An airborne radar designed for ground imaging is also capable of detecting vehicles in motion at a distance of about 3 miles.

The synthetic aperture radar looks through the side-door of the carrier aircraft and several images of the landscape, separated by a small time lapse (or multiple looks ) are computed from the reflected radiowaves. Vehicles in motion have a position varying from view to view allowing for automatic detection. Their apparent positions, however, are shifted away from the real positions as a consequence of the frequency alteration of their echoes (Doppler effect ) due to their proper speed. The reason is that the computation of the images is based on the sorting of the echoes according to their Doppler frequency shifts under the natural "hypothesis" that the ground is motionless.

The real position (hence the real speed) of the vehicle can, however, be retrieved with appropriate computations.