how does LIDAR use electromagnetic waves to measure velocity?

Question

how does LIDAR use electromagnetic waves to measure velocity?

Answer 1

The commonest application I can think of is police "speed guns".



They directly measure distance, by time-of flight; the time from a short laser burst being sent to the reflection of that being received.



That measurement is repeated several times per second, while the gun is active.





Velocity is then an indirect calculation from repeated distance measurements.



eg. If the range to the vehicle has reduced by 30 metres over one second, it's velocity towards the speed gun is 30 m/sec (~67 MPH).





ps. Doppler effect is a change of signal frequency caused by relative motion; that's commonly used in radar, including radar type burglar alarm sensors and radar speed traps. It's not used in lidar, which by definition is a time of flight system.

Answer 2

Lidar, which stands for Light Detection and Ranging, is a remote sensing method that uses light in the form of a pulsed laser to measure ranges (variable distances).

It does not typically measure speed, just distance.

Answer 3

It is called Doppler effect. An object is moving toward the LIDAR.

The transmitter sends a pulse to the object. The pulse is reflected back to the LIDAR receiver It takes x microseconds. This is the distance.

 1 millisecond later, a second pulse is sent and received. The distance is less. The object has moved closer by y feet in 1 millisecond.

The object is moving closer by y feet per millisecond.