Fine classification of saltmarsh vegetation based on Google Earth Engine in Yancheng,China
Since the introduction of Spartina alterniflorain Jiangsu Province in 1982,the landscape pattern of coastal saltmarsh vegetation has changed dramatically.The area of Phragmites australis and Spartina alterniflora has increased continuously,squeezing the niche of Suaeda salsaand leading to the destruction of ecosystem.Coastal saltmarsh wetland is one of the three blue carbon ecosystems,playing an important ecological role in sequestering carbon and neutralizing greenhouse gas emission.Remote sensing is used to monitor the temporal and spatial dynamic changes of coastal saltmarsh vegetation,providing scientific support for the protection and restoration of coastal saltmarsh wetland ecosystems.In this paper,Jiangsu coastal areas with rich vegetation types are selected as the study area.Based on the Landsat 5,7,8 and Sentinel-2 images from 2000 to 2020 selected on the Google Earth Engine(GEE)platform,a wetland vegetation extraction method is proposed.First of all,the classification system of Yancheng saltmarsh wetland surface coverage is constructed,followed by the selection of sample points,calculation of characteristic indexes,and classification of surface features;Then,the time harmonic analysis method is used to analyze the change characteristics of normalized vegetation index(NDVI)of saltmarsh vegetation,and determine the phenological differences of the three types of saltmarsh vegetation;Finally,based on the phenological characteristics,random forest(RF)is used to extract the land cover information of saltmarsh vegetation in Yancheng coastal wetland in recent 20 years.The results show that:(1)compared with the traditional monitoring method,our proposed wetland vegetation extraction method can effectively subdivide and monitor the vegetation.(2)From 2000 to 2020,the area of reed and Spartinaflora showed a trend of expansion,while the area of alkali canopy was constantly decreasing.(3)The NDVI values of the three typical salt marsh vegetation in Yancheng show different changing characteristics.(4)Precipitation has a significant impact on the vegetation growth of salt marsh,while temperature has little influence on the growth of salt marsh vegetation.The results provide scientific support for the protection of natural heritage of Yancheng marsh wetland and the sustainable development of wetland ecology.
Google Earth Enginesaltmarsh vegetationfeature extractionrandom forestharmonic analysis of time series
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