Dual band framing reconnaissance camera

• US 6,477,326 B1
• Filed: 08/31/2000
• Issued: 11/05/2002
• Est. Priority Date: 08/31/2000
• Status: Expired due to Term

• Current Assignee: Goodrich Corporation (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Recon/Optical, Inc. (Bourns Incorporated)
• Inventors: Baker, Allie M., Jones, John, Beran, Stephen R., Wyatt, Stephan, Partynski, Andrew J.
• Primary Examiner(s): Adams, Russell
• Assistant Examiner(s): KOVAL, MELISSA J
• Application Number:
  US09/652,524
• Time in Patent Office: 796 Days
• Field of Search: 396/7, 396/8, 396/12, 396/13, 348/144, 348/145, 348/146, 348/147
• US Class Current: 396/7
• CPC Class Codes: G01C 11/025 by scanning the object
• CPC Class Codes: G02B 17/0808 on-axis systems with at least one of the mirrors having a central aperture
• CPC Class Codes: G02B 17/0852 having a field corrector only
• CPC Class Codes: G02B 17/0896 with variable magnification or multiple imaging planes, including multispectral systems systems with only refractive elements G02B15/14
• CPC Class Codes: G02B 7/18 for prisms; for mirrors
• CPC Class Codes: H04N 23/50 Constructional details

Abstract

A framing aerial reconnaissance camera is described which has a Cassegrain optical system forming an objective lens that directs radiation to a spectrum-dividing prism. The prism directs radiation in the visible portion of the electromagnetic spectrum into a first optical path having a two-dimensional image-recording medium, such as a framing CCD array. Radiation in the infrared (IR) band of the spectrum is directed to a second optical path, which has a two-dimensional framing IR-sensitive image-recording medium. The entire camera can be either rotated about the aircraft roll axis in a continuous fashion or stepped in a series of steps to generate frames of imagery, providing panoramic coverage of the scene across the line of flight in two bands of the spectrum simultaneously.

Claims

1. A dual band framing aerial reconnaissance camera for installation in an aerial reconnaissance vehicle, comprising;

(a) an optical system incorporated into a camera housing, comprising;

(1) an objective optical subassembly for receiving incident radiation from a scene external of said vehicle;

(2) a spectrum dividing element receiving radiation from said objective optical subassembly, 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;

(3) 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

(4) 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;

(b) a first motor system coupled to said camera housing rotating said camera 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 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; and

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

2. The camera of claim 1, wherein said first and second image recording media comprise two dimensional area array electro-optical detectors.

3. The camera of claim 2, wherein one of said electro-optical detectors is sensitive to radiation in the ultraviolet (UV) 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.

4. The camera of claim 3, 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 to 2.5 microns.

5. The camera as claimed in claim 2, wherein said electro-optical detectors comprise an array of pixel elements arranged in a plurality of rows and columns, and wherein said means for compensation for roll motion of said camera housing comprises electronic circuitry for 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.

6. The camera as claimed in claim 5, wherein said camera further comprises a camera control computer calculating said pixel information transfer rate from system inputs comprising f, the focal length of said optical system, and ω

, the rate of rotation of said camera housing about said roll axis.

7. The camera as claimed in claim 1, wherein at least one of said image-recording media comprises photosensitive film.

8. The camera as claimed in claim 7, wherein said means for compensating for roll motion of said camera housing comprises a mechanism for moving said 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.

9. The camera as claimed in claim 8, wherein said camera further comprises a camera control computer calculating said rate of movement of said film from system inputs comprising f, the focal length of said optical system, and ω

, the rate of rotation of said camera housing about said roll axis.

10. The camera as claimed in claim 1, wherein said objective optical subassembly comprises a catoptric Cassegrain optical system which forms an image at a Cassegrain image plane, and wherein said catoptric 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.

11. The camera as claimed in claim 10, wherein said second motor system comprises a Cassegrain motor coupled to said primary mirror, said secondary mirror and said azimuth mirror, and wherein to compensate for forward motion of said vehicle said Cassegrain motor rotates said primary and secondary mirrors in the flight direction at a rate equal to V/R 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 rotates said azimuth mirror at rate equal to ½

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

12. The camera as claimed in claim 11, wherein the value of R is derived from the height of said vehicle above the earth and a camera depression angle below a horizontal reference frame.

13. The camera as claimed in claim 11, wherein the value of R is derived using a range finder on board the vehicle.

14. The camera as claimed in claim 11, wherein the value of R is derived from a global positioning system.

15. The camera as claimed in claim 11, wherein the value of R is derived from processing successive frames of imagery from at least one of said image-recording media.

