Observation and modelling of the Saint-Etienne-de-Tinée landslide using SAR interferometry

SAR interferometry has been shown to lead to accurate e surface displacements mapping. The study of the La Clapiere' landslide, located in Southern France on the left bank of the Tinee river, was carried out in order to demonstrate the capability of interferometry to monitor displacements of small spatial extension. In a first study, six different interferograms have been derived from ERS-1 SAR images acquired during the Commissioning Phase The coherence of the associated images was shown to remain significant over most of the surface of the landslide during the two weeks of the survey, The interferograms, generated on a massively parallel computer, clearly evidenced deformation fringes associated with the landslide. They were remarkably similar, and indicated steady-state displacements over at least 12 days The displacement field derived from the interferograms was modeled and shown to be characterized by a non-uniform displacement gradient from the top to the bottom. It also revealed a significantly faster motion of the western part of the landslide, The amplitude of the motion was shown to be in good agreement with ground measurements. Furthermore, the interferograms allowed us to evidence a small-scale instability which could not be observed with discrete ground measurements Finally, we present preliminary results obtained on the same site with images acquired during the second Tandem mission. It provided the opportunity to extend the study of the landslide, which displacements are too high to be observed with images acquired on the standard orbital cycles of 35 days.