Imaging lidar system

• US 5,231,401 A
• Filed: 08/10/1990
• Issued: 07/27/1993
• Est. Priority Date: 08/10/1990
• Status: Expired due to Fees

• Current Assignee: Kaman Aerospace Corporation (Kaman Corporation)
• Original Assignee: Kaman Aerospace Corporation (Kaman Corporation)
• Inventors: Kaman, Charles H., Ulich, Bobby L., Mayerjak, Robert, Schafer, George
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US07/565,631
• Time in Patent Office: 1,082 Days
• Field of Search: 342/55, 356/5, 356/6, 250/332, 358/95, 358/209, 358/213.26, 358/83, 358/100, 358/99, 358/211, 358/113, 358/125, 358/110
• US Class Current: 342/55
• CPC Class Codes: G01S 17/89 for mapping or imaging

Abstract

An airborne imaging lidar (light detection and ranging) sensor is provided which employs multiple pulsed laser transmitters, multiple gated and intensified array camera receivers, an optical scanner for increased field of regard, and a computer for system control, automatic target detection and display generation. The laser transmitters and multiple camera receivers are optically boresighted to the optical scanner (e.g., oscillating flat mirror) for an increased swath width perpendicular to the aircraft heading. The several laser transmitters are coupled for increased power and system sensitivity.

Claims

1. An apparatus for detecting and imaging an object enveloped by a backscattering medium which is at least partially transmitting to light comprising:

generating means for selectively generating short pulses of light;

mirror means in optical communication with said generating means, said mirror means receiving said pulses of light from said generating means and projecting said short pulses of light toward the backscattering medium and at an object enveloped by the medium, said mirror means being selectively oriented to also receive said pulses of light reflected back from said object after a time delay corresponding to the round-trip propagation time of said light pulses to and from said object;

detecting means in optical communication with said scanning mirror means, said detecting means detecting said reflected pulses of light received by said mirror means; and

converting means for converting said detected pulses of light to a video image of said object.

2. The apparatus of claim 1 wherein:

said generating means and said detecting means are optically oriented to a common line of sight along said mirror means.

3. The apparatus of claim 1 wherein said apparatus is mounted on an airborne platform with said airborne platform having a longitudinal axis and wherein:

said mirror means is oriented on said airborne platform so that said generated pulses of light are projected, and said reflected pulses of light are detected from a nominally horizontal direction perpendicular to the airborne platform heading direction.

4. The apparatus of claim 3 including:

drive means for selectively rotating said mirror means around an axis parallel to the airborne platform longitudinal axis wherein images are viewed laterally of said airborne platform longitudinal axis.

5. The apparatus of claim 4 including:

angle measuring means for measuring the angle of said mirror means.

6. The apparatus of claim 4 wherein:

said drive means rotates said mirror means in steps configured to produce overlapping images.

7. The apparatus of claim 1 wherein:

said mirror means comprises a single mirror.

8. The apparatus of claim 7 wherein:

said mirror means comprises a flat mirror.

9. The apparatus of claim 1 wherein:

said mirror means comprises a plurality of synchronized discrete movable mirrors, one each of said mirrors being associated with said detector means and said generator means.

10. The apparatus of claim 3 wherein:

said detector means comprises a plurality of cameras mounted perpendicularly with respect to said longitudinal axis.

11. The apparatus of claim 3 wherein:

said detector means comprises a plurality of cameras mounted parallel with respect to said longitudinal axis.

12. The apparatus of claim 1 wherein:

said mirror means comprises movable scanning mirror means.

13. The apparatus of claim 1 wherein said generating means comprises at least one laser.

14. The apparatus of claim 13 wherein said generating means comprises a plurality of lasers.

15. The apparatus of claim 1 wherein said detecting means comprises at least one camera means.

16. The apparatus of claim 1 wherein said detecting means comprises a plurality of camera means.

17. The apparatus of claim 16 wherein said detecting means comprises six camera means.

18. The apparatus of claim 13 wherein said detecting means comprises at least one camera means.

19. The apparatus of claim 18 including:

laser projection means for transforming said pulses of light into a rectangular field of view; and

means in said camera means for configuring said camera means field of view as rectangular.

