Thursday, November 16, 2006

Recently in several news publications microwave and laser police traffic radar's method of determining speed have been misreported. The terminology can be confusing and depends somewhat on how one uses certain terms. Some terms (unfortunately) are commonly misused. Below is precise language used in the strict sense of proper definitions.

There are 2 very different types of police radar that measure vehicle (really anything big enough and moving) speed;
-- microwave radar,
-- lidar (laser radar).

BACKGROUND
Police microwave radars have been around since the late 1940's and are still the most common today. These radars, as implied by the name, use microwaves (high frequency radio waves) to detect Doppler shifts (echo's from moving targets are frequency shifted off transmit frequency -- Doppler shift). Microwaves are typically defined as any frequency between about 2 GHz to about 36 GHz (2 billion cycles per second to about 36 billion cycles per second).

Police lidar laser radar) started showing up in the early 1990's. Lidars use pulsed infrared (IR) laser light invisible to the human eye to detect a vehicle's reflection. Lidar measures change in range versus time to calculate speed (speed = change in range / change in time). While microwaves and IR waves are both electromagnetic in nature, different physical characteristics apply to each (the frequency difference forces distinct variations).

CopRadar