Dongting Lake is the second largest freshwater lake in China, and the water body fluctuates greatly and frequently in dry and wet seasons. The high-frequency observation of water body changes in Dongting Lake by satellite is important for timely and accurate monitoring of its hydrological dynamic changes.This study aims to reconstruct and analyze the elaborate time series information of Dongting Lake water area from 2017 to 2020 by using Sentinel-1 and Sentinel-2 images (10 m) under the condition of high time-frequency and high spatial resolution. In addition, this study develops a method to reconstruct the whole lake water area and encrypt the time series of lake area based on the partially cloudless image of the lake area. This method uses the statistical fitting relationship between the block area and total area extracted from Sentinel-1 full image to establish an empirical model for obtaining a dense time series of Dongting Lake water area.Fitting results show that the area of each block is significantly positively correlated with the lake total area, and the average R² value is 0.94. From 2017 to 2020, 119 Sentinel-1 images and 38 Sentinel-2 images were obtained to extract the block inundation range of Dongting Lake for reconstructing the whole lake area. After all Sentinel-1 and Sentinel-2 images were combined, the average observation images available in each month are 6. In some months, the monitoring times can reach 10 times, and the time interval is 3—6 days. It can conduct fine monitoring of the water area change of Dongting Lake. Besides, the time series of water area reconstructed in this study can accurately describe the significant seasonal fluctuations and interannual changes. The water area reaches the peak in July and the valley from November to February. The average ratio of maximum area to minimum area in a month is 1.36. The most violent fluctuation in surface waters occurred in November, with a ratio of 1.52. After Sentinel-1/2 image observation time series were integrated, the average water area of Dongting Lake from 2017 to 2020 is about 1147.13 km².Compared with the water area time series of Dongting Lake constructed based on Sentinel-1/2 images, the water area time series combined with landsat-8 image can improve the time resolution of water observation. However, it has little effect on the monthly and annual averages of water area. This study combines sentinel series radar and optical images of high temporal and spatial resolution to develop a fine extraction method of high time-frequency water area series. In summary, this study can provide scientific and technological support for improving remote sensing monitoring and fine management of water resources in Dongting Lake and high dynamic lakes in the middle and lower reaches of the Yangtze River.

remote sensing monitoring;Dongting Lake;Sentinel;Watershed Area;time series;Yangtze River Basin