WATER AREA OBSERVATION EXPERIMENT USING OPTICAL SENSOR FOR EXTRACTING INUNDATION BOUNDARY AT NIGHT

Abstract. During the occurrence of floods, the government generally tries to determine the extent of the continuously changing inundation (water) area as a disaster response for planning evacuations and designing drainage systems. One of the most common methods to identify this area during the daytime involves the interpretation of aerial optical images and videos that are obtained using an airplane, helicopter, or satellite. However, these aerial approach methods have not been established convincingly for their use during the night time. Therefore, to identify the water area at night, two hand-held optical sensors were used in this study, namely: an ultrasensitive camera (Sony SL camera α7S), and a thermal infrared camera (Optris thermography PI640). The night-time aerial performance was evaluated using a helicopter, along with a supplementary night-time examination on the ground. Herein, we targeted river water areas during normal conditions. As a result, it was determined that the water area could be identified clearly with an ultrasensitive camera that has an ISO sensitivity between 51200 and 102400. The thermal infrared camera was able to identify the water area to have a higher temperature than that of the surrounding area. However, in some cases, the water area boundaries were not clear. Thus, as the thermal infrared camera was susceptible to varying conditions, supplemental use of an ultrasensitive camera was determined to be effective for the identification of inundation (water) areas at night. The significance of this study is established by the fact that the studied sensors can be easily transported in a helicopter or mounted on a UAV for night-time applications.