16. The camera of claim 11, wherein said secondary mirror is centrally located in the entrance aperture of said catoptric Cassegrain optical system.

17. The camera as claimed in claim 1, wherein said optical system has an overall focal length of between 50 and 100 inches and a f/number of between 4.0 and 8.0.

18. The camera as claimed in claim 1, further comprising a camera control computer operative of said image recording media and said first and second motor systems to generate a series of overlapping frames of imagery across the line of flight of said vehicle as said camera housing is rotated about said first axis, and wherein each of said overlapping frames of imagery is recorded in two different portions of said electromagnetic spectrum by said first and second image recording media.

19. The camera as claimed in claim 18, wherein said camera further comprises a spot mode of operation, said camera control computer in said spot mode of operation operative of said first and second motor systems to orient said Cassegrain optical system at a selected camera depression angle below a horizontal reference plane and fore/aft azimuth angle, and operative of said first and second image recording media to generate first and second frames of imagery of said scene at said camera depression angle and fore/aft azimuth angle.

20. The camera as claimed in claim 19, wherein said objective optical subassembly comprises a 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.

21. The camera as claimed in claim 20, wherein said second motor system comprises a Cassegrain motor coupled to said primary mirror and said azimuth mirror, and wherein to compensate for forward motion of said vehicle said Cassegrain motor rotates said primary and secondary mirrors in the flight direction at a rate equal to V/R 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 is rotated at rate equal to ½

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

22. The camera as claimed in claim 21, wherein the value of R is derived from the height of said vehicle above the earth and a camera depression angle below a horizontal reference frame.

23. The camera as claimed in claim 21, wherein the value of R is derived using a range finder on board the vehicle.

24. The camera as claimed in claim 21, wherein the value of R is derived from a global positioning system.

25. The camera as claimed in claim 21, wherein the value of R is derived from a processing of successive images generated by at least one of said image-recording media.

26. The camera as claimed in claim 20 wherein said secondary mirror is centrally located in the entrance aperture of said Cassegrain optical system.

27. The camera of claim 2, wherein one of said electro-optical detectors is 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 camera of claim 3, wherein said electro-optical detector sensitive to radiation in the infrared portion of the electromagnetic spectrum is sensitive to radiation having a wavelength of between 3.0 and 5.0 microns.

29. The camera of claim 3, wherein said electro-optical detector sensitive to radiation in the infrared portion of the electromagnetic spectrum is sensitive to radiation having a wavelength of between 8.0 and 14.0 microns.

30. The camera of claim 27 wherein said electro-optical 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.

31. The camera of claim 27, wherein said electro-optical detector sensitive to radiation in the infrared portion of the electromagnetic spectrum is sensitive to radiation having a wavelength of between 3.0 and 5.0 microns.

32. The camera of claim 27, wherein said electro-optical detector sensitive to radiation in the infrared portion of the electromagnetic spectrum is sensitive to radiation having a wavelength of between 8.0 and 14.0 microns.

33. A framing aerial reconnaissance camera for installation in an aerial reconnaissance vehicle, comprising;

(a) an optical system incorporated into a camera housing, comprising;

(1) an objective optical subassembly receiving incident radiation from a scene external of said vehicle;

(2) an optical channel receiving radiation from said objective optical subassembly, and

(3) a two-dimensional image recording medium in said optical channel for generating frames of imagery in a band of the electromagnetic spectrum, said optical channel including one or more optical elements focusing radiation from said scene on said two-dimensional image recording medium;

(b) a first motor system coupled to said camera housing rotating said camera 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 medium is exposed to said scene to generate frames of imagery as said first motor system rotates said camera in a continuous fashion about said first axis, said image recording medium having a means for compensating for image motion due to said rotation of said camera housing; and

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

34. The camera of claim 33, wherein said image recording medium comprises a two-dimensional area array electro-optical detector.

35. The camera of claim 34, wherein said electro-optical detector is sensitive to radiation in the ultraviolet portion of the electromagnetic spectrum.

36. The camera of claim 34, wherein said electro-optical detector is sensitive to radiation in the infrared portion of the electromagnetic spectrum.

37. The camera of claim 36, wherein said electro-optical detector is sensitive to radiation having a wavelength of between 1.0 to 2.5 microns.

38. The camera as claimed in claim 34, wherein electro-optical detector comprises an array of pixel elements arranged in a plurality of rows and columns, and wherein said means for compensation for roll motion of said camera housing comprises electronic circuitry for transferring pixel information in said electro-optical detector 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 detector due to roll of said camera housing.

