Vehicle mounted night vision imaging system and method

• US 7,733,464 B2
• Filed: 08/05/2003
• Issued: 06/08/2010
• Est. Priority Date: 08/05/2002
• Status: Active Grant

• Current Assignee: Elbit Systems Limited
• Original Assignee: Elbit Systems Limited
• Inventors: David, Ofer, Borenstein, Yehuda
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Ratcliffe; Luke D
• Application Number:
  US10/523,340
• Publication Number:
  US 20050269481A1
• Time in Patent Office: 2,499 Days
• Field of Search: 356 301- 315, 356 401- 41, 356 501- 515, 356 6- 22, 356/128, 356/128.5, 356/139.09, 356/139.1
• US Class Current: 356/5.03
• CPC Class Codes: G01S 17/18 wherein range gates are used
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/484 Transmitters
• CPC Class Codes: G01S 7/489 Gain of receiver varied automatically during pulse-recurrence period
• CPC Class Codes: G01S 7/495 Counter-measures or counter-counter-measures using electronic or electro-optical means
• CPC Class Codes: G01S 7/51 Display arrangements
• CPC Class Codes: G02B 2027/0118 comprising devices for improving the contrast of the display / brillance control visibility
• CPC Class Codes: G02B 2027/012 comprising devices for attenuating parasitic image effects
• CPC Class Codes: G02B 2027/0127 comprising devices increasing the depth of field
• CPC Class Codes: G02B 2027/0138 comprising image capture systems, e.g. camera
• CPC Class Codes: G02B 2027/014 comprising information/image processing systems
• CPC Class Codes: G02B 23/12 with means for image conversion or intensification
• CPC Class Codes: G02B 27/01 Head-up displays
• CPC Class Codes: G02B 27/0101 characterised by optical features G02B27/0172 takes precedence
• CPC Class Codes: G02B 5/30 Polarising elements light-modulating devices with active elements G02F1/00

Abstract

A vehicle mounted imaging system and method, enabling selective imaging of objects in a low-visibility environment. The system includes a light source providing non-visible light pulses and a camera having an image intensifier enabled to gate selected received images. The light source may be a laser generator, which may be enabled to generate a pulse width related to the depth of a field to be imaged. The gated image intensifier may determine gating time spans according to the depth of a field to be imaged.

Claims

1. A vehicle mounted imaging system, comprising:

a light source, for providing a pulse like light energy, said pulse like light energy defining a substantial pulse width (T_Laser); and

a camera, for receiving said pulse like light energy reflected from objects, said camera enabled for gated detection of said pulse like light energy reflected from objects located within a depth of field to be imaged, said depth of field having a minimal range (R_min), said camera starting to detect light energy after a delay timing substantially given by the time it takes said substantial pulse width of said pulse like light energy to reach said minimal range and complete reflecting back to said camera from said minimal range;

said system being characterized in that;

said gated detection defines an ON time span (T_II) during which said camera receives reflections from objects, an OFF time span (T_off) during which said camera remains in an off position after transmission of said pulse like light energy, and a synchronization timing defining an overlap between said ON time span and the time said pulse like light energy reflects from objects located within said depth of field to be imaged,

wherein said gated detection is utilized to create a sensitivity as a function of range through said synchronization timing, such that said overlap between said pulse like light energy reflected from objects and said ON time span increases as a function of range up to an optimal range (R₀) of said depth of field to be imaged, thereby increasing the portion of said substantial pulse width of said pulse like light energy reflected from objects located between said minimal range and said optimal range reaching said camera during said ON time span.

2. The system according to claim 1, further comprising:

an image-processor, coupled with said camera, for producing a video signal in accordance with images obtained by said camera.

3. The system according to claim 2, wherein said image-processor comprises means for locating areas in said camera in a state of saturation.

4. The system according to claim 2, wherein said image-processor comprises means for processing a variable number of exposures.

