Waltham
MA
|
Family ID: |
44947173 |
Appl. No.: |
13/022104 |
Filed: |
February 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61317923 |
Mar 26, 2010 |
|
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|
Current U.S.
Class: |
244/3.16 ;
348/116 |
Current CPC
Class: |
F41G 7/2253 20130101;
F41G 7/008 20130101; F41G 7/226 20130101; F41G 7/2213 20130101;
F41G 7/2246 20130101; F41G 7/2293 20130101 |
Class at
Publication: |
244/3.16 ;
348/116 |
International
Class: |
F41G 7/22 20060101
F41G007/22 |
Claims
1. A multi-mode seeker configured to be utilized in conjunction
with a predetermined laser designator, the multi-mode seeker
comprising: a focal plane array, comprising: a detector array; and
a Read-Out Integrated Circuit (ROIC) operatively coupled to the
detector array; and a bi-modal processing system operatively
coupled to ROIC and switchable between: (i) an imaging mode wherein
the bi-modal processing system generates video data as a function
of signals received from ROIC indicative of irradiance across the
detector array, and (ii) a semi-active laser guidance mode wherein
the bi-modal processing system generates line-of-sight data as a
function of signals received from ROIC indicative of laser pulses
detected by the detector array and qualified as corresponding to
the predetermined laser designator.
2. A multi-mode seeker according to claim 1 wherein the ROIC
comprises: video processing circuitry coupled to a first input of
the bi-modal processing system; and laser pulse processing
circuitry coupled to a second input of the bi-modal processing
system.
3. A multi-mode seeker according to claim 2 wherein the ROIC
further comprises: a first ROIC layer containing the video
processing circuitry; and a second ROIC layer containing the laser
pulse processing circuitry, the first ROIC layer, the second ROIC
layer, and the detector array joined together in a laminate
arrangement.
4. A multi-mode seeker according to claim 2 wherein the laser pulse
processing circuitry is configured to: (i) determine if laser pulse
signals has been registered by at least one cell of the detector
array, and (ii) transmit data to the bi-modal processing system
indicative the laser pulse signals registered by the at least one
cell.
5. A multi-mode seeker according to claim 4 wherein the laser pulse
processing circuitry is further configured to: (i) extract pulse
feature data describing at least one feature of the laser pulse
signals registered by the at least one cell, and (ii) provide to
the bi-modal processing system the pulse feature data.
6. A multi-mode seeker according to claim 5 wherein the pulse
feature data comprises at least one of the group consisting of rise
time, fall time, amplitude, and time of arrival.
7. A multi-mode seeker according to claim 5 wherein the laser pulse
processing circuitry is further configured to qualify the laser
pulse signals registered by the at least one cell as corresponding
to the predetermined laser designator utilizing the extracted pulse
feature data.
8. A multi-mode seeker according to claim 1 wherein the multi-mode
seeker further comprises: a seeker dome; and at least one optical
element configured to guide laser energy and infrared radiation
received through the seeker dome along a common optical path to the
detector array.
9. A multi-mode seeker according to claim 1 wherein the detector
array is responsive to energy within the short wavelength infrared
spectrum, wherein the video processing circuitry is configured to
process optical signals indicative of the irradiance received
across the detector array within the short wavelength infrared
spectrum, and wherein the laser pulse processing circuitry is
configured to process optical signals indicative of laser pulse
signals registered by the detector array within the short
wavelength infrared spectrum.
10. A multi-mode seeker according to claim 1 wherein the detector
array comprises a detector material responsive to wavelengths of
approximately 1.064 microns and to approximately 1.617 microns, and
wherein the laser pulse processing circuitry is configured to
process optical signals indicative of laser pulse signals
registered by the detector array corresponding wavelengths of
approximately 1.064 microns and to approximately 1.617 microns.
11. A multi-mode seeker according to claim 1 wherein the processing
system operates in the semi-active laser guidance mode by
default.
12. A multi-mode seeker according to claim 1 wherein the multi-mode
seeker is configured to be utilized in conjunction with a main
navigational computer, and wherein the bi-modal processing system
is configured to switch from the semi-active laser guidance mode to
the image guidance mode in response to input received from the main
navigational computer.
13. A multi-mode seeker, comprising: a focal plane array,
comprising: a detector array; and a Read-Out Integrated Circuit
(ROIC) operatively coupled to the detector array; and a bi-modal
processing system operatively coupled to ROIC and switchable
between an imaging mode and a semi-active laser guidance mode;
wherein the ROIC comprises: (i) video processing circuitry coupled
to a first input of the bi-modal processing system and configured
to generate signals indicative of irradiance across the detector
array, and (ii) laser pulse processing circuitry coupled to a
second input of the bi-modal processing system and configured to
provide data to bi-modal processing system indicative of laser
pulse signals detected by the detector array.
14. A multi-mode seeker according to claim 13 wherein the laser
pulse processing circuitry is further configured to extract pulse
feature data describing at least one feature of the registered
laser pulse signals.
15. A multi-mode seeker according to claim 14 wherein multi-mode
seeker is configured to be utilized in conjunction with a
predetermined laser designator, and wherein the laser pulse
processing circuitry is further configured to qualify the laser
pulse signals registered by the at least one cell as corresponding
to the predetermined laser designator utilizing the extracted pulse
feature data.
16. A guided munition configured to be utilized in conjunction with
a predetermined laser designator, the guided munition comprising: a
multi-mode seeker, comprising: a focal plane array including a
detector array and a Read-Out Integrated Circuit (ROIC) operatively
coupled to the detector array; a bi-modal processing system
operatively coupled to ROIC and switchable between: (i) an imaging
mode wherein the bi-modal processing system generates video data as
a function of signals received from ROIC indicative of irradiance
across the detector array, and (ii) a semi-active laser guidance
mode wherein the bi-modal processing system generates line-of-sight
data as a function of signals received from ROIC indicative of
laser pulses registered by the detector array and qualified as
corresponding to the predetermined laser designator; and a main
navigational computer coupled to an output of the bi-modal
processing system and configured to receive therefrom video data
when the bi-modal processing system is operating in the imaging
mode and line-of-sight data when the bi-modal processing system is
operating in the semi-active laser guidance mode.
