Hyper temporal lidar using multiple matched filters to determine target retro-reflectivity
A lidar system comprises a photodetector circuit and a signal processing circuit. The photodetector circuit comprises an array of pixels for sensing incident light. The signal processing circuit processes a signal representative of the sensed incident light to detect a reflection of a laser pulse from a target within a field of view. The signal processing circuit can comprise a matched filter corresponding to a retro-reflective target that is tuned to a reflected pulse shape that exhibits a vertical clipping relative to a transmitted pulse shape for the laser pulse that is indicative of the retro-reflective target, and wherein the signal processing circuit determines a retro-reflector status for the target based how the matched filter responds to the applied signal.
1 . A lidar system comprising:
a photodetector circuit, the photodetector circuit comprising an array of pixels for sensing incident light; and
a signal processing circuit for processing a signal representative of the sensed incident light to detect a reflection of a laser pulse from a target within a field of view, wherein the signal processing circuit comprises a matched filter corresponding to a retro-reflective target that is tuned to a reflected pulse shape that exhibits a vertical clipping relative to a transmitted pulse shape for the laser pulse that is indicative of the retro-reflective target, wherein the matched filter is tuned according to a function that computes a minimum as between (1) a specified vertical clip level corresponding to a saturation threshold of at least one of the array of pixels or an analog-to-digital converter and (2) a reference pulse shape corresponding to the transmitted pulse shape, and wherein the signal processing circuit determines a retro-reflector status for the target based how the matched filter responds to the signal.
2 . The lidar system of claim 1 , wherein the matched filter includes a plurality of matched filters corresponding to different amounts of retro-reflectivity for the target that are tuned to different reflected pulse shapes for reflections from the target at different amounts of retro-reflectivity.
3 . The lidar system of claim 2 , wherein the signal processing circuit determines an amount of retro-reflectivity for the target based on which of the plurality of matched filters produces a largest response to the signal.
4 . The lidar system of claim 2 , wherein the different amounts of retro-reflectivity include non-retro-reflectivity.
5 . The lidar system of claim 2 , wherein the plurality of matched filters include:
a first matched filter tuned to a reflected pulse shape for a reflection from a non-retro-reflective target; and
a second matched filter tuned to a reflected pulse shape for a reflection from a retro-reflective target.
6 . The lidar system of claim 5 , wherein the signal processing circuit classifies the target as retro-reflective or non-oblique not retro-reflective based on which of the first matched filter and the second matched filter produces a larger response to the signal.
7 . The lidar system of claim 2 , wherein the plurality of matched filters include:
a first matched filter tuned to a reflected pulse shape for a reflection from a non-retro-reflective target;
a second matched filter tuned to a reflected pulse shape for a reflection from a retro-reflective target at a first amount of retro-reflectivity; and
a third matched filter tuned to a reflected pulse shape for a reflection from a retro-reflective target at a second amount of retro-reflectivity.
8 . The lidar system of claim 7 , wherein the signal processing circuit determines whether the target exhibits non-retro-reflectivity, the first amount of retro-reflectivity, or the second amount of retro-reflectivity based on which of the first matched filter, the second matched filter, and the third matched filter produces a largest response to the signal.
9 . The lidar system of claim 2 , wherein each of the plurality of matched filters is tuned according to a function that computes a minimum as between (1) a specified vertical clip level corresponding to a defined amount of retro-reflectivity and (2) a reference pulse shape, wherein different matched filters are associated with different specified vertical clip levels corresponding to different amounts of retro-reflectivity.
10 . The lidar system of claim 9 , wherein the reference pulse shape is a convolution of a stretch factor box pulse with a reference pulse shape corresponding to a transmitted laser pulse shot, wherein the stretch factor box pulse corresponds to a stretch factor that is indicative of an extent of target obliquity, and wherein the different matched filters are associated with different stretch factor box pulses corresponding to different stretch factors that are indicative of different extents of target obliquity.
11 . The lidar system of claim 9 , further comprising:
a lookup table of precomputed minimum functions; and
a control circuit that tunes the plurality of matched filters based on the precomputed minimum functions in the lookup table.
12 . The lidar system of claim 2 , wherein the signal processing circuit applies the signal to the plurality of matched filters in parallel.
