An exciting and promising technique for using radar data is synthetic aperture radar interferometry (InSAR). Using interferometry, it is possible to produce detailed three-dimensional relief maps of the Earth's surface with an accuracy of a few metres, direct from ERS-1 data.

This image of the Bay of Naples is a combination of a normal backscatter-intensity radar image and an interferogram of Vesuvius and its vicinity. The interferogram does not use the intensity but the phase information of the backscattered signals. What are actually calculated are the phase differences between two images taken from slightly different positions in consecutive overpasses of the same region. These phase differences, translated into a colour scale, directly correlate with the altitude of the terrain: the typical interference fringes on this image correspond to lines of equal altitude on a topographical map. Subtract relief with an existing Digital Elevation Model and differential InSAR can be performed, revealing ground motion occurring between acquisitions.