A laser designator system using modulated CW laser diodes and a conventional high pixel count image sensor array, such as CCD or CMOS array. These two technologies, diode lasers and imaging sensor arrays are reliable, widely used and inexpensive technologies, as compared with prior art pulsed laser
A laser designator system using modulated CW laser diodes and a conventional high pixel count image sensor array, such as CCD or CMOS array. These two technologies, diode lasers and imaging sensor arrays are reliable, widely used and inexpensive technologies, as compared with prior art pulsed laser systems. These systems are distinguished from the prior art systems in that they filter the laser signal spatially, by collecting light over a comparatively long period of time from a very few pixels out of the entire field of view of the image sensor array. This is in contrast to the prior art systems where the laser signal is filtered temporarily, over a very short time span, but over a large fraction of the field of view. By spatially filtering the signal outputs of the individual pixels, it becomes possible to subtract the background illumination from the illuminated laser spot.
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1. A method of imaging a field of view, the method comprising: illuminating the field of view by means of the output beam of a CW laser, modulated at a first rate to provide a stream of laser pulses;imaging the field of view using a multi-pixel sensor array;accumulating signals obtained from said pi
1. A method of imaging a field of view, the method comprising: illuminating the field of view by means of the output beam of a CW laser, modulated at a first rate to provide a stream of laser pulses;imaging the field of view using a multi-pixel sensor array;accumulating signals obtained from said pixels during the detection of laser pulses reflected from said field of view in a first set of pixel signal accumulators, for the duration of a predetermined plurality of pulses, to obtain from those pixels a first set of accumulated pixel signals arising from said reflected laser pulses;reading out said first set of accumulated pixel signals to image said field of view, after completion of said predetermined plurality of pulses;accumulating signals obtained from said pixels in periods between the detection of pulses reflected from said field of view, in a second set of pixel signal accumulators, for said duration of said predetermined plurality of pulses, to obtain from those pixels a second set of accumulated pixel signals; andreading out said second set of accumulated pixel signals after completion of said predetermined plurality of pulses,wherein said pixel signals accumulated in each of said first and second sets of pixel signal accumulators and read out therefrom, are subtracted, to generate image signals of said field of view in which the effect of background illumination is subtracted out. 2. A method according to claim 1, further providing the step of repeating the accumulating of signals obtained from said pixels for further durations of said predetermined plurality of pulses, to obtain further sets of accumulated pixel signals, and reading out said further sets of accumulated pixel signals at a second rate substantially lower than said first rate. 3. A method according to claim 2, wherein said second rate is sufficiently low that it is compatible with the frame rate of standard CCD or CMOS devices. 4. A method according to claim 2, wherein said second rate is in the tens of Hz. range. 5. A method according to claim 1, wherein said first rate is varied according to a predetermined coding scheme. 6. A method according to claim 1, wherein said accumulating is performed in the charge registers of a multi-pixel CCD or CMOS array. 7. A method according to claim 1, wherein said first rate is higher than the expected environmental rate of change in said imaged field of view. 8. A method according to claim 7, where said expected environmental rate of change in said imaged field of view is that arising from any of natural movements, personnel movements, vehicular movements or atmospheric turbulence occurring in said field of view. 9. The method of claim 1, wherein said first and said second sets of accumulated pixel signals are read out separately after completion of said predetermined plurality of pulses, at said second rate substantially lower than said first rate. 10. The method of claim 1, wherein said first and second sets of pixel signal accumulators are sets of charge registers of an interlaced CCD or CMOS image sensor, with said first set being associated with charges collected from said pixels, arising from laser pulses reflected from said field of view and said second set being associated with charges collected from said pixels in periods between the detection of pulses reflected from said field of view. 11. The method of claim 1, wherein said first and second sets of pixel signal accumulators are sets of charge registers of a CMOS or CCD image sensor, each pixel having two isolated charge sensors, with said first set being associated with charges collected from said pixels arising from laser pulses reflected from said field of view, and said second set being associated with charges collected from said pixels in periods between the detection of pulses reflected from said field of view. 12. The method of claim 1, wherein said first and second sets of pixel signal accumulators are sets of adjacent charge registers of a progressive scan CMOS or CCD image sensor, the signal from each pixel being accumulated in either of said two sets of adjacent charge registers according to the shifted position of the vertical register, with said first set being associated with charges collected from said pixels arising from laser pulses reflected from said field of view, and said second set being associated with charges collected from said pixels in periods between the detection of pulses reflected from said field of view. 13. The method of claim 1, wherein said subtraction of the effect of background illumination enables the point of impingement of said laser pulses to be determined in said image of said field of view, even if said background illumination dominates the intensity of said point of impingement of said laser pulses. 