Absolute Phase Offset in SAR Interferometry: Estimation by Spectral Diversity and Integration into Processing

Abstract

In SAR interferonmetry, prior to DEM generation or any other evaluation (differential interferometric processing, velocity computation in case of along track interferometry), an unknown phase offset has to be estimated and subtracted from the unwrapped phase. This usually is referred to as absolute phase estimation. In most cases tiepoints (e.g. corner reflectors) are used to estimate this offset, or it is computed from the overlap region of adjacent or crossing swaths (e.g. in case of SRTM). It is shown that the absolute phase offset can be related to range co-registration parameters. After a review of the co-registration method based on spectral diversity, its benefits for the measurement of the absolute phase offset are discussed. It is essential to note that the applied coregistration function must be taken into account to allow correct computation of the absolute phase offset. Finally, the most suited integration into a SAR processing chain, which is based on efficient high precision algorithms (e.g. Extended Chirp Scaling) is proposed. The performance of the adopted approach is demonstrated using single-pass interferometric data acquired by the E-SAR sensor in X-Band.