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Identification of landslides in La Reunion Island with JERS and Radarsat radar interferometry

Daniel Raucoules(1) and Denis FEURER(1)

(1) BRGM, 117 ave de Luminy, bp 167, 13276 Marseille cedex 09, France


Due to its geological and climatic conditions, La Réunion Island is very affected by landslide hazard. Huge landslides (several kilometres wide) severely affect infrastructures (especially roads) and habitations. In order to prevent this risk, there is a need for new solutions to be added to the traditional monitoring methods. In this framework, this presentation describes a study based on radar interferometry for assessing its potential in landslides detection on the Island using both Radarsat (C-band) and JERS (L-band) images. 15 Radarsat images have been acquired between 1999 and 2001 and 6 JERS-1 images covering the year 1997. The dense vegetation over the Island generally hampers the analysis of interferograms in C band. Indeed, this loss of coherence limits the possibility of using large time spans. Radarsat interferograms with a time span of more than 24 days appear very noisy in the landsliding areas. On the other hand, strong atmospheric effects (up to 2 C-band fringes) affect the phase measurement because of the particular meteorological conditions. We therefore need long time span in order to increase the deformation/atmosphere ratio for slow landslides. L-Band JERS 1 images have been used to overcome the loss of coherence observed in the C band and to investigate longer time span. Nevertheless, due to the sparse JERS archive on the island, the study was limited to 5 months time spans. A high coherence level was observed with JERS conversely to Radarsat. The Grand Ilet and Hellbourg landslides have been investigated. These areas are currently monitored using ground based methods (GPS) in order to evaluate/mitigate their associated risk. Two independent JERS-1 interferometric pairs show unambiguously the limits of the active part of the Hellbourg Landslide, which can also be observed on a unique 24 days Radarsat pair. The interpretation of the fringe patterns in relation with additional information such as geodetic measurements and geomorphology has been carried out. The good performances of the JERS-1 data in this study show that the future L Band missions (ALOS, SAOCOM) should provide an interesting complementary tool to conventional ground based techniques in such a densely vegetated context.


Full paper

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry