Potentials and limitations of coupling ASTER and airborne geophysical data for improvement of geological mapping in arid region (Namibia, Rehoboth region)

Abstract

The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) launched on NASA’s Terra satellite ranks lately among potential tools for Earth Observation. ASTER measures reflected radiations in 3 bands between 0.52 to 0.86 μm (VNIR) and in 6 bands between 1.6 to 2.43 μm (SWIR). An ASTER image has been acquired on the Southern margin of the Damara orogen (Namibia, northern margin of the Nama marine sedimentary sequence) essentially composed by limestone, sandstone and shale. Furthermore, a program initiated by the Geological Survey of Namibia has permitted to obtain a radiometric data set (Thorium, Uranium and Potassium) of Rehoboth region in Namibia. The combined ASTER and airborne geophysical data have been processed and interpreted for improving the existing geological map. First, a Principal Component Analysis (PCA) on the 9 ASTER bands is realized and only the first five components are kept. Then, the Maximum Likelihood approach is used to identify lithological formations from radiometric data and PCA components. Importance of random training data has been pointed out. Finally the coupling of ASTER and radiometric data is the best approach for the improvement of geological map with a proportion of correctly mapped surface of 63.4% from initial geological map.