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Hyperspectral mapping of surface mineralogy in the Lake Magadi area in Kenya.

Loku Kodikara, Gayantha Roshana (2009) Hyperspectral mapping of surface mineralogy in the Lake Magadi area in Kenya.

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Abstract:Hyperion and Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) data were used to identify, map and model the spatial distribution of the mineral precipitates at the Lake Magadi area in Kenya. Mapping was coupled with laboratory analysis, including reflectance and emittance spectroscopic measurements and X‐ray diffraction for selected rock and soil samples. In addition to that, land surface temperature mapping, stratigraphic information and drainage network extraction of the area were carried out using remote sensing techniques and later integrated and modelled. The spectral responses of 92 rock and soil samples were studied and identified. The spectral signatures of Magadiite (NaSi7O13 (OH) 3 ∙3H2O) and Kenyaite (NaSi11O20.5 (OH) 4 ∙3H2O), which are not known from the work of others, were established in this research. The Magadiite shows diagnostic absorption feature at 1.464 μm. The characteristic absorption features of the Kenyaite are at 1.153 μm and 1.464 μm wavelength regions. In addition to that, spectral signatures of trona, chert, diatomite, basalt/trachyte, erionite, Green bed and High Magadi bed were studied and identified. Chert samples show the broad Si‐OH absorption feature at 2.2 μm while, Green bed, High Magadi bed and diatomite exhibit carbonate absorption feature at 2.35 μm with broad Si‐OH absorption feature at 2.2 μm. Trona exhibits six common absorption features at 1.50, 1.74, 1.94, 2.03, 2.22 and 2.39 μm. Thermal Infrared spectra of trona also exhibit three characteristics features at 6.66, 9.35 and 11.71 μm wavelength regions. The spectroscopic studies of undisturbed soil samples revealed that the evaporites have been restricted to the uppermost part of the surface and the change in mineral phase is possible due to the temperature changes. Mapping of different stages of evaporites and other surface minerals using combination of ASTER and Hyperion images facilitated by different types of mapping techniques including spectral mapping methods (SAM & MTMF) and band rationing method substantially improved the existing knowledge of the geology of the area. Stratigraphic information extracted from remote sensing methods showed that the mineral precipitates are restricted to the low lying areas associated with water. Drainage network extracted from the ASTER DEM showed the influence of runoff for mineral reactions and formations that were described in existing hydro‐geochemical models of the area. The contribution of spatial and temporal land surface temperature variations for the evaporitic mineral formations in the area was identified after mapping surface temperatures from ASTER TIR (Thermal Infrared) bands. Finally, this study concludes that the usage of remote sensing techniques with existing geochemical knowledge of the area significantly enhanced the capability to derive substantial information related to the distribution and formation of precipitates and evaporites in the area. Keywords: Hyperion; ASTER; Lake Magadi; Reflectance and emittance spectroscopy; X‐ray Diffraction; Surface mineral mapping; Land surface temperature mapping; Drainage network extraction; Magadiite; Kenyaite; Trona; Chert; Diatomite; Remote sensing
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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