17. A guided munition according to claim 16 wherein the bi-modal
processing system normally operates in the semi-active laser
guidance mode, and wherein the main navigational computer is
configured to command the bi-modal processing system to switch from
the semi-active laser guidance mode to the imaging mode during
munition flight.
18. A guided munition according to claim 17 wherein the main
navigational computer is configured to command the bi-modal
processing system to switch from the semi-active laser guidance
mode to the imaging mode during munition flight when determining
that target lock-on has been achieved in the semi-active laser
guidance mode.
19. A guided munition according to claim 18 wherein the guided
munition further comprises a wireless transmitter coupled to the
main navigational computer, and wherein the main navigational
computer is configured to transmit a signal via the wireless
transceiver indicating when target lock-on has been achieved in the
semi-active laser guidance mode.
20. A guided munition according to claim 17 wherein the guided
munition further comprises a wireless receiver coupled to the main
navigational computer, and wherein the main navigational computer
is configured to command the bi-modal processing system to switch
from the semi-active laser guidance mode to the imaging mode in
response to receipt of a command signal by the wireless receiver.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 61/317,923, filed Mar. 26, 2010, the entire
contents of which are hereby incorporated by reference.
TECHNICAL FIELD
[0002] The following disclosure relates generally to homing
guidance systems and, more specifically, to embodiments of a
multi-mode seeker including a dual function focal plane array
device operable in both imaging and semi-active laser guidance
modes.
BACKGROUND
[0003] Munition guidance systems have evolved considerably since
the initial introduction of heat-seeking missiles in the late
1950's. Missiles, rockets, and other munitions are now commonly
equipped with advanced homing guidance systems referred to as
"seekers." Modern seekers often include two or three independent
detector subsystems, which each support a different guidance
modality. These detector subsystems are independent in the sense
that each subsystem includes at least one dedicated electro-optic
sensor (e.g., a detector array sensitive to wavelengths in the
visible or infrared spectrum) positioned within a distinct focal
plane. Additionally, each detector subsystem typically includes a
separate, dedicated processor, which processes signals provided by
the subsystem's detector array indicative of registered
electromagnetic energy. Each detector subsystem then supplies this
data to a main navigational computer (commonly referred to as the
"mission computer") deployed onboard the guided munition. The
navigational computer utilizes the data supplied by the seeker
subsystems, often in combination with data generated by other
systems deployed onboard the munition (e.g., a global positioning
system and an inertial navigational system) and possibly telemetry
data provided by external control sources, to determine the manner
in which one or more flight control surfaces should be manipulated
to provide aerodynamic guidance to the munition during flight.
[0004] The independent guidance systems employed by dual- and
tri-mode seekers commonly include separate infrared imaging and
Semi-Active Laser ("SAL") subsystems. Conventionally-implemented
infrared imaging systems often include a detector array containing
a relatively high number of detector cells (e.g., a 640.times.480
cell grid) fabricated from a detector material (e.g., HgCdTe and
InSB) sensitive to infrared energy within the thermal bands (i.e.,
mid- to long-wave infrared energy). A single read-out integrated
circuit is positioned behind the detector array and, during seeker
operation, transmits signals indicative of the irradiance received
across the detector array to a dedicated imaging processor. The
processor then compiles the irradiance data to produce a composite
intensity image of the seeker's field-of-view, which is supplied to
the munition's main navigational computer for image-based guidance
purposes. By comparison, a conventionally-implemented SAL subsystem
typically includes a separate detector array comprised of a
relatively small number of detector cells (e.g., four wedge-shaped
cells, which collectively form a four-quadrant circular detector
array). Analog circuitry operably coupled to each of the detector
cells detects photocurrents induced by photons striking the
detector array and supplies corresponding signals to a dedicated
temporal processor. The temporal processor then compares intensity
ratios across the detector cells to determine the centroid of any
detected laser spot, which is provided to the main navigational
computer as line-of-sight guidance data.
[0005] There is a continual demand to reduce the complexity, part
count, weight, envelope, and cost of the various components (e.g.,
optical components, sensors, digital and analog processing
elements, etc.) included within multi-mode seekers while
maintaining or improving the seeker's guidance capabilities. More
specifically, there exists an ongoing need to provide embodiments
of a multi-mode seeker that reliably provides both imaging and
Semi-Active Laser guidance capabilities with fewer components, with
an enhanced reliability, and with an improved accuracy. Embodiments
of such a multi-mode seeker are provided herein. Other desirable
features and characteristics of the present invention will become
apparent from the subsequent Detailed Description and the appended
Claims, taken in conjunction with the accompanying Drawings and
this Background.
BRIEF SUMMARY
[0006] Embodiments of a multi-mode seeker are provided for use in
conjunction with a predetermined laser designator. In one
embodiment, the multi-mode seeker includes a focal plane array and
a bi-modal processing system. The focal plane array includes a
detector array and a Read-Out Integrated Circuit (ROIC) operatively
coupled to the detector array. The bi-modal processing system is
operatively coupled to ROIC and is switchable between: (i) an
imaging mode wherein the bi-modal processing system generates video
data as a function of signals received from ROIC indicative of
irradiance across the detector array, and (ii) a semi-active laser
guidance mode wherein the bi-modal processing system generates
line-of-sight data as a function of signals received from ROIC
indicative of laser pulses detected by the detector array and
qualified as corresponding to the predetermined laser
designator.
