Radar micro-doppler signatures for characterization of human motion

As human beings we are able to derive much additional information about our environment from the exploitation of motion as well as from static objects. For example, we are all used to evaluating the speed of a vehicle to decide whether or not it is safe to cross the street. Radar systems are also able to measure motion using the well-known Doppler effect. Indeed this has long been exploited in moving target indication (MTI) and pulse Doppler systems for bulk velocity measurement [1]. These systems usually measure the velocity and use this to track an object such as in air traffic control. However, the Doppler principle can also be used to measure motion at a much finer level of detail. Staying with the aircraft example, it is possible to measure the motion associated with the turbines in a jet engine. This means that not only can the presence of an aircraft be determined but, potentially, also its type. This is an example of a micro-Doppler signature.