Factors that contribute to the occurrence of shallow landslides due to rainfall include slope topography, the thickness of the ground surface soil layer, the geology of the soil layer, and the moisture conditions within it. In this study, the distribution of the canopy surface temperature as measured by a thermal infrared sensor was analyzed, and an efficient method to analyze the spatial distribution of moisture conditions in the soil layer was studied at the Sumiyoshi River basin in the Rokko Mountain Range, and the applicability of the method was evaluated.
First, the data on the canopy surface temperature measured with a thermal infrared sensor was corrected using data on elevation and amount of solar radiation. The mean for the corrected surface temperatures were calculated for each sub]basin area, covering from 0.03]0.15km2 on the slope surface, and areas with decreased temperatures were determined using deviation values, which were obtained by subtracting the mean from the corrected value for each sub]area. The soil moisture was measured on]site, and it was found that the decreased temperature areas were determined based on deviation values coincided with the areas with high levels of measured soil moisture and lower slope surface adjacent to the areas. Next, a spatial correlation between the areas with decreased surface temperatures, landslide sites, and faults was analyzed. The results showed that new landslide sites caused by rainfall tended to coincide with areas with decreased surface temperatures. Within such areas, areas with smaller catchment areas tended to be concentrated near faults. These results suggest the possibility that areas identified as having lower canopy temperatures represent areas susceptible to landslides due to a concentration of groundwater and areas where groundwater gathers because of the geological structure there.

Key wordsFremote sensing, thermography, soil moisture distribution, transpiration, canopy surface temperature, ground water, shallow landslide