DEM Corrections Before Unwrapping in a Small Baseline Strategy for InSAR Time Series Analysis

Synthetic aperture radar interferometry (InSAR) is limited by temporal decorrelation and topographic errors, which can result in unwrapping errors in partially incoherent and mountainous areas. In this paper, we present an algorithm to estimate and remove local digital elevation model (DEM) errors from a series of wrapped interferograms. The method is designed to be included in a small baseline subset (SBAS) approach for InSAR time series analysis of ground deformation in natural environment. It is easy to implement and can be applied to all pixels of a radar scene. The algorithm is applied to a series of wrapped interferograms computed from ENVISAT radar images acquired across the Himalayan mountain range. The DEM error correction performance is quantified by the reduction of the local phase dispersion and of the number of residues computed during the unwrapping procedure. It thus improves the automation of the spatial unwrapping step.