Hyper temporal lidar with switching between a baseline scan mode and a pulse burst mode
A lidar system comprises (1) a lidar transmitter that switches from a baseline scan pattern to a pulse burst mode in response to a detection of a target in a field of view for the lidar transmitter, wherein the lidar transmitter transmits a pulse burst toward the target when in the pulse burst mode, and (2) a lidar receiver that refines an angle to the target based on returns from the pulse burst.
1 . A lidar system comprising:
a lidar transmitter that switches from a baseline scan pattern to a pulse burst mode in response to a detection of a target in a field of view for the lidar transmitter, wherein the lidar transmitter transmits a pulse burst toward the target when in the pulse burst mode; and
a lidar receiver that refines an angle to the target based on returns from the pulse burst.
2 . The lidar system of claim 1 , wherein the pulse burst includes a time separation between pulses of the pulse burst that is less than a time separation between laser pulse shots of the baseline scan pattern by a factor in a range between 10× and 100×.
3 . The lidar system of claim 1 , wherein the lidar receiver detects the target in the field of view based on a return from a previous laser pulse shot when operating according to the baseline scan pattern.
4 . The lidar system of claim 3 , further comprising:
a control circuit that schedules the pulse burst in response to the detection of the target based on the return from the previous laser pulse shot.
5 . The lidar system of claim 4 , wherein the pulse burst comprises a first pulse at a first shot angle and a second pulse at a second shot angle, wherein the previous laser pulse shot was fired at a third shot angle, and wherein the control circuit defines the first and second shot angles to surround the third shot angle.
6 . The lidar system of claim 5 , wherein the first and second shot angles are offset from the third shot angle by a value within a range between 0.025 degrees and 0.1 degrees.
7 . The lidar system of claim 5 , wherein the lidar receiver refines the angle to the target based on (1) the first, second, and third shot angles and (2) energy amounts in the returns from the previous laser pulse shot and the pulse burst.
8 . The lidar system of claim 7 , wherein the lidar receiver (1) determines a fit for energies within the returns from the previous laser pulse shot and the pulse burst to a curve that models expected return energy as a function of an offset angle to the target and (2) refines the angle to the target based on the determined fit to the curve.
9 . The lidar system of claim 8 , wherein the lidar receiver (1) determines the fit by (i) computing an energy ratio of return energy from the first pulse of the pulse burst relative to return energy from the second pulse of the pulse burst and (ii) retrieving an offset angle from a lookup table based on the computed return energy, wherein the lookup table indexes return energy ratios derived from the curve as a function of offset angles, and (2) refines the angle to the target based on the retrieved offset angle.
10 . The lidar system of claim 5 , wherein the control circuit further schedules the pulse burst according to a laser energy model that models available energy for laser pulse shots by the lidar transmitter over time.
11 . The lidar system of claim 10 , wherein the lidar transmitter comprises a mirror that is scannable over an axis with respect to the field of view, wherein the lidar transmitter scans the mirror between a plurality of shot angles with respect to the axis to define where the lidar transmitter is aimed in the field of view with respect to the axis, and wherein the control circuit schedules the pulse burst according to the laser energy model and a mirror motion model that models shot angles for the mirror over time.
12 . The lidar system of claim 11 , wherein the control circuit (1) defines shot times for the first and second shot angles based on the mirror motion model and (2) evaluates the pulse burst for the defined shot times with respect to the laser energy model.
13 . The lidar system of claim 12 , wherein the control circuit repeats the shot times definition and the pulse burst evaluation for one or more different return scans until a return scan is found where the laser energy model indicates sufficient energy is available for the pulse burst.
14 . The lidar system of claim 11 , wherein the lidar transmitter scans the mirror in a resonant mode.
15 . The lidar system of claim 11 , wherein the mirror is a first mirror, wherein the axis is a first axis, wherein the lidar transmitter further comprises a second mirror that is scannable over a second axis with respect to the field of view, wherein the lidar transmitter scans the second mirror between a plurality of shot angles with respect to the second axis so that the combination of the shot angles with respect to the first and second axes defines where the lidar transmitter is aimed in the field of view.
16 . The lidar system of claim 15 , wherein the lidar transmitter scans the second mirror in a point-to-point mode that varies as a function of a plurality of scheduled laser pulse shots for the lidar transmitter.
17 . The lidar system of claim 11 , wherein the lidar transmitter scans the mirror at a scan frequency in a range between 100 Hz and 20 KHz.
18 . The lidar system of claim 11 , wherein the lidar transmitter scans the mirror at a scan frequency in a range between 10 kHz and 15 kHz.
19 . The lidar system of claim 11 , wherein the target detection occurs during a first scan of the mirror, and wherein the control circuit schedules the pulse burst for a second scan of the mirror.
20 . The lidar system of claim 19 , wherein the second scan is a next return scan following the previous laser pulse shot.
21 . The lidar system of claim 3 , wherein the lidar transmitter fires the pulse burst sufficiently quickly after the previous laser pulse shot for the target to exhibit a range that is deemed common for the previous laser pulse shot and the pulse burst.
22 . The lidar system of claim 3 , wherein the target has a known velocity relative to the system, wherein the lidar transmitter fires the pulse burst sufficiently slowly after the previous laser pulse shot for the target to have changed range over the course of the previous laser pulse shot and the pulse burst, and wherein the lidar receiver compensates for the changed range based on the known velocity.
23 . The lidar system of claim 22 , wherein the target and/or the lidar system is moving.
24 . The lidar system of claim 1 , wherein the pulse burst exhibits a time separation between a first pulse of the pulse burst and a second pulse of the pulse burst in a range between 100 nsec and 10 μsec.
25 . The lidar system of claim 24 , wherein the time separation is in a range between 200 nsec and 500 nsec.
26 . The lidar system of claim 1 , wherein the refined angle comprises an azimuth angle.
27 . The lidar system of claim 1 , wherein the baseline scan pattern corresponds to a scan pattern where laser pulse shots are fired at a fixed time interval.
28 . The lidar system of claim 1 , wherein the baseline scan pattern corresponds to a scan pattern for a software-defined shot pattern frame.
29 . An article of manufacture for use by a lidar system to refine an angle to a target based on returns from a plurality of laser pulse shots, the article comprising:
machine-readable code that is resident on a non-transitory machine-readable storage medium, wherein the code defines processing operations to be performed by a processor to cause the processor to:
switch the lidar system from a baseline scan pattern to a pulse burst mode in response to a detection of a target in a field of view for the lidar system, wherein the lidar system transmits a pulse burst toward the target when in the pulse burst mode; and
refine an angle to the target based on returns from the pulse burst.
30 . A lidar method comprising:
detecting a target in a field of view;
switching a lidar transmitter from a baseline scan pattern to a pulse burst mode in response to the detected target;
the lidar transmitter transmitting a pulse burst toward the target when in the pulse burst mode; and
refining an angle to the target based on returns from the pulse burst.