ALOS/PALSAR DInSAR processing for the monitoring of landslides characterized by large displacements.

Schlögel, R. (1), Doubre, C. (1), Malet, J.-P. (1), Lebourg T. (2)

(1) Institut de Physique du Globe de Strasbourg, CNRS UMR 7516, Université de Strasbourg, 5 rue Descartes, F-67084 Strasbourg Cedex
(2) Géosciences Azur, CNRS UMR 6526, Université de Nice-Sophia Antipolis, 250 Avenue A. Einstein, F-06560 Valbonne

In mountainous areas, the interferograms created for the monitoring of active landslides are often difficult to interpret because of the complex topography, the presence of vegetation coverage and the changing soil humidity conditions (e.g. snow cover). In addition, the studied landslides are characterized by important surface changes.
The objective of this study is to propose a method for the interpretation of L-band ALOS/PALSAR interferograms created by conventional Differential Interferometric Synthetic Aperture Radar (DInSAR). Three large and continuously active landslides (La Valette, Poche, La Clapière), exhibiting displacement rates between 0.1-4.0 cm.day-1, are used as case studies to develop and explain the methodology. After a selection of the interferograms characterized by small temporal (B_T < 46 days) and perpendicular (B_Perp < 1200 m) baselines, the method is applied only for the areas characterized by a coherence value > 0.25 and a slope gradient value < 37.4°. As automatic unwrapping is difficult to apply in such topographical situations and for the tracked surface displacements, a geomorphologically guided unwrapping approach is proposed in order to characterize the displacement. The results allow detecting landslide sub-units characterized by different kinematic pattern, and to propose a quantitative measurement of the displacement projected along slope and along the vertical component. The InSAR displacements are in agreement with on-site field measurements (permanent dGNSS observations, DGNSS campaigns on benchmarks, and terrestrial laser scanner surveys).