[0007] Embodiments of a guided munition configured to be utilized
in conjunction with a predetermined laser designator are further
provided. In one embodiment, the guided munition includes a
multi-mode seeker and a main navigational computer. The multi-mode
seeker includes, in turn, a bi-modal processing system and a focal
plane array, which has a detector array and a Read-Out Integrated
Circuit (ROIC) operatively coupled to the detector array. The
bi-modal processing system is operatively coupled to ROIC and is
switchable between: (i) an imaging mode wherein the bi-modal
processing system generates video data as a function of signals
received from ROIC indicative of irradiance across the detector
array, and (ii) a semi-active laser guidance mode wherein the
bi-modal processing system generates line-of-sight data as a
function of signals received from ROIC indicative of laser pulses
registered by the detector array and qualified as corresponding to
the predetermined laser designator. The main navigational computer
is coupled to an output of the bi-modal processing system and is
configured to receive therefrom video data when the bi-modal
processing system is operating in the imaging mode and
line-of-sight data when the bi-modal processing system is operating
in the semi-active laser guidance mode.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] At least one example of the present invention will
hereinafter be described in conjunction with the following figures,
wherein like numerals denote like elements, and:
[0009] FIG. 1 is a simplified cross-sectional view of a tri-mode
seeker illustrated in accordance with the teachings of prior art
and including independent Semi-Active Laser ("SAL") and image
guidance subsystems;
[0010] FIG. 2 is a simplified block diagram of a guided munition
equipped with the tri-mode seeker shown in FIG. 1;
[0011] FIG. 3 is a simplified cross-sectional view of a tri-mode
seeker illustrated in accordance with an exemplary embodiment of
the present invention and including a dual function focal plane
array capable of providing both SAL and image guidance
functionalities;
[0012] FIG. 4 is a simplified block diagram of a guided munition
equipped with the tri-mode seeker shown in FIG. 3;
[0013] FIG. 5 is a graph of sensor responsivity (vertical axis)
versus wavelength (horizontal axis) illustrating the responsivity
of an exemplary conventional silicon-based detector and the
responsivity of two exemplary detector materials (i.e.,
Indium-Gallium-Arsenide and Mercury-Cadmium-Telluride) from which
the detector array may be fabricated in preferred embodiments of
the multi-mode seeker;
[0014] FIG. 6 is a graph of Noise Equivalent Power (vertical axis)
versus Avalanche Photodetector (APD) gain (horizontal axis)
illustrating the sensitivity profile of an exemplary conventional
silicon-based detector compared to the sensitivity profiles of
several InGaAs sensors of varying array sizes; and
[0015] FIGS. 7-10 are simplified block diagrams illustrating
several exemplary manners in which the processing components of the
tri-mode seeker shown in FIG. 4 can be configured to provide pulse
detection, feature extraction, qualification, and correlation when
the tri-mode seeker is operating in a SAL guidance mode.
DETAILED DESCRIPTION
[0016] The following Detailed Description is merely exemplary in
nature and is not intended to limit the invention or the
application and uses of the invention. Furthermore, there is no
intention to be bound by any theory presented in the preceding
Background or the following Detailed Description. As appearing
herein, the term "bi-modal processing system" is utilized to denote
a processing system operable in at least two different processing
modes (e.g., in semi-active laser and image guidance modes) and is
defined to include processing systems operable in three or more
processing modes.
[0017] Embodiments of a multi-mode seeker having Semi-Active Laser
("SAL") and image tracking guidance capabilities are provided.
Embodiments of the multi-mode seeker may also include one or more
other guidance functionalities in addition to SAL and image
guidance functionalities; however, this is by no means necessary.
As a specific example, the multi-mode seeker may assume the form of
a dual-mode seeker having only SAL and image guidance
functionalities. Alternatively, and as a second example,
embodiments of the multi-mode seeker may assume the form of a
tri-mode seeker having SAL and image guidance functionalities
further paired with a third guidance functionality, such as
radiofrequency guidance. In contrast to traditional multi-mode
seekers having image tracking and SAL guidance capabilities,
embodiments of the inventive multi-mode seeker utilize a single
optical train, a single focal plane array, and a single processing
train to perform both image and SAL tracking functionalities, which
allows a significant reduction in cost, part count, weight, and
envelope of the seeker, as described more fully below.
[0018] Embodiments of the multi-mode seeker system are well-suited
for utilization within or use in conjunction with Laser Detection
and Ranging ("LADAR") systems deployed aboard precision, small
form-factor airborne munitions and sub-munitions. This
notwithstanding, embodiments of the multi-mode seeker are by no
means limited to deployment aboard airborne munitions and
sub-munitions. A non-exhaustive list of additional platforms and
vehicles on which embodiments of the multi-mode seeker can be
deployed or with which embodiments of the seeker can be utilized
includes Airborne Targeting Systems, Ground Vehicles, Autonomous
(Robotic) Systems, and Unmanned Aerial Vehicles included within
Unmanned Aircraft Systems.
[0019] FIG. 1 is a simplified cross-sectional view of a tri-mode
seeker 20 illustrated in accordance with a commonly-implemented,
conventionally-known design and provided for comparison purposes.
Tri-mode seeker 20 includes a seeker dome 22, a gimbal assembly 24,
and a number of optical components 28. Gimbal assembly 24 is
rotatably coupled to a focal plane support structure 27, which is,
in turn, mounted to the body or airframe of a guided munition (not
shown). Tri-mode seeker 20 is further equipped with three
independent guidance subsystems, which each support a different
guidance functionality of seeker 20. In particular, tri-mode seeker
20 includes: (i) a Semi-Active Laser ("SAL") subsystem 30, (ii) a
radiofrequency ("RF") subsystem 32, and (iii) an infrared ("IR")
subsystem 34. As generally shown in FIG. 1, SAL subsystem 30 is
mounted to gimbal assembly 24 and housed within a forward portion
of seeker dome 22. In a similar manner, RF subsystem 32 is mounted
to gimbal assembly 24 immediately behind (i.e., to the aft of) SAL
subsystem 30. Lastly, IR subsystem 34 is mounted to an optical
bench 26 included within an aft portion of gimbal assembly 24. SAL
subsystem 30 and IR subsystem 34 are further described in
conjunction with FIG. 2 below.
[0020] In the exemplary embodiment shown in FIG. 1, optical
components 28 include a primary mirror 28(a), a secondary dichroic
mirror 28(b), and two focal lens 28(c) and 28(d). During operation
of seeker 20, optical components 28 guide electromagnetic radiation
received through seeker dome 22 along three different optical paths
and to the detectors of subsystems 30, 32, and 34. As indicated in
FIG. 1 by dashed line 36, radiofrequency energy received through
seeker dome 22 is guided along a first optical path and ultimately
focused on the sensor of RF subsystem 32 by primary mirror 28(a).
