干旱区生态环境知识资源中心

Water is a precious resource since the lives and livelihoods of human societies depend on their ability to access this resource. This is particularly true in arid and semiarid regions like the Sahel where permanent surface waters are rare and hydrological solutions (e.g., accessing deep aquifers) are often not feasible. This work is devoted to the determination of the spatial and temporal variations of surface water extent at 250m over 9years (2003-2011) for the Soudan-Sahel region using visible and infrared imagery from the Moderate Resolution Imaging Spectroradiometer (MODIS) from both Terra and Aqua platforms. The methodology is automatic and could be applied to other regions and sensors. We utilized a combination of two MODIS spectral indices: the Normalized Difference Vegetation Index and the Modified Normalized Difference Water Index. Accuracy assessments carried out on 743 lakes across 37 Landsat images selected in Sahelian Africa on the basis of a stratified sampling show that the new product is (i) reliably able to detect surface water bodies of approximately 50ha and larger, (ii) improves on existing surface water body products, and (iii) can be used to monitor the seasonal distribution of surface water in semiarid regions.