Improvement of phase and coherence map quality using azimuth prefiltering: examples from ERS-1 and X-SAR

Interferometric processing of SAR data is possible only if the two observations were made under nearly the same aspect angles. However, even slightly different antenna squint angles lead to a misalignment of the data spectra in the azimuth dimension. This possible relative azimuth frequency band shift causes an additional phase noise contribution in SAR interferograms as well as a reduction of the coherence. In the paper, the authors propose a suitable azimuth bandpass filtering method to improve the quality of interferograms and coherence maps. It is demonstrated that this kind of filtering is especially valuable when processing data acquired by unstable platforms like the Space Shuttle. An example from the X-SAR sensor illustrates the achievable coherence improvement.