Similarly, as indicated in FIG. 1 by dot-dashed line 38, infrared
energy received through dome 22 is guided by along a second optical
path by mirror 28(a) and 28(b) and is ultimately focused on the
detector array of IR subsystem 34 by focal lens 28(c). Finally, as
indicated in FIG. 1 by solid line 40, laser pulse energy received
through seeker dome 22 is focused on the detector array of SAL
subsystem 30 by focal lens 28(d).
[0021] FIG. 2 is a simplified block diagram illustrating tri-mode
seeker 20 deployed onboard a generalized guided munition 42, such
as a guided missile. Certain components are omitted from FIG. 2 for
clarity including gimbal assembly 24, focal plane support structure
27, optical components 28, and RF subsystem 32. As can be seen in
FIG. 2, SAL subsystem 30 includes a detector array 44; a
Read-Out-Integrated-Circuit ("ROIC") 46, which is operatively
coupled to and positioned immediately behind detector array 44; and
a dedicated video processor 48, which is operably coupled to an
output of ROIC 46. In one common implementation, detector array 44
comprises a relatively high number of detector cells (e.g., a
640.times.480 cell grid) fabricated from a detector material (e.g.,
HgCdTe or InSb) sensitive to infrared energy within the thermal
bands (i.e., mid- to long-wave infrared energy). During operation
of seeker 20, and as generally described in the foregoing section
entitled "Background," ROIC 46 transmits signals indicative of the
irradiance received across detector array 44 to video processor 48.
Processor 48 then compiles the irradiance data to produce a
composite intensity image of the seeker's field-of-view, which is
then supplied to a main navigational computer 50 deployed onboard
munition 42. Main navigational computer 50 utilizes this data, in
combination with data provided by other sources (e.g., data
provided by RF subsystem 32 shown in FIG. 1, data provided by an
onboard GPS device, data provided by an onboard inertial guidance
system, telemetry data, and so on), to determine the manner in
which a plurality of flight control surfaces 52 (e.g., fins,
canards, and/or wings) should be manipulated to provide aerodynamic
guidance to munition 42 during flight. After determining the
appropriate adjustments to provide the desired guidance, main
navigational computer 50 then commands a control actuation system
54 to implement the determined adjustments to flight control
surfaces 52.
[0022] In the exemplary embodiment illustrated in FIGS. 1 and 2,
and referring specifically to FIG. 2, SAL subsystem 30 includes a
four-quadrant detector array 56 and a dedicated pulse processor 58,
which is coupled to each of the cells or quadrants included within
array 56. During operation of seeker 20, analog circuitry
associated with array 56 (not shown) detects photocurrents induced
by photons striking detector array 56 and supplies corresponding
signals to a pulse processor 58. Pulse processor 58 then compares
intensity ratios across the detector cells to determine the
centroid of a detected laser spot and thereby provide line-of-sight
guidance data to main navigational computer 50. Computer 50 then
utilizes this line-of-sight guidance data, in combination with the
other data sources described above, to determined the manner in
which flight control surfaces 52 should be manipulated to provide
aerodynamic guidance to munition 42 in the above described
manner
[0023] Conventional multi-mode seekers, such tri-mode seeker 20,
have been extensively engineered and are cap providing reliable and
highly accurate guidance during munition flight. However,
conventionally-implemented multi-mode seekers remain limited in
certain respects. For example, the provision of two separate
guidance subsystems in the case of dual-mode seekers and the
provision of three separate guidance subsystems in the case of
tri-mode seekers (e.g., in the case of tri-mode seeker 20, the
provision of SAL subsystem 30 shown in FIGS. 1 and 2, RF subsystem
32 shown in FIG. 1, and IR subsystem 34 shown in FIGS. 1 and 2)
adds undesired complexity, cost, weight, and bulk to seeker. To
overcome these limitations, the following describes exemplary
embodiments of a multi-mode seeker, such as dual- or tri-mode
seeker, employing a dual function focal plane array and a bi-modal
processing system that cooperate or combine to provide both image
guidance and SAL guidance functionalities.
[0024] FIG. 3 is a simplified cross-sectional view of a tri-mode
seeker 60 illustrated in accordance with an exemplary embodiment of
the present invention. In certain respects, tri-mode seeker 60 is
similar to seeker 20 described above in conjunction with FIGS. 1
and 2. For example, as does seeker 20 (FIGS. 1 and 2), tri-mode
seeker 60 includes a seeker dome 62, a gimbal assembly 64, and a
number of optical components 68. As was the case previously, gimbal
assembly 64 is rotatably coupled to a focal plane support structure
67, which is mounted to the body or airframe of a guided munition
(e.g., airframe 82 shown in FIG. 4). However, in contrast to seeker
20, tri-mode seeker 60 includes only two discrete guidance
subsystems: (i) a RF subsystem 70, and a (ii) a dual function
imaging/Semi-Active Laser ("SAL") guidance subsystem 72, 74. Dual
function imaging/SAL guidance subsystem 72, 74 includes, in turn, a
dual function focal plane array ("FPA") 72 and a bi-modal
processing system 74. As shown in FIG. 3, dual function FPA 72 may
be mounted to an optical bench 66 included within an aft portion of
gimbal assembly 64, and RF subsystem 70 may be mounted to a forward
portion of gimbal assembly 24. Dual function FPA 72 and bi-modal
processing system 74 are each described in detail below; a detailed
discussion of RF subsystem 70 is not provided herein, however, as
the implementation and functioning of RF sensors and systems (e.g.,
Ka-band radar systems) are well-known within the aerospace and
munition industries.
