Evaluating the Effect of the Observation Time on the Distribution of Sar Permanent Scatterers

This paper deals with the problem of temporal decorrelation in the application of Differential SAR Interferometry (DInSAR) to surface deformation monitoring. Special attention has been paid to the impact of reflectivity changes on the so-called Permanent Scatterers (PS). Semi-PS (SPS) and Temporary PS (TPS) are first defined and possible solutions to their detection are then proposed. The impact of the temporal baseline and satellite repeat-cycle is then discussed based on the analysis of two ERS data-sets of 26 scenes each acquired over Rome. The first one is characterized by a 3-day repeat cycle (Second Ice Phase 1993-1994) and the second spans a 5-year temporal window (1995-2000, 35-day repeat cycle) mimicking the normal baseline distribution of the former. Preliminary results obtained by applying the PS technique to the 3-day repeat cycle data-set shows a much higher PS density than the usual figures obtained with a monthly acquisition scheme, and the possibility to get many measurement points over agricultural fields. The velocity field shows a peculiar behaviour still to be investigated.