Technical cooperation in East Africa: Contribution of remote sensing unit
Report of the project:
Sentinel-2 satellite image (band combination 4-3-2) of the central part of Djibouti. The study area is represented by the yellow polygon, with the Lake Asal to the West and the Lake Ghoubbet to the South (contains modified Copernicus Sentinel data 2020)
Source: BGR
Remote sensing methods for geothermal exploration is not well established in partner countries with geographic locations in the East African Rift Valley Region. The use and evaluation of free and open multispectral data (Landsat, Sentinel-2) and elevation models (e.g. SRTM) provide a significant basis for the assessment of the geothermal potential and should be integrated as a standard into the prefeasibility studies of an exploration site. This type of support is particularly relevant in technical cooperation, as the exploration of geothermal sites sometimes involves high financial efforts (e.g., drilling) that might inhibit the geothermal development in a region. The above-mentioned freely available satellite data enables initial, low-cost preliminary studies without high financial expenditure
Lineament map for the study area North Ghoubbet in Djibouti with a combination of SRTM digital elevation model and a Sentinel-2 scene (band combination 12-8a-5) in the background (contains modified Copernicus Sentinel data 2020)
Source: BGR
The need for assistance in using geothermal energy as an important sustainable energy resource is particularly high, as the geothermal potential in most of these countries is not used so far. Kenya is the only country where geothermal energy significantly contributes to electricity generation (support by BGR: thermal remote sensing, ground movement studies). Another geothermal plant is situated in Ethiopia but with negligible production.
The current project includes collaboration with the Djiboutian partner ODDEG (Office Djiboutien de Développement de l’Energie Géothermique). The working area North Ghoubbet bordering Lake Ghoubbet to the Northwest is analyzed by using different remote sensing methods. Sentinel-2 and SRTM data are used for structural mapping. The knowledge of geological structures is of main importance for the assessment of a geothermal site, as structures essentially contribute to the permeability of a system and therefore to the circulation of geothermal fluids. In North Ghoubbet, especially the southern part of the area is estimated to have high potential. There, the lineament network is particularly dense, and in addition, fumaroles above 100°C provide evidence of hydrothermal activity along significant structures.
Additionally, high-resolution satellite data from the Worldview-3 mission complement the studies in North Ghoubbet. Geothermal manifestations often are associated with extensive alteration zones. The high spatial and spectral resolution of the Worldview-3 data enables the mapping of these alteration zones through their characteristic mineral assemblages. In turn, these zones indicate locations with increased hydrothermal activity.
The combination of these different remote sensing data and methods significantly contributes to the assessment of the geothermal potential in North Ghoubbet. Based on these studies, areas for further ground-based analyses are defined.
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