Mapping Surface Water Stored in Small Reservoirs in the Volta Basin, West Africa
van de Giesen, N1; Liebe, J2; Annor, F3; van der Zaag, P4
1Delft University of Technology; 2Cornell University; 3Kwame N'krumah University of Science and Technology; 4UNESCO-IHE

Thousands of small reservoirs can be found in the savanna of West Africa. Monitoring water stored in these reservoirs is useful for the general assessment of water availability for food production and as hydrological observation. During the hydrologically more active part of the year, the wet season from May to October, clouds tend to cover more than 90% of the sky, making optical satellites less useful. Instead of, or in addition to, optical satellites, SAR imagery can be used to map reservoir areas.

In this paper, we present the possibilities and limitations of developing time series of water stored in small reservoirs. Different acquisition times and polarization schemes for Envisat ASAR imagery will be discussed. We will also show how such a time series can be used to monitor the onset of surface runoff, which lags significantly behind the onset of the rainy season.


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