Gated imaging

• US 20070058038A1
• Filed: 07/27/2006
• Published: 03/15/2007
• Est. Priority Date: 02/04/2004
• Status: Active Grant

• Current Assignee: Elbit Systems Limited
• Original Assignee: Elbit Systems Limited
• Inventors: Inbar, Shamir, David, Ofer
• Granted Patent: US 8,194,126 B2
• Time in Patent Office: Days
• US Class Current: 348/135
• 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 7/483 Details of pulse systems
• CPC Class Codes: G01S 7/4868 Controlling received signal intensity or exposure of sensor

Abstract

An imaging system, including a transmission source providing pulse(s), and a gated sensor for receiving pulse reflections from objects located beyond a minimal range. The pulse and the gate timing are controlled for creating a sensitivity as a function of range, such that the amount of the energy received progressively increases with the range. Also an imaging method, including emitting pulse(s) to a target area, receiving reflections of pulses reflected from objects located beyond a minimal range, the receiving includes gating detection of the reflections, and progressively increasing the received energy of the reflections, by controlling the pulses and the timing of the gating.

Claims

1. A portable, moveable or stationary mounted imaging system comprising:

a transmission source, said transmission source providing at least one energy pulse;

a sensor for receiving pulse reflections of said at least one energy pulse reflected from objects within a depth of a field to be imaged,

characterized in that said depth of field having a minimal range, R_MIN, said sensor enabled to gate detection of said pulse reflections, with a gate timing controlled such that said sensor starts to receive said pulse reflections after a delay timing substantially given by the time it takes said at least one energy pulse to reach said minimal range and complete reflecting to said sensor from said minimal range,

wherein each of said at least one energy pulse and said gate timing are controlled for creating a sensitivity as a function of range for said system, such that an amount of received energy of said pulse reflections, reflected from objects located beyond said minimal range, progressively increases with the range along said depth of a field to be imaged.

2. The system according to claim 1, wherein said at least one energy pulse and said gate timing are controlled for creating a sensitivity as a function of range for said system, such that an amount of received energy of said pulse reflections, reflected from objects located beyond said minimal range, progressively increases with the range along said depth of a field to be imaged until an optimal range, R₀.

3. The system according to claim 2, wherein said at least one energy pulse and said gate timing are controlled for creating a sensitivity as a function of range for said system, such that an amount of received energy of said pulse reflections, reflected from objects located beyond said optimal range, is maintained detectable until a maximal range, R_MAX.

4. The system according to claim 3, wherein said at least one energy pulse and said gate timing are controlled for creating a sensitivity as a function of range for said system, such that said amount of received energy of said pulse reflections, reflected from objects located beyond said optimal range, is maintained substantially constant until said maximal range.

5. The system according to claim 3, wherein said at least one energy pulse and said gate timing are controlled for creating a sensitivity as a function of range for said system, such that said amount of received energy of said pulse reflections, reflected from objects located beyond said optimal range, gradually decreases until said maximal range.

6. The system according to claim 1, wherein said at least one energy pulse and said gate timing are controlled for creating a sensitivity as a function of range for said system, such that an amount of received energy of said pulse reflections is directly proportional to the ranges of said objects to be imaged.

7. The system according to claim 1, wherein

said at least one energy pulse defines a substantial pulse width, T_LASER, commencing at a start time, T₀;

said delay timing is substantially given by the time elapsing from said start time, T₀, until twice said minimal range, R_MIN, divided by the speed at which said at least one energy pulse travels, v, in addition to said pulse width, T_LASER;

$\frac{2\times <br><br>R_{\mathrm{MIN}}}{v}+T_{\mathrm{LASER}}.$

8. The system according to claim 1, wherein said at least one energy pulse and said gate timing are controlled for creating a sensitivity as a function of range for said system through synchronization between the timing of said at least one energy pulse and the timing of said gate detection.

9. The system according to claim 1, wherein

said at least one energy pulse defines a substantial pulse width, T_LASER, a pulse pattern, a pulse shape, and a pulse energy;

said sensor is enabled to gate detection of said pulse reflections, with a gating time span said sensor is activated, T_ON, a duration of time said sensor is deactivated, T_OFF, and a synchronization timing of the gating with respect to said at least one energy pulse; and

wherein at least one of said delay timing, said pulse width, said pulse shape, said pulse pattern, said pulse energy, said gating time span, said sensor is activated, T_ON, said duration of time said sensor is deactivated, T_OFF, and said synchronization timing, is determined according to at least one of said depth of a field to be imaged, specific environmental conditions said system is used in, a speed said system is moving at, and specific characteristics of different objects expected to be found in said depth of field.

