Estimation of flow in various sizes of streams using the Sentinel-1 Synthetic Aperture Radar (SAR) data in Han River Basin, Korea

Abstract

This study proposes a novel approach of estimating stream discharge using the European Space Agency Sentinel-1 satellite data. Fifteen hydrological stations with a mean discharge ranging between 2 m3 s−1 and 305 m3 s−1 in the Han River Basin in Korea were chosen as test sites. A series of Sentinel-1 Synthetic Aperture Radar (SAR) images and observed streamflow data were selected to develop and validate the methodology. The methodology relates the stream discharge to the water area that is extracted from the satellite image analysis. The satellite image analysis involved the following sequential steps: (1) A series of SAR images for a given test site is pre-processed for thermal noise, radiometric calibration, speckle filtering and terrain correction; (2) The histogram matching technique is applied to all images to unify the backscatter distribution; (3) The polygonal area including the stream is manually delineated along the reach and the image filter with the shape of the polygon is applied to all images so that only the water area of the stream is extracted; (4) A single backscatter threshold value is applied to all images to extract a series of water area; (5) the power-law relationship between the series of the water area and the corresponding stream discharge is established and the correlation coefficient of the relationship is calculated; (6) The process of (4) and (5) was repeated to identify the optimal backscatter threshold that maximizes the correlation coefficient of the relationship. A clear relationship was developed for the 13 stations except for the two at which flow is highly influenced by hydraulic structures such as dam. At the 13 stream locations, the R value of the power-law relationship varied between 0.68 and 0.98 with a mean value of 0.89. The relationship was influenced by the geometric properties of the stream such as the size and side slope.