Method of framing reconnaissance with motion roll compensation

• US 6,658,207 B1
• Filed: 08/31/2000
• Issued: 12/02/2003
• Est. Priority Date: 08/31/2000
• Status: Expired due to Fees

• Current Assignee: Goodrich Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Recon/Optical, Inc. (Bourns Incorporated)
• Inventors: Beran, Stephen R., Partynski, Andrew J.
• Primary Examiner(s): Adams, Russell
• Assistant Examiner(s): Koval, Melissa J.
• Application Number:
  US09/654,031
• Time in Patent Office: 1,188 Days
• Field of Search: 396/7, 396/8, 396/12, 396/13, 348/146, 348/147, 348/144, 348/145
• US Class Current: 396/7
• CPC Class Codes: G01C 11/025 by scanning the object

Abstract

An electro-optical roll-framing camera is described in which successive overlapping frames of scene imagery are generated by an electro-optical imaging array. Image motion compensation is performed electronically to stop or freeze image motion caused by the roll motion. The image motion compensation is performed by the array during the generation of the frames of imagery. The successive frames of imagery are made during a continuous roll motion of the entire camera (including the array). The image motion due to roll is stopped or frozen without mechanically stopping the roll motion, such as found in prior art step frame cameras. The roll framing cycles of the camera generate sweeping coverage of the terrain of interest. The roll rate for a given electro-optical array is a function of the frame size and the framing rate, and is controllable by a master camera control computer.

Claims

1. A method for imaging a scene with a framing camera installed in an aerial reconnaissance vehicle, the camera comprising a two dimensional framing array of photosensitive cells, an optical system directing scene radiation onto said array, and a mechanism for rolling said camera about a roll axis, said array of cells storing pixel information and arranged in a plurality of rows and columns, comprising the steps of:

(a) continuously rotating said camera about said roll axis with said roll mechanism to thereby direct scene information onto said two dimensional array;

(b) exposing said array while said camera is rotating and transferring pixel information in said array at a rate substantially equal to an image motion rate due to said rotation of said camera;

(c) reading out said pixel information from said array; and

(d) repeating said steps (b), and (c) while said vehicle flies past a scene of interest and while said camera continuously rotates about said roll axis.

2. The method of claim 1, wherein said step of continuously rotating comprises the step of rotating said camera about an axis substantially parallel to the direction of forward motion of said aerial reconnaissance vehicle.

3. The method of claim 1, wherein said step of continuously rotating comprises the step of rotating said camera about an axis in the direction substantially orthogonal to the direction of forward motion of said aerial reconnaissance vehicle.

4. The method of claim 1, wherein said steps (a), (b), (c), and (d) are performed in a a series of cycles as said aircraft flies past a scene of interest.

5. The method of claim 1, wherein said camera generates imagery in a single band of the electromagnetic spectrum.

6. The method of claim 1, wherein said camera includes a second electro-optical detector and wherein said camera generates imagery in two bands of the electromagnetic spectrum simultaneously from said first and second detectors.

7. The method of claim 1, wherein said camera includes an hyperspectral electro-optical detector and optical system.

8. The method of claim 1, wherein said optical system further comprises a derotation prism.

9. The method of claim 1, wherein said optical system further comprises a derotation mirror.

10. The method of claim 1, wherein the camera further comprises a catoptric Cassegrain objective subassembly, wherein said roll mechanism rotates said catoptric Cassegrain objective subassembly, said optical system, and said array about said roll axis.

11. An electro-optical roll framing camera with electronic roll motion compensation, said camera for installation in an aerial reconnaissance vehicle, comprising:

an electro-optical detector comprising a two-dimensional array of photosensitive cells, said array of cells storing pixel information and arranged in a plurality of rows and columns and having at least one readout register for reading out pixel information from said array;

an optical system directing scene radiation onto said array,

a servo-mechanical system coupling said camera to said vehicle adapted for continuously rotating said camera about a rotation axis to thereby direct scene information onto said optical system and said array; and

rotation motion compensation circuitry electronically transferring pixel information in said array of photosensitive cells at a rate substantially matching the rate of image motion due to said rotation of said camera, whereby the resolution of images generated by said array may be preserved.

