Landsatデータからの地熱変質帯広域抽出の試み

抄録

A basic study aimed at the extraction of the distribution of geothermally altered surface using Landsat computer compatible tape (CCT) has been done choosing Gochogake of the Hachimantai area, northern Japan as a model field. Spectral characteristics of pixels which represent typical geothermally altered flat surface without influence of vegetation were measured in terms of brightness value of CCT. However, the distribution of typical pixels is rare and it was felt that the necessity to set a category of geothermally altered surface + retarded vegetation for the purpose. The extraction of pixels included in this category is comparatively easy because most of geothermal areas develop in thick vegetated mountainous area and this brings strong spectral contrast between the target and the surrounding area. The application was made in the northern Kyushu area where large-scale geothermal exploration was being done. CCT used and described in this paper is the one which was taken on 22nd, Oct., 1973. Image analysis was done using IMAGE 100 system. Pre-processing such as geometric correction, UTM map conversion, and atmospheric correction was made before the analysis. The output was evaluated correlating the resemblance of distribution pattern of the categorized pixels with the existing alteration mapping data. Among the experiment, the case of the Garandake area where develops larger scale geothermal field and thus made possible the setting of better training area led better result.