A New Algorithm for Monitoring Backflow from River to Lake (BRL) Using Satellite Images: A Case of Poyang Lake, China

Backflow from river to lake (BRL) usually happens in inland lakes and affects water exchange, matter migration, and variations in the water quality and eco-environment. However, at present, discharge data derived from hydrological stations are the only way to monitor BRL, and the influence scope of BRL has not been monitored through hydrological stations. To address this problem, we propose a novel algorithm to monitor BRL using satellite images of Poyang Lake (the largest freshwater lake in China). The following results were obtained: (1) According to the difference in suspended sediment from rivers and lakes, an algorithm using the total suspended sediment (TSS), which was used as a tracer, was designed for monitoring BRL in Poyang Lake. (2) An innovative extraction method for the mutation line using the TSS was developed to analyze BRL via satellite images. A gradient variation method was developed to extract the mutation line accurately. (3) The satellites with daily acquisition or higher-frequency resolution images (e.g., Moderate-Resolution Imaging Spectroradiometer (MODIS)) were satisfactory for monitoring the characteristics of BRL. The MODIS-derived band combination R-rs(645) - R-rs(859))/(R-rs(555) - R-rs(859) yielded a higher fitting accuracy (R-2 = 0.858, RMSE = 10.25 mg/L) derived from an exponential model, which was helpful to highlighting the mutation line. (4) The important parameters of BRL, such as the beginning time, the duration, the end time, and the influence scope, were quantitatively determined by judging the movement of the mutation line. This algorithm was applied to quickly and effectively extract the information of two instances of BRL in Poyang Lake in July 2000 and July to August 2007, and the results were accurate and reasonable. This algorithm can save a great deal on monitoring costs. A BRL monitoring algorithm using remote sensing is an efficient government measure supplement to address the limitations of hydrological stations. These results provide technological support for lake management and can serve as a valuable reference for water bodies similar to Poyang Lake worldwide.