GEE开发之降雨(CHIRPS)数据获取和分析

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前言：主要获取和分析UCSB-CHG/CHIRPS/DAILY的日数据、月数据和年数据。

1.数据介绍

• 数据集： CHIRPS Daily: Climate Hazards Group InfraRed Precipitation With Station Data (Version 2.0 Final)
• 数据说明： Climate Hazards Group InfraRed Precipitation with Station data (CHIRPS) 是一个记录了1981年到当前全球降雨量的数据集。CHIRPS将0.05°分辨率的卫星图像与in-situ站点数据结合，创建网格化的降雨时间序列，用于趋势分析和季节性干旱监测。

2.初识CHIRPS

2.1 代码一

var geometry = ee.FeatureCollection('users/www/luyixian'); var dataset = ee.ImageCollection('UCSB-CHG/CHIRPS/DAILY') .filterDate('2020-01-01', '2020-12-31') .filterBounds(geometry) .select('precipitation'); print(dataset) 

2.2 代码二

var geometry = ee.FeatureCollection('users/www/luyixian'); Map.centerObject(geometry,7); var dataset = ee.ImageCollection('UCSB-CHG/CHIRPS/DAILY') .filterDate('2020-01-01', '2020-12-31') .filterBounds(geometry) .select('precipitation'); var precipitationVis = { 
    min: 1.0, max: 17.0, palette: ['001137', '0aab1e', 'e7eb05', 'ff4a2d', 'e90000'], }; Map.addLayer(dataset.mean().clip(geometry), precipitationVis, 'pre'); 

3.逐日数据分析和获取

var geometry = ee.FeatureCollection('users/www/luyixian'); Map.centerObject(geometry,7); var dataset = ee.ImageCollection('UCSB-CHG/CHIRPS/DAILY') .filterDate('2020-05-01', '2020-05-31') .filterBounds(geometry) .select('precipitation'); 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_'+indexs[i], fileNamePrefix: 'pre_'+indexs[i], folder: 'pre', region: geometry, scale: 1000, crs: "EPSG:4326", maxPixels: 1e13 }); } }); } exportImageCollection(dataset); 

4.逐月数据分析和获取

4.1 代码一

var geometry = ee.FeatureCollection('users/www/luyixian'); var dataset = ee.ImageCollection('UCSB-CHG/CHIRPS/DAILY').filterBounds(geometry).select('precipitation'); //时间范围 var years = ee.List.sequence(2020, 2020); 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')) .sum().set('year', y).set('month', m).set('system:time_start', ee.Date.fromYMD(y, m, 1)); }); }).flatten()); print(monthlysum); print(ui.Chart.image.series(monthlysum, 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(monthlysum); 

4.2 代码二(简洁)

var geometry = ee.FeatureCollection('users/www/luyixian'); Map.centerObject(geometry,6); var dataset =ee.ImageCollection("UCSB-CHG/CHIRPS/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('precipitation'); break; case 4: case 6: case 9: case 11: data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-30').select('precipitation'); break; case 2: data_collection = dataset.filterDate(i+'-'+j+'-01',i+'-'+j+'-28').select('precipitation'); break; } var YR_collection = data_collection.sum().clip(geometry); Export.image.toDrive({ 
    image: YR_collection, description: i+'-'+j, fileNamePrefix: i+'-'+j, scale: 1000, region: geometry, maxPixels: 1e13, folder: 'pre' }) } } 

5.逐年数据分析和获取

5.1 代码一

var geometry = ee.FeatureCollection('users/www/luyixian'); // 选择数据集并进行波段比例换算 var collection = ee.ImageCollection("UCSB-CHG/CHIRPS/DAILY").filterDate('2000-01-01', '2020-12-31').select("precipitation"); //进行年平均值的计算 var years = ee.List.sequence(2000, 2020); 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.sum()).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('precipitation_sum'), region: geometry, reducer: ee.Reducer.mean(), scale: 500, xProperty: 'year', }).setOptions({ 
    interpolateNulls: true, lineWidth: 2, title: 'pre Yearly Seires', vAxis: { 
   title: 'pre'}, hAxis: { 
   title: 'Date'}, }); 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: 'pre_'+indexs[i], fileNamePrefix: 'pre_'+indexs[i], folder: 'pre', region: geometry, scale: 1000, crs: "EPSG:4326", maxPixels: 1e13 }); } }); } exportImageCollection(collectYear); 

5.2 代码二(简洁)

var geometry = ee.FeatureCollection('users/www/luyixian'); Map.centerObject(geometry,6); var dataset =ee.ImageCollection("UCSB-CHG/CHIRPS/DAILY"); for(var i=2018;i<=2020;i++){ 
    var data_collection = dataset.filterDate(i+'-01-01',i+'-12-31').select('precipitation'); print(data_collection) var YR_collection = data_collection.sum().clip(geometry); Export.image.toDrive({ 
    image: YR_collection, description: i, fileNamePrefix: i, scale: 1000, region: geometry, maxPixels: 1e13, folder: 'pre' }); }