10. The system according to claim 9, wherein said pulse width, said duration of time said sensor is deactivated, and said gating time span said sensor is activated define a cycle time, wherein

said at least one energy pulse is provided for a duration of said pulse width, the opening of said sensor is delayed for a duration of said duration of time said sensor is deactivated, and said pulse reflections are received for a duration of said gating time span said sensor is activated.

11. The system according to claim 9, wherein said determination according to at least one of said depth of a field, said specific environmental conditions, said speed said system is moving at, and said specific characteristics of different objects expected to be found in said depth of field, is a dynamic determination.

12. The system according to claim 11, wherein said pulse width and said gating time span are limited to reduce the sensitivity of said system to ambient light sources.

13. The system according to claim 12, wherein said pulse width is shortened progressively, said delay timing is lengthened progressively, and said cycle time does not change.

14. The system according to claim 12, wherein said gating time span is shortened progressively, said delay timing is lengthened progressively, and said cycle time does not change.

15. The system according to claim 12, wherein said pulse width and said gating time span are shortened progressively, said delay timing is lengthened progressively, and said cycle time does not change.

16. The system according to claim 1, wherein the gating of said sensor is utilized to create a sensitivity as a function of range for said system by changing a parameter selected from the group consisting of changing the shape of said at least one energy pulse, changing the pattern of said at least one energy pulse, changing the energy of said at least one energy pulse, changing a gating time span said sensor is activated, T_ON, changing a duration of time said sensor is deactivated, T_OFF, changing a pulse width, T_LASER, of said at least one energy pulse, changing said delay timing, and changing a synchronization timing between said gating and the timing of providing said at least one energy pulse.

17. The system according to claim 16, wherein said changing of a parameter is utilized according to at least one of:

said depth of field, specific environmental conditions said system is used in, a speed said system is moving at, and characteristics of different objects expected to be found in said depth of field.

18. The system according to claim 8, further comprising a controller for controlling said synchronization.

19. The system according to claim 18, wherein at least one repetition of said cycle time forms part of an individual video frame, and a number of said repetitions forms an exposure number per said video frame.

20. The system according to claim 19, further comprising a control mechanism for dynamically controlling and varying said exposure number.

21. The system according to claim 20, wherein said exposure number is varied by said control mechanism according to a level of ambient light.

22. The system according to claim 21, further comprising an image intensifier.

23. The system according to claim 22, wherein said exposure number is varied by said control mechanism according to a level of current consumed by said image intensifier.

24. The system according to claim 20, wherein said control mechanism comprises image processing means for locating areas in said sensor in a state of saturation.

25. The system according to claim 2, wherein a pulse width, T_LASER, of said at least one energy pulse is substantially defined in accordance with the following equation:

$2\times <br><br>\frac{R_0-R_{\mathrm{MIN}}}{v},$

where v is the speed at which said at least one energy pulse travels.

26. The system according to claim 2, wherein said sensor is enabled to gate detection of said pulsed reflections, with a gating time span said sensor is activated, T_ON, and a duration of time said sensor is deactivated, T_OFF, which are substantially defined in accordance with the following equations:

$T_{\mathrm{ON}}=2\times <br><br>\frac{R_0-R_{\mathrm{MIN}}}{v}$

and

$T_{\mathrm{OFF}}=\frac{2\times <br><br>R_{\mathrm{MIN}}}{v}+T_{\mathrm{LASER}},$

where T_LASER is the pulse width of said at least one energy pulse, and v is the speed at which said at least one energy pulse travels.

27. The system according to claim 1, further comprising a transmission device for transmitting images constructed from said pulse reflections received in said sensor.

28. The system according to claim 1, further comprising a pulse detector for detection of pulses emitting from a similar system.

29. The system according to claim 1, further comprising a polarizer for filtering out incoming energy, which does not conform to the polarization of said pulse reflection.

