Application of multi-temporal MERIS-FR and ASAR-WS data for large scale vegetation monitoring in the West African Sahel zone

This paper presents results achieved within the AQUIFER project from applying a remote sensing approach for regional scale vegetation monitoring in the Sahel. The present study is focussing on vegetation monitoring over parts of Niger, Nigeria and Mali, three countries sharing the common Iullemeden Aquifer System. This Aquifer system is affected by progressive over-extraction, water quality degradation, human induced pollution, associated with soil degradation, and the impacts of variability and climatic change. The specific vegetation types in these arid regions are good indicators for environmental changes. In many parts of the Sahel there are no continuous ground truth measurements available to allow statements about the extension of vegetation. Earth Observation data may provide the only approach to detect and analyse long-term changes. This study demonstrates the performance and suitability of ENVISAT MERIS-FR and ASAR-WS data for this purpose. The application of radar capabilities to detect the moisture content and optical information for the phenological state monitoring of the vegetation is demonstrated. Land cover classification maps of four different points intime within one growth period were generated using a rule based (object oriented) classification approach. Additionally, the changes between the four different dates as well as the seasonal vegetation dynamics were analysed.