GEE开发之ERA5（气温、降水、压力、风速等）数据获取和分析

前言：ERA5主要提供DAILY和MONTHLY两大类别数据，其中主要包括“mean_2m_air_temperature"、“minimum_2m_air_temperature”、“maximum_2m_air_temperature”、“dewpoint_2m_temperature”、“total_precipitation”、“surface_pressure”、“mean_sea_level_pressure”、“u_component_of_wind_10m”、"v_component_of_wind_10m"数据。
本博客参考《 GEE数据集：ERA5 每日汇总 - 由 ECMWF / Copernicus Climate Change Service制作的最新气候再分析数据集》

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1.ERA5介绍

• ERA5是ECMWF（欧洲中期天气预报中心）对全球气候的第五代大气再分析。再分析将模型数据与来自世界各地的观测数据结合起来，形成一个全球完整的、一致的数据集。ERA5取代了其前身ERA-Interim再分析。
• ERA5 DAILY提供每天7个ERA5气候再分析参数的汇总值：2米空气温度、2米露点温度、总降水量、平均海平面气压、表面气压、10米u风分量和10米v风分量。（参数较多，其他参数可自行查看）此外，根据每小时的2米空气温度数据，计算出2米处的每日最低和最高空气温度。每日总降水值以每日总和给出。所有其他参数都以日平均数提供。
• ERA5 MONTHLY提供的都是月数据。
• ERA5的数据从1979年到实时的三个月都有。
• 空间分辨率：0.1°×0.1°
• 时间跨度：1950年1月-至今

2.初始ERA5数据

2.1 DAILY代码

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
var dataset = ee.ImageCollection('ECMWF/ERA5/DAILY')
.filterDate('2019-01-01', '2019-12-31')
.filterBounds(geometry);
print(dataset)

2.2 MONTHLY代码

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
var dataset = ee.ImageCollection('ECMWF/ERA5/MONTHLY')
.filterDate('2019-01-01', '2019-12-31')
.filterBounds(geometry);
print(dataset)

3.遥感影像查看（DAILY之mean_2m_air_temperature）

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,7);
var dataset = ee.ImageCollection('ECMWF/ERA5/DAILY').select('mean_2m_air_temperature')
.filterDate('2019-05-01', '2019-05-31')
.filterBounds(geometry);

var vis2mt = {
  min: 250,
  max: 320,
  palette: [
    '#000080', '#0000D9', '#4000FF', '#8000FF', '#0080FF', '#00FFFF', '#00FF80',
    '#80FF00', '#DAFF00', '#FFFF00', '#FFF500', '#FFDA00', '#FFB000', '#FFA400',
    '#FF4F00', '#FF2500', '#FF0A00', '#FF00FF'
  ]
}

Map.addLayer(dataset.mean().clip(geometry), vis2mt,'mean_2m_air_temperature');

4.逐日数据分析和获取(以mean_2m_air_temperature为例)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,7);
var dataset = ee.ImageCollection('ECMWF/ERA5/DAILY')
.filterDate('2018-05-01', '2018-05-31')
.filterBounds(geometry)
.select('mean_2m_air_temperature');
//换算单位 
var subtract= function(image){ 
 var img = image.subtract(273.15);  
 return img.set('system:time_start',image.get('system:time_start'));
};
dataset = dataset.map(subtract);//mean_2m_air_temperature1 开氏度(开尔文)=-272.15 摄氏度
print(ui.Chart.image.series(dataset, geometry, ee.Reducer.mean(), 1000));
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);
      //tif数据下载
      Export.image.toDrive({
        image: image,
        description: 'mean_2m_air_temperature_'+indexs[i],
        fileNamePrefix: 'mean_2m_air_temperature_'+indexs[i],
        folder: 'mean_2m_air_temperature',
        region: geometry,
        scale: 1000,
        crs: "EPSG:4326",
        maxPixels: 1e13
      });
    }
  });
}
exportImageCollection(dataset);

5.逐月数据分析和获取(以mean_2m_air_temperature为例)

5.1 代码一（ERA5/MONTHLY）

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,7);
var dataset = ee.ImageCollection('ECMWF/ERA5/MONTHLY')
.filterDate('2018-01-01', '2018-12-31')
.filterBounds(geometry)
.select('mean_2m_air_temperature');
//换算单位 
var subtract= function(image){ 
 var img = image.subtract(273.15);  
 return img.set('system:time_start',image.get('system:time_start'));
};
dataset = dataset.map(subtract);//mean_2m_air_temperature1 开氏度(开尔文)=-272.15 摄氏度
print(ui.Chart.image.series(dataset, geometry, ee.Reducer.mean(), 1000));
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);
      //tif数据下载
      Export.image.toDrive({
        image: image,
        description: 'mean_2m_air_temperature_'+indexs[i],
        fileNamePrefix: 'mean_2m_air_temperature_'+indexs[i],
        folder: 'mean_2m_air_temperature',
        region: geometry,
        scale: 1000,
        crs: "EPSG:4326",
        maxPixels: 1e13
      });
    }
  });
}
exportImageCollection(dataset);

5.2 代码二（ERA5/DAILY）

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
var dataset = ee.ImageCollection('ECMWF/ERA5/DAILY').filterBounds(geometry).select('mean_2m_air_temperature');
//时间范围
var years = ee.List.sequence(2018, 2018);
var months = ee.List.sequence(1, 12);