5. The system according to claim 4, wherein said image processor receives at least two video frames, one with a high exposure number, the other with a low exposure number, determines exposure numbers for said at least two video frames, and combines said at least two video frames to form a single video frame by combining dark areas from frames with a high exposure number and saturated areas from frames with a low exposure number.

6. The system according to claim 1, further comprising:

a narrow band pass filter, coupled with said camera, for filtering said reflected pulse like light energy having selected wavelengths from reaching said camera.

7. The system according to claim 1, further comprising:

a display apparatus, for displaying images obtained by said camera.

8. The system according to claim 1, further comprising:

a spatial light modulator, coupled with said camera, for enabling regional blocking of the light entering said camera, to overcome blooming in said system.

9. The system according to claim 1, further comprising:

a blinding light source, placed near said light source, for emitting bright visible light to cause a viewer in proximity to said system to avert their gaze from said light source.

10. The system according to claim 1, wherein said gated detection is utilized to create said sensitivity as a function of range through said synchronization timing, such that said overlap between said pulse like light energy reflected from objects located beyond said optimal range and said ON time span, is maintained detectable as a function of range until a maximal range (R_max) of said depth of field to be imaged, thereby maintaining the portion of said substantial pulse width of said pulse like light energy reflected from objects located between said optimal range and said maximal range reaching said camera during said ON time span.

11. The system according to claim 10, wherein said gated detection is utilized to create said sensitivity as a function of range through said synchronization timing, such that said overlap between said pulse like light energy reflected from objects located beyond said optimal range and said ON time span, is maintained substantially constant as a function of range until said maximal range, thereby maintaining substantially constant the portion of said substantial pulse width of said pulse like light energy reflected from objects located between said optimal range and said maximal range reaching said camera during said ON time span.

12. The system according to claim 10, wherein said gated detection is utilized to create said sensitivity as a function of range through said synchronization timing, such that said overlap between said pulse like light energy reflected from objects located beyond said optimal range and said ON time span, decreases as a function of range until said maximal range, thereby decreasing the portion of said substantial pulse width of said pulse like light energy reflected from objects located between said optimal range and said maximal range reaching said camera during said ON time span.

13. The system according to claim 1, wherein

said pulse like light energy defines a pulse shape and pattern.

14. The system according to claim 1, further comprising a controller, coupled with said camera and said light source, for determining and changing at least one parameter selected from the group consisting of:

said ON time span;

said OFF time span;

said pulse width;

said delay timing;

said synchronization timing;

a pulse shape and pattern;

an exposure number; and

a frequency of exposures,

wherein the duration of said pulse width, said OFF time span, and said ON time span defines a cycle time, and

wherein at least a repetition of said cycle time forms part of an individual frame, and a number of said repetitions forms said exposure number for each said frame.

15. The system according to claim 14, wherein said controller determines said parameter according to at least one of:

said depth of field;

specific environmental conditions;

the level of ambient light;

a speed of said vehicle;

characteristics of different targets expected to be found in said depth of field;

brightness level of said frame;

image processing; and

the presence of a system similar to said system mounted on an approaching vehicle.

16. The system according to claim 14, wherein said pulse width and said ON time span are limited by said controller to eliminate or reduce the sensitivity of said system to ambient light sources.

17. The system according to claim 14, wherein

said pulse like light energy is sent for a duration of said pulse width, the opening of said camera is delayed for a duration of said OFF time span, and said pulse like light energy reflected from objects is received for a duration of said ON time span.

18. The system according to claim 17, wherein said pulse width is progressively shortened, and said delay timing is progressively lengthened, while said cycle time is not changed, for increasing said sensitivity as a function of range when accumulating reflections of pulses for an individual frame.

19. The system according to claim 17, wherein said ON time span is progressively shortened said, said delay timing is progressively lengthened, while said cycle time is not changed, for increasing said sensitivity as a function of range when accumulating reflections of pulses for an individual frame.

20. The system according to claim 17, wherein each of said pulse width and said ON time span is progressively shortened, said delay timing is progressively lengthened, while said cycle time is not changed, for increasing said sensitivity as a function of range when accumulating reflections of pulses for an individual frame.

