Digital signal processing in optical systems used for ranging applications
First Claim
1. A method for increasing the signal to noise ratio of the signal waveforms generated by an apparatus for optically sensing a remote object in relative motion along the line of sight of said apparatus, comprising the steps of:
- (a) providing said apparatus for optically sensing said object, said apparatus including means for(a1) sending a predetermined number N.sub.S of optical pulses towards said object,(a2) receiving a number N.sub.S of optical signals reflected by said object,(a3) converting said number N.sub.S of optical signals into a number N.sub.S of digital signal waveforms S.sub.k, k=1, 2, 3, . . . , N.sub.S, each of the said digital signal waveforms being formed of data sampled at a predetermined number N.sub.p of range values R.sub.i, i=1, 2, 3, . . . , N.sub.p, and(a4) numerically processing said digital signal waveforms,(b) selecting a set of range shift parameter values RSP.sub.j, j=1, 2, 3, . . . , N.sub.R,(c) performing a range shift of each said waveform S.sub.k by the value (k−
1).times.RSP.sub.j,(d) generating a waveform SA.sub.j by computing the average of the N.sub.S said waveforms S.sub.k range shifted according to step (c),(e) finding the peak signal amplitude comprised in the averaged signal waveform SA.sub.j,(f) repeating steps (c) to (e) for the N.sub.R values of said range shift parameter RSP.sub.j as selected in step (b),(g) finding the values of said range shift parameter that give averaged signal waveforms having peak signal amplitudes exceeding a predetermined threshold,(h) combining the averaged signal waveforms determined in step (g) and updating a previously measured signal waveform having the maximum peak signal amplitude with said waveform combination.
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Abstract
Methods and apparatuses for reducing the response time along with increasing the probability of ranging of optical rangefinders that digitize the signal waveforms obtained from the pulse echoes returned from various types of objects to be ranged, the pulse echoes being too weak to allow successful ranging from a single waveform or the objects being possibly in motion during the capture of the pulse echoes. In a first embodiment of the invention, the response time at close range of a digital optical rangefinder is reduced by using a signal averaging process wherein the number of data to be averaged varies with the distance according to a predetermined function. In a second embodiment of the invention, the probability of ranging objects in motion along the line of sight of a digital optical rangefinder is increased and the object velocity measured by performing a range shift of each acquired signal waveform prior to averaging. In a third embodiment of the invention, the signal waveforms acquired in the line of sight of a digital optical rangefinder are scanned over a predetermined zone and range shifted and averaged to allow for early detection and ranging of objects that enter in the zone.
27 Citations
12 Claims
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1. A method for increasing the signal to noise ratio of the signal waveforms generated by an apparatus for optically sensing a remote object in relative motion along the line of sight of said apparatus, comprising the steps of:
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(a) providing said apparatus for optically sensing said object, said apparatus including means for (a1) sending a predetermined number N.sub.S of optical pulses towards said object, (a2) receiving a number N.sub.S of optical signals reflected by said object, (a3) converting said number N.sub.S of optical signals into a number N.sub.S of digital signal waveforms S.sub.k, k=1, 2, 3, . . . , N.sub.S, each of the said digital signal waveforms being formed of data sampled at a predetermined number N.sub.p of range values R.sub.i, i=1, 2, 3, . . . , N.sub.p, and (a4) numerically processing said digital signal waveforms, (b) selecting a set of range shift parameter values RSP.sub.j, j=1, 2, 3, . . . , N.sub.R, (c) performing a range shift of each said waveform S.sub.k by the value (k−
1).times.RSP.sub.j,(d) generating a waveform SA.sub.j by computing the average of the N.sub.S said waveforms S.sub.k range shifted according to step (c), (e) finding the peak signal amplitude comprised in the averaged signal waveform SA.sub.j, (f) repeating steps (c) to (e) for the N.sub.R values of said range shift parameter RSP.sub.j as selected in step (b), (g) finding the values of said range shift parameter that give averaged signal waveforms having peak signal amplitudes exceeding a predetermined threshold, (h) combining the averaged signal waveforms determined in step (g) and updating a previously measured signal waveform having the maximum peak signal amplitude with said waveform combination. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. An apparatus for optically sensing a remote object in relative motion along a line of sight of said apparatus, said apparatus comprising:
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an optical emitter for sending a predetermined number Ns of optical pulses towards said object; an optical receiver for receiving a number Ns of optical signals reflected by said object and for converting said number N.sub.s of optical signals into a number N.sub.s of digital signal waveforms S.sub.k, k=1, 2, 3, . . . , N.sub.s, each of the digital signal waveforms being formed of data sampled at a predetermined number N.sub.p of range values R.sub.i, i=1, 2, 3, . . . , N.sub.p, and a control and processing unit for numerically processing said digital signal waveforms, said control and processing unit being further adapted to; (a) select a set of range shift parameter values RSP.sub.j, j=1, 2, 3, . . . , N.sub.R, (b) perform a range shift of each said waveform S.sub.k by the value (k−
1).times.RSP.sub.j,(c) generate a waveform SA.sub.j by computing the average of the N.sub.S said waveforms S.sub.k range shifted according to step (b), (d) find the peak signal amplitude comprised in the averaged signal waveform SA.sub.j, (e) repeat steps (b) to (d) for the N.sub.R values of said range shift parameter RSP.sub.j as selected in step (a), (f) find the values of said range shift parameter that give averaged signal waveforms having peak signal amplitudes exceeding a predetermined threshold, (g) combine the averaged signal waveforms determined in step (f) and update a previously measured signal waveform having the maximum peak signal amplitude with said waveform combination.
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Specification