A Map of Temporary Water Bodies in Western Africa

Abstract

An algorithm developed for the SPOT VEGETATION (VGT) sensor makes it possible to detect temporary small water bodies in arid and semi-arid areas by analysing the spectral contrast of each pixel compared to its neighbourhood. This algorithm captures surface water and humid areas, the last category being likely to include vegetation. These maps are generated every 10 days allowing to monitor the small temporary water bodies and humid area seasonality. In addition, a reference map of the temporary water bodies was prepared by validating the historical record of the small water body detection. The procedure consists in checking individually any SPOT VGT water bodies detection that lasted for more than 3 consecutive dekads between 1999 and late 2004. The validation has been done over Western Africa. Several sources of information have been used to validate the detections: the Global Lakes and Wetlands Database (GLWD), the Drainage Network of the Digital Chart of the World, Spot VGT colour composite images, the SRTM digital elevation model, Landsat quicklook images and Google Earth. Pixels of the history of occurrence that were not referenced in the GLWD or DCW database have been checked manually. This validation process resulted in a map of three categories: validated water bodies, positive vegetation anomaly with no obvious sign of water but indicating water availability in arid areas and false detections.JRC.H.3-Global environement monitorin