## 3 Data and Methods
### Research Methods  
Remote sensing technology, with its advantages of long time series, wide coverage, and multi-source data fusion [41; 42], provides an efficient dynamic monitoring tool for river evolution studies. Remote sensing technology can quickly capture changes in the process of river evolution and provide long-term data to help researchers reveal the patterns and mechanisms of river evolution [43]. This study used ENVI 5.6 software to perform geometric, radiometric, and atmospheric corrections on satellite imagery. These corrections removed errors from sensors and the atmosphere, standardized the data, and improved their quality. This ensured that the subsequent analysis was scientific and repeatable. Using ArcMap 10.8 software, spectral information from different bands of Landsat series satellites was combined into multi-band composites to enhance the identification of vegetation, water bodies, and bare land. For Landsat 5-TM and Landsat 7-ETM+, bands B3 (red), B2 (green), and B1 (blue) were used, while for Landsat 8/9-OLI, bands B4 (red), B3 (green), and B2 (blue) were selected. True color imagery was generated, with vegetation appearing green, water bodies in deep blue, and bare land in gray-brown. To quickly and accurately extract water body boundaries, false color composites are commonly used. For Landsat 5-TM and Landsat 7-ETM+, bands B4 (near-infrared), B3 (red), and B2 (green) were applied, while for Landsat 8/9-OLI, bands B5 (near-infrared), B4 (red), and B3 (green) were selected. In the synthesized image, vegetation appears bright red (with hue reflecting density), water bodies appear deep black, and bare land appears cyan-blue [44; 45]. In order to achieve accurate registration of multi-year remote sensing images, a polynomial model + DEM-assisted method is used to correct the terrain of Landsat images. The whole process will eliminate the projection displacement caused by topographic relief and improve the registration accuracy of multi-temporal images. The 2018 Copernicus DEM was used to perform topographic correction on Landsat images, and the DEM was re-projected into the UTM coordinate system of Landsat images and re-sampled to a spatial resolution of 30 m. Based on the RPC parameters in the Landsat MTL metafile and the DEM elevation data (Landsat5-TM and Landsat7-ETM + no RPC files, which need to be replaced by ground control points + polynomial correction), the terrain displacement is iteratively solved by the collinear equation model, and the orthophoto product is gener \begin{table}
\begin{tabular}{c c c} \hline
**Satellite Identification** & **Satellite Image Row** & **Acquisition Time** \\
**Number** & **and Column Numbers** & **18/07/1993, 25/12/1993, 19/06/1994, 22/08/1994, 18/03/1995, \\ \hline Landsat5-TM & 145/032 & 05/05/1995, 27/08/1996, 01/12/1996, 30/08/1997, 18/11/1997, 04/10/1998 \\ \hline Landsat7-ETM+ & 145/032 & 25/08/2004, 13/11/2004, 13/09/2005, 18/12/2005, 30/07/2006, 21/12/2006, 18/08/2007, 08/12/2007, 20/08/2008, 23/10/2008, 07/08/2009, 29/12/2009, 23/06/2010, 16/12/2010, 14/09/2011, 17/11/2011, 31/08/2012, 02/10/2012, 28/07/2017 \\ \hline Landsat8-OLI & 145/032 & 20/11/2015, 02/08/2016, 06/11/2016, 09/09/2018, 30/12/2018, 28/09/2019, 17/12/2019, 14/09/2020, 17/11/2020, 15/07/2021, 20/11/2021, 18/07/2022, 25/12/2022 \\ \hline Landsat9-OLI & 145/032 & 13/07/2023, 30/08/2023, 10/04/2024, 29/06/2024 \\ \hline \end{tabular}
\end{table} 
Table 1: Satellite imagery utilized in the study ([[http://www.gscloud.cn](http://www.gscloud.cn)]([http://www.gscloud.cn](http://www.gscloud.cn))). ated by the bilinear interpolation method. Through correction, the geometric accuracy is improved, the timing consistency is guaranteed, and all time-phase images are unified to the orthographic projection datum, so that the pixel-level residuals of multi-year change detection are controlled within 0.5 pixels. The radiation distortion is suppressed, and the radiation comparability between different time-phase images is enhanced by eliminating the slope illumination difference [46].