On the Way of Estimation of the Reliability of the Interferometric Pixels for Correct Phase Unwrapping in the DEM Generation

Stage of phase unwrapping is of highest importance in the DEM generation by means of SAR interferometry. In the case of interferometric fringes merging in the areas of steep topography or in the case of poor quality of interferogram because of spatial/temporal/noise decorrelation the chances to resolve phase ambiguity across the entire SAR scene may become very low. We propose new way of local estimations of the quality of the interferogram, which allows to simplify stage of the phase unwrapping. The main feature of our approach is calculation of fringes spatial frequency for each pixel by means of two-dimensional FFT within small window around the pixel of the interferometric image accompanied by amplitude information. Our experience with processing the ERS interferometric pairs shows, that selection of the pixels with zero spatial frequency for further phase unwrapping allows to exclude practically all of the problematic pixels from the areas of layover/foreshortening, or low coherence. The map of valid pixels may be applied at the next stage for formal phase unwrapping. New technique of the phase unwrapping with a use of a map of invalid pixels described in a paper is being tested on the ERS tandem data obtained over Baikal lake area famous for the steep topography.