如何在 Google Earth Engine 上的单个图中合并具有不同时间步长的时间序列数据集

Question

我目前正在尝试在同一张图表中绘制月度和年度土壤湿度的时间序列。我有一个 ImageCollection，它有 480 张图片（每月一张），另一个 ImageCollection 有 40 张图片（每年一张）。

我可以分别绘制它们，但我还没有找到将两个图堆叠在一个图表中的方法。我查找的一些选项是 (a) 预先执行 innerJoin()，但这会将每月收集的图片从 480 张缩减到 40 张图像，或者 (b) 用 Na 填充年度收集中的空白（类似于 fillNa with pandas), 但我想不出办法。

这是代码示例：

// --- GLOBALS ---

var dateStart = ee.Date('1980-01-01'); 
var dateEnd = ee.Date('2019-12-31');
var scale = 1000;
var studyArea = ee.FeatureCollection('TIGER/2018/States').filterMetadata('NAME', 'equals', 'Nevada');

var monthlySoil = ee.ImageCollection('IDAHO_EPSCOR/TERRACLIMATE') // Load data
                .filter(ee.Filter.date(dateStart, dateEnd))
                .select('soil');

// --- TIME SERIES ---

// Create list of dates for time series
var dateListYearly = ee.List.sequence(0,dateEnd.difference(dateStart,'year').round(),1);
var makeDateListYearly = function(n) {return dateStart.advance(n,'year')};
dateListYearly = dateListYearly.map(makeDateListYearly);

// Yearly data
var yearlySoil = [];
yearlySoil = dateListYearly.map(function(d){ // Resample yearly
  var start = ee.Date(d);
  var end = ee.Date(d).advance(1,'year');
  var dateRange = ee.DateRange(start,end);
  var yearlySoilInter = monthlySoil
                      .filterDate(dateRange)
                      .mean()
                      .clip(studyArea)
                      .rename('Yearly');
  return(yearlySoilInter.set('system:time_start', start.millis())); // Add time band
});
yearlySoil = ee.ImageCollection(yearlySoil);

// --- PLOT ---

var options1 = { // Monthly 
  title: 'SM Monthly',
  fontSize: 12,
  hAxis: {title: 'Date'},
  vAxis: {title: 'SM (mm)'},
  series: {0: {color: 'red'}}
};
print(ui.Chart.image.series(monthlySoil, studyArea, ee.Reducer.mean(), scale).setOptions(options1));

var options2 = { // Yearly 
  title: 'SM yearly',
  fontSize: 12,
  hAxis: {title: 'Date'},
  vAxis: {title: 'SM (mm)'},
  series: {0: {color: 'blue'}}
};
print(ui.Chart.image.series(yearlySoil, studyArea, ee.Reducer.mean(), scale).setOptions(options2));

和link：https://code.earthengine.google.com/1443f7796cd2d1527e4ca9fec145f4b7

Answer 1

与您用 NA 填补空白的想法类似，我向每个集合添加了一个空波段以匹配另一个集合中的相应波段。然后我把合集合并做了个图表。

s2sr = s2sr.filterBounds(roi).filter(ee.Filter.calendarRange(2020, 2020, 'year'))
l8sr = l8sr.filterBounds(roi).filter(ee.Filter.calendarRange(2020, 2020, 'year'))

// compute some bands to add to each collection
var addS2Bands = function(image){
  var s2nd = image.normalizedDifference(['B4','B3']).rename('s2_nd')
  var l8nd = ee.Image().rename('l8_nd') // must add an empty band for select() to work on all images
  return image.addBands(s2nd).addBands(l8nd)
}
var addL8Bands = function(image){
  var l8nd = image.normalizedDifference(['B4','B3']).rename('l8_nd')
  var s2nd = ee.Image().rename('s2_nd')
  return image.addBands(l8nd).addBands(s2nd)
}
l8sr = l8sr.map(addL8Bands)
s2sr = s2sr.map(addS2Bands)


// merge the collections
var merged = l8sr.merge(s2sr).select(['l8_nd', 's2_nd'])

// plot the collection
var chart = ui.Chart.image.series({
  imageCollection: merged,
  region: roi,
  reducer: ee.Reducer.mean(),
  scale: 30
})
print(chart)

https://code.earthengine.google.com/?scriptPath=users%2Fcaseyengstrom%2Freprex%3AuiChartMultiCollection

如何在 Google Earth Engine 上的单个图中合并具有不同时间步长的时间序列数据集

How to combine time-series datasets with different timesteps in a single plot on Google Earth Engine

javascript

plot

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google-earth-engine