39. The camera as claimed in claim 38, wherein said camera further comprises a camera control computer calculating said pixel information transfer rate from system inputs comprising f, the focal length of said optical system, and ω

, the rate of rotation of said camera housing about said roll axis.

40. The camera as claimed in claim 33, wherein said image recording medium comprises photosensitive film.

41. The camera as claimed in claim 40, wherein said means for compensating for roll motion of said camera housing comprises a mechanism for moving said 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.

42. The camera as claimed in claim 41, wherein said camera further comprises a camera control computer calculating said rate of movement of said film from system inputs comprising f, the focal length of said optical system, and ω

, the rate of rotation of said camera housing about said roll axis.

43. The camera as claimed in claim 33, wherein said optical has an overall focal length of between 50 and 100 inches and a f/number of between 4.0 and 8.0.

44. The camera as claimed in claim 33, further comprising a camera control computer operative of said image recording medium and said first and second motor systems to generate a series of overlapping frames of imagery across the line of flight of said vehicle as said camera housing is rotated about said first axis.

45. The camera as claimed in claim 44, wherein said camera further comprises a spot mode of operation, said camera control computer in said spot mode of operation operative of said first motor systems to orient said objective optical subassembly at a selected camera depression angle about the roll axis of said vehicle and fore/aft azimuth angle, and operative of said first and second image recording media to generate first and second frames of imagery of said scene at said camera depression angle and fore/aft azimuth angle.

46. The camera of claim 34, wherein said electro-optical detector is sensitive to radiation in the visible portion of the electromagnetic spectrum.

47. The camera of claim 36, wherein said electro-optical detector is sensitive to radiation having a wavelength of between 3.0 and 5.0 microns.

48. The camera of claim 36, wherein said electro-optical detector is sensitive to radiation having a wavelength of between 8.0 and 14.0 microns.

49. A framing aerial reconnaissance camera for installation in an aerial reconnaissance vehicle, comprising;

(a) an optical system incorporated into a camera housing, comprising;

(1) a Cassegrain optical system for receiving incident radiation from a scene external of said vehicle;

(2) an optical channel receiving radiation from said Cassegrain optical system, and

(3) a two-dimensional electro-optical detector in said optical channel for generating frames of imagery in a band of the electromagnetic spectrum, said optical channel including one or more optical elements focusing radiation from said scene on said two-dimensional electro-optical detector;

(b) a first motor system coupled to said camera housing rotating said camera 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 detector is exposed to said scene to generate frames of imagery as said first motor system rotates said camera in a continuous fashion about said first axis, and

(c) a second motor system coupled to said Cassegrain optical system, said second motor system rotating said Cassegrain optical system about a second axis in the direction of forward motion of said vehicle about an axis to compensate for forward motion of said aerial reconnaissance vehicle,

wherein said electro-optical detector comprises an array of pixel elements arranged in a plurality of rows and columns, and wherein said detector further comprises electronic circuitry coupled to said array transferring pixel information in array 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;

said electronic circuitry and said second motor system operative to achieve roll motion compensation and forward motion compensation simultaneously in said array to thereby enable high resolution images to be obtained from said electro-optical detector.

50. The camera as claimed in claim 49, wherein said camera further comprises a camera control computer calculating said pixel information transfer rate from system inputs comprising f, the focal length of said optical system, and so, the rate of rotation of said camera housing about said roll axis.

51. A method of generating frames of imagery of a scene of interest with an aerial reconnaissance camera in two different bands of the electromagnetic spectrum simultaneously, comprising the steps of:

providing two photosensitive electro-optical detectors in said camera, each of said detectors comprising an array of pixel elements arranged in a plurality of rows and columns;

rotating said camera in a continuous fashion about a roll axis either coincident with or parallel to a roll axis of an aerial reconnaissance vehicle carrying said camera;

while rotating said camera, simultaneously exposing said electro-optical detectors to a scene of interest in a series of exposures;

while rotating said camera and while exposing said electro-optical detectors to said scene, rotating an optical system providing an objective lens for said camera in the direction of forward motion of said vehicle at a predetermined rate to cancel out image motion due to forward motion of said vehicle; and

while said electro-optical detectors are being exposed to said scene, moving pixel information in said arrays at a rate and in a direction substantially equal to the rate of image motion due to rotation of said camera about said roll axis to thereby preserve resolution of an image generated by said detectors.