使用GEE获取遥感影像非常迅速便捷。今天主要学习一下如何获取一定时间段的去云哨兵2和Landsat8影像。

废话不多说，直接上代码。直接将矢量区域换成自己研究区即可。

获取并下载Landsat8影像代码如下

var region=ee.FeatureCollection('projects/ee-huiengine/assets/beijing');



function maskL8sr(image) {
  // The third bit is cloud and the fourth bit is cloudshadow。
  var cloudShadowBitMask = 1 << 4;
  var cloudsBitMask = 1 << 3;

  // Get QA_PIXEL band.
  var qa = image.select('QA_PIXEL');

  // Set the cloud mask to zero
  var mask = qa.bitwiseAnd(cloudShadowBitMask).eq(0)
      .and(qa.bitwiseAnd(cloudsBitMask).eq(0));

  // Update the cloudmask
  return image.updateMask(mask)
      .select("SR_B.*")
      .copyProperties(image, ["system:time_start"]);
}

// Map the function over 3 months of data and take the median.
// Load Landsat-8 surface reflectance data.
var landsat8 = ee.ImageCollection("LANDSAT/LC08/C02/T1_L2")
		.filterBounds(region)
              .filterDate('2020-12-01','2021-2-28')
              // Pre-filter to get less cloudy granules.
              .filter(ee.Filter.lte('CLOUD_COVER',5))
              .map(maskL8sr)
              .median()
              .clip(region);
landsat8 = landsat8.uint16();
print(landsat8);// visualize the datasets
var rgbVis = {
  min: 8400,
  max: 15000,
  gamma:1.5,
  bands: ['SR_B4', 'SR_B3', 'SR_B2'],
};

Map.addLayer(landsat8,rgbVis,'landsat8');
var Landsat_collection = landsat8.select('SR_B2','SR_B3','SR_B4','SR_B5');

//Export image to google drive and then download

Export.image.toDrive({
  image:Landsat_collection,
  description:'s4',
  scale:30,
  region:region,
  folder:"result",
  crs: "EPSG:4326",
  maxPixels: 1e13
});

获取并下载Sentinel-2影像代码如下

//define your study area here!
var studyarea = table;
Map.addLayer(studyarea)

//prepare sentinel imagecollection/;
/**
 * Function to mask clouds using the Sentinel-2 QA band
 * @param {ee.Image} image Sentinel-2 image
 * @return {ee.Image} cloud masked Sentinel-2 image
 */
function maskS2clouds(image) {
  var qa = image.select('QA60');
  // Bits 10 and 11 are clouds and cirrus, respectively.
  var cloudBitMask = 1 << 10;
  var cirrusBitMask = 1 << 11;
  // Both flags should be set to zero, indicating clear conditions.
  var mask = qa.bitwiseAnd(cloudBitMask).eq(0)
      .and(qa.bitwiseAnd(cirrusBitMask).eq(0));
  return image.updateMask(mask).divide(10000);
}  //去云处理


var dataset = ee.ImageCollection('COPERNICUS/S2_SR')
                  .filterDate('2020-01-01', '2020-12-31')   //影像时间
                  // Pre-filter to get less cloudy granules.
                  .filter(ee.Filter.lt('CLOUDY_PIXEL_PERCENTAGE',20))  //云量
                  .map(maskS2clouds)  //去云
                  .map(function(image) {
                   var ndvi = image.normalizedDifference(['B8', 'B4']).rename('B5');
                   return image.addBands(ndvi);
                   })   //添加指数
                   .map(function(image){
                   var B1 = image.select("B2").rename("B1");//blue
                   var B2 = image.select("B3").rename("B2");//green
                   var B3 = image.select("B4").rename("B3");//red
                   var B4 = image.select("B8").rename("B4");//nir
                   return image.addBands(B1)
                               .addBands(B2)
                               .addBands(B3)
                               .addBands(B4)
                   })  //重命名
                   .select(["B1","B2","B3","B4","B5"/*,"B6","B7","B8","B9"*/]);  //影像集
                   
var study_img = dataset.median().clip(studyarea);  //中值影像，裁剪出研究区影像
Map.addLayer(study_img, {bands:["B4", "B3", "B2"], min:0, max:0.3}, 'RGB');

//导出哨兵2号影像数据
Export.image.toDrive({
  image:study_img.select(["B1","B2","B3","B4","B5"]),
  description:"sentinel2_region",
  region:studyarea,
  scale:10,
  maxPixels:1e13
})