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FRINGE '96 Workshop: ERS SAR Interferometry, 30 September - 2 October 1996
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Wetland monitoring in Mali using SAR interferometry

Jeremy Morley University College London, Gower Street, London. WC1E 6BT, U.K.
Jan-Peter Muller University College London, Gower Street, London. WC1E 6BT, U.K.


Wetland environments are found worldwide, from the Sudd Marshes in Africa to the Amazon river basin. Wetlands are important elements of continental hydrological networks, attenuating flood surges, forming sinks or stores for runoff and providing an important link in the hydrological cycle between river channels and the atmosphere.
The study area in this project is a region of wetlands in Mali on the River Niger ~(15degN, 5degW). These wetlands were chosen for environmental and pragmatic reasons. The wetlands lie in the Sahelian semi-arid zone and are therefore a major regional source of water to the atmosphere through evapotranspiration. The wetlands also lie in both Libreville and Maspalomas receiving station masks, increasing the available coverage by ERS SAR. SAR data are being provided at no cost by ESA under data grant AO-L.UK202.
Our project aims to use SAR data firstly to extract the areal extent of flooding and secondly to derive water volume storage. Flooded extents are to be derived by segmentation of both amplitude and phase coherence images. Water storage is to be derived first by building a DEM of the wetland basin by interferometry during the dry season, and then intersecting flooded extents with the DEM to give the flooded volume.
In this paper we examine the use of phase coherence data in delineation of the flooded extents, comparing a pair of scenes from the dry season (January/February 1993) with scenes from the wet season (September/October 1993). Phase coherence is shown to provide greatly increased contrast between flooded and non-flooded regions. The results of attempts to segment the images will also be presented. We hope also to compare the results with L-Band imagery from SIR-C, acquired in October 1994 - the different interaction of L-Band SAR with vegetation may be more robust to vegtation growing up in flodded areas.
Keywords: SAR Interferometry, Monitoring, Wetlands, Africa, Hydrology

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