基于GEE平台，选取Sentinel-2数据，对研究区2016-2024年植被覆盖度（FVC）进行监测分析。先通过云雪掩膜和最大合成法计算归一化植被指数（NDVI）。然后采用像元二分法，利用NDVI的5%和95%分位数确定区域内植被与裸土的NDVI极值，从而计算FVC。
var geometry = table;Map.centerObject(geometry, 7);var colorizedVis = {min: 0,max: 1,palette: ['blue', 'white', 'green'],};function maskS2clouds(image) {var qa = image.select('QA60');var mask = qa.bitwiseAnd(1 << 10).eq(0).and(qa.bitwiseAnd(1 << 11).eq(0)).and(qa.bitwiseAnd(1 << 12).eq(0));return image.updateMask(mask).divide(10000).set(image.toDictionary(image.propertyNames()));}function createNDVI(image) {return image.addBands(image.normalizedDifference(["B8", "B4"]).rename('NDVI'));}var S2_COL = ee.ImageCollection("COPERNICUS/S2_HARMONIZED").filterDate("2016-01-01", "2024-12-31").filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE', 20)).filterBounds(geometry).map(maskS2clouds).map(createNDVI).select('NDVI');function calculateFVC(NDVI, region, scale) {var percentile = NDVI.reduceRegion({reducer: ee.Reducer.percentile([5, 95]),geometry: region,scale: scale,maxPixels: 1e13});var NDVI_min = ee.Number(percentile.get('NDVI_p5'));var NDVI_max = ee.Number(percentile.get('NDVI_p95'));var FVC = NDVI.subtract(NDVI_min).divide(NDVI_max.subtract(NDVI_min)).clamp(0, 1).rename('FVC');return FVC;}var years = ee.List.sequence(2016, 2024);var fvcList = [];function exportAnnualFVC(year) {var annualNDVI = S2_COL.filter(ee.Filter.calendarRange(year, year, 'year')).max().set('year', year).set('system:time_start', ee.Date.fromYMD(year, 1, 1));var annualFVC = calculateFVC(annualNDVI, geometry, 20);var fvcMean = annualFVC.reduceRegion({reducer: ee.Reducer.mean(),geometry: geometry,scale: 20,maxPixels: 1e13}).get('FVC');fvcList.push(fvcMean);Map.addLayer(annualFVC.clip(geometry), colorizedVis, 'FVC_' + year);Export.image.toDrive({image: annualFVC.clip(geometry),description: 'FVC_' + year,fileNamePrefix: 'FVC_' + year,folder: 'sentinel_FVC',region: geometry,scale: 20,crs: "EPSG:4326",maxPixels: 1e13});}years.getInfo().forEach(exportAnnualFVC);