20. The apparatus of claim 1 wherein said light pulse generating means, mirror means and detecting means are mounted on a pod and further including:

attachment means for attaching said pod to an airborne platform, said attachment means including means for angularly orienting the pod independently of the airborne platform orientation.

21. The apparatus of claim 20 wherein said attachment means includes:

three linear actuators for adjusting the orientation of said pod with respect to the angular attitude of said airborne platform.

22. The apparatus of claim 1 including:

switching means in said airborne platform for enabling or disabling operation of said light pulse generating means.

23. An apparatus for detecting and imaging an object enveloped by a backscattering medium which is at least partially transmitting to light comprising:

generating means for selectively generating short pulses of light;

projecting means for projecting said pulses of light toward the backscattering medium and at an object enveloped by the medium;

movable scanning mirror means for receiving said pulses of light reflected back from said object after a time delay corresponding to the roundtrip propagation time of said light pulses to and from said object;

detecting means for detecting said reflected pulses of light received by said scanning mirror; and

converting means for converting said detected pulses of light to a video image of said object.

24. An apparatus for detecting and imaging from an airborne platform an object enveloped by a backscattering medium which is at least partially transmitting to light, the airborne platform having instrumentation for measuring platform angular attitude, comprising:

pulsed light source generating means generating short pulses of light from the airborne platform;

projecting means for projecting said short pulses of light toward the backscattering medium and at an object enveloped by the backscattering medium;

computer means for monitoring the angular attitude of the airborne platform in response to input from the instrumentation, said angular attitude input being generated independently of said pulsed light source generating means;

camera means for detecting said pulses of light reflected back from said object, said camera means being gated open by input from delay generator means, said camera means being gated open after a selected time delay corresponding to the roundtrip propagation time of said light pulses to and from said object;

said computer means calculating said selected time delay based on input data which includes the angular attitude input from said instrumentation, said computer means inputting said selected time delay to said delay generator means; and

converting means for converting said detected pulses of light to a video image of said object.

25. The apparatus of claim 24 wherein said airborne platform has instrumentation for measuring altitude platform and wherein:

said computer means monitors the altitude of the airborne platform in response to altitude input from the instrumentation and wherein said computer means calculates said selected time delay based on input data which includes the altitude input from said instrumentation.

26. The apparatus of claim 24 wherein said angular attitude input includes pitch angle and roll angle.

27. An imaging lidar apparatus for detecting and imaging an object enveloped by a backscattering medium which is at least partially transmitting to light, the imaging lidar apparatus being mounted on an airborne platform and including light pulse generating means, reflected light pulse detection means and computer control means, and further including:

a pod for housing said light pulse generating means and said light pulse detection means; and

attachment means for attaching the pod to the airborne platform, said attachment means including means for angularly orienting the pod independently of the airborne platform orientation.

28. The apparatus of claim 27 wherein said attachment means includes:

three linear actuators for adjusting the orientation of said pod with respect to the attitude of said airborne platform.

29. An imaging lidar apparatus for detecting and imaging an object enveloped by a backscattering medium which is at least partially transmitting to light, the imaging lidar apparatus being mounted on an airborne platform and including light pulse generating means, reflected light pulse detection means and computer control means, and further including:

a pod for housing said light pulse generating means and said light pulse detection means, said pod comprising a plurality of inerconnected trusses arranged in a generally pyramidical shaped section and having a plurality of internal chambers for said light pulse generating means.

30. The apparatus of claim 29 including:

a support beam with an "H" shape cross-section in one of said chambers and wherein said light pulse generating means is supported on said support beam.

31. The apparatus of claim 30 wherein:

said support beam is comprised of a polymer impregnated fiber composite or metal.

32. The apparatus of claim 30 including"

at least three "V" shaped mounts connecting said support beam to said pod.

33. The apparatus of claim 29 wherein:

said pod includes a lower section rectangularly attached to said pyramidical shaped section, said lower section including said light pulse detection means.

34. The apparatus of claim 33 wherein:

said lower section further includes scanning mirror means in optical alignment with said light pulse detection means.

35. The apparatus of claim 29 including:

cooling means in one of said chambers for transferring heat away from the other of said chambers.

