前言：主要介绍Modis下的ET数据的获取和下载（日数据、月数据、年数据的下载）。

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1 ET(蒸散量)

土壤蒸发和植物蒸腾的总耗水量，植物群落蒸散量和CO2交换量的测定方法多种多样.该文以水分、CO2动态的区域性整合为目标,开创了一种新的、同时测定群落蒸散量和CO2交换量的方法–LI-6262 CO2/H2O分析仪接气室法.
注意：Modis下的ET数据属于红外遥感法获得。

2 MOD16A2(500米/8天)

2.1 MOD16A2下的所有指数

MOD16A2主要有ET、LE等指数。

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset = ee.ImageCollection("MODIS/006/MOD16A2")
.filter(ee.Filter.date('2020-01-01', '2020-12-31'))
.filterBounds(geometry);
print(dataset);

2.2 ET影像获取和查看

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset = ee.ImageCollection("MODIS/006/MOD16A2")
.filter(ee.Filter.date('2001-01-01', '2001-12-31'))
.filterBounds(geometry)
.select('ET');
print(dataset);
var colorizedVis = {min: 0.0,  max: 1.0,  palette: ['FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718', '74A901', '66A000', '529400', '3E8601', '207401', '056201', '004C00', '023B01',  '012E01', '011D01', '011301']};
Map.addLayer(dataset.mean().clip(geometry), colorizedVis, 'ET');

3 ET日数据下载(以MOD16A2为例)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset = ee.ImageCollection("MODIS/006/MOD16A2")
.filter(ee.Filter.date('2020-01-01', '2020-12-31'))
.filterBounds(geometry)
.select('ET');

var colorizedVis = {min: 0.0,  max: 1.0,  palette: ['FFFFFF', 'CE7E45', 'DF923D', 'F1B555', 'FCD163', '99B718', '74A901', '66A000', '529400', '3E8601', '207401', '056201', '004C00', '023B01',  '012E01', '011D01', '011301']};

function exportImageCollection(imgCol) {
  var indexList = imgCol.reduceColumns(ee.Reducer.toList(), ["system:index"]).get("list");
  indexList.evaluate(function(indexs) {
    for (var i=0; i<indexs.length; i++) {
      var image = imgCol.filter(ee.Filter.eq("system:index", indexs[i])).first();
      image = image.clip(geometry);
      Map.addLayer(image, colorizedVis, indexs[i]);//查看具体的遥感影像
      //tif数据下载
      Export.image.toDrive({
        image: image,
        description: 'modis_et_'+indexs[i],
        fileNamePrefix: 'modis_et_'+indexs[i],
        folder: 'Modis',
        region: geometry,
        scale: 500,
        crs: "EPSG:4326",
        maxPixels: 1e13
      });
    }
  });
}
exportImageCollection(dataset);

4 ET月数据下载(以MOD16A2为例)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
var dataset = ee.ImageCollection("MODIS/006/MOD16A2");
for(var i=2018;i<=2020;i++){
  for(var j=1;j<=12;j++){
    var data_collection = null;
    switch(j){
      case 1:
      case 3:
      case 5:
      case 7:
      case 8:
      case 10:
      case 12:
        data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-31').select('ET');
        break;
      case 4:
      case 6:
      case 9:
      case 11:
        data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-30').select('ET');
        break;
      case 2:
        data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-28').select('ET');
        break;
    }
    var YR_collection = data_collection.mean().clip(geometry);
    Export.image.toDrive({
      image: YR_collection,
      description: i+'-'+j,
      fileNamePrefix: i+'-'+j,
      scale: 500,
      region: geometry,
      maxPixels: 1e13,
      folder: 'Modis'
    })
  }
}

5 ET年数据下载(以MOD16A2为例)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
var dataset = ee.ImageCollection("MODIS/006/MOD16A2");
for(var i=2018;i<=2020;i++){
  var data_collection = dataset.filterDate(i+'-01-01',i+'-12-31').select('ET');
  // print(data_collection)
  var YR_collection = data_collection.mean().clip(geometry);
  Export.image.toDrive({
    image: YR_collection,
    description: i,
    fileNamePrefix: i,
    scale: 500,
    region: geometry,
    maxPixels: 1e13,
    folder: 'Modis'
  });
}