GEE开发之降雨(CHIRPS)数据获取和分析

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

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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/www1573979951/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/www1573979951/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/www1573979951/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/www1573979951/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/www1573979951/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/www1573979951/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/www1573979951/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'});
}