Google Earth Engine（GEE）提取水体
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-8
function 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);
},
//NDVI
NDVI: function(image) {
return image.addBands(image.normalizedDifference(["B5", "B4"])
.rename("NDVI"));
},
//MNDWI
MNDWI: function(image) {
return image.addBands(image.normalizedDifference(["B3", "B6"])
.rename("MNDWI"));
},
// EVI
EVI: 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;
}
};
//export
function 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 = 2014;
var endYear = 2021;
for (var year=startYear; year<=endYear; year++) {
processYearWaterImage(year, roi);
}
}
提取结果展示：
感谢关注，欢迎转发！
声明：仅供学习使用！如果对你有帮助的话记得给小编点个赞