How do radar speed measurement devices measure speed?

Radar speed measurement devices utilize the Doppler effect to measure speed, which is a fundamental principle in physics. When a radar unit emits a radio wave towards a moving object, the frequency of the wave changes based on the relative motion between the radar and the object.

As the object moves toward the radar, the waves are compressed, leading to a higher frequency (blue shift). Conversely, if the object is moving away, the waves are stretched, which results in a lower frequency (red shift). The radar device detects these frequency changes and calculates the speed of the object based on the extent of the frequency shift. This method is highly reliable and allows for real-time speed measurement, making it effective for law enforcement in traffic enforcement situations.

The other options do not accurately reflect how radar speed measurement devices function. Tracking GPS locations relies on satellite data rather than frequency shifts, calculating average speed over distance is not instantaneous and typically requires more complex algorithms, and assessing visual speed cues is subjective and not as precise as the Doppler effect measurement.