21. The system according to 14, further comprising:

a pulse detector, coupled with said controller, for detecting pulses emitting from a system similar to said system mounted on an approaching vehicle.

22. The system according to 14, further comprising:

an interface, coupled with said controller, for interfacing with other systems of said vehicle.

23. The system according to claim 13, wherein said pulse shape and pattern comprises an intensity higher at the beginning of said pulse than at the end of said pulse, for increasing said sensitivity as a function of range.

24. The system according to claim 1, wherein

said pulse width (T_Laser) commences at a start time (T₀);

and

said delay timing is substantially defined in accordance with the following equation;

$T_{\mathrm{Laser}}+\frac{2\times <br><br>R_{\min }}{c}$

where c is the speed of light.

25. The system according to claim 1, wherein said pulse width (T_Laser) is substantially defined in accordance with the following equation:

$2\times <br><br>\left(\frac{R_o-R_{\min }}{c}\right)$

where c is the speed of light.

26. The system according to claim 1, wherein said ON time span and said OFF time span are substantially defined in accordance with the following equations:

$\begin{array}{c}{T}_{\mathrm{II}}=2\times <br><br>\left(\frac{R_{\max }-R_{\min }}{c}\right)\\ T_{\mathrm{off}}=\frac{2\times <br><br>R_{\min }}{c}\end{array}$

where c is the speed of light.

27. The system according to claim 14, further comprising:

at least one ambient light sensor, coupled with said controller, for determining the level of ambient light.

28. The system according to claim 1, further comprising:

a light polarizer, coupled with said camera, wherein said light source emits polarized light and wherein said reflections having a particular polarization are prevented from entering said camera, to overcome blooming in said system.

29. The system according to claim 14, wherein mutual blinding between said system and a similar system passing one another is eliminated by statistical solutions selected from the group consisting of:

said controller lowering said exposure number; and

said controller changing the frequency of exposures.

30. The system according to claim 14, wherein mutual blinding between said system and a similar system passing one another is eliminated by synchronic solutions selected from the group consisting of:

establishing a communication channel between said system and said similar system;

letting each of said system and said similar system go into listening modes from time to time in which said pulse like light energy is not emitted for a listening period, after said period any of said system and said similar system resume emitting said pulse like light energy if no pulses were collected during said listening period, and after said period said system and said similar system wait until an end of a cyclic sequence of pulse like light energy before resuming emitting said pulse like light energy if pulses were collected during said listening period; and

having said systems change a pulse start transmission time, pulse frequency, number of pulses, or exposure number, in said individual video frames.

31. The system according to 1, wherein said pulse like light energy is non-visible light and said light received in said camera is non-visible light.

32. The system according to 1, wherein the intensity of said pulse like energy pulses is adjusted according to said speed of said vehicle, for increasing radiation safety.

33. The system according to claim 1, wherein said light source is selected from the group consisting of:

a laser generator;

an array of laser diodes;

an array of LEDs; and

a visible light source.

34. The system according to claim 1, wherein said camera is selected from the group consisting of:

CMOS cameras;

CCD cameras;

a camera having a gated image intensifier; and

a camera with shutter capabilities.

35. The system according to claim 7, wherein said display apparatus is selected from the group consisting of:

a Head Up Display (HUD) apparatus;

an LCD display apparatus; and

a holographic based flat optic apparatus.

36. The system according to claim 8, wherein said spatial light modular is selected from the group consisting of:

an area shutter;

a liquid crystal; and

a suspended particle display.

