Electro-optical reconnaissance system with forward motion compensation

• US 6,256,057 B1
• Filed: 05/19/1998
• Issued: 07/03/2001
• Est. Priority Date: 11/05/1996
• Status: Expired due to Term

• Current Assignee: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Mathews, Bruce Albert, Coon, Bryan Huntington
• Primary Examiner(s): Kelley, Chris S.
• Assistant Examiner(s): An, Shawn S.
• Application Number:
  US09/080,452
• Time in Patent Office: 1,141 Days
• Field of Search: 348/144, 348/146-148, 348/269, 348/229, 354/402
• US Class Current: 348/144
• CPC Class Codes: G01C 11/02 Picture taking arrangements specially adapted for photogrammetry or photographic surveying, e.g. controlling overlapping of pictures
• CPC Class Codes: H04N 25/53 Control of the integration time
• CPC Class Codes: H04N 25/71 Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
• CPC Class Codes: H04N 25/711 Time delay and integration [TDI] registers; TDI shift registers

Abstract

An electro-optical framing camera forward motion compensation (FMC) reconnaissance system comprising a moving shutter and a full frame focal plane array detector is designed to minimize the variation of image motion from a target scene across the focal plane array. The full frame focal plane array, such as a Charge Coupled Device (CCD), is designed to transfer and add the image from pixel to pixel at a predetermined rate of image motion corresponding to the region exposed by the focal plane shutter. The focal plane shutter aperture and velocity are set to predetermined values coordinated with the available illumination. The CCD image transfer rate is set to minimize the smear effects due to image motion in the region of the scene exposed by the focal plane shutter. This rate is variable with line of sight depression angle, aircraft altitude, and aircraft velocity/altitude ratio. Further, a method of FMC utilizes a comparison of a measured light level to a standard value in order to determine the appropriate exposure time and shutter motion rate. An optimal FMC clocking signal is calculated based on image motion equations incorporated in the processing unit of the reconnaissance system.

Claims

1. An electro-optical reconnaissance system, comprising:

a focal plane array including a main format area having a plurality of photo-sensitive cells arranged in rows and columns, wherein said focal plane array is configured to detect a projected image of a scene and to convert said image into an electronic charge representation of said image; and

a shutter having a controllable exposure slit proximate to said focal plane array, wherein said exposure slit is moved across said focal plane array to define areas of exposure, each area of exposure having an associated image motion that is substantially uniform across said area of exposure, wherein said electronic charges representing said image are transferred at a charge transfer rate corresponding to said image motion in said associated area of exposure exposed by said shutter exposure slit, as said exposure slit is moved across said focal plane array.

2. The electro-optical reconnaissance system of claim 1, further comprising:

a camera control electronics unit driving said plurality of photo-sensitive cells with a clocking signal for an exposed portion of said focal plane array corresponding to said charge transfer rate, wherein said clocking signal corresponds to a position of said exposure slit and said image motion.

3. The electro-optical reconnaissance system of claim 2, wherein a width and a speed of said exposure slit are adjustable, and wherein said camera control electronics unit controls said exposure slit width.

4. The electro-optical reconnaissance system of claim 3, wherein said focal plane array is a charge coupled device (CCD).

5. The electro-optical reconnaissance system of claim 4, wherein said focal plane array further comprises:

a horizontal output register having a predetermined number of segments, wherein each of said segments includes an output detector/amplifier structure.

6. The electro-optical reconnaissance system of claim 2, wherein the reconnaissance system is installed in a vehicle capable of moving in a forward direction, and wherein said camera control electronics unit comprises:

an imaging electronics section comprising

an analog processor to process said transferred electronic charges representing said image,

focal plane array (FPA) drive electronics to generate said clocking signal to drive said FPA,

a shutter exposure control unit to control shutter parameters, wherein said shutter parameters include said exposure slit width and said speed of said exposure slit;

a signal processing electronics unit comprising

a digital preprocessor coupled to said FPA drive electronics and to said analog processor, to receive and further process said electronic charge representation of said image, and to provide a digital processed image signal; and

a camera central processing unit (CPU), to process mission parameter inputs and provide processed mission parameter information to said imaging section to perform forward motion compensation (FMC) of said image.

