Electro-optical reconnaissance system with forward motion compensation

• US 6,373,522 B2
• Filed: 02/02/2001
• Issued: 04/16/2002
• 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: BAE Systems Information and Electronic Systems Integration Incorporated (BAE Systems Plc)
• Inventors: Mathews, Bruce Albert, Coon, Bryan Huntington
• Primary Examiner(s): Kelley, Chris
• Assistant Examiner(s): An, Shawn S.
• Application Number:
  US09/773,733
• Publication Number:
  US 20010015755A1
• Time in Patent Office: 438 Days
• Field of Search: 348/144, 348/229, 348/314, 348/441, 348/275, 348/208, 396/130, 396/236, 244/17.19
• 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) system comprising a moving shutter and a full frame focal plane array detector is disclosed. The reconnaissance system 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;

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 having approximately equal image motions and wherein said charges representing said image are transferred at a charge transfer rate corresponding to said image motion in said area of said scene exposed by said shutter exposure slit; 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 said clocking signal corresponds to a position of said exposure slit and said image motion;

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) control electronics to generate said clocking signal to drive said FPA, and

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;

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 vertical 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;

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

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

2. The 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, wherein said exposure slit is moved across said focal plane array to define areas of exposure having approximately equal motions, and wherein said charges representing said image are transferred at a charge transfer rate corresponding to said image motion in said area of said scene exposed by said shutter exposure slit;

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;

wherein the reconnaissance system is installed in a vehicle capable of moving in a forward direction, 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) control electronics to generate said clocking signal to drive said FPA, and

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 parameters inputs and provide processed mission parameter information to said imaging section to perform forward motion compensation (FMC) of said image;

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 image 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;

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

wherein said digital preprocessor comprises;

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

3. The electro-optical reconnaissance system of claim 2, 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.

4. The electro-optical reconnaissance system of claim 3, 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.