Flood Identification Using Sentinel 1 SAR Imagery in Bila Walanae Watershed
Syaeful Rahmat(a*), Sigit Herlambang Asmorojati(b), Andang Suryana Soma(b,c)

a) Study Programs Remote Sensing and Geographic Information System, Faculty of Vocational, Hasanuddin University, Makassar, Indonesia
b) Watershed Management Laboratory, Faculty of Forestry Hasanuddin University, Makassar Indonesia
c) Forest Hidrology and Watersheds Management Research Group, Faculty of Forestry Hasanuddin University

Abstract

Indonesia is a tropical climate with a high rainfall intensity, so almost all areas in Indonesia have the potential to be affected by flood disasters. Bila-Walanae watershed is included in WS Walanae - Cenranae which is a National Strategic River Area. The strategic issue that occurs in the watershed when Walanae shallowing lake Tempe due to sedimentation that empties into lake Tempe and more than half of the area is flat-roofed and sloping with land closures in the form of forests that leave 15.47% of the total watershed area, thus increasing the potential for flooding in this region. This study aims to identify flooded areas in the Bila Walanae Watershed using Sentinel-1 SAR imagery data before and at the time of the flood event on July 19, 2020. Identify floods using the Normalized Difference Sigma Index method. The number of samples in the study was used as many as 102 samples used for reference data. Simple random sampling techniques are used for sampling methods. Results from the Normalized Difference Sigma Index analysis identified floodwaters covering an area of 36,593.51 ha with an accuracy rate of 90.2%. Floodwaters spread to seven sub-districts in Wajo Regency, five sub-districts in Sidenreng Rappang Regency, two sub-districts in Soppeng regency, and three sub-districts in Bone regency. The results of the analysis showed that the elevation and Digital Elevation Model were very influential on the identification of flooded areas by using sentinel-1 imagery in the Bila Walanae watershed. Flood identification using Sentinel 1 imagery should be used in open land-covered areas to avoid factors that can affect the backscatter, namely double-bounce vegetation layer and lookalikes.

Keywords: Flood, NDSI, Sentinel-1 SAR, Watershed

Topic: Topic B: Applications of Remote Sensing