[0025] During operation of seeker 60, optical components 68 guide
electromagnetic radiation received through seeker dome 22 along two
different optical paths and to subsystems 70 and 72, 74. In the
exemplary embodiment illustrated in FIG. 3, optical components
include a primary mirror 68(a), a secondary dichroic mirror 68(b),
and a focal lens 68(c). As indicated in FIG. 3 by dot-dashed line
78, both imaging energy and laser pulse energy received through
seeker dome 62 is reflected from primary mirror 68(a), is reflected
from dichroic secondary mirror 68(b), and is ultimately focused by
lens 68(c) on the detector array included within dual function FPA
72. By comparison, radiofrequency energy is received through seeker
dome 62 is reflected from a primary mirror 68(a), propagates
through a dichroic secondary mirror 68(b), and is ultimately
focused onto the detector included within RF subsystem 70, as
indicated in FIG. 3 by dashed line 76.
[0026] The structural features and functionality of exemplary dual
function imaging/SAL guidance subsystem 72, 74 will be described in
detail below in conjunction with FIG. 4. However, at this juncture
in the description, it is useful to note that several benefits have
been achieved by combining imaging and SAL guidance functionalities
into a single, bi-modal subsystem. First, as may be appreciated by
comparing FIG. 3 to FIG. 1, an optical component (i.e., focal lens
28(d)) and a detector subsystem (i.e., SAL subsystem 30) have been
eliminated from tri-mode seeker 60 thereby reducing the overall
weight, cost, and part count of seeker 60 relative to conventional
seeker 20. Second, due to the elimination of focal lens 28(d) and
SAL subsystem 30 (FIG. 1), a considerable volume of space has been
made available in the forward nose of seeker 62. This newly-freed
space is of significant value in the context of munition design and
can be utilized in a variety of different manners; e.g., the size,
and therefore the capabilities, of RF subsystem 70 can be
increased, RF subsystem 70 can be provided with a plurality of
forward-extending cooling fins (not shown), one or more additional
components (e.g., an illuminator) can be incorporated into seeker
60 immediately forward of RF subsystem 70, and/or the overall
dimensions of seeker 62 can be reduced.
[0027] FIG. 4 is a simplified block diagram illustrating tri-mode
seeker 60 deployed onboard a generalized guided munition 80, such
as a guided missile, in accordance with a further exemplary
embodiment. Certain components are omitted from FIG. 4 for clarity
including gimbal assembly 64, focal plane support structure 67,
optical components 68, and RF subsystem 62. As generically
illustrated in FIG. 4, guided munition 80 includes a main
navigational computer 84, a control actuation system 86, and a
plurality of manipulable flight control surfaces 88. Main
navigational computer 84, control actuation system 86, and flight
control surfaces 88 operate in essentially the same manner as do
main navigational computer 50, control actuation system 54, and
flight control surfaces 52, respectively, described above in
conjunction with FIG. 2. Furthermore, the various manners in which
navigational computer 84, control actuation system 86, and flight
control surfaces 88 can be implemented and function are well-known
in the aerospace and munition industries and will consequently be
described only briefly herein. Additional conventionally-known
components that may be incorporated into guided munition 80 and
which are not shown in FIG. 4 include, but are not limited to,
additional guidance components (e.g., global positioning systems
and/or inertial navigational systems), power supplies (e.g.,
battery packs), data links (e.g., a networked radio antenna), one
or more warheads, and one or more solid propellant rocket motors or
other propulsion devices.
[0028] As be seen in FIG. 4, dual function FPA 72 includes two main
components: (i) a detector array 90, and (ii) an ROIC 92, 94
positioned immediately behind detector array 90. ROIC 92, 94
includes a first set of circuitry dedicated to image or video
processing, which is generically represented in FIG. 4 by block 92
and which is referred to hereafter as "ROIC video processing
circuitry 92." ROIC 92, 94 further includes a second set of
circuitry dedicated to temporal or pulse processing, which is
generically represented in FIG. 4 by block 94 and which is referred
to hereafter as "ROIC pulse processing circuitry 94." As indicated
in FIG. 4, ROIC video processing circuitry 92 and ROIC pulse
processing circuitry 94 can be implemented as two independent or
discrete layers, which are joined with detector array 90 in a
monolithic, stacked, or laminate arrangement. In alternative
embodiments of dual function FPA 72, ROIC video processing
circuitry 94 and ROIC pulse processing circuitry 94 can be
integrated or combined into a single layer positioned immediately
behind detector array 90.
[0029] The geometry and number of cells included within detector
array 90 will inevitably vary amongst different embodiments of the
present invention; however, by way of non-limiting example,
detector array 90 may assume the form of a rectangular grid
containing 4.sup.2 to 32.sup.2 detector cells. Detector array 90
may be fabricated from any suitable material, currently-known or
later-developed, that is sensitive to electromagnetic radiation
within the one or more bands of the electromagnetic spectrum
supportive of both imaging and laser guidance functions. In
preferred embodiments, the chosen detector material is sensitive
over the majority of, if not the entirety of, the Short Wave
Infrared ("SWIR") spectrum; and both imaging and laser guidance
functionalities are performed by detection of electromagnetic
energy within the SWIR spectrum. Performance of imaging within the
SWIR spectrum provides several advantages relative to imaging
within the thermal bands (i.e., imaging within the mid- to
long-wave infrared bands), as is typically performed by guided
munitions equipped with HgCdTe or InSb sensors. These advantages
include the elimination of any need for active cooling of the
detector array, higher resolutions per aperture size, and an
overall reduction in the cost of optics, sensors, and dome
materials. Relative to mid- to long-wave infrared energy, SWIR
energy typically has a higher transmissivity in maritime
environments thereby providing a sensing range advantage when
guided munition is launched from an aircraft, surface boat,
submarine, or other vessel operating within or near an ocean, sea,
or other large body of water. As a still further advantage,
conventional seeker dome materials (e.g., sapphire) may become less
transmissive to mid- to long-waver infrared energy as they heat
during munition flight, especially during flight of high speed
(e.g., supersonic) missiles, while the transmissivity of such
materials to SWIR energy typically remains largely unaffected by
dome heating.
