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Detection and monitoring of sand dune mobility in southeast Niger using multi-temporal coherence images

Catherine Bodart(1) and Andre Ozer(1)

(1) University of Liege, Allee du 6 Aout 2-B11, 4000 Liege, Belgium

Abstract

ERS and Envisat ASAR images have been processed by interferometry in order to evaluate their potential in the study of sandy desertification. Research focus has been on interferometric coherence and its utility to detect and map sand dune mobility. Combined with amplitude images, one-day interval coherence images derived from pairs of ERS SAR tandem acquisitions enabled us to estimate the extension of the reactivation process of ancient dunes in southeast Niger. In this Sahel area, sand encroachment is the dominant form of desertification. Seven tandem pairs have been processed and the analysis of the coherence values has been compared to high-resolution satellite data (SPOT 5) and field observations. The results illustrate the high potential of tandem interferometric coherence images as a useful source of information for the detection of light sand dune movements in semi-arid zones. In addition, two methods have been developed to monitor active sand dunes and to detect changes by using multi-temporal tandem coherence images. By doing so, the temporal change of active sand surfaces has been highlighted in the direction of the main wind component. Furthermore, coherence with temporal separation of more than one day has been tested with programmed Envisat Asar images on the study area. The preliminary results at 35 days interval are not encouraging, as the average coherence for the whole area has been found to be very low. These images have thus little relevance for mapping and studying sand dunes dynamic by interferomeric coherence.

 

Workshop presentation

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