Complimentary measurement of geophysical deformation using repeat-pass SAR

Differential radar interferometry has proven to be an excellent method to measure displacements associated with geophysical phenomena such as glacier flow, subsidence, tectonic plate motion, and earthquake displacement. Since the technique utilizes the interferometric phase, it is limited in cases where large displacements in the slant range direction result in complete decorrelation. Similarly, if the surface deformation causes rotation of the scene or other disturbances the interferometric signal will be lost. The geophysical displacement field can also be measured via incoherent or coherent cross-correlation of small image chips. This method has the advantages that it does not require phase unwrapping. In cases where there is some degree of interferometric coherence between data acquisitions, the single-look complex image speckles themselves become features that can be accurately tracked. This method is complimentary to the phase-based approach since it works well with the large displacements. Examples for the successful application of the two techniques are found in the mapping of the velocity fields of surging glaciers and displacement fields of major earthquakes. Furthermore, image cross-correlation measurements yield the two-dimensional displacement field while measurements of the phase yield deformation only along the line-of-sight. Accuracy of the cross-correlation method is dependent on the scene content, correlation, and image chip size.