The inverse synthetic aperture radar (ISAR) technique provides images of a satellite orbiting at a distance above 500 miles with a resolution above one meter. A radar sends a pulse of radio waves along a very narrow beam and measures the time lapse between the emission and the reception of the echo reflected by a target. The screen of a classical radar displays the intensity of the echo as a function of the distance for several orientations of the antenna (which generally scans along the horizon).

The angular resolution of a radar aerial is largely below what is needed for imaging at the distance of an orbiting satellite. The range resolution , however, remains the same whatever the observing distance is. We can make use of the motion of the satellite along its orbit for measuring its range profile under several orientations. We compute thereafter its high resolution image by a technique similar to the computer aided tomography .