12. The camera of claim 11, wherein said camera is installed in said vehicle such that said servo-mechanical system continuously rotates said camera about an axis substantially parallel to the direction of forward motion of said vehicle.

13. The camera of claim 11, wherein said camera is installed in said vehicle such that said servo-mechanical system continuously rotates said camera about an axis substantially orthogonal to the direction of forward motion of said vehicle.

14. The camera of claim 11, wherein said array generates imagery in a single band of the electro-magnetic spectrum.

15. The camera of claim 11, wherein said camera includes a second electro-optical detector and wherein said camera generates imagery in two bands of the electromagnetic spectrum simultaneously from said first and second detectors.

16. The camera of claim 11, wherein said camera includes a hyperspectral electro-optical detector and optical system.

17. The camera of claim 11, wherein said optical system further comprises a derotation prism.

18. The camera of claim 11, wherein said optical system further comprises a derotation mirror.

19. The method of claim 11, wherein the camera further comprise a catoptric Cassegrain objective lens, wherein said servo-mechanical system rotates said catoptric Cassegrain objective lens, said optical system, and said array about said rotation axis.

20. A method of generating a frame of imagery of a scene of interest by an aerial reconnaissance camera installed in a moving airborne vehicle, said camera comprising an optical system and at least one framing image recording medium, said optical system and framing image recording medium incorporated into a camera housing mounted to the vehicle, comprising the steps of:

(1) continuously rotating the camera housing, including said optical system and said framing image recording medium, about a roll axis parallel to the roll axis of said vehicle;

(2) simultaneously and independently rotating said optical system in an direction orthogonal to said roll axis and in a direction of flight of said vehicle to thereby compensate for forward motion of said vehicle;

(3) while said camera is rotating about said roll axis and said optical system is rotating in said direction of flight, exposing said image recording medium to radiation from said scene to thereby generate said frame of imagery; and

(4) compensating for the roll motion of said camera housing to thereby prevent blurring of an image generated by said framing image recording medium due to said roll motion.

21. The method of claim 20, wherein said framing image recording medium is exposed to said scene in a series of exposures as said camera continuously rotates about said roll axis.

22. The method of claim 20, wherein said series of exposures overlap in the cross-line of flight direction.

23. The method of claim 20, wherein said camera incorporates a spectrum dividing element and a second framing image recording medium, and wherein said camera operates to generate two frames of imagery of said scene in two different portions of the electromagnetic spectrum simultaneously.

24. The method of claim 20, wherein said optical system forms an image at an image plane, and wherein said optical system comprises a Cassegrain optical system having a primary mirror, a secondary mirror rigidly coupled to said primary mirror, and a flat azimuth mirror located in the optical path between the secondary mirror and the Cassegrain image plane.

25. The method of claim 24, wherein to compensate for forward motion of said vehicle said said primary and secondary mirrors are rotated in the flight direction at a rate equal to V/R (in units of radians per second) where V is the velocity of aerial reconnaissance vehicle and R is either the range to the scene of interest or an approximation of said range, and wherein said azimuth mirror rotates at a rate equal to ½

(V/R) in the same direction as the rotation of said primary and secondary mirrors.

26. The method of claim 20, wherein said image recording medium comprises a two dimensional area framing array electro-optical detector.

27. The method of claim 23, wherein both of said framing image recording media comprise two dimensional array electro-optical detectors, one of said electro-optical detectors sensitive to radiation in the visible portion of the electromagnetic spectrum and wherein the other of said electro-optical detectors is sensitive to radiation in the infrared portion of the electromagnetic spectrum.

28. The method of claim 27, wherein the detector sensitive to radiation in the infrared portion of the electromagnetic spectrum is sensitive to radiation having a wavelength of between 1.0 and 2.5 microns, 3.0 and 5.0 microns, or 8.0 and 14.0 microns.

