| Poyang Lake is an important natural wetland in China.It not only plays an important ecological role in maintaining regional and national ecological security,but also serves as an important support for regional ecological and economic development.In recent years,due to the influence of natural and human activities,a series of ecological problems have appeared.The use of remote sensing to monitor and analyze it is of great significance to the sustainable development of the lake area.Through the use of multi-source remote sensing images combined with water samples collected in the field,the time series of hydrological dynamic changes and water body classification studies have been carried out on Poyang Lake,which can better understand the law of lake hydrological changes and the spatial differences of water optical characteristics.The main research results of this article are as follows:Taking into account the dynamic variability of the height of Poyang Lake,this article uses the 8-day synthetic MODIS reflectance product MOD09Q1 with a higher time resolution to analyze the changes in the area of the Poyang Lake water body,the changes in the submergence frequency,and the relationship between the water area and the water level.The results show that Poyang Lake has obvious seasonal characteristics,and the water area of the year presents a normal distribution;Since 2003,there has been an obvious trend of prolonging and advancing the dry season;The inundation frequency of water bodies generally presents a spatial distribution trend opposite to the topography.The annual inundation area presents a"riverlike"spatial distribution,accounting for 13.79%of the maximum inundation area in the lake.The inundation frequency in the northern access area is mostly more than 60%,and the inundation frequency in the central beach area is basically 50%,with a sharp change.The water level of Poyang Lake has an obvious decreasing trend during the dry season from 2002to 2016,and there is a nonlinear correlation between the water level and the water area.Poyang Lake has a large area,and the optical characteristics of the water bodies are quite different in space.By optically classifying the water bodies,the spatial division of the water bodies according to the degree of similar optical characteristics is an important method to solve the low applicability of the inversion model.The measured reflectivity of water bodies in Poyang Lake was clustered by K-means algorithm,and the water bodies in Poyang Lake were divided into four categories.Combined with the concentration of water color parameters,the bio-optical characteristics of each category of water bodies were analyzed.The effect of Landsat8,GF-1 and MODIS images on water classification was evaluated.Combined with the classification results,the inversion model of the optimal suspended sediment concentration of different water bodies from Landsat8 images was established.The results show that the inversion accuracy is improved obviously after classification.Based on Landsat8 images,the water body types and the temporal and spatial changes of suspended sediment in Poyang Lake from 2013 to 2020 were analyzed.In terms of distribution,the water bodies in Poyang Lake are dispersed in dry season,while concentrated in wet season.The water bodies with high suspended sediment concentration are mainly distributed in the entrance passage to the river and the waters near Songmen Mountain.The driving factors of water dynamics in Poyang Lake are mainly climate and human activities.River runoff was the main factor for the change of water area,with an R~2 of 0.98,while precipitation in the basin had a low correlation with water area,with an R~2 of 0.218,which mainly played an indirect role.Sand mining activities and the operation of the Three Gorges Reservoir to some extent explain the reason of the water level drop in the dry season,soil erosion,sediment carried by rivers and the reservoir are the main influencing factors of the variation of suspended sediment concentration. |
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