Topographic phase recovery from stacked ERS interferometry and a low-resolution digital elevation model

A hybrid approach to topographic recovery from ERS interferometry is develo ped and assessed. Tropospheric/ionospheric artifacts, imprecise orbital inf ormation, and layover are key issues in recovering topography and surface d eformation from repeat-pass interferometry. Previously, we developed a phas e gradient approach to stacking interferograms to reduce these errors and a lso to reduce the short-wavelength phase noise (see Sandwell and Pi-ice [19 98] and Appendix A). Here the method is extended to use a low-resolution di gital elevation model to constrain long-wavelength phase errors and an iter ation scheme to minimize errors in the computation of phase gradient. We de monstrate the topographic phase recovery on 16-m postings using 25 ERS synt hetic aperture radar images from an area of southern California containing 2700 m of relief. On the basis of a comparison with 81 GPS monuments, the E RS-derived topography has a typical absolute accuracy of better than 10 m e xcept in areas of layover. The resulting topographic phase enables accurate two-pass, real-time interferometry even in mountainous areas where traditi onal phase unwrapping schemes fail. As an example, we form a topography-fre e (127-m perpendicular baseline) interferogram spanning 7.5 years; fringes from two major earthquakes and aseismic slip on the San Andreas Fault are c learly isolated.