36. An apparatus for detecting and imaging an object at least partially enveloped by a backscattering medium which is at least partially transmitting to light comprising:

light pulse generating means for selectively generating short pulses of light;

light projection means for receiving said pulses of light from said light pulse generating means and transforming the cross-section of said light pulse from a first shape to a preselected second shape;

projecting means for projecting said short pulses of light toward the backscattering medium and at an object enveloped by the medium;

camera means for detecting said pulses of light reflected back from said object after a time delay corresponding to the round-trip propagation time of said light pulses to and from said object; and

converting means for converting said detected pulses of light to a video image of said object.

37. The apparatus of claim 36 wherein:

said preselected second shape comprises a polygonal shape.

38. The apparatus of claim 37 wherein said light projection means comprises:

tube means having a plurality of sides and having a polygonal cross-section with respect to the length of said tube means, said polygonal cross-section increasing between a first end of said tube means and a second end of said tube means at a preselected angle wherein a beam of light having said first shape entering said first end is substantially transformed to a beam of light having said polygonal cross-section exiting said second end; and

mirror means on an interior surface of said tube means.

39. The apparatus of claim 38 including:

entrance optics means in said first end of said tube means, said entrance optic means expanding a beam of light entering said tube means.

40. The apparatus of claim 39 wherein:

said entrance optics means comprises a plano-concave or concave-concave lens.

41. The apparatus of claim 38 including:

exit optic means in said second end of said tube means, said exit optics means including refractive means for refracting light rays back towards a preselected field of view corresponding to said polygonal cross-section.

42. The device of claim 41 wherein:

said refractive means comprises beveled edges extending from each side of said polygonal cross-section.

43. The apparatus of claim 42 wherein adjoining pairs of said beveled edges terminate at a corner and including:

a facet formed in said corner.

44. The apparatus of claim 38 wherein said tube means is sealed defining an internal cavity and including:

a moisture free environment in said cavity.

45. The apparatus of claim 38 wherein:

said polygonal cross-section comprises a rectangle or square.

46. The apparatus of claim 36 including:

means in said camera means for configuring said camera means field of view as said preselected second shape.

47. The apparatus of claim 46 wherein:

said preselected second shape has a polygonal cross-section.

48. The apparatus of claim 47 wherein:

said polygonal cross-section comprises a rectangle or square.

49. An apparatus for detecting and imaging an object enveloped by a backscattering medium which is at least partially transmitting to light comprising:

at least one laser generating means for selectively generating short pulses of light toward the backscattering medium and at an object enveloped by the medium;

detecting means for detecting said pulses of light reflected back from said object after a time delay corresponding to the round-trip propagation time of said light pulses to and from said object; and

converting means for converting said detected pulses of light to a video image of said object; and

wherein said laser generating means further includes;

a first amplifier for amplifying the strength of said generated pulses of light; and

a second amplifier spaced from said first amplifier and in optical communication with said first amplifier, said second amplifier further increasing the strength of said generated pulses of light.

50. The apparatus of claim 49 wherein said laser generating means further comprises:

at least two discrete lasers having means for simultaneous triggering of light pulses.

51. An apparatus for detecting and imaging an object enveloped by a backscattering medium which is at least partially transmitting to light comprising:

at least two laser generating means for selectively simultaneously generating short pulses of light toward the backscattering medium and at an object enveloped by the medium;

detecting means for detecting said pulses of light reflected back from said object after a time delay corresponding to the round-trip propagation time of said light pulses to and from said object; and

converting means for converting said detected pulses of light to a video image of said object.

52. A method of detecting or imaging an object using an imaging lidar system having a plurality of cameras for viewing range gates of varying depths and being mounted on an airborne platform comprising the steps of:

(1) directing the imaging lidar system to search over a large swath width to locate objects of interest;

(2) storing the coordinates of any located objects of interest detected by the imaging lidar system;

(3) returning the imaging lidar system to selected of said stored coordinates and again detecting an object of interest;

(4) directing at least two of said cameras to the sa range gate corresponding to the depth of the object of interest to enhance an image of the object of interest.

53. The method of claim 52 including the step for:

averaging the images of said at least two cameras to enhance the image of the object of interest.

54. The method of claim 52 including the step of:

positioning said airborne platform at a lower altitude in Step 3 relative to the altitude in Step 1.