Abstract:
Hyperion hyperspectral (VNIR-SWiR) satellite image data was used to map the spatial
distribution of mineral precipitates at Lake Magadi area, in the southernmost part of the
eastern Kenya rift, Kenya. Mapping was coupled with laboratory analysis, including
reflectance spectroscopic measurements and X-ray diffraction for selected rock and soil
samples.
The spectral responses of 92 rock and soil samples including trona, chert, diatomite,
basalt/trachyte, erionite, Green bed and High Magadi bed were studied and identified.
The spectral signatures of Chert samples show the broad Si-OH absorption feature at 2.2
pm while, Green bed, High Magadi bed and diatomite exhibit carbonate absorption
feature at 235 pm with broad Si-OH absorption feature at 2.2 pm. Trona exhibits six
common absorption features at 1.50, 1.74, 1.94,2.03, 2.22 and 2.39 pm. These characteristics
spectral absorption features with general shape of the spectral curve are used to identify the
surface minerals of the area.
In the mapping of different stages of evaporites and other surface minerals using Hyperion
data, various image processing techniques including, the Minimum Noise Fraction (MNF),
Pixel Purity Index (PPI) and Mixture Tuned Matched Filtering (MTMF) were applied. These
spectral mapping methods coupled with geochemical knowledge of the area substantially
improved the existing geological knowledge and enhanced the capability to derive
substantial information related to the distribution and formation of precipitates and evaporites
in the area.