30. The system according to claim 29, wherein said transmission source provides at least one polarized energy pulse.

31. The system according to claim 10,

wherein said sensitivity of said system relates to a gain and responsiveness of said sensor in proportion to an amount of energy received by said sensor,

wherein said gain received by said sensor as a function of range R is defined by the follow convolution formula:

$I_r<br><br>\left(R\right)=\frac{{\int <br><br>}_{T_{\mathrm{LASER}}+T_{\mathrm{OFF}}}^{T_{\mathrm{LASER}}+T_{\mathrm{OFF}}+T_{\mathrm{ON}}}<br><br>L<br><br>\left(t-\frac{2<br><br>R}{v}\right)·<br><br>C<br><br>\left(t\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>d<br><br>t}{T_{\mathrm{LASER}}}$

wherein L(t) defines a Boolean function representing an on/off status of said transmission source, irrespective of a state of said sensor,

wherein L(t)=1 if said transmission source is on and L(t)=0 if said transmission source is off,

wherein C(t) defines a Boolean function representing an ability of said sensor to receive incoming pulse reflections according to a state of said sensor,

wherein C(t)=1 if said sensor is in an activated state and C(t)=0 if said sensor is in a deactivated state,

and where v is the speed at which said at least one energy pulse travels.

32. The system according to claim 31, wherein a value for radiant intensity is obtained by multiplying said convolution formula by a geometrical propagation attenuation function.

33. An imaging system comprising:

a transmission source, said transmission source providing at least one energy pulse;

a sensor for receiving pulse reflections of said at least one energy pulse reflected from objects within a depth of a field to be imaged,

characterized in that said depth of field having a minimal range, R_MIN, said sensor enabled to gate detection of said pulse reflections, with a gate timing controlled such that said sensor starts to receive said pulse reflections after a delay timing substantially given by the time it takes said at least one energy pulse to reach said minimal range and complete reflecting to said sensor from said minimal range,

wherein said at least one energy pulse and said gate timing are controlled for creating a sensitivity as a function of range for said system, such that an amount of received energy of said pulse reflections, reflected from objects located beyond said minimal range, progressively increases with the range along said depth of a field to be imaged,

said at least one energy pulse defines a substantial pulse width, T_LASER, a pulse pattern, a pulse shape, and a pulse energy;

said sensor is enabled to gate detection of said pulse reflections, with a gating time span said sensor is activated, T_ON, a duration of time said sensor is deactivated, T_OFF, and a synchronization timing of the gating with respect to said at least one energy pulse,

wherein said sensitivity of said system relates to a gain and responsiveness of said sensor in proportion to an amount of energy received by said sensor,

wherein said gain received by said sensor as a function of range R is defined by the follow convolution formula;

$I_r<br><br>\left(R\right)=\frac{{\int <br><br>}_{T_{\mathrm{LASER}}+T_{\mathrm{OFF}}}^{T_{\mathrm{LASER}}+T_{\mathrm{OFF}}+T_{\mathrm{ON}}}<br><br>L<br><br>\left(t-\frac{2<br><br>R}{v}\right)·<br><br>C<br><br>\left(t\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>d<br><br>t}{T_{\mathrm{LASER}}}$

wherein L(t) defines a Boolean function representing an on/off status of said transmission source, irrespective of a state of said sensor,

wherein L(t)=1 if said transmission source is on and L(t)=0 if said transmission source is off,

wherein C(t) defines a Boolean function representing an ability of said sensor to receive incoming pulse reflections according to a state of said sensor,

wherein C(t)=1 if said sensor is in an activated state and C(t)=0 if said sensor is in a deactivated state,

and where v is the speed at which said at least one energy pulse travels.

34. The imaging system according to claim 33, wherein a value for radiant intensity is obtained by multiplying said convolution formula by a geometrical propagation attenuation function.

35. A portable, moveable or stationary imaging method, the method comprising the procedures of:

emitting at least one energy pulse to a target area;

receiving at least one reflection of said at least one energy pulse reflected from objects within a depth of a field to be imaged,

characterized in that said depth of field having a minimal range, R_MIN, said receiving comprises gating detection of said at least one reflection such that said at least one energy pulse is detected after a delay timing substantially given by the time it takes said at least one energy pulse to reach said minimal range and complete reflecting; and

progressively increasing the received energy of said at least one reflection reflected from objects located beyond said minimal range along said depth of a field to be imaged, by controlling each of said at least one energy pulse and the timing of said gating.

36. The method according to claim 35, wherein said procedure of increasing comprises increasing the received energy of said at least one reflection reflected from objects located beyond said minimal range along said depth of a field to be imaged up to an optimal range, R₀.

37. The method according to claim 36, further comprising the procedure of maintaining detectable the received energy of said at least one reflection reflected from objects located beyond said optimal range along said depth of a field to be imaged up to a maximal range, R_MAX.

