What is “The Doppler Effect?”

Posted Tuesday, April 18, 2017 by Andrew Charles Huff

We have all seen police officers standing by their patrol car aiming a radar gun at oncoming traffic. But how do these handheld devices actually work and are the accurate?

Radar guns work by directing a radio signal towards a vehicle, then receiving back the same signal as it bounces off the vehicle. Then using what is known as the “Doppler Effect,” the device can calculate the speed of the vehicle based on changes in the value of the returning signal.

In addition to radar guns, law enforcement also routinely use Light Detection and Ranging (LIDAR) technology, which operates in much the same way as radar, but using lasers instead of radio waves.

Both types of devices are sensitive tools of measurement that require regular calibration and adjustment. Radar guns, for example, requires the use of a tuning fork to make sure that the device is producing accurate readings. Most manufacturers of the devices recommend calibration before and after every use.

Officers using these speed measurement devices must go through approved and certified training programs before operating them.

But remember that like any technology, these devices do have their weaknesses and it’s critical to know and understand where to look and what to look for.

If you have received a traffic ticket, please call my office and let’s talk.