Lidar sensor assembly calibration based on reference surface

1. A LIDAR sensor assembly comprising:

a stationary portion having a fixed reference surface, the stationary portion comprising:

a first support rib and a second support rib; and

an elongated spine extending between and coupled to the first support rib and the second support rib, the elongated spine serving as the fixed reference surface; and

a rotatable assembly mechanically coupled to, and rotatable relative to, the stationary portion, the rotatable assembly comprising:

an elongated chassis having an axis of rotation about which the rotatable assembly is rotatable, wherein the first support rib is rotatably coupled to a first end of the elongated chassis and the second support rib is rotatably coupled to a second end of the elongated chassis;

a laser light source to emit laser light; and

a light sensor configured to produce a light signal in response to sensing reflected light corresponding to reflection of the laser light emitted by the laser light source from the fixed reference surface; and

a controller communicatively coupled to the laser light source and the light sensor, the controller being operative to:

transmit a firing signal to the light source to cause the light source to emit a pulse of laser light;

receive a signal from the light sensor indicating detection of reflected light corresponding to reflection of the pulse of laser light from the fixed reference surface; and

calibrate the LIDAR sensor assembly based at least in part on the signal indicating detection of the reflected light corresponding to the reflection of the pulse of laser light from the fixed reference surface.

2. The LIDAR sensor assembly of claim 1 , wherein the controller is operative to calibrate the LIDAR sensor assembly by:

measuring a time of flight from the transmission of the firing signal to the detection of the reflected light by the light sensor;

comparing the time of flight to an expected time of flight for the pulse of laser light to travel a known distance from the laser light source to the fixed reference surface and back to the light sensor; and

adjusting a distance calculation based at least in part on the comparing.

3. The LIDAR sensor assembly of claim 1 , wherein the fixed reference surface is substantially opaque and limits a detection angle of the LIDAR sensor assembly.

4. The LIDAR sensor assembly of claim 1 , wherein the fixed reference surface comprises a light diffuser.

5. The LIDAR sensor assembly of claim 1 , wherein the elongated spine comprises a light diffuser disposed on at least a portion of a surface of the elongated spine closest to the rotatable assembly.

6. The LIDAR sensor assembly of claim 1 , wherein the elongated spine is substantially parallel to the axis of rotation of the elongated chassis.

7. The LIDAR sensor assembly of claim 1 , wherein the elongated spine comprises a mount for mounting the LIDAR sensor assembly to a vehicle.

8. The LIDAR sensor assembly of claim 1 , wherein the stationary portion comprises a housing at least partially enclosing the rotatable assembly, the housing including a ring lens at least partially encircling a portion of the rotatable assembly from which the laser light is emitted and by which the reflected light is received.

9. A method of calibrating a LIDAR system, the method comprising:

transmitting a firing signal to a laser light source of a LIDAR sensor assembly to cause the laser light source to emit a pulse of laser light toward a reference surface mechanically coupled to the LIDAR sensor assembly, the reference surface being part of a stationary portion of the LIDAR sensor assembly, the stationary portion comprising:

a housing at least partially enclosing a rotatable assembly mechanically coupled to, and rotatable relative to, the stationary portion, the housing including a ring lens at least partially encircling a portion of the rotatable assembly from which the laser light is emitted, the ring lens serving as the reference surface;

receiving a signal from a light sensor of the LIDAR sensor assembly, the signal indicating detection of reflected light corresponding to reflection of the pulse of laser light from the reference surface; and

calibrating the LIDAR sensor assembly based at least in part on the signal indicating detection of the reflected light corresponding to the reflection of the pulse of laser light from the reference surface.

10. The method of claim 9 , wherein calibrating the LIDAR sensor assembly comprises:

measuring a time of flight from the transmitting of the firing signal to the detection of the reflected light by the light sensor;

comparing the time of flight to an expected time of flight for the pulse of laser light to travel a known distance from the laser light source to the reference surface and back to the light sensor; and

adjusting a distance calculation based at least in part on the comparing.

11. The method of claim 9 , further comprising causing rotation of the rotatable assembly including the laser light source and the light sensor about an axis of rotation to scan a detection angle of the LIDAR sensor assembly.

12. The method of claim 11 , wherein the generating, the receiving, and the calibrating are performed periodically.

13. The method of claim 11 , wherein the generating, the receiving, and the calibrating are performed responsive to a triggering event.

14. A system comprising:

a LIDAR sensor assembly comprising:

a stationary portion comprising a housing, the housing including a ring lens;

a rotatable assembly mechanically coupled to, and rotatable relative to, the stationary portion, the rotatable assembly at least partially enclosed by the housing, the rotatable assembly comprising:

a laser light source to emit laser light; and

a light sensor configured to produce a light signal in response to sensing reflected light corresponding to reflection of the laser light emitted by the laser light source from a reference surface that is mechanically coupled to the LIDAR sensor assembly at a known distance in relation to the laser light source and light sensor,

wherein the ring lens at least partially encircles a portion of the rotatable assembly from which the laser light is emitted and at which the reflected light is received, the ring lens serving as the reference surface; and

a controller communicatively coupled to the laser light source and the light sensor, the controller being operative to:

transmit a firing signal to the laser light source to cause the laser light source to emit a pulse of laser light;

receive a signal from the light sensor indicating detection of reflected light corresponding to reflection of the pulse of laser light from the reference surface; and

calibrate the LIDAR sensor assembly based at least in part on the signal indicating detection of the reflected light corresponding to the reflection of the pulse of laser light from the reference surface.

15. The system of claim 14 , wherein the controller is operative to calibrate the LIDAR sensor assembly by:

measuring a time of flight from the transmission of the firing signal to the detection of the reflected light by the light sensor;

comparing the time of flight to an expected time of flight for the pulse of laser light to travel a known distance from the laser light source to the reference surface and back to the light sensor; and

adjusting a distance calculation based at least in part on the comparing.

16. The system of claim 14 , wherein the reference surface is substantially transparent.

17. The system of claim 14 , wherein the stationary portion of the LIDAR sensor assembly comprises the reference surface that is fixed at the known distance in relation to the laser light source and light sensor.

18. The system of claim 14 , wherein the ring lens comprises at least one of:

an antireflective material; or

interior and exterior surfaces coated with an antireflective coating.

19. The system of claim 14 , further including a spine, wherein the LIDAR sensor assembly is calibrated independent of a received signal associated with reflection of the laser light emitted by the laser light source from the spine.

20. The system of claim 14 , wherein the controller is further operative to filter out return signals corresponding to a reflection of the ring lens in a subsequent distance measurement.