Systems and methods for efficient multi-return light detectors
Described herein are systems and methods that may efficiently detect multi-return light signals. A light detection and ranging system, such as a LiDAR system, may fire a laser beam that may hit multiple objects with a different distance in one line, causing multi-return light signals to be received by the system. Multi-return detectors may be able to analyze the peak magnitude of a plurality of peaks in the return signals and determine a multitude of peaks, such as the first peak, the last peak and the maximum peak. One embodiment to detect the multi-return light signals may be a multi-return recursive matched filter detector. This detector comprises a matched filter, peak detector, centroid calculation and a zeroing out function. Other embodiments may be based on a maximum finder that algorithmically selects the highest magnitude peaks from samples of the return signal and buffers for regions of interests peaks.
1. A multiple-return light signal detection method for a light detection and ranging (LIDAR) system, the method comprising:
receiving a multi-return signal having a plurality of peaks in a time period;
filtering the multi-return signal based, at least in part, on a pulse shape of an emitted laser beam, to produce a filtered signal;
identifying a sequence of two or more peaks of the filtered signal in the time period; and
identifying, from the sequence, at least two of:
a largest peak in the sequence;
a temporally first peak in the sequence; and
a temporally last peak in the sequence.
2. The method of claim 1 , wherein filtering the multi-return signal comprises correlating the multi-return signal with a signal having the pulse shape of the emitted laser beam.
3. The method of claim 1 , wherein filtering the multi-return signal comprises convolving the multi-return signal with a signal having the pulse shape of the emitted laser beam.
4. The method of claim 1 , wherein filtering the multi-return signal comprises using one or more matched filters to produce the filtered signal.
5. The method of claim 4 , wherein using the one or more matched filters to produce the filtered signal optimizes a signal-to-noise (S/N) ratio of the filtered signal.
6. The method of claim 1 , wherein identifying the sequence of two or more peaks of the filtered signal in the time period comprises identifying each peak of the filtered signal having a respective amplitude that exceeds a pre-set threshold value.
7. The method of claim 6 further comprising adjusting the pre-set threshold based on at least one of a target rate error or an operating noise environment.
8. The method of claim 1 , wherein identifying the sequence of two or more peaks of the filtered signal comprises deriving a temporal position and a relative amplitude of each of the two or more peaks in the sequence.
9. The method of claim 8 , wherein for each of the two or more peaks, deriving the temporal position of the respective peak comprises determining a centroid of the respective peak.
10. The method of claim 8 , wherein deriving the temporal position and the relative amplitude of each of the two or more peaks in the sequence comprises iteratively performing operations including:
detecting, by a peak detector, a current maximum peak of the filtered signal;
deriving the temporal position of the current maximum peak based on a centroid of the current maximum peak; and
eliminating the current maximum peak from the filtered signal.
11. The method of claim 1 further comprising emitting the laser beam prior to receiving the multi-return signal.
12. A light detection and ranging (LIDAR) system comprising:
one or more signal processing components configured to:
receive a multi-return signal comprising a plurality of peaks in a time period;
filter the multi-return signal based, at least in part, on a pulse shape of an emitted laser beam, to produce a filtered signal;
identify a sequence of two or more peaks of the filtered signal in the time period; and
identify, from the sequence, at least two of:
a largest peak in the sequence;
a temporally first peak in the sequence; or
a temporally last peak in the sequence.
13. The system of claim 12 , wherein filtering the multi-return signal comprises correlating the multi-return signal with a signal having the pulse shape of the emitted laser beam.
14. The system of claim 12 , wherein filtering the multi-return signal comprises convolving the multi-return signal with a signal having the pulse shape of the emitted laser beam.
15. The system of claim 12 , wherein producing the filtered signal optimizes a signal-to-noise (S/N) ratio of the filtered signal.
16. The system of claim 12 , wherein identifying the sequence of two or more peaks of the filtered signal in the time period comprises identifying each peak of the filtered signal having a respective amplitude that exceeds a pre-set threshold value.
17. The system of claim 16 , wherein the pre-set threshold value is selectively adjustable based on at least one of a target rate error or an operating noise environment.
18. The system of claim 12 , wherein identifying the sequence of two or more peaks of the filtered signal comprises deriving a temporal position and a relative amplitude of each of the two or more peaks in the sequence.
19. The system of claim 18 , wherein for each of the two or more peaks, deriving the temporal position of the respective peak comprises determining a centroid of the respective peak.
20. The system of claim 19 , wherein deriving the temporal position and a relative amplitude of each of the two or more peaks in the sequence comprises iteratively performing operations including:
detecting a current maximum peak of the filtered signal;
deriving the temporal position of the current maximum peak based on a centroid of the current maximum peak; and
eliminating the current maximum peak from the filtered signal.
21. The system of claim 12 further comprising a transmitter configured to emit the laser beam prior to receiving the multi-return signal.