本文記錄了在GEE（GoogleEarthEngine）平臺(tái)上，使用UCSB-CHG/CHIRPS/DAILY數(shù)據(jù)集，繪制一個(gè)指定點(diǎn)的一段時(shí)間內(nèi)的降水量累計(jì)值折線圖的代碼，也記錄了繪制一個(gè)區(qū)域一段時(shí)間內(nèi)的降水量均值的折線圖代碼。其中累積降水量使用每日數(shù)據(jù)累積，降水量均值折線圖使用的是每周的降水量數(shù)據(jù)。即本文記錄了將影像集合按天 ‘day’ 合成和按周 ‘week’ 合成的方法。

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文章目錄

• • • 一、累積降雨量折線圖
    • • • 結(jié)果展示
        • 代碼實(shí)現(xiàn)
    • 二、降水量均值折線圖繪制
    • • • 結(jié)果展示
        • 代碼實(shí)現(xiàn)

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一、累積降雨量折線圖

操作對(duì)象：一個(gè)點(diǎn)
研究區(qū)：一個(gè)點(diǎn)的緩沖區(qū)
累計(jì)值：一個(gè)點(diǎn)一段時(shí)期內(nèi)降水量的累積值

結(jié)果展示

代碼實(shí)現(xiàn)

var chirpsDaily = ee.ImageCollection("UCSB-CHG/CHIRPS/DAILY");// 定義時(shí)間區(qū)間 var startDate = ee.Date('2020-06-01') var endDate = ee.Date('2020-09-30')var days = endDate.difference(startDate, 'day') var daysList = ee.List.sequence(1, days)// Map()在天列表上的函數(shù) var cumulativeImages = daysList.map(function(day) {// 篩選從開(kāi)始日期到計(jì)算當(dāng)天的集合var begin = startDatevar current = startDate.advance(day, 'day')var filtered = chirpsDaily.filter(ee.Filter.date(begin, current))// 使用sum()計(jì)算該時(shí)期的總降雨量// 確保設(shè)置了圖像的start_timevar cumulativeImage = filtered.reduce(ee.Reducer.sum()).set('system:time_start', current.millis())return cumulativeImage })// 把包含累積降雨的圖像列表收集起來(lái) var cumulativeCol = ee.ImageCollection.fromImages(cumulativeImages)// 創(chuàng)建一個(gè)上海的點(diǎn) var point = ee.Geometry.Point(121.1649, 31.0614)// 累積降雨量圖繪制 var chart = ui.Chart.image.series({imageCollection: cumulativeCol, region: point, reducer: ee.Reducer.mean(), scale: 5566, }).setOptions({interpolateNulls: true,lineWidth: 1,pointSize: 3,title: 'Cumulative Monsoon Rainfall at Shanhai (2020)',vAxis: {title: 'Cumulative Rainfall (mm)'},hAxis: {title: 'Month', format: 'YYYY-MMM'}}); print(chart);Map.setCenter(121.1649, 31.0614, 12); Map.addLayer(point, {}, 'point');

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二、降水量均值折線圖繪制

操作對(duì)象：整個(gè)影像
研究區(qū)：一個(gè)矩形區(qū)域
均值：整個(gè)影像的均值

結(jié)果展示

代碼實(shí)現(xiàn)

var roi = ee.Geometry.Rectangle({coords: [[120, 30], [122, 32]],geodesic: false }); Map.addLayer(roi); Map.centerObject(roi,7)var yrly_rain = ee.ImageCollection('UCSB-CHG/CHIRPS/DAILY') .filter(ee.Filter.calendarRange(2019, 2019, 'year')).sum().clip(roi) print(yrly_rain) Map.addLayer(yrly_rain,{},'Yrly Rainfall')var chirps = ee.ImageCollection('UCSB-CHG/CHIRPS/DAILY') // .filter(ee.Filter.calendarRange(2019, 2019, 'year'))print(chirps.limit(500))var weeks = ee.List.sequence(1,52) //print(weeks)var startD = ee.Date.fromYMD(2019,01,01)var wkrf = function(Week) {var weekStartD = startD.advance (Week,'week')var weekEndD = weekStartD.advance(1, 'week')var wk = chirps.filterDate(weekStartD,weekEndD).sum().clip(roi)return wk.set({'Week': ee.Number(Week)}) }var wk_rf = weeks.map(wkrf) var wk_rfcoll = ee.ImageCollection.fromImages(wk_rf) print(wk_rfcoll);var wkrf_series = ui.Chart.image.series({imageCollection:wk_rfcoll, region: roi, reducer:ee.Reducer.mean(), scale:5000, xProperty:'Week' }) print(wkrf_series) Map.addLayer(wk_rfcoll,{},'wkly Rainfall')

總結(jié)

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