37. An imaging method for a vehicle mounted system, the method comprising the procedures of:

emitting from a light source a pulse like light energy to a target area, said pulse like light energy defining a substantial pulse width (T_Laser);

receiving by a gated camera at least one image from a reflection of said pulse like light energy reflected from objects located within a depth of a-field to be imaged, said depth of field having a minimal range (R_min);

gating detection of said at least one image, wherein the gating starts to detect said pulse like light energy after a delay timing substantially given by the time it takes said pulse width of said pulse like light energy to reach said minimal range and complete reflecting back to said camera from said minimal range; and

intensifying said at least one images received,

said method being characterized in that;

said gating detection defines an ON time span (T_II) during which reflections from objects are received by said camera, an OFF time span (T_off) during which said camera remains in an off position after transmission of said pulse like light energy, and a synchronization timing defining an overlap between said ON time span and the time said pulse like light energy reflects from objects located within said depth of field to be imaged,

wherein said procedure of gating detection is utilized to create a sensitivity as a function of range for said vehicle mounted system, through said synchronization timing, such that said overlap between said pulse like light energy reflected from objects and said ON time span increases as a function of range up to an optimal range (R₀) of said depth of field to be imaged, thereby increasing the portion of said substantial pulse width of said pulse like light energy reflected from objects located between said minimal range and said optimal range reaching said camera during said ON time span.

38. The method according to claim 37, wherein said pulse like light energy defines a pulse shape and pattern.

39. The method according to claim 37, further comprising the procedure of determining and changing at least one parameter selected from the group consisting of:

said ON time span;

said OFF time span;

said pulse width;

said delay timing;

said synchronization timing;

a pulse shape and pattern;

an exposure number; and

a frequency of exposures,

wherein the duration of said pulse width, said OFF time span, and said ON time span defines a cycle time, and

wherein at least a repetition of said cycle time forms part of an individual frame, and a number of said repetitions forms said exposure number for each said frame.

40. The method according to claim 39, wherein said procedure of determining is performed according to at least one of:

said depth of field;

specific environmental conditions;

the level of ambient light;

a speed of said vehicle;

characteristics of different targets expected to be found in said depth of field;

brightness level of said frame;

image processing; and

the presence of a system similar to said system mounted on an approaching vehicle.

41. The method according to claim 39, wherein said pulse width and said ON time span are limited to eliminate or reduce said sensitivity to ambient light sources.

42. The method according to claim 39, wherein said procedure of determining comprises the sub-procedures of:

sending said pulse like light energy for a duration of said pulse width;

delaying the opening of said camera for a duration of said OFF time span; and

receiving said pulse like light energy reflected from objects for a duration of said ON time span.

43. The method according to claim 42, wherein said procedure of determining comprises shortening said pulse width progressively, and lengthening said delay timing progressively, while retaining said cycle time unchanged, for increasing said sensitivity as a function of range when accumulating reflections of pulses for an individual frame.

44. The method according to claim 42, wherein said procedure of determining comprises shortening said ON time span progressively, and lengthening said delay timing progressively, while retaining said cycle time unchanged, for increasing said sensitivity as a function of range when accumulating reflections of pulses for an individual frame.

45. The method according to claim 42, wherein said procedure of determining comprises shortening said pulse width and said ON time span progressively, lengthening said delay timing progressively, while retaining said cycle time unchanged, for increasing said sensitivity as a function of range when accumulating reflections of pulses for an individual frame.

46. The method according to claim 38, wherein said pulse shape and pattern comprises an intensity higher at the beginning of said pulse than at the end of said pulse, for increasing said sensitivity as a function of range.

47. The method according to claim 37, wherein

said procedure of emitting from a light source commences at a start time (T₀);

and

said delay timing is substantially calculated in accordance with the following equation;

$T_{\mathrm{Laser}}+\frac{2\times <br><br>R_{\min }}{c}$

where c is the speed of light.

48. The method according to claim 37, wherein said pulse width (T_Laser) is substantially calculated in accordance with the following equation:

$2\times <br><br>\left(\frac{R_o-R_{\min }}{c}\right)$

where c is the speed of light.

49. The method according to claim 37, wherein said ON time span and said OFF time span are substantially calculated in accordance with the following equations:

$\begin{array}{c}{T}_{\mathrm{II}}=2\times <br><br>\left(\frac{R_{\max }-R_{\min }}{c}\right)\\ T_{\mathrm{off}}=\frac{2\times <br><br>R_{\min }}{c}\end{array}$

where c is the speed of light.

