今天分享一下如何用MNDWI水体指数来提取研究区的水体，主要使用的数据为landsat8
GEE代码如下：
var roi = ee.Geometry.Polygon([[[118.78042247007194, 32.632228406133],[118.78042247007194, 30.819493246253046],[120.90078379819694, 30.819493246253046],[120.90078379819694, 32.632228406133]]], null, false);Map.centerObject(roi,7)var styling = {color:"red",fillColor:"00000000"};// reomove cloud for Landsat-8function rmL8Cloud(image) { var cloudShadowBitMask = (1 << 3); var cloudsBitMask = (1 << 5); var qa = image.select('pixel_qa'); var mask = qa.bitwiseAnd(cloudShadowBitMask).eq(0) .and(qa.bitwiseAnd(cloudsBitMask).eq(0));var mask2 = image.select('B1').gt(2000);return image.updateMask(mask).updateMask(mask2.not()).copyProperties(image).copyProperties(image, ["system:time_start",'system:time_end']);} var l8_sr = ee.ImageCollection("LANDSAT/LC08/C01/T1_SR").map(rmL8Cloud).filter(ee.Filter.lte('CLOUD_COVER',5))//云量过滤;//MNDWI水体指数function calcWater(image) {var MNDWI = image.select("MNDWI");var NDVI = image.select("NDVI");var EVI = image.select("EVI");var water = EVI.lt(0.1).and(MNDWI.gt(NDVI).or(MNDWI.gt(EVI)));return image.addBands(water.rename("water"));}var Landsat8 = {scaleImage: function(image) {var time_start = image.get("system:time_start");image = image.select(["B2","B3","B4","B5","B6","B7"]);image = image.divide(10000);image = image.set("system:time_start", time_start);return image;},srCloudMask: function(image) {var cloudShadowBitMask = (1 << 3);var snowBitMask = (1 << 4);var cloudsBitMask = (1 << 5);var qa = image.select('pixel_qa');var mask = qa.bitwiseAnd(cloudShadowBitMask).eq(0).and(qa.bitwiseAnd(snowBitMask).eq(0)).and(qa.bitwiseAnd(cloudsBitMask).eq(0));return image.updateMask(mask);},//NDVINDVI: function(image) {return image.addBands(image.normalizedDifference(["B5", "B4"]).rename("NDVI"));},//MNDWIMNDWI: function(image) {return image.addBands(image.normalizedDifference(["B3", "B6"]).rename("MNDWI"));},// EVIEVI: function(image) {var evi = image.expression("EVI = 2.5 * (NIR - R) / (NIR + 6*R -7.5*B + 1)", {NIR: image.select("B5"),R: image.select("B4"),B: image.select("B2")});return image.addBands(evi);},/*获取Landsat8的SR数据*/getL8SRCollection : function(startDate, endDate, roi) {var dataset = l8_sr.filterDate(startDate, endDate).filterBounds(roi).map(Landsat8.srCloudMask).map(Landsat8.scaleImage).map(Landsat8.NDVI).map(Landsat8.MNDWI).map(Landsat8.EVI).map(calcWater).select("water");return dataset;}};//exportfunction exportImageToDrive(image, key, roi) {Export.image.toDrive({image: image, description: "Water"+key,fileNamePrefix: key, region: roi,scale: 30,maxPixels: 1e13});}//去掉阴影function removeShadow(image, roi) {var hand = ee.ImageCollection('users/gena/global-hand/hand-100');var hand30 = hand.mosaic().focal_mean(0.1).rename('elevation');var hillShadowMask = hand30.select('elevation').lte(50);var waterMask = image.updateMask(hillShadowMask.and(image.gte(0.8))).gte(0.25).clip(roi);waterMask = waterMask.connectedPixelCount(50, true);waterMask = waterMask.updateMask(waterMask.gte(50));return image.updateMask(waterMask);}//生成每一年的水体 function processYearWaterImage(year, roi) {var startDate = ee.Date.fromYMD(year, 1, 1);var endDate = ee.Date.fromYMD(year+1, 1, 1);var l8Water = Landsat8.getL8SRCollection(startDate, endDate, roi);var waterImgs = l8Water/*计算水体的频率*/var waterImg = waterImgs.sum().divide(waterImgs.count()).clip(roi);waterImg = waterImg.updateMask(waterImg).clip(roi);var key = "landsatWater-"+year;Map.addLayer(waterImg, {min:0,max:1,palette:['000000','blue']}, "water"+key, true);exportImageToDrive(waterImg, key, roi);print('waterImgs_'+year,waterImgs);var stats2 = waterImg.reduceRegion({reducer: ee.Reducer.sum(),geometry: roi,scale: 30,maxPixels: 1e13});print(stats2,year)}//循环导出所有的水体function main() {//开始年份和结束年份var startYear = ;var endYear = ;for (var year=startYear; year<=endYear; year++) {processYearWaterImage(year, roi);}}
提取结果展示：
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