[0030] Detector array 90 is preferably fabricated utilizing a
detector material sensitive to two disparate wavelengths falling
within the SWIR spectrum (referred herein as a "dual SWIR band
detector material"). While a wide range of detector materials
sensitive various different sets of wavelengths within the SWIR
spectrum can be utilized, in one preferred embodiment, detector
array 90 is fabricated from a dual SWIR band detector material
responsive to a first wavelength of approximately 1.06 .mu.m and to
a second wavelength of approximately 1.55 .mu.m. By selecting a
detector material sensitive to wavelengths of approximately 1.06
.mu.m, compatibility is ensured with 1.06 .mu.m laser designators,
which have been widely adopted in conjunction with conventional
seekers employing silicon-based detectors. By selecting a detector
material that is also sensitive to wavelengths of approximately
1.55 .mu.m, usage is further enabled with next-generation 1.55
.mu.m laser designators, which offer several advantages over
currently-adopted 1.06 .mu.m laser designators. As one advantage,
1.55 .mu.m lasers are generally more difficult to detect than are
1.06 .mu.m lasers. As a second advantage, 1.55 .mu.m lasers are
considered eye-safe and are consequently better suited for usage
within urban combat scenarios. By way of non-limiting example,
suitable dual SWIR band detector materials include
Indium-Gallium-Arsenide ("InGaAs") and specially-formulated Mercury
Cadmium Telluride ("HgCdTe") detector materials. As indicated in
FIG. 5, which is a graph of sensor responsivity (vertical axis)
versus wavelength (horizontal axis), InGaAs sensors exhibit peak
responsivity between approximately 1.064 .mu.m and approximately
1.617 .mu.m and are consequently ideal for detecting wavelengths
within the short wave infrared spectrum, including the two
wavelengths identified above. As further indicated in FIG. 5,
HgCdTe sensors exhibit peak responsivity over a broader range
(approximately 1.064 .mu.m to approximately 2.5 .mu.m) and are
consequently also well-suited for detecting the above-identified
wavelengths, as well as longer wavelengths within the SWIR
spectrum. To provide a basis for comparison, the responsivity of a
conventionally-known silicon-based detector (referred to herein
simply as a "silicon detector") is also shown in FIG. 5. As can be
seen, the silicon detector exhibits a peak responsivity near 1.0
.mu.m and is substantially less responsive to wavelengths exceeding
approximately 1.064 .mu.m. The foregoing examples notwithstanding,
it is emphasized that preferred embodiments of the multi-mode
seeker can include detector arrays fabricated from detector
materials, whether currently known or later developed, responsive
to any wavelength or set of wavelengths within the SWIR spectrum
(approximately 0.9 .mu.m to approximately 2.5 .mu.m).
[0031] Advantageously, the InGaAs or HgCdTe sensor included within
preferred embodiments of seeker 60 achieves relatively high quantum
efficiency (e.g., approaching or exceeding 90%) as compared to
conventional silicon detectors of the type described above, which
tend to have quantum efficiencies closer to approximately 40%. This
may be more fully appreciated by referring to FIG. 6, which is a
graph of Noise Equivalent Power (vertical axis) versus Avalanche
Photodetector ("APD") gain (horizontal axis) illustrating the
sensitivity profile of an exemplary conventional silicon-based
detector compared to the sensitivity profiles of InGaAs sensors of
varying array sizes (4.sup.2 to 32.sup.2). Similar quantum
efficiencies can also be achieved utilizing HgCdTe sensors of
corresponding array sizes. In addition, due, at least in part, to a
more focused instrument field of view, InGaAs or HgCdTe sensors (or
other such dual SWIR band sensors) are significantly less sensitive
to solar background noise as compared to conventional silicon
detectors. As a result, employment of InGaAs or HgCdTe sensors can
enable a reduction in aperture and/or designator power without a
corresponding loss of performance
[0032] During operation of multi-mode seeker 60, ROIC video
processing circuitry 94 provides bi-modal processing system 74 with
signals indicative of the irradiance across detector array 90,
while ROIC pulse processing circuitry 94 provides processing system
74 with signals indicative of laser pulse energy detected by array
90. When operating in the imaging mode, bi-modal processing system
74 generates video data as a function of signals received from ROIC
video processing circuitry 94 and supplies the video data to main
navigational computer 84. Conversely, when operating in the SAL
guidance mode, processing system 74 generates line-of-sight data as
a function of signals received from ROIC pulse processing circuitry
94 and supplies line-of-sight data to main navigational computer
84. When operating in the SAL guidance mode, processing system 74
generates line-of-sight data based upon only those signals that are
indicative of laser pulse energy that has been verified or
qualified as corresponding to at least one predetermined laser
designator. To qualify detected laser pulse signals as originating
from a predetermined laser designator, the optical signals detected
by array 90 are analyzed by ROIC circuitry 94 and/or processing
system 74 to first measure certain features of the detector laser
pulses (commonly referred to herein as "pulse feature extraction")
and to subsequently compare the extracted pulse features to
expected values associated with the predetermined laser designator.
Pulse feature extraction and qualification can be performed in the
analog circuitry of ROIC circuitry 94, in the digital circuitry of
processing system 74, or a combination thereof, as described more
fully below in conjunction with FIGS. 7-10.
[0033] FIG. 7 is a simplified block diagram illustrating a first
exemplary implementation of ROIC pulse processing circuitry 94 and
bi-modal processing system 74 wherein pulse feature extraction and
pulse qualification is performed solely by processing system 74. As
generically illustrated in FIG. 7, ROIC pulse processing circuitry
94 includes an array of laser pulse-sensitive preamplifiers 96 and
analog-to-digital ("A/D") converters 98; while digital processing
system 74 includes pulse feature extraction circuitry 100, pulse
qualification circuitry 102, and correlation circuitry 104. ROIC
preamplifiers 96 are each operatively coupled to a different cell
included within detector array 90, and A/D converters 98 are each
operatively coupled to a different one of preamplifiers 96. The
outputs of A/D converters 98 are, in turn, coupled to inputs of
processing system 74 and, specifically, to inputs of pulse feature
extraction processing 100. Pulse feature extraction circuitry 100
is coupled, in processing series, with pulse qualification
processing 102 and correlation processing 104. During operation of
bi-modal processing system 74, pulse feature extraction processing
100 cooperates with pulse qualification processing 102 and
correlation processing 104 to sequentially process data provided by
ROIC circuitry 94 pertaining to laser pulse signals registered by
detector array 90, as further described below. In one embodiment,
digital processing system 74 is implemented as an interface board
populated with at least one field programmable gate array and at
least one digital signal processor. Although other implementations
are possible, pulse feature extraction processing 100, pulse
qualification processing 102, and correlation processing 104 are
preferably implemented as one or more algorithms utilizing field
programmable gate array programming (firmware) and/or as software
programming.