29. The method of claim 27, wherein said electro-optical detectors comprise an array of pixel elements arranged in a plurality of rows and columns, compensation for roll motion of said camera housing is performed by electronic circuitry transferring pixel information in said electro- optical detectors from row to adjacent row at a pixel information transfer rate substantially equal to the rate of image motion in the plane of said electro-optical detectors due to roll of said camera housing.

30. The method as claimed in claim 20, wherein said image recording medium comprises photo-sensitive film.

31. The method of claim 30, wherein compensation for roll motion of said camera housing is performed by moving the film at a rate substantially equal to the rate of image motion in the plane of said film due to roll of said camera housing.

32. The method of claim 20, wherein said camera further comprises:

a spectrum dividing element receiving radiation from said optical system, said element directing radiation in a first band of the electromagnetic spectrum into a first optical path and directing radiation in a second band of the electromagnetic spectrum into a second optical path different from said first optical path;

a first two-dimensional image recording medium in said first optical path for generating frames of imagery in said first band of the electromagnetic spectrum; and

a second two-dimensional image recording medium in said second optical path for generating frames of imagery in said second band of the electromagnetic spectrum;

a first motor system coupled to said camera housing rotating said camera housing about a first axis, said camera housing installed in said aerial reconnaissance vehicle such that said first axis of rotation is parallel to the roll axis of said aerial reconnaissance vehicle,

wherein said image recording media are exposed to said scene to generate frames of imagery as said first motor system rotates said camera housing in a continuous fashion about said first axis, said first and second image recording media having a means for compensating for image motion due to said rotation of said camera housing; and

a second motor system coupled to said optical system, said second motor system rotating said optical system about a second axis in the direction of forward motion of said vehicle to compensate for forward motion of said aerial reconnaissance vehicle.

33. A method for dual band framing reconnaissance in which frames of imagery of a scene of interest are taken by an aerial reconnaissance camera installed in a moving airborne vehicle, said camera comprising a Cassegrain optical system, a first framing image recording medium and a second framing image recording medium, said Cassegrain optical system and said first and second framing image recording media incorporated into a camera housing mounted to the vehicle, the method comprising the steps of:

1) continuously rotating the camera housing, including said optical system and said first and second framing image recording media, from a first position to a second position about a roll axis parallel to the roll axis of said vehicle;

2) dividing radiation from a scene of interest into two different optical paths including a first optical path and a second optical path, said first framing image recording medium placed in said first optical path and said second framing image recording medium placed in said second optical path;

3) simultaneously and independently rotating said Cassegrain optical system in an direction orthogonal to said roll axis and in a direction of flight of said vehicle to thereby compensate for forward motion of said vehicle;

4) while said camera is rotating about said roll axis and said Cassegrain optical system is rotating in said direction of flight, exposing said image recording media to radiation from said scene in a series of exposures to thereby generate said frames of imagery; and

5) compensating for the roll motion of said camera housing to thereby prevent smearing of an image generated by said first and second framing image recording media due to said roll motion.

34. The method of claim 33, further comprising the step of returning said camera housing to said first roll position after it has rotated from said first roll position to said second roll position, and thereafter repeating steps 1, 2, 3, 4 and 5.

35. The method of claim 33, wherein during said rotation of said camera housing from said first roll position to said second roll position, said first and second image recording media are exposed N times, where N is an integer number of frames between 2 and 20.

36. The method of claim 33, wherein the angular difference between said first roll position and said second roll position is less than 10 degrees.

37. The method of claim 33, wherein said camera is rotated through nadir.

38. The method of claim 33, wherein said series of exposures overlap in the cross-line of flight direction.

39. The method of claim 33, wherein said Cassegrain optical system forms an image at a Cassegrain image plane, and wherein said Cassegrain optical system comprises a primary mirror, a secondary mirror rigidly coupled to said primary mirror, and a flat azimuth mirror located in the optical path between the secondary mirror and the Cassegrain image plane.

