抄録
Reflectance and emissivity spectra of geologic materials have been used to discriminate mineral compositions and produce geological maps from remotely-sensed data. This paper presents a new application of such spectral data and remote sensing technique to estimate weathering degree of rock masses. For this purpose, two field spectrometers with interference filters and FT-IR were used to obtain reflectance data within 0.485 to 2.5, um and emissivity data within 8 to 14, um, respectively, of several rock types. The weathering degrees of rock samples were evaluated by X-ray CT value or P-wave velocity (Vp). Four indexes were proposed by focusing on the change patterns of reflectance and emissivity spectra with the progress of weathering. Two are IFe and Iclay that are based on the absorption depths resulting from the occurrence and abundance of ferric oxide minerals and clay minerals, respectively. The others are related to the wavelength and depth of emissivity absorption, λmin and Δε, which result from the changes in mineral compositions and crystal structures of silicates. The weathering of rock samples could be characterized by increase of the reflectance spectra and flattening of the emissivity spectra. By comparing the four indexes with the CT and V, values of granite, sandstone, granodiorite, and diorite samples, Iclay was specified to have the highest correlation with the weathering degree, and AE was subordinate to it. We demonstrate that L, is applicable to field measurement data by selecting two test sites, an amphibolite site with a fracture zone and a weathered granite site, in northern Kumamoto Prefecture, southwest Japan. Interval Vp at these sites is used in the correlation analysis with Iclay. Homogenous mixture of clay minerals, which makes area ratio of clay minerals being similar to volume ratio, can be considered as a reason why Hay, is a suitable index for evaluating the weathering degree of rocks.