[0034] When bi-modal processing system 74 is operating in a SAL
guidance mode, pulse feature extraction processing 100 first
determines whether the digital inputs signals provided by A/D
converters 98 are indicative of detected pulses and, if so,
processing 100 then measures or extracts data indicative of various
features of the detected laser pulses. These features may include,
but are not limited to, pulse detection, rise time, fall time,
amplitude, and time of arrival, pixel address, and noise. Pulse
feature extraction processing 100 then outputs digital signals
indicative of the extracted pulse features to pulse qualification
processing 102, which analyzes the extracted pulse feature data to
determine if the detected laser pulses correspond to a
predetermined laser designator. In one embodiment, pulse
qualification processing 102 determines if the detected laser
pulses correspond to the predetermined designator by comparing the
amplitude, time of arrival, and/or the pixel address of the
detected laser pulses to expected values. If the features of the
detected laser pulse are determined to correspond to the
predetermined designator, correlation processing 104 then processes
the data received from pulse qualification processing 102 to
generate line-of-sight data (e.g., pitch and yaw angles) indicating
the location of seeker 60 relative to the designated target from
which the laser pulses were reflected. As will be appreciated by
one of ordinary skill in the industry, various different processing
techniques can be utilized to generate line-of-sight data as a
function of the extracted and qualified pulse feature data provided
by pulse qualification processing 102 including, for example, a
last pulse/first pulse logic. Correlation processing 104 then
outputs the line-of-sight data to main navigational computer 84
(FIG. 4), which utilizes the data to determine the appropriate
guidance adjustments to flight control surfaces 88 to provide
inflight guidance to munition 80 in the manner previously
described.
[0035] The foregoing has thus provided one exemplary manner in
which ROIC pulse processing circuitry 94 and processing system 74
can be implemented wherein the primary function of ROIC pulse
processing circuitry 94 is to sample or digitize all optical
signals registered across detector array 90. Processing system 74
then performs pulse detection, feature extraction, pulse
qualification, and correlation functions in the above-described
manner to generate the desired line-of-sight guidance data. While
certainly feasible, the above-described exemplary implementation
places considerable processing demands on processing system 74. The
processing demands placed on bi-modal processing system 74 can,
however, be significantly reduced by providing ROIC circuitry 94
with analog circuitry that first determines whether the optical
signals registered by detector array 90 are indicative of detected
laser pulses prior to relaying data to processing system 74 for
further processing. To further illustrate this point, a second
exemplary implementation of ROIC pulse processing circuitry 94 and
bi-modal processing system 74 wherein ROIC circuitry 94 further
performs a pulse detection function is described below in
conjunction with FIG. 8.
[0036] FIG. 8 is a simplified block diagram illustrating a second
exemplary implementation of ROIC pulse processing circuitry 94 and
bi-modal processing system 74. In the exemplary implementation
shown in FIG. 8, each ROIC cell 94(a) (only one of which is shown
in FIG. 8) includes analog pulse detection circuitry 106, a shift
register 108, and a multiplexer 110 in addition to a preamplifier
96 and A/D converter 98. Analog pulse detection circuitry 106
includes an input, which is coupled to preamplifier 96, and an
output, which is coupled to a first input of shift register 108. A
second input of shift register 108 is coupled to an output of
preamplifier 96, and an output of shift register 108 is coupled to
multiplexer 110. During operation, pulse detection circuitry 106
compares the signal provided by preamplifier 96 to a predetermined
threshold value. If the preamplifier signal surpasses the threshold
value, pulse detection circuitry 106 signals shift register 108 to
record the signal's value around the detected pulse and transfer
the signals to multiplexer 110. In this manner, shift register 108
stores only data pertaining to detected laser pulse signals.
Multiplexer 110 then transmits the output signal values to A/D
converter 98, which provides a corresponding digital signals to
pulse feature extraction processing 100 of digital processing
system 74. Digital processing system 74 then performs pulse feature
extraction, qualification, and correlation in the above-described
manner. In this manner, ROIC circuitry 94 serves as a data gate,
which transmits data to digital processing system 74 only after
determining that laser pulse signals have been detected. In so
doing, ROIC circuitry 94 greatly reduces the processing demands
placed on processing system 74.
[0037] FIG. 9 is a simplified block diagram illustrating a third
exemplary implementation of ROIC pulse processing circuitry 94 and
bi-modal processing system 74 wherein pulse detection and feature
extraction is performed by ROIC circuitry 94 and wherein pulse
qualification and correlation is performed by processing system 74.
As was the case previously, ROIC circuitry 94 includes a number of
cells 94(b), each corresponding to a different cell of detector
array 90 (only a limited number ROIC cells 94(b) are shown in FIG.
9 for clarity). In the exemplary embodiment illustrated in FIG. 9,
each ROIC cell 94(b) includes a laser pulse-sensitive preamplifier
96; pulse detection circuitry 112, which is coupled to an output of
its corresponding preamplifier 96; and feature extraction circuitry
114, which is likewise coupled to an output of its corresponding
preamplifier 96. During operation, analog pulse detection circuitry
112 compares the input signals provided by preamplifier 96 to a
predetermined threshold value. If the input signals provided by
preamplifier 96 surpass the threshold value, it is determined that
the inputs signals are indicative of detected laser pulses, and
pulse detection circuitry 112 relays the input signals to pulse
feature extraction circuitry 114. Pulse feature extraction
circuitry 114 then measures various parameters of the input signals
provided by preamplifier 96 and supplies corresponding data to a
multiplexer 116. Multiplexer 116 then applies the analog signals
provided by each of the ROIC cells with the appropriate pixel
address to an A/D converter 98, which provides a corresponding
digital signal to processing system 74. As pulse detection and
feature extraction has already been performed by ROIC circuitry 94,
processing system 74 need only include pulse qualification
processing 102 and correlation processing 104, which qualify and
correlate the incoming laser pulses signals, respectively, as
previously described. By moving pulse feature detection and
extraction into the analog domain of the ROIC unit cell, the
processing demands place on processing system 74 are further
reduced. As an additional benefit, the data rate applied to
processing system 74 does not increase with an increase in array
size and is, instead, determined by the number of detected laser
pulses and the number of extracted features per detected laser
pulse.