40. The method of claim 39, wherein to compensate for forward motion of said vehicle said primary and secondary mirrors are rotated in the flight direction at a rate equal to V/R (in units of radians per second) where V is the velocity of aerial reconnaissance vehicle and R is either the range to the scene of interest or an approximation of said range, and wherein said azimuth mirror rotates at rate equal to ½

(V/R) in the same direction as the rotation of said primary and secondary mirrors.

41. The method of claim 33, wherein said first and second framing image recording media comprise two-dimensional array electro-optical detectors, one of said electro-optical detectors sensitive to radiation in the visible portion of the electromagnetic spectrum and wherein the other of said electro-optical detectors is sensitive to radiation in the infrared portion of the electromagnetic spectrum.

42. The method of claim 41, wherein the detector sensitive to radiation in the infrared portion of the electromagnetic spectrum is sensitive to radiation having a wavelength of between 1.0 and 2.5 microns, 3.0 and 5.0 microns, or 8.0 and 14.0 microns.

43. The method of claim 41, wherein said electro-optical detectors comprise an array of pixel elements arranged in a plurality of rows and columns, and wherein compensation for roll motion of said camera housing is performed by electronic circuitry transferring pixel information in said electro-optical detectors from row to adjacent row at a pixel information transfer rate substantially equal to the rate of image motion in the plane of said electro-optical detectors due to roll of said camera housing.

44. A method for imaging a scene with a framing camera installed in an aerial reconnaissance vehicle, the camera comprising a two dimensional array of photosensitive cells, said array of cells storing pixel information and arranged in a plurality of rows and columns, a scan head directing scene radiation onto said array, and a mechanism for rotating said scan head about a rotation axis in a continuous manner, comprising the steps of:

(a) continuously rotating said scan head about said rotation axis with said roll mechanism to thereby direct an image containing scene information towards said two dimensional array;

(b) derotating said image containing scene information;

(c) while said scan head is continuously rotating, transferring pixel information in said array at a rate substantially equal to an image motion rate;

(d) reading out said pixel information from said array; and

(e) repeating said steps (b), (c) and (d) while said vehicle flies past a scene of interest and while said scan head continuously rotates about said rotation axis.

45. The method of claim 44, wherein said step of continuously rotating comprises the step of rotating said scan head about an axis substantially parallel to the direction of forward motion of said aerial reconnaissance vehicle.

46. The method of claim 44, wherein said step of continuously rotating comprises the step of rotating said scan head about an axis in the direction substantially orthogonal to the direction of forward motion of said aerial reconnaissance vehicle.

47. The method of claim 44, wherein said steps (a), (b), (c), and (d) and (e) are performed in a series of cycles as said aircraft flies past a scene of interest.

48. A method for imaging a scene with a framing camera installed in an aerial reconnaissance vehicle, the camera comprising a two dimensional array of photosensitive cells, said array of cells storing pixel information and arranged in a plurality of rows and columns, a scan head directing scene radiation onto said array, and a mechanism for rotating said scan head about a rotation axis in a continuous manner, comprising the steps of:

(a) continuously rotating said scan head about said rotation axis with said roll mechanism to thereby direct an image containing scene information towards said two dimensional array;

(b) rotating said two dimensional array in synchronism with said rotation of said scan head to thereby derotate said image containing scene information;

(c) while said scan head and said two dimensional array are continuously rotating, transferring pixel information in said array at a rate substantially equal to an image motion rate due to said rotation of said scan head;

(d) reading out said pixel information from said array; and

(e) repeating said steps (b), (c) and (d) while said vehicle flies past a scene of interest and while said scan head continuously rotates about said rotation axis.

49. The method of claim 48, wherein said step of continuously rotating comprises the step of rotating said scan head about an axis substantially parallel to the direction of forward motion of said aerial reconnaissance vehicle.

50. The method of claim 48, wherein said step of continuously rotating comprises the step of rotating said scan head about an axis in the direction substantially orthogonal to the direction of forward motion of said aerial reconnaissance vehicle.

51. The method of claim 48, wherein said steps (a), (b), (c), and (d) and (e) are performed in a series of cycles as said aircraft flies past a scene of interest.