Aquatic Vegetation Extraction Of The Middle And Lower Reaches Of The Yangtze River Supported By The Google Earth Engine Platform

Aquatic vegetation is an important part of the ecology of shallow lakes.The changes in abundance and coverage affect the balance of lake ecosystems.The middle and lower reaches of the Yangtze River are one of the most concentrated areas of lakes in China,and one of the most developed areas in China.The deterioration of the lake's ecological environment will affect the lives of urban residents around the lake and restrict the economic development of surrounding cities.Therefore,it is particularly important to monitor the aquatic vegetation in the middle and lower reaches of the Yangtze River and to construct the historical aquatic vegetation distribution in the middle and lower reaches of the Yangtze River.Remote sensing technology is an effective means to extract aquatic vegetation from lakes.Remote sensing images can be used to obtain ground information quickly and efficiently.Macroscopic,comprehensive and rapid remote sensing technology has become one of the main technologies for environmental monitoring.Satellite remote sensing data is used to extract aquatic vegetation from lakes.It is currently a mainstream method for extracting aquatic vegetation.However,the amount of satellite data required for long-term,large-scale remote sensing monitoring is too large,and traditional remote sensing techniques are difficult to process such massive data quickly and efficiently.With the rapid changes in network and computer technology,cloud storage and cloud computing technologies have developed rapidly.The Google Earth Engine(GEE)cloud platform integrates commonly used remote sensing data sets such as Landsat,MODIS and Sentinel,and can use these data sets.The calculation is performed directly in the cloud platform,thereby eliminating a lot of preliminary work such as downloading data and pre-processing data,and greatly improving the efficiency of remote sensing data processing.Based on the GEE platform,this paper proposes a spectral characteristic index FVZI of aquatic vegetation that can be applied to different regions and at different times.The Landsat-5TM surface reflectance data from 1988 to 2010 is obtained and extracted by decision tree method.The aquatic vegetation cover maps of 28 lakes larger than 50 km~2in the middle and lower reaches of the Yangtze River,combined with spatial and temporal factors,analyzed the changes of aquatic vegetation in these 28 lakes.Through research,the paper draws the following conclusions:(1)Under the GEE platform,it can quickly and efficiently acquire massive remote sensing data for parallel computing,which greatly improves efficiency compared with traditional remote sensing data processing methods.(2)The time series analysis of the aquatic vegetation area of typical lakes in the middle and lower reaches of the Yangtze River shows that the aquatic vegetation area of Dongting Lake and Poyang Lake is the largest and the change is also significant,while the average aquatic vegetation area of Taihu Lake and Chaohu Lake is small,and the change is not obvious.(3)The driving factor analysis of the changes of aquatic vegetation coverage in typical lakes in the middle and lower reaches of the Yangtze River revealed that the water vegetation cover of Poyang Lake has a high correlation with the water level of Poyang Lake,and it is negatively correlated;the coverage of aquatic vegetation in Dongting Lake and the area of Dongting Lake The correlation was good and negatively correlated;the area of aquatic vegetation in Taihu Lake was less correlated with the nutrient content of lakes,and it was more correlated with time after 1998.The aquatic vegetation in Chaohu Lake has little change and there is no obvious driving factor.(4)According to the coverage of aquatic vegetation,the middle and lower reaches of the Yangtze River can be divided into three parts:east,middle and west.The eastern aquatic vegetation has the lowest coverage,followed by the middle,and the western aquatic vegetation has the highest coverage.(5)In 1998,the catastrophic flood disaster had a great impact on the lakes in the middle and lower reaches of the Yangtze River.During the period,the coverage of aquatic vegetation in most lakes decreased significantly and slowly returned to normal values in the following years.