An acronym for “Radio Detection And Ranging,” radar involves the transmission of electromagnetic waves that reflect off a moving object. When the wave is reflected, it changes frequency and is interpreted by the radar unit in a speed calculation. This change is referred to as the Doppler effect or Doppler shift. In the simplest terms, the Doppler effect explains how as a sound gets closer to a person, it gets louder. For example, consider the sound a passing car makes as it approaches you then moves away. Radar may be used in both moving and stationary modes.
This is the most popular technology for speed enforcement as evidence by the variety of radar detectors on the consumer market. These devices emit a beeping sound when radar waves are detected, warning drivers of approaching police officers.
Radar however is full of problems and it must be used in the correct fashion or else it will not be admissible in Court.
On of the more recent devices used in law enforcement for speed measurement is laser or LIDAR (Light Detection And Ranging). LIDAR devices use an infrared light wave emitted at frequencies that allow the beam to be focused into an extremely narrow target area. The devices are usually operated in the hand-held mode. Although they can be used through the glass it reduces the device’s range; therefore, an open window or exterior use is preferred.
LIDAR has become more popular with the frequency of consumer’s radar detectors. Detection of laser beams is possible but the devices that detect laser beams are limited in their effectiveness. This is due to the fact that when the device intercepts the laser beam, this corresponds to the clocking of the vehicle with the LIDAR device.
In addition, most LIDAR devices are mounted inside the vehicle, further limiting their detection by another device. The theory behind laser technology is that speed is calculated by dividing the distance by the time of the light pulses of the laser (S=D/T of light pulses).
More recently there have been handhelds that are frequently being used by the CHP to catch speeders. The biggest problem with Lidar is that it has not met the required scientific showing of reliability in a California Court room.