Research On The Assessment Method Of Hydrological Change In The Yangtze River Basin Based On SAR Image

As an important component of life,water is closely related to the global ecological environment,and the width,distribution and change of rivers and changes in soil water content play a crucial role in the global surface water cycle,and at the same time affect a variety of climatic processes.Hydrological analysis,ecological environment improvement,etc.are very important parameters,which always affect the natural environment and various human production activities.Synthetic Aperture Radar（SAR）has all-day and all-weather surface observation capabilities,and is not affected by clouds and rain.It is of great significance in hydrological assessment,monitoring and other research.Using SAR images,river distribution and surface water content distribution can be extracted to assess regional hydrological changes.The work of this paper is mainly divided into the following four aspects:（1）In this paper,the maximum inter-class variance method（Otsu）is improved,and the improved Otsu threshold segmentation algorithm is used to perform rough river extraction on the preprocessed SAR（Synthetic Aperture Radar）image.For mountainous areas with large undulations,DEM（Digital Elevation Model）data is used to remove the influence of hill shadows on river extraction results.Compared with the traditional Otsu algorithm,the improved Otsu threshold segmentation algorithm reduces the false alarm rate from 34.1% to 9.8%,and the obtained river extraction results are more conducive to the assessment of regional hydrological changes.（2）Combined with the extracted river results and the river width calculation method based on distance transformation,the river width was calculated.First,remove bridges from the river extraction results and perform a series of morphological processing on the river area to obtain the river centerline;then perform distance transformation according to the initial river extraction results,and multiply the obtained distance transformation map with the river centerline map to obtain information including width.the middle of the river.The river width calculation method proposed in this paper does not need to make a vertical line according to the center line of the river,nor is it limited by the selection of width calculation points,but calculates the width of the entire river extraction result.（3）Use the improved change detection algorithm to estimate soil moisture.Although the traditional change detection algorithm can estimate soil moisture without relying on surface parameters,it has the disadvantage of ignoring changes in vegetation layers and surface roughness.The improved change detection algorithm eliminates the influence of roughness changes in different time series of the same plot.And combined with the soil moisture products of the SMAP satellite,the relative moisture content was converted into absolute moisture content.The soil moisture accuracy obtained by the inversion can reach86.61%,which is higher than 64.24% of the traditional change detection algorithm.（4）Based on the results of river extraction,soil water content inversion results and historical monthly average precipitation in the study area,analysis and research are carried out.The analysis results show that the changes of river width and surface soil water content have the same trend as the monthly average precipitation.Therefore,the variation trends of river width and soil water content obtained by remote sensing technology can be used to assess regional hydrological changes.