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A monthly composite can be made using the following code, I take example from Sentinel 2 L1C:

var geometry = ee.Geometry.Point([109.061, 11.78]); 
var col = ee.ImageCollection('COPERNICUS/S2')
          .filterBounds(geometry).filterDate('2018-01-01','2019-01-01');
//Monthly Images
var months = ee.List.sequence(1,12);
var years = ee.List.sequence(2018,2018); 
// monthly composite
var monthlyImages =  ee.ImageCollection.fromImages(
  years.map(function (y) {
  return months.map(function(m){
  var w = col.select('B1').filter(ee.Filter.calendarRange(y, y, 'year'))
           .filter(ee.Filter.calendarRange(m, m, 'month'))
           .mean()
           //.median()
           //.min()
           .set('system:time_start',ee.Date.fromYMD(y,m,1));
  return w.set('year', y)
           .set('month', m)
           .set('date', ee.Date.fromYMD(y,m,1))
           .set('system:time_start',ee.Date.fromYMD(y,m,1)) 

});
}).flatten());

print(monthlyImages)

How do I do a decadal composite (every 10 days)?

3

First make a ten day interval list:

// settings for the years to filter on
var interval = 10;
var increment = 'day';
var start = '2018-01-01';
// make a list of start years
var startDate = ee.Date(start);
var secondDate = startDate.advance(interval, increment).millis();
var increase = secondDate.subtract(startDate.millis());
var list = ee.List.sequence(startDate.millis(), ee.Date('2019-01-01').millis(), increase);

Then map over that list and filter to get images in that daterange:

// monthly composite
var tenDaysMeans =  ee.ImageCollection.fromImages(list.map(function(date){
  return col.select('B1').filterDate(ee.Date(date), ee.Date(date).advance(interval, increment))
           .mean().set('system:time_start',ee.Date(date).millis());
}));

print(tenDaysMeans)

As a side note, sentinel-2 has a five-day return period, so within a 10 day composite you will possibly have too less images to create meaningfull composites.

link code

| improve this answer | |
  • works perfectly. Thanks @Kiuk very much! – Minh Shines May 7 '19 at 9:10

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