This paper presents results of a comparative assessment of usefulness and comparability of Landsat TM and AATSR data for mapping of green vegetation and hydrological features in semi-arid environments. The study was conducted in the Namibian part of the Cuvelai basin, central northern Namibia, a basin shared between Angola and Namibia. A comparison of SAVI and NDVI based on both Landsat TM and AATSR reveals that the two platforms correspond significantly. However, the lower resolution of the AATSR imagery results in loss of detail, which might negatively influence its usefulness for monitoring initiatives requiring high levels of detail. Furthermore, values recorded by Landsat TM are systematically lower than values recorded by AATSR. The displacement is linear and can therefore be compensated for by adding a constant to the values of one of the two sensors. Surface water maps were developed. Preliminary findings indicate that both platforms provide comparable and accurate information about surface water. Results indicate that Landsat TM is the best sensor to use for surface water detection in the study area. The lower spatial resolution of AATSR leads to an underestimate of surface water, since most water bodies in the area are smaller than the spatial resolution of the satellite, leading to mixed pixel problems. Keywords: Cuvelai river basin, surface water, ephemeral river, oshana, NDVI, SAVI.