7. The electro-optical reconnaissance system of claim 6 further comprising:

a lens to focus said scene onto said focal plane array;

signal recording means coupled to an output of said signal compression means to record a forward motion corrected image of said scene; and

a power supply to provide power for said camera control electronics unit.

8. The electro-optical reconnaissance system of claim 7, further comprising

a light sensor in communication with said shutter control unit;

and

a thermo-electric cooler to control an operating temperature of said focal plane array.

9. The electro-optical reconnaissance system of claim 8, wherein said focal plane array is mounted on an adjustable mount coupled to said vehicle, wherein the electro-optical reconnaissance system performs forward motion compensation in a forward oblique mode of operation, a side oblique mode of operation, and a vertical mode of operation.

10. The electro-optical reconnaissance system of claim 6, wherein said shutter control unit comprises:

a buffer to receive a signal generated by said light sensor indicating lighting conditions of the scene;

an analog to digital converter coupled to said buffer to convert said light sensor signal into a digital signal; and

a look-up table to convert said digitized signal into a look up table value to drive said shutter, wherein said look-up table provides drive signals corresponding to said exposure slit speed and said exposure slit width.

11. The electro-optical reconnaissance system of claim 6, wherein said FPA control electronics comprise:

a timing generator to generate a master timing signal and to provide for focal plane array readout and FMC, wherein said master timing signal is divided by a predetermined value to provide a local timing signal;

a horizontal counter to provide a time base for pixel counting operations;

a vertical counter to provide a time base in the vertical direction of said focal plane array;

a horizontal clock generator coupled to said horizontal and vertical counters, to provide a horizontal clocking signal to said focal plane array;

a vertical clock generator coupled to said horizontal and vertical counters, to provide a vertical clocking signal to said focal plane array; and

a frame synchronization unit, coupled to said horizontal and vertical counters, to generate frame sync signals and line sync signals.

12. The electro-optical reconnaissance system of claim 11, wherein said FPA control electronics further comprise:

a plurality of multi-tap delay lines to define a phase relationship of said horizontal and vertical clocking signals.

13. The electro-optical reconnaissance system of claim 11, wherein said digital preprocessor comprises:

a circuit card assembly (CCA) to process inputs from said imaging electronics section.

14. The electro-optical reconnaissance system of claim 13, wherein said CCA comprises:

a Static Random Access Memory (SRAM) configured as First In/First Out (FIFO) memory to store pixel data from said focal plane array, wherein said FIFO memory facilitates replacing defective pixels with nearest neighbor processing;

a timing generator coupled to said frame sync and line sync signals;

a Field Programmable Gate Array (FPGA) address generator coupled to said timing generator to generate memory addressing;

a Programmable Read Only Memory (PROM) coupled to said FPGA address generator to store locations of said defective pixels;

an Automatic Gain Control (AGC) ASIC to reduce said pixel data without degradation of the original image, wherein said pixel data is reduced from twelve-bit form to eight-bit form;

an illumination chip to correct for vignetting effects of said image; and

an image bus coupled to said AGC ASIC to receive said eight-bit data format.

15. The electro-optical reconnaissance system of claim 14, wherein said AGC ASIC includes means to subtract out specular reflections contained on said image, subtract out haze contributions contained on said image, and maintain a running average of said image data.

