Reduction of the need for phase unwrapping in radar interferometry

Monitoring of a small change by synthetic aperture radar (SAR) has previously been demonstrated for several sites, We derive two methods for detecting small displacements in the general case of differential interferometry: (1) the topographic elimination method and (2) the three-pass method. We explain the reasons which make us favor the former method. Validation and calibration of both methods are described. The topographic elimination method is preferred because of the limited need for phase unwrapping. Although phase unwrapping is usually considered to be a key component of radar interferometry, we show that it can be avoided most of the time by using a rough digital elevation model available throughout the world and a new technique, the integer interferometric combination (IIC). Several examples validating the IIC technique are presented as well as considerations about the probability and cost of having a successful study on a given site, which is not a site of opportunity. We conclude with some examples of topography-free, map-registered interferograms, which were produced automatically from SAR raw data and digital elevation models of various quality using the above methods. This validates these methods from an operational point of view.