14. A method of imaging a field of view, according to claim 1, further comprising the step of: adding said signals accumulated in said first and second sets of signal accumulators and read out therefrom, to provide an additive image of said field of view; andimpressing on said additive image of said field of view, said image of said field of view with the point of impingement of said laser pulses accentuated therein, to obtain an indication of the position of impingement of said laser pulses on an image of said field of view. 15. A method for determining the range of an object, comprising: illuminating the object by means of the output beam of a CW laser, modulated at a first rate to provide a stream of transmitted laser pulses; imaging the field of view using a multi-pixel sensor array;accumulating signals obtained from said pixels during the detection of laser pulses reflected from said field of view for the duration of a predetermined plurality of pulses, at a second rate substantially less than said first rate, to obtain from said pixels a first set of accumulated pixel signals arising from said reflected laser pulses modulated at the rate equal to the difference between the first and second rates;accumulating signals obtained from said pixels in periods between the detection of pulses reflected from said field of view, in a second set of pixel signal accumulators, for said duration of said predetermined plurality of pulses, to obtain from those pixels a second set of accumulated pixel signals modulated at the rate equal to the difference between the first and second rates;subtracting said pixel signals accumulated in each of said first and second sets of pixel signal accumulators and read out therefrom, to generate image signals of said field of view in which the effect of background illumination is subtracted out, and which are modulated at the rate equal to the difference between the first and second rates;reading out said image signals of said field of view in which the effect of background illumination is subtracted out, and which are modulated at the rate equal to the difference between the first and second rates;repeating said step of generating image signals of said field of view in which the effect of background illumination is subtracted out for further durations of said predetermined plurality of pulses, to obtain further sets of accumulated pixel signals arising from said reflected laser pulses; said reading out of said further sets of accumulated pixel signals being performed at a rate substantially lower than that of said first rate;obtaining from said repeated accumulating and reading out, a train of image signal outputs of said object modulated at a rate equal to the difference between said first and second rates; anddetermining the range of said object from the difference in phase detected between said train of image signal outputs of said object and said modulated stream of transmitted laser pulses, said determining being performed at a rate equal to the difference between the first and second rates. 16. A method for determining the range of an object according to claim 15, wherein said difference between said first and second rates is sufficiently small that said phase difference can be measured electronically concurrently for millions of pixels of an imaging array. 17. A method according to claim 15, wherein said accumulating of pixel signals is performed in the charge registers of a multi-pixel CCD or CMOS array. 18. A method according to claim 15, wherein said reading out rate is sufficiently low that it is compatible with the frame rate of standard CCD or CMOS devices. 19. A method according to claim 18, wherein said reading out is performed at a rate in the tens of Hz. range. 20. A method of imaging a field of view, the method comprising: illuminating the field of view by means of the output beam of a CW laser, modulated at a first rate to provide a stream of laser pulses;imaging the field of view using a multi-pixel sensor array;accumulating signals obtained from said pixels during the detection of laser pulses reflected from said field of view in a first set of pixel signal accumulators, for the duration of a predetermined plurality of pulses, to obtain from those pixels a first set of accumulated pixel signals arising from said reflected laser pulses;reading out said first set of accumulated pixel signals after completion of said predetermined plurality of pulses;accumulating signals obtained from said pixels in periods between the detection of pulses reflected from said field of view, in a second set of pixel signal accumulators, for said duration of said predetermined plurality of pulses, to obtain from said pixels a second set of accumulated pixel signals;reading out said second set of accumulated pixel signals after completion of said predetermined plurality of pulses; andsubtracting said second set of accumulated signals from said first set of accumulated signals, such that a difference set of accumulated signals is obtained representative of the imaged field of view in which the effect of background illumination is subtracted out. 21. A method according to claim 20, wherein the steps of accumulating and reading out said first and second sets of accumulated pixel signals after completion of said predetermined plurality of pulses, is repeated after further predetermined pluralities of said pulses at a second rate substantially lower than that of said first rate. 22. The method of claim 20, wherein said first and second sets of pixel signal accumulators are first and second sets of charge register capacitors of an interlaced CCD or CMOS image sensor, with said first set being associated with charges collected from said pixels arising from laser pulses reflected from said field of view, and said second set being associated with charges collected from said pixels in periods between the detection of pulses reflected from said field of view. 23. A method according to claim 22, wherein each of the pixels has associated therewith a single charge register capacitor, the signals on alternate pixels being transferred to their associated charge register capacitors such that alternate charge registers collect respectively (i) the charges due to signals arising from laser pulses reflected from said field of view, and (ii) the charges due to signals in periods between the detection of pulses reflected from said field of view. 24. A method according to claim 22, wherein the pixels have associated therewith a pair of charge registers, one associated with the first set of charge registers, and the other associated with the second set of charge registers. 25. A method according to claim 22, wherein the read out rate is compatible with the frame rate of standard CCD or CMOS devices. 26. A method according to claim 22, wherein the read out rate is in the tens of Hz. range. 27. A method according to claim 22, wherein subtraction of the read out charges from the two sets of charge register capacitors provides the image output of the field of view without the effect of the background illumination from said field of view. 28. A method according to claim 20, wherein the modulation rate is substantially higher than the rate of change in the illuminated field of view occurring in the region of the object. 29. A method according to claim 20, wherein the signals from any pixel during the detection of laser pulses reflected from said field of view are transferred to a first charge register of a progressive scan CCD, the method further comprising the steps of shifting the vertical register of the progressive scan CCD such that the signals from that pixel in periods between the detection of pulses reflected from said field of view are transferred to a second charge register, and reading out the first and second charge registers at a second rate substantially less than said first rate.
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이 특허에 인용된 특허 (10)
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Paxman Richard G. (Ann Arbor MI) Marron Joseph C. (Brighton MI), System and method for three-dimensional imaging of opaque objects using frequency diversity and an opacity constraint.
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