I use both calibrated radar and lidar to collect speed measurements. Radar uses the Doppler effect which emits pulses of radio or microwave energy from an antenna. These radio waves bounce off objects and return to the radar. By measuring the precise time it takes for the signal to echo back and the change in frequency (Doppler effect), the radar determines an object’s speed.
Lidar works by emitting rapid, invisible eye-safe laser pulses—about 200 per second—that bounce off objects and return to a sensor, which calculates distance to and speed of an object based on the travel time. Lidar has a much more narrow beam than radar. At 1000' from the lidar, the laser beam is only 3 feet wide. The radar I use has a 12 degree beam which encompasses an area of just over 200 feet wide at 100'.
Bot radar and lidar are calibrated yearly by an FCC licensed technician to ensure accuracy.