Mapping of hydrothermally altered rocks by the EO-1 Hyperion sensor, Northern Danakil Depression, Eritrea

An EO-1 Hyperion scene was used to identify and map hydrothermally altered rocks and a Precambrian metamorphic sequence at and around the Alid volcanic dome, at the northern Danakil Depression, Eritrea. Mapping was coupled with laboratory analyses, including reflectance measurements, X-ray diffraction, and petrographic examination of selected rock samples. Thematic maps were compiled from the dataset, which was carefully pre-processed to evaluate and to correct interferences in the data. Despite the difficulties, lithological mapping using narrow spectral bands proved possible. A spectral signature attributed to ammonium was detected in the laboratory measurements of hydrothermally altered rocks from Alid. This was expressed as spectral absorption clues in the atmospherically corrected cube, at the known hydrothermally altered areas. The existence of ammonium in hydrothermally altered rocks within the Alid dome has been confirmed by previous studies. Spectral information of endmember's mineralogy found in the area (e.g. dolomite) enables a surface mineral map to be produced that stands in good agreement with the known geology along the overpass. These maps are the first hyperspectral overview of the surface mineralogy in this arid terrain and may be used as a base for future studies of remote areas such as the Danakil.