Spatial decorrelation due to topography in the interferometric SAR coherence imagery

A modified spatial decorrelation function for SAR interferometry is derived as a function of both the baseline and the terrain slope. This function has been used to explain the total decorrelation phenomenon on slopes directly facing radar illumination, which is an obstacle for a side-looking radar interferometry. A zone of critical incidence angle (or, critical terrain slope) can be determined using the function. Within this zone, radar signals from two acquisitions separated by a baseline will become completely decorrelated regardless of any other conditions. The width of the critical incidence angle zone increases with the increase of baseline separation. An analytic method, ratio coherence imagery, is then introduced to identify the topographic total decorrelation of the radar-facing slope from other temporal decorrelation features and to analyse the nature of different coherence features effectively. An application of the new methodology in the east of Sahara desert, Algeria is presented.