38. The method according to claim 37, wherein said procedure of maintaining comprises maintaining substantially constant said received energy of said at least one reflection reflected from objects located beyond said optimal range along said depth of a field to be imaged up to said maximal range.

39. The method according to claim 37, wherein said procedure of maintaining comprises gradually decreasing said received energy of said at least one reflection reflected from objects located beyond said optimal range along said depth of a field to be imaged up to said maximal range.

40. The method according to claim 35, wherein said procedure of increasing comprises increasing the received energy of said at least one reflection in direct proportion to the ranges of said objects within said depth of field to be imaged.

41. The method according to claim 35, wherein

said at least one energy pulse defines a substantial pulse width, T_LASER, commencing at a start time, T₀;

and

said delay timing is substantially given by the time elapsing from said start time, T₀, until twice said minimal range divided by the speed at which said at least one energy pulse travels, v, in addition to said pulse width, T_LASER;

$T_{\mathrm{LASER}}+\frac{2\times <br><br>R_{\mathrm{MIN}}}{v}.$

42. The method according to claim 35, wherein

said at least one energy pulse defines a substantial pulse width, T_LASER, a pulse pattern, a pulse shape, and a pulse energy;

said procedure of gating comprises a gating time span a sensor utilized for said receiving is activated, T_ON, a duration of time said sensor is deactivated, T_OFF, and a synchronization timing of said gating with respect to said at least one energy pulse; and

wherein at least one of said delay timing, said pulse width, said pulse shape, said pulse pattern, said pulse energy, said gating time span said sensor is activated, T_ON, said duration of time said sensor is deactivated, T_OFF, and said synchronization timing is determined according to at least one of said depth of a field, specific environmental conditions said method is used in, a moving speed of said sensor, and specific characteristics of different objects expected to be found in said depth of field.

43. The method according to claim 35, wherein said procedure of controlling comprises progressively changing at least one parameter selected from the group consisting of changing a pattern of said at least one energy pulse, changing a shape of said at least one energy pulse, changing the energy of said at least one energy pulse, changing a gating time span a sensor utilized for said receiving is activated, T_ON, changing a duration of time said sensor is deactivated, T_OFF, changing an energy pulse width, T_LASER, of said at least one energy pulse, changing said delay timing, and changing a synchronization timing between said gating and said emitting.

44. The method according to claim 43, wherein said procedure of controlling comprises changing said at least one parameter according to at least one of said depth of field, said specific environmental conditions said method is used in, said moving speed of said sensor, and characteristics of different objects expected to be found in said depth of field.

45. The method according to claim 43, wherein said procedure of controlling comprises the sub-procedures of providing said at least one energy pulse for a duration of said pulse width, delaying the opening of said sensor for a duration of said time said sensor is deactivated, T_OFF, and receiving energy pulses reflected from objects for a duration of said gating time span said sensor is activated, T_ON, and wherein said pulse width, said duration of said time said sensor is deactivated, T_OFF, and said gating time span said sensor is activated, T_ON, define a cycle time.

46. The method according to claim 45, wherein at least one repetition of said cycle time forms part of an individual video frame, and a number of said repetitions forms an exposure number for said video frame.

47. The method according to claim 46, further comprising the procedure of dynamically varying said exposure number by a control mechanism.

48. The method according to claim 47, wherein said procedure of dynamically varying comprises adjusting said exposure number according to a level of ambient light by said control mechanism.

49. The method according to claim 47, further comprising the procedure of intensifying said detection of said at least one reflection, and wherein said procedure of dynamically varying comprises adjusting said exposure number by said control mechanism according to a level of current consumed by an image intensifier utilized for said intensifying.

50. The method according to claim 47, further comprising the procedure of image processing by locating areas in said sensor in a state of saturation by said control mechanism.

51. The method according to claim 47, further comprising the procedure of image processing for a variable number of exposures by said control mechanism.

52. The method according to claim 51, wherein said procedure of image processing comprises:

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.

53. The method according to claim 43, wherein said procedure of increasing is dynamic.

54. The method according to claim 43, wherein said pulse width and said gating time span said sensor is activated, T_ON, are limited to eliminate or reduce the sensitivity of said sensor to ambient light sources.

55. The method according to claim 43, wherein said procedure of controlling comprises shortening said pulse width progressively and lengthening said delay timing progressively, while retaining a cycle time of the said gating unchanged.

56. The method according to claim 43, wherein said procedure of controlling comprises shortening said gating time span progressively and lengthening said delay timing progressively, while retaining a cycle time of said gating unchanged.