//将逐日数据生成月平均数据
var monthlysum =  ee.ImageCollection.fromImages(
  years.map(function (y) {
    return months.map(function(m) {
      return dataset.filter(ee.Filter.calendarRange(y,y, 'year'))
      .filter(ee.Filter.calendarRange(m, m, 'month'))
      .mean().set('year', y).set('month', m).set('system:time_start', ee.Date.fromYMD(y, m, 1));
    });
  }).flatten());

//换算单位 
var subtract= function(image){ 
 var img = image.subtract(273.15);  
 return img.set('system:time_start',image.get('system:time_start'));
};
dataset = monthlysum.map(subtract);//mean_2m_air_temperature1 开氏度(开尔文)=-272.15 摄氏度

print(dataset);
print(ui.Chart.image.series(dataset, geometry, ee.Reducer.mean(), 1000));

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);
      //tif数据下载
      Export.image.toDrive({
        image: image,
        description: 'pre_2020_'+indexs[i],
        fileNamePrefix: 'pre_2020_'+indexs[i],
        folder: 'pre',
        region: geometry,
        scale: 1000,
        crs: "EPSG:4326",
        maxPixels: 1e13
      });
    }
  });
}
exportImageCollection(dataset);

5.3 代码三（ERA5/DAILY）

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset =ee.ImageCollection("ECMWF/ERA5/DAILY");
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('mean_2m_air_temperature');
        break;
      case 4:
      case 6:
      case 9:
      case 11:
        data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-30').select('mean_2m_air_temperature');
        break;
      case 2:
        data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-28').select('mean_2m_air_temperature');
        break;
    }
    var YR_collection = data_collection.mean().subtract(273.15).clip(geometry);//mean_2m_air_temperature1 开氏度(开尔文)=-272.15 摄氏度
    Export.image.toDrive({
      image: YR_collection,
      description: i+'-'+j,
      fileNamePrefix: i+'-'+j,
      scale: 1000,
      region: geometry,
      maxPixels: 1e13,
      crs: "EPSG:4326",
      folder: 'mean_2m_air_temperature'
    })
  }
}

6.逐年数据分析和获取(以mean_2m_air_temperature为例)

6.1 代码一（ERA5/MONTHLY）

 var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
// 选择数据集并进行波段比例换算
var collection = ee.ImageCollection("ECMWF/ERA5/MONTHLY").filterDate('2000-01-01', '2010-12-31').select("mean_2m_air_temperature");
//换算单位
var subtract = function(image){ 
  var img = image.subtract(273.15);  
  return img.set(image.toDictionary(image.propertyNames()));
};
collection = collection.map(subtract);
//进行年平均值的计算
var years = ee.List.sequence(2000, 2010);
var collectYear = ee.ImageCollection(years
  .map(function(y) {
    var start = ee.Date.fromYMD(y, 1, 1);
    var end = start.advance(12, 'month');
    return collection.filterDate(start, end).reduce(ee.Reducer.mean()).float().set('system:time_start',y).set('year',y);
}));
print(collectYear);

//年均值的时间序列展示
var Yearly_chart = ui.Chart.image.series({
    imageCollection: collectYear.select('mean_2m_air_temperature_mean'),
    region: geometry,
    reducer: ee.Reducer.mean(),
    scale: 500,
    xProperty: 'year',
    }).setOptions({
      interpolateNulls: true,
      lineWidth: 2,
      title: 'temperature Yearly Seires',
      vAxis: {title: 'temperature'},
      hAxis: {title: 'Date'},
      //trendlines: { 0: {title: 'NDVI_trend',type:'linear', showR2: true,  color:'red', visibleInLegend: true}}
    });
print(Yearly_chart);
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);
      //tif数据下载
      Export.image.toDrive({
        image: image,
        description: 'mean_2m_air_temperature_mean'+indexs[i],
        fileNamePrefix: 'mean_2m_air_temperature_mean'+indexs[i],
        folder: 'tem',
        region: geometry,
        scale: 1000,
        crs: "EPSG:4326",
        maxPixels: 1e13
      });
    }
  });
}
exportImageCollection(collectYear);

6.2 代码二（ERA5/DAILY）

在6.1的基础上把MONTHLY改成DAILY即可

6.3 代码三 （ERA5/MONTHLY）(下载遥感影像推荐)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset=ee.ImageCollection("ECMWF/ERA5/MONTHLY");

for(var i=2010;i<=2015;i++){
  var data_collection = dataset.filterDate(i+'-01-01',i+'-12-31').select('mean_2m_air_temperature');
  print(data_collection)
  var YR_collection = data_collection.mean().subtract(273.15).clip(geometry);
  Export.image.toDrive({
    image: YR_collection,
    description: i,
    fileNamePrefix: i,
    scale: 1000,
    region: geometry,
    maxPixels: 1e13,
    crs: "EPSG:4326",
    folder: 'temperature'
  });
}

6.4 代码四（ERA5/DAILY）(下载遥感影像推荐)

var geometry = ee.FeatureCollection('users/www1573979951/luyixian');
Map.centerObject(geometry,6);
var dataset=ee.ImageCollection("ECMWF/ERA5/DAILY");

for(var i=2010;i<=2015;i++){
  var data_collection = dataset.filterDate(i+'-01-01',i+'-12-31').select('mean_2m_air_temperature');
  print(data_collection)
  var YR_collection = data_collection.mean().subtract(273.15).clip(geometry);
  Export.image.toDrive({
    image: YR_collection,
    description: i,
    fileNamePrefix: i,
    scale: 1000,
    region: geometry,
    maxPixels: 1e13,
    crs: "EPSG:4326",
    folder: 'temperature'
  });
}