What is Doppler velocity sensor?

A Doppler velocity sensor is a specialized Doppler radar that uses the Doppler effect to measure the three orthogonal velocity components referenced to the aircraft. When aircraft true heading, pitch and roll are provided by other aircraft systems, it can function as a navigation sensor to perform stand-alone dead reckoning navigation calculations as a Doppler Navigation Set.

Doppler navigation systems are independent of surrounding conditions, perform with high accuracy over land and sea anywhere in the world, and are independent of ground-based aids and space-based satellite navigation systems.