57. The method according to claim 43, wherein said procedure of controlling comprises shortening said pulse width and said gating time span progressively, lengthening said delay timing progressively, while retaining a cycle time of said gating unchanged.

58. The method according to claim 36, comprising calculating said energy pulse width, T_LASER, substantially defined in accordance with the following equation:

$2\times <br><br>\frac{R_0-R_{\mathrm{MIN}}}{v},$

where v is the speed said at least one energy pulse travels at.

59. The method according to claim 35, wherein said procedure of receiving comprises receiving several pulses of said at least one energy pulse reflected from objects during a gating time span a sensor utilized for said receiving is activated, T_ON.

60. The method according to claim 41, wherein said procedure of receiving comprises receiving several pulses of said at least one energy pulse reflected from objects during a gating time span a sensor utilized for said receiving is activated, T_ON;

said procedure of gating comprises a duration of time said sensor is deactivated, T_OFF; and

said procedure of controlling comprises controlling said gating time span said sensor is activated, T_ON, and a duration of time said sensor is deactivated, T_OFF, substantially defined in accordance with the following equations;

$T_{\mathrm{ON}}=2\times <br><br>\frac{R_0-R_{\mathrm{MIN}}}{v}$

and

$T_{\mathrm{OFF}}=\frac{2\times <br><br>R_{\mathrm{MIN}}}{v}+T_{\mathrm{LASER}},$

where R₀ is an optimal range.

61. The method according to claim 35, further comprising the procedure of intensifying said detection of said at least one reflection.

62. The method according to claim 35, further comprising the procedure of transmitting at least one image constructed from said received at least one reflection.

63. The method according to claim 35, further comprising the procedure of determining the level of ambient light in said target area.

64. The method according to claim 35, further comprising the procedure of determining if other energy pulses are present in said target area.

65. The method according to claim 61, further comprising the procedure of overcoming glare from other energy pulses by locally darkening the entrance of an image intensifier utilized for said intensifying.

66. The method according to claim 35, wherein said procedure of emitting comprises emitting at least one polarized electromagnetic pulse, and said procedure of receiving comprises filtering received energy according to a polarization conforming to an expected polarization of said at least one reflection.

67. An imaging method, the method comprising the procedures of:

emitting at least one energy pulse to a target area;

receiving at least one reflection of said at least one energy pulse reflected from objects within a depth of a field to be imaged,

characterized in that said depth of field having a minimal range, R_MIN, said receiving comprises gating detection of said at least one reflection such that said at least one energy pulse is detected after a delay timing substantially given by the time it takes said at least one energy pulse to reach said minimal range and complete reflecting; and

progressively increasing the received energy of said at least one reflection reflected from objects located beyond said minimal range along said depth of a field to be imaged, by controlling said at least one energy pulse and the timing of said gating,

said at least one energy pulse defines a substantial pulse width, T_LASER, a pulse pattern, a pulse shape, and a pulse energy,

said procedure of gating comprises a gating time span a sensor utilized for said receiving is activated, T_ON, a duration of time said sensor is deactivated, T_OFF, and a synchronization timing of said gating with respect to said at least one energy pulse,

wherein a sensitivity of a sensor utilized for said receiving relates to a gain and responsiveness of said sensor in proportion to an amount of energy received by said sensor,

wherein said gain received by said sensor as a function of range R is defined by the follow convolution formula;

$I_r<br><br>\left(R\right)=\frac{{\int <br><br>}_{T_{\mathrm{LASER}}+T_{\mathrm{OFF}}}^{T_{\mathrm{LASER}}+T_{\mathrm{OFF}}+T_{\mathrm{ON}}}<br><br>L<br><br>\left(t-\frac{2<br><br>R}{v}\right)·<br><br>C<br><br>\left(t\right)<br><br>d<br><br>t}{T_{\mathrm{LASER}}}$

wherein L(t) defines a Boolean function representing an on/off status of a transmission source utilized for said emitting, irrespective of a state of said sensor,

wherein L(t)=1 if said transmission source is on and L(t)=0 if said transmission source is off,

wherein C(t) defines a Boolean function representing an ability of said sensor to receive incoming pulse reflections according to a state of said sensor,

wherein C(t)=1 if said sensor is in an activated state and C(t)=0 if said sensor is in a deactivated state,

and where v is the speed at which said at least one energy pulse travels.

68. The imaging method according to claim 67, wherein a value for radiant intensity is obtained by multiplying said convolution formula by a geometrical propagation attenuation function.