Flood Inundation Distribution In Lamongan Regency Using Sentinel-1 SAR Data And Automatic Water-S1 Method

Abstract The study of SAR data in mapping distribution flood inundation has yielded relevant results. The ease of obtaining data has made development application of Sentinel-1 SAR, for flood mapping. A common method used in flood mapping is thresholding, mainly by determining the threshold generated through visual observation that presented color contrast histograms. However, surface conditions of surrounding terrain can create misinformation due to increased surface roughness, like double bounce on vegetation make it more challenging. Moreover, manual threshold methods are less-time effective in trial error process from visual image interpretation. The results tend to be subjective because distribution mapping heavily relies on the operator’s visual interpretation of threshold value. To address this challenge, distribution of flood inundation will be mapped with an automatic threshold method, called Water-S1 and expected to provide more objective results. The images divided into tiles with 10 km size, each selected tiles will be modeled with data probability parameters. Distribution modeling then iterated get probability model distribution that represents each selected tile. The result is probability map of the water surface during and after flood, then subtracts to get the distribution area of flood inundation. In this research the method was applied to Lamongan Regency. The result show that the method can identify flood inundation quite satisfactory. The spatial distribution of flood inundation are detected clustered in paddy fields center of Lamongan Regency with flood area around 19,680.75 hectares.