16. An electro-optical reconnaissance system for performing forward motion compensation, wherein said reconnaissance system is installed in a vehicle capable of moving in a forward direction, comprising:

a focal plane array including a main format area having a plurality of photo-sensitive cells arranged in rows and columns, wherein said focal plane array is configured to detect a projected image of a scene and to convert said image into an electronic charge representation of said image, and wherein said focal plane array is oriented to view said scene in a forward oblique mode of operation; and

a focal plane shutter, having a controllable exposure slit proximate to said focal plane array, wherein said exposure slit is moved across said focal plane array to define areas of exposure, each area of exposure having an associated image motion that is substantially uniform across said area of exposure, wherein said exposure slit is oriented parallel to a direction of said rows, and wherein said electronic charges representing said image are transferred at a charge transfer rate corresponding to said image motion in said associated area of exposure exposed by said shutter exposure slit, as said exposure slit is moved across said focal plane array.

17. The electro-optical reconnaissance system of claim 16, further comprising:

a lens to focus said scene onto said focal plane array; and

a camera control electronics unit driving said plurality of photo-sensitive cells with a clocking signal for an exposed portion of said focal plane array corresponding to said charge transfer rate, wherein a width and a speed of said exposure slit are adjustable, wherein said camera control electronics unit controls said exposure slit width, wherein said clocking signal corresponds to a position of said exposure slit and said speed of said exposure slit, and wherein said clocking signal corresponds to a rate of motion of objects contained in a portion of said scene viewed by said focal plane array.

18. The electro-optical reconnaissance system of claim 17, wherein said clocking signal is generated in accordance with an in-track image motion, wherein said in-track image motion is determined by $\frac{\mathrm{FV}}{\mathrm{ALT}}$

sin2

(γ

±

θ

)cos2

θ



 



and

 



V

 



FALT

 



sin2

γ

where

F=Focal length,

ALT=Altitude of the vehicle,

V=velocity,

θ

=in track angle, and

γ

=depression angle.

19. The electro-optical reconnaissance system of claim 16, wherein said focal plane array is a column-segmented charge coupled device (CCD).

20. An electro-optical reconnaissance system for performing forward motion compensation, wherein said reconnaissance system is installed in a vehicle capable of moving in a forward direction, comprising:

a focal plane array including a main format area having a plurality of photo-sensitive cells arranged in rows and columns, wherein said focal plane array is configured to detect a projected image of a scene and to convert said image into an electronic charge representation of said image, and wherein said focal plane array is oriented to view said scene in a side oblique mode of operation; and

a focal plane shutter, having a controllable exposure slit proximate to said focal plane array, wherein said exposure slit is moved across said focal plane array to define areas of exposure, each area of exposure having an associated image motion that is substantially uniform across said area of exposure, wherein said exposure slit is oriented parallel to a direction of said columns, and wherein said electronic charges representing said image are transferred at a charge transfer rate corresponding to said image motion in said associated area of exposure exposed by said shutter exposure slit, as said exposure slit is moved across said focal plane array.

21. The electro-optical reconnaissance system of claim 20, further comprising:

a lens to focus said scene onto said focal plane array; and

a camera control electronics unit driving said plurality of photo-sensitive cells with a clocking signal for an exposed portion of said focal plane array corresponding to said charge transfer rate, wherein a width and a speed of said exposure slit are adjustable, wherein said camera control electronics unit controls said exposure slit width, wherein said clocking signal corresponds to a position of said exposure slit and to said image motion in said area of said scene exposed by said shutter exposure slit.

22. The electro-optical reconnaissance system of claim 21, wherein said clocking signal is generated in accordance with an in-track image motion, wherein said in-track image motion is determined by $\frac{V}{}$

 



FALT

 



sin

 



γ



 



and

 



FVALT

sin

(γ

±

θ

)cos

 



θ

where

F=Focal length,

ALT=Altitude,

V=velocity,

φ

=in track angle,

θ

=cross track angle, and

γ

=depression angle.

23. The electro-optical reconnaissance system of claim 20, wherein the focal plane array is a column-segmented charge coupled device (CCD).

