Spatio-temporal monitoring of evaporitic processes using multi-resolution C band radar remote sensing data: example over the Chott el Djerid
Résumé
This paper gives an illustration of the contribution of spatio-temporal multi-resolution of spaceborne radar data for the monitoring of land surfaces. More precisely, it illustrates the potential of C band spaceborne radar data, by using in synergy scatterometer and SAR (Synthetic Aperture Radar) sensors, for the spatio-temporal monitoring of evaporitic processes over a vast playa, the Chott el Djerid, located in central Tunisia. Scatterometer data from the ASCAT (Advanced Scatterometer) instrument are characterized by a high temporal frequency of acquisition, about 3 days over the Chott, with a spatial resolution of 25 km. It is well suited for an interpretation of radar temporal signatures in relationship with seasonal variations of surface states. SAR images obtained from both ASAR (Advanced SAR) and RADARSAT-2 sensors are less frequent (about 20 days) but provide a higher spatial resolution, allowing the discrimination of spatial patterns related to evaporitic processes. ASAR Wide Swath mode, associated to 150m of spatial resolution, allows for the monitoring of the whole Chott area, while RADARSAT-2, realizing full polarimetric acquisitions with a spatial resolution of 8 m over, allows for the discrimination of finer spatial patterns over a sub-area within the Chott. Both scatterometer and SAR data show an overall good agreement in radiometry. Polarimetry, available for the RADARSAT-2 data, allows to highlight striking spatial patterns in relation with the various sedimentation processes within the saline deposit over the chott.