50. The method according to claim 39, further comprising the procedure of eliminating mutual blinding between said system and a similar system passing one another by statistical solutions selected from the group consisting of:

lowering said exposure number; and

changing the frequency of exposures.

51. The method according to claim 39, further comprising the procedure of eliminating mutual blinding between said system and a similar system passing one another by synchronic solutions selected from the group consisting of:

establishing a communication channel between said system and said similar system;

letting each of said system and said similar system go into listening modes from time to time in which said pulse like light energy is not emitted for a listening period, after which period any of said system and said similar system resume emitting said pulse like light energy if no pulses were collected during said listening period, and after which period said system and said similar system wait until an end of a cyclic sequence of pulse like light energy before resuming emitting said pulse like light energy if pulses were collected during said listening period; and

having said systems change a pulse start transmission time, pulse frequency, number of pulses, or exposure number in said individual video frames.

52. The method according to claim 37, further comprising the procedure of image processing by locating areas in said camera in a state of saturation.

53. The method according to claim 37, further comprising the procedure of image processing for a variable number of exposures.

54. The method according to claim 37, wherein said procedure of image processing comprises the procedures of:

taking at least two video frames, one with a high exposure number, the other with a low exposure number, by image processing of a variable number of exposures;

determining exposure numbers for said at least two video frames; and

combining frames to form a single video frame by combining dark areas from frames with a high exposure number and saturated areas from frames with a low exposure number.

55. The method according to claim 37, wherein said procedure of emitting from a light source comprises emitting non-visible light and said procedure of receiving by a gated camera comprises receiving non-visible light.

56. The method according to claim 37, further comprising the procedure of adjusting the intensity of said pulse like light energy according to a speed of said vehicle, for controlling radiation safety.

57. The method according to claim 37, further comprising the procedure of placing a blinding light source near the light source emitting said pulse like light energy.

58. The method according to claim 37, further comprising the procedure of displaying said at least one image on a display apparatus for displaying images constructed from said pulse like light energy received by said gated camera.

59. The method according to claim 37, further comprising the procedure of determining ambient light in said target area.

60. The method according to claim 37, further comprising the procedure of determining if other light pulses are present in said target area.

61. The method according to claim 37, further comprising the procedure of filtering received wavelengths of received reflections using a narrow band pass filter.

62. The method according to claim 37, further comprising the procedure of overcoming glare from light pulses by locally darkening the entrance of said camera.

63. The method according to claim 37, further comprising the procedure of overcoming glare from light pulses by polarizing light emitted by said light source and preventing said reflections having a particular polarization from entering said camera.

64. The method according to claim 37, wherein said procedure of gating detection is utilized to create said sensitivity as a function of range for said vehicle mounted system, through said synchronization timing, such that said overlap between said pulse like light energy reflected from objects located beyond said optimal range and said ON time span is maintained as a function of range until a maximal range (R_max) of said depth of field to be imaged, thereby maintaining the portion of said substantial pulse width of said pulse like light energy reflected from objects located between said optimal range and said maximal range reaching said camera during said ON time span.

65. The method according to claim 64, wherein said procedure of gating detection is utilized to create said sensitivity as a function of range for said vehicle mounted system, through said synchronization timing, such that said overlap between said pulse like light energy reflected from objects located beyond said optimal range and said ON time span, is maintained substantially constant as a function of range until said maximal range, thereby maintaining substantially constant the portion of said substantial pulse width of said pulse like light energy reflected from objects located between said optimal range and said maximal range reaching said camera during said ON time span.

66. The method according to claim 64, wherein said procedure of gating detection is utilized to create said sensitivity as a function of range for said vehicle mounted system, through said synchronization timing, such that said overlap between said pulse like light energy reflected from objects located beyond said optimal range and said ON time span decreases as a function of range until said maximal range, thereby decreasing the portion of said substantial pulse width of said pulse like light energy reflected from objects located between said optimal range and said maximal range reaching said camera during said ON time span.