24. A method for providing forward motion compensation (FMC) for an electro-optical reconnaissance system in a vehicle capable of forward motion, said optical reconnaissance system including a moveable shutter exposure slit and a focal plane array configured to detect a projected image of a scene and to convert said image into an electronic charge representation of said image, comprising the steps of:

(1) moving the shutter exposure slit across the focal plane array to define areas of exposure, each area of exposure having an associated image motion that is substantially uniform across said area of exposure;

(2) transferring electronic charges representing the image at a charge transfer rate corresponding to said image motion in said associated area of exposure exposed by said shutter exposure slit, as said exposure slit is moved across said focal plane array;

(3) a measuring a light level of a scene to be imaged by the reconnaissance system;

(4) comparing the measured light level to a predetermined light level value;

(5) determining an exposure time by comparing the measured light level to an exposure time look-up table,

(6) determining a forward motion compensation profile corresponding to the exposure time and mission parameter inputs; and

(7) sending a signal corresponding to said forward motion compensation profile to an electronics unit of the electro-optical reconnaissance system to perform FMC.

25. The method of claim 24, wherein step (3) comprises the steps of:

(a) determining an exposure time by comparing the measured light level to a primary exposure time look-up table, if the measured light level is greater than the predetermined light level value; and

(b) determining an exposure time by comparing the measured light level to a low light exposure time look-up table, if the measured light level is less than the predetermined light level value.

26. The method according to claim 24, wherein step 3(a) further comprises the step of:

sending a shutter speed signal corresponding to the determined exposure time to a shutter exposure control unit, wherein a faster shutter speed corresponds to shorter exposure times, and wherein a slower shutter speed corresponds to longer exposure times.

27. The method according to claim 24, wherein step 3(b) further comprises the step of:

utilizing a set of instantaneous mission parameters to determine the exposure time, wherein the set of instantaneous mission parameters includes at least one of aircraft velocity, altitude, and camera look angle.

28. The method according to claim 24, further comprising the step of:

(6) determining a exposure slit width for the exposure slit corresponding to product of the exposure time and the exposure slit speed.

29. The method according to claim 24, wherein the forward motion compensation profile determined in step (4) corresponds to a look-up table value, wherein said look up table value is calculated based on in-track image motion rate equations, and wherein the in-track image motion rate equations utilize a set of mission parameter inputs that include:

aircraft velocity, V;

aircraft altitude, H;

depression angle of camera (fixed for flight);

camera installation location (fixed for flight);

shutter trigger pulse; and

focal length.

30. The method according to claim 29, wherein the electro-optical reconnaissance system is operating in a side oblique mode of operation, wherein the in-track image motion is determined by $\frac{V}{}$

 



FALT

 



sin

 



γ



 



and

 



FVALT

sin

(γ

±

θ

)cos

 



θ

where

F=Focal length,

ALT=Altitude,

V=Aircraft velocity,

φ

=in track angle,

θ

=cross track angle, and

γ

=depression angle.

31. The method according to claim 29, wherein the electro-optical reconnaissance system is operating in a forward oblique mode of operation, wherein the in-track image motion is determined by $\frac{\mathrm{FV}}{\mathrm{ALT}}$

sin2

(γ

±

θ

)cos2

θ



 



and

 



V

 



FALT

 



sin2

γ

where

F=Focal length,

ALT=Altitude,

V=Aircraft velocity,

θ

=in track angle, and

γ

=depression angle.

32. An electro-optical reconnaissance system, comprising:

a focal plane array including a main format area having a plurality of photo-sensitive cells arranged in rows and columns, wherein said focal plane array is configured to detect a projected image of a scene and to convert said image into an electronic charge representation of said image;

a shutter having a controllable exposure slit proximate to said focal plane array;

means for moving said exposure slit across said focal plane array to define areas of exposure, each area of exposure having an associated image motion that is substantially uniform across said area of exposure, and

means for transferring said electronic charges representing said image at a charge transfer rate corresponding to said image motion in said associated area of exposure exposed by said shutter exposure slit, as said exposure slit is moved across said focal plane array.