The oscillation effect was mostly caused by the poor interpolation of the complex image (i.e. the slave). The phase part is more sensitive to the interpolation method used than the intensity part. To avoid the oscillation effect, the best way is to use the Bi-Sinc 21-point interpolation method. For DEM interpolation, other interpolation methods can be used.
This is the slave intensity (3 bursts) after Backgeocoding.
This is coherence after deburst, multilooking and terrain correction.