13 . The lidar system of claim 1 , wherein the matched filter comprises:
a register in which data corresponding to a pulse reflection reference shape is stored to thereby tune the matched filter to a given reflected pulse shape; and
correlation logic that performs a cross-correlation between the data in the register and the signal.
14 . The lidar system of claim 13 , wherein the pulse reflection reference shape is stored in the register as a plurality of samples, and wherein the correlation logic performs the cross-correlation between the plurality of samples in the register and a plurality of samples representative of the signal.
15 . The lidar system of claim 1 , wherein the signal processing circuit further comprises an analog-to-digital converter (ADC) that generates a plurality of digital samples that are representative of the sensed incident light, and wherein the signal comprises the plurality of digital samples.
16 . The lidar system of claim 15 , wherein the signal processing circuit further comprises a cache memory for caching the plurality of digital samples to be applied to the matched filter.
17 . The lidar system of claim 1 , wherein the signal processing circuit comprises an application-specific integrated circuit (ASIC) on which the matched filter is deployed.
18 . The lidar system of claim 1 , wherein the signal processing circuit comprises a field programmable gate array (FPGA) on which the matched filter is deployed.
19 . The lidar system of claim 1 , further comprising:
a lidar transmitter; and
a control circuit;
wherein the control circuit defines a shot energy for a laser pulse shot to be transmitted by the lidar transmitter and for use in producing a pulse reflection from which a retro-reflectivity for the target is determined, wherein the defined shot energy provides a desired amount of signal-to-noise ratio for producing a desired amount of accuracy with respect to the determined retro-reflectivity for the target.
20 . The lidar system of claim 1 , wherein the laser pulse exhibits a transmitted laser pulse shape that is Gaussian.
21 . The lidar system of claim 1 , wherein the target is a road surface.
22 . The lidar system of claim 1 , wherein the target is an object above a road surface.
23 . The lidar system of claim 22 , wherein the object comprises a moving object.
24 . The lidar system of claim 23 , wherein the object comprises a street sign.
25 . The lidar system of claim 1 , further comprising:
a laser source;
a lidar transmitter, wherein the lidar transmitter comprises a plurality of scannable mirrors, and wherein the lidar transmitter transmits a plurality of laser pulses from the laser source toward a plurality of targets in the field of view via the plurality of scannable mirrors according to a shot list; and
a control circuit that schedules laser pulses in the shot list for targeting defined range points in the field of view based on (1) a laser energy model that models energy available for laser pulses from the laser source over time and (2) a mirror motion model that models motion for at least one of the plurality of scannable mirrors over time.
26 . The lidar system of claim 25 , wherein the lidar transmitter scans a first scannable mirror in a resonant mode and scans a second scannable mirror in a point-to-point mode according to a step function that varies as a function of the defined range points targeted by the shot list.
27 . A lidar method comprising:
sensing incident light via an array of pixels, wherein the incident light includes a reflection of a laser pulse from a target within a field of view;
applying a signal representative of the sensed incident light to a matched filter corresponding to a retro-reflective target that is tuned to a reflected pulse shape that exhibits a vertical clipping relative to a transmitted pulse shape for the laser pulse that is indicative of the retro-reflective target, wherein the matched filter is tuned according to a function that computes a minimum as between (1) a specified vertical clip level corresponding to a saturation threshold of at least one of the array of pixels or an analog-to-digital converter and (2) a reference pulse shape corresponding to the transmitted pulse shape; and
determining a retro-reflector status for the target based on how the matched filter responds to the applied signal.
28 . An article of manufacture for a lidar receiver, the article of manufacture comprising:
machine-readable code that is resident on a non-transitory computer-readable storage medium, wherein the machine-readable code defines processing operations to be performed by a processor to cause the processor to:
apply a signal to a matched filter corresponding to a retro-reflective target, wherein the applied signal is representative of incident light sensed by an array of pixels, wherein the incident light includes a reflection of a laser pulse from a target within a field of view for the lidar receiver, and wherein the matched filter is tuned to a reflected pulse shape that exhibits a vertical clipping relative to a transmitted pulse shape for the laser pulse that is indicative of the retro-reflective target, where the matched filter is tuned according to a function that computes a minimum as between (1) a specified vertical clip level corresponding to a saturation threshold of at least one of the array of pixels or an analog-to-digital converter and (2) a reference pulse shape corresponding to the transmitted pulse shape; and
determine a retro-reflector status for the target based on how the matched filter responds to the applied signal.