[0038] FIG. 10 is a simplified block diagram illustrating a fourth
exemplary implementation of ROIC pulse processing circuitry 94 and
bi-modal processing system 74 wherein pulse feature extraction and
pulse qualification are performed entirely by ROIC circuitry 94. In
this case, each ROIC cell 94(c) (only one of which is shown in FIG.
10) includes pulse detection circuitry 112, pulse feature
extraction circuitry 114, pulse qualification logic 120, and
qualified pulse data gate 122 in addition to preamplifier 96 and
A/D converter 98. Preamplifier 96, pulse detection circuitry 112,
and pulse feature extraction circuitry 114 function in essentially
the same manner as described above in conjunction with FIG. 9.
However, in contrast to the above-described exemplary embodiment,
the output of pulse feature extraction circuitry 114 is not applied
directly to A/D converter 98. Instead, the output of pulse feature
extraction circuitry 114 is applied to pulse qualification logic
120 and to a qualified pulse data gate 122. During operation of
ROIC cell 94(c), pulse qualification logic 120 analyzes the
extracted pulse feature data provided by pulse feature extraction
circuitry 114 to determine if the extracted pulse feature data
corresponds to the predetermined laser designator or laser
designators. If the extracted pulse feature data corresponds to the
predetermined laser designator, pulse qualification logic 120 sends
an appropriate signal to qualified pulse data gate 122, which then
transmits the qualified pulse feature data to A/D converter 98. A/D
converter 98 then applies a corresponding digital signal to
bi-modal processing system 74, which correlates the qualified pulse
feature data to generate the desired line-of-sight guidance data in
the manner previously described.
[0039] The foregoing has thus described several exemplary
embodiments of a multi-mode seeker (e.g., tri-mode seeker 60 shown
in FIGS. 3 and 4) operable in both semi-active laser and image
tracking guidance modes. In preferred embodiments, the default or
starting mode of tri-mode seeker 60 is the SAL guidance mode, and
seeker 60 switches or is caused to switch to the imaging tracking
mode after target acquisition or lock-on. During an exemplary
targeting sequence, a target may first be designated by anointment
with a predetermined laser designator. A guided missile or other
munition carrying seeker 60 may then be launched. Seeker 60,
initially operating in a SAL guidance mode, detects the pulsed
laser energy reflected from the designated target. After verifying
the pulsed laser energy as emitted from a qualified laser
designator, seeker 60 may then lock-on to the target reflecting the
pulsed laser energy. After target lock-on, seeker 60 switches or is
switched into the image guidance mode. In one embodiment, seeker 60
transmits a signal indicating that SAL lock-on has been achieved to
a remote command source (e.g., a pilot of an aircraft), and the
remote command source then transmits a command signal to seeker 60
to switch in the image tracking mode. In such a case, guided
munition 80 may receive the wireless command signal via a receiver
or transceiver operatively coupled to main navigational computer
84, as generally indicated in FIG. 4 at 130. In a second
embodiment, seeker 60 may automatically switch into the image
tracking mode after target lock-on has been achieved. In this
latter case, seeker 60 may simultaneously transmit a signal to a
remote command source (e.g., a pilot of an aircraft) indicating
that the seeker is now operating in an image guidance mode. After
seeker 60 has transitioned to the image guidance mode, anointment
of the designated target by the laser designator is no longer
required as seeker 60 will now track the image previously
designated by laser anointment. Thus, in contrast to munition
requiring continued laser input until target impact, the operator
of the laser designator (e.g., on-the-ground personnel or a
neighboring aircraft) is now freed to relocate and designate a new
target, as desired. Switching of seeker 60, and specifically of
digital processing system 74 (FIG. 4), can be achieved in a
relatively straightforward manner by switching between high and low
inputs each corresponding to a different guidance mode on a single
bit control line of processing system 74 (represented in FIG. 4 by
arrow 132).
[0040] There has thus been provided multiple exemplary embodiments
of a multi-mode seeker, such as a dual- or tri-mode seeker,
operable in both Semi-Active Laser and image tracking guidance
modes. In contrast to traditional multi-mode seekers having image
tracking and SAL guidance capabilities, embodiments of the
above-described multi-mode seeker utilize a single optical train, a
single focal plane array, and a single processing train to perform
both image and SAL tracking functionalities. As a result,
embodiments of the multi-mode seeker have a reduced complexity,
part count, weight, envelope, and cost. At the same time,
reliability and guidance accuracy of the above-described multi-mode
seekers is also maintained or improved relative to conventional
seekers due, in certain embodiments, to the usage of a high
resolution SWIR detector array to provide SAL guidance. Several
exemplary implementations of the manner in which the seeker may be
configured to perform pulse feature extraction, qualification, and
correlation when operating in a SAL guidance mode have also been
provided.
[0041] While at least one exemplary embodiment has been presented
in the foregoing Detailed Description, it should be appreciated
that a vast number of variations exist. It should also be
appreciated that the exemplary embodiment or exemplary embodiments
are only examples, and are not intended to limit the scope,
applicability, or configuration of the invention in any way.
Rather, the foregoing Detailed Description will provide those
skilled in the art with a convenient road map for implementing an
exemplary embodiment of the invention. It being understood that
various changes may be made in the function and arrangement of
elements described in an exemplary embodiment without departing
from the scope of the invention as set-forth in the appended
Claims.
* * * * *