Dual detector lidar system and method
First Claim
1. A light detection and ranging (LIDAR) method for remotely detecting and identifying the location of an object in a target area comprising:
- (a) transmitting a first pulse of laser energy at known coordinates in the target area from a location spaced from the target area;
(b) receiving with a receiver a first return pulse of laser energy comprising a reflection of the first pulse from an object within the target area and forming a first return signal therefrom;
(c) directing the first return signal to a low resolution detector to develop a first output signal representative of the first return pulse and including an object signature for the object within the target area;
(d) processing the first output signal to measure the time at which the object signature is observed in the first output signal relative to the time at which said first pulse is transmitted, whereby a round-trip signal transmission time is determined, said round-trip signal transmission time providing a measure of the depth of said object within the target area;
(e) transmitting a second pulse of laser energy at the same coordinates of the target area as was the first pulse of laser energy;
(f) receiving with the receiver a second return pulse of laser energy after waiting said round-trip signal transmission time from the transmission of said second pulse, whereby said second return pulse contains primarily laser energy reflected from said object, and forming a second return signal therefrom;
(g) directing the second return signal to a high resolution detector to develop a second output signal representative of the second return signal; and
(h) electronically processing the second return pulse to form an image of the detected object.
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Accused Products
Abstract
A light detection and ranging (LIDAR) system uses dual detectors to provide three-dimensional imaging of underwater objects (or other objects hidden by a partially transmissive medium). One of the detectors is a low resolution, high bandwidth detector. The other is a high resolution, narrow bandwidth detector. An initial laser pulse is transmitted to known x-y coordinates of a target area. The photo signals returned from the target area from this initial pulse are directed to the low resolution, high bandwidth detector, where a preliminary determination as to the location (depth, or z coordinate) of an object in the target area is made based on the time-of-receipt of the return photo signal. A second laser pulse is then transmitted to the target area and the return photo signals from such second laser pulse are directed to the high resolution, narrow bandwidth detector. This high resolution detector is gated on at a time so that only photo signals returned from a narrow "slice" of the target area (corresponding to the previously detected depth of the object) are received. An image of the detected object is then reconstructed from the signals generated by the high resolution detector. In a preferred embodiment, the two detectors are housed in a single digicon tube, with magnetic deflection being used to steer the beam to the appropriate detector.
176 Citations
41 Claims
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1. A light detection and ranging (LIDAR) method for remotely detecting and identifying the location of an object in a target area comprising:
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(a) transmitting a first pulse of laser energy at known coordinates in the target area from a location spaced from the target area; (b) receiving with a receiver a first return pulse of laser energy comprising a reflection of the first pulse from an object within the target area and forming a first return signal therefrom; (c) directing the first return signal to a low resolution detector to develop a first output signal representative of the first return pulse and including an object signature for the object within the target area; (d) processing the first output signal to measure the time at which the object signature is observed in the first output signal relative to the time at which said first pulse is transmitted, whereby a round-trip signal transmission time is determined, said round-trip signal transmission time providing a measure of the depth of said object within the target area; (e) transmitting a second pulse of laser energy at the same coordinates of the target area as was the first pulse of laser energy; (f) receiving with the receiver a second return pulse of laser energy after waiting said round-trip signal transmission time from the transmission of said second pulse, whereby said second return pulse contains primarily laser energy reflected from said object, and forming a second return signal therefrom; (g) directing the second return signal to a high resolution detector to develop a second output signal representative of the second return signal; and (h) electronically processing the second return pulse to form an image of the detected object. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A light detection and ranging (LIDAR) system for remotely detecting and identifying the location of an object in a target area comprising:
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(a) transmitter means for transmitting a first pulse of laser energy at known coordinates in the target area from a location above the target area and for transmitting a second pulse of laser energy at the same coordinates of the target area as was the first pulse of laser energy; (b) receiver means for (i) receiving a first return pulse of laser energy comprising a reflection of the first pulse from an object within the target area and (ii) for receiving a second return pulse of laser energy during a window of time following the transmission of the second laser pulse, whereby the second return pulse contains laser energy from the second pulse reflected primarily from said object; (c) high bandwidth, low resolution signal detection means; (d) high resolution signal detection means; (e) means for forming first and second return signals from and representative of the first and second return pulses; (f) return signal control means for directing the first return signal to the high bwadwidth, low resolution detector means to develop a first output signal representative of the first return pulse and for directing the second return signal to the high resolution detector means to develop a second output signal representative of the second return pulse; (g) timing and control means responsive to the first output signal for (i) measuring the time at which an object signature is present in said first return pulse relative to the time at which said first pulse is transmitted, whereby a round-trip signal transmission time is determined, said round-trip signal transmission time providing a measure of the depth of said object within the target area and (ii) generating a gate signal for opening the receiver means during the window of time including the round-trip signal transmission time after the second pulse is transmitted; (h) means for electronically processing the second output signal to form an image of the detected object. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
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32. A dual detector digicon, said dual detector digicon comprising:
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an evacuated tube having a longitudinal axis; photocathode means at one end of said evacuated tube for respectively receiving a return pulse of laser energy and converting it to an electron beam; gating means behind said photocathode means for selectively gating said electron beam ON or OFF; acceleration/focusing means for accelerating said electron beam along said longitudinal axis and selectively focusing it on one of two anode detectors, each positioned at the other end of said evacuated tube, a first anode detector comprising a low resolution detector having a high bandwidth adapted to receive an electron beam corresponding to a first return pulse, and a second anode detector comprising a high resolution detector having a narrow bandwidth adapted to receive a gated electron beam corresponding to a second return pulse; and means for extracting respective electrical signals from said first and second anode detectors that are representative of the magnitude of the electron beam striking the corresponding anode detector, and hence representative of the first or second return pulse, whereby said digicon detector electronically amplifies said first and second return pulses and provides respective electrical output signals representative of said first and second return pulses. - View Dependent Claims (33, 34, 35, 36, 37, 38, 39, 40)
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41. A method of three-dimensional light detection and ranging (LIDAR) for remotely detecting and imaging an object in a target area comprising:
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(a) transmitting a first pulse of laser energy at known coordinates in the target area from a location spaced from the target area; (b) detecting a first return pulse of optical energy reflected from a surface of an object within the target area and measuring the time at which said return pulse is detected relative to the time at which said first laser pulse is transmitted, whereby a round-trip signal transmission time is determined, said round-trip signal transmission time providing a measure of the depth of said object within the target area; (c) transmitting a second pulse of laser energy at the same coordinates of the target area as was the first pulse of laser energy; (d) detecting a second return pulse of optical energy after waiting said round-trip signal transmission time from the transmission of said second laser pulse, whereby said second return pulse contains primarily laser energy reflected from the surface of said object at the measured depth of said object; (e) electronically processing the second return pulse to form an image of the detected surface of the object at the measured depth of said object; (f) repeating steps (c)-(e) a plurality of times, with each repetition of step (d) including a wait time that comprises said round-trip signal transmission time adjusted by an incremental amount from the previous wait time, whereby each repetition of steps (c)-(e) forms an image of the detected surface of the object and its shadow at different depths; and (g) electronically processing the images formed to form a three-dimensional image of the detected object and its shadow.
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Specification