DAMAGE ESTIMATION OF BUILDINGS’ ROOFS DUE TO THE 2019 TYPHOON FAXAI USING THE POST-EVENT AERIAL PHOTOGRAPHS

Abstract

 The 2019 Typhoon Faxai landed on September 9, 2019, in Chiba City of Chiba Prefecture, with a very strong power. It damaged more than 70 thousand houses in Chiba Prefecture. In this study, we used the post-event aerial photographs taken on September 19-20 and September 27-28 to extract bluesheets covering on the damaged roofs in Kyonan Town, Minamiboso City and Tateyama City. First, the visual interpretation was conducted in three small areas. Then four indices were proposed to extract bluesheets. By comparing with the results of the visual interpretation, the best index and the associated threshold value were defined. The ratio of the bluesheets on a roof was calculated by the area ratio of the extracted bluesheet and the building footprint. As a result, the ratios of 46,145 buildings in the study area were estimated. Finally, the functions to estimate the ratio of the bluesheets on a roof were constructed based on the maximum instantaneous wind speed.