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Question

I am trying to filter an ImageCollection by multiple time intervals (rain seasons) that change from year to year. Hence, I can't just use the ee.Filter.calendarRange.

I tried to merge the dates together and filter the collection but it does not work. What do I have to do?

var ROI = /* color: #0b4a8b */ee.Geometry.Polygon([
      [36.5048217773437, 0.560293804172086],
      [37.9302978515625, 0.560293804172086],
      [37.9302978515625, 1.875580463973453],
      [36.5048217773437, 1.875580463973453]
  ]);
    Map.centerObject(ROI,8);  

var s2 = ee.ImageCollection('COPERNICUS/S2')
  .filterBounds(ROI);

var longRain2016 = s2.filterDate('2025-08-04','2025-08-04');
var shortRain2016 = s2.filterDate('2025-08-04','2025-08-04');
var longRain2017 = s2.filterDate('2025-08-04','2025-08-04');
var shortRain2017 = s2.filterDate('2025-08-04','2025-08-04');
var longRain2018 = s2.filterDate('2025-08-04','2025-08-04');
var dateFilter = ee.ImageCollection(longRain2016.merge(shortRain2016).merge(longRain2017).merge(shortRain2017).merge(longRain2018));

var s2dateFilter = s2.filter(dateFilter);


var count = s2dateFilter.size();
print('Number of filtered images in the region of interest: ', count);

Answer 1

Your Code

These lines don't seem to work out:

var dateFilter = ee.ImageCollection(longRain2016.merge(shortRain2016).merge(longRain2017).merge(shortRain2017).merge(longRain2018));

var s2dateFilter = s2.filter(dateFilter);

You are trying to construct another ee.ImageCollection passing existing ImageCollections to it. According to the API, this won't work.

I also think that it is not necessary to achieve what you want because ee.ImageCollection.merge returns an ImageCollection anyway.

This should work:

var allSeasons = longRain2016.merge(shortRain2016).merge(longRain2017).merge(shortRain2017).merge(longRain2018);

Now, since you already should have a merged ImageCollection of all the seasons in allSeasons, you don't need the second step. (Actually this wouldn't work because your dateFilter object is not a Filter and filter() only accepts a Filter.)

You can simply proceed with var count = allSeasons.size();

Alternative way ("The Multiple-Filter-Method")

You could first create the Filters and then Filter.or()-join them together. Next you could apply this joint Filter to the ImageCollection:

//Create Filters
var longRain2016Filter = ee.Filter.date('2025-08-04','2025-08-04');
var shortRain2016Filter = ee.Filter.date('2025-