Topographic phase corrected coherence estimation using multi-pass differential SAR interferometry: differential coherence

To improve the reliability of repeat-pass interferometric synthetic aperture radar (InSAR) coherence imagery as a tool for random temporal change detection in relief areas, topographic phase in the interferogram should be removed to satisfy homogeneous and stationary assumptions for sample coherence estimation. Multi-pass differential SAR interferometry (DInSAR) is applied to produce topographic phase-corrected coherence estimation, so called differential coherence, in conjunction with differential interferogram. The topographic phase can be removed using a reference interferogram scaled by the ratio of baselines after phase unwrapping, without referring to DEM or slope estimation method. The remaining phase that replaces the phase term in the coherence estimator depends on random change, volume scattering, and surface block deformation. An example using ERS-1 and -2 SAR data of Granada, Spain, shows up to 16% rms improvement and slight contrast enhancement of coherence on steep terrain slope compared with the coherence in the presence of topographic phase. In the areas of which the reference interferogram has low coherence and contains phase unwrapping error, the differential coherence degrades