I was just curious as to what wikipedia has to say. Some may argue that wikipedia is not a very accurate source, but I believe more do than do not
Copied and pasted from wikipedia:
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LIDAR does not suffer from “sweep” error when the operator uses the equipment correctly and when the LIDAR unit is equipped with algorithms that are able to detect when this has occurred. A combination of signal strength monitoring, receive gate timing, target position prediction and pre-filtering of the received signal wavelength prevents this from occurring.
Should the beam illuminate sections of the vehicle with different reflectivity or the aspect of the vehicle changes during measurement that causes the received signal strength to be changed then the LIDAR unit will reject the measurement thereby producing speed readings of high integrity.
For LIDAR units to be used in law enforcement applications a rigorous approval procedure is usually completed before deployment. The use of many reflections and an averaging technique in the speed measurement process increase the integrity of the speed reading. Vehicles are usually equipped with a horizontally oriented registration plate that, when illuminated, causes a high integrity reflection to be returned to the LIDAR - despite the shape of the vehicle. In locations that do not require that a front or rear registration plate is fitted, headlamps and rear-reflectors provide almost ideal retro-reflective surfaces overcoming the reflections from uneven or non-compliant reflective surfaces thereby eliminating “sweep” error. It is these mechanisms which cause concern that LIDAR is somehow unreliable.
Most traffic LIDAR systems send out a stream of approximately 100 pulses over the span of three-tenths of a second. A "black box" proprietary statistical algorithm picks and chooses which progressively shorter reflections to retain from the pulses over the short fraction of a second.
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Reference:
Under Military and law enforcement section
http://en.wikipedia.org/wiki/LIDAR