CHARACTERISTICS OF TRANSPARENCY DISTRIBUTION OFF HIROSHIMA PREFECTURE BEFORE AND AFTER IN THE WEST JAPAN HEAVY RAIN DISASTER USING FIELD SURVEY AND SATELLITE DATA

Abstract

 The onjecttive of this study is to investigate the influence on the light environment in the Seto Inland Sea off Hiroshima Prefecture during the heavy rainfall in West Japan that occurred in the beginning of July 2018. Specifically, I tried to understand the transparency distribution characteristics of the Seto Inland Sea and its recovery status using measured transparency data, vertical turbidity data, and satellite data before and after the disaster. As a result, the following main results were obtained. First, based on the measured data, there was a drop in transparency of 68% of the average as a whole, off Hiroshima Prefecture. In addition, the transparency returned to the average value in about one month after the disaster (August 2017). Furthermore, a significant high correlation (R² = 0.90, p <0.01) was obtained for the "band 3 to band 4 ratio" (offset corrected) of the Landsat-8 reflectance product and transparency. Also, the transparency distribution off Hiroshima Prefecture derived from the Landsat-8 data showed that a large-scale loss of several kilometers occurred at the mouths of the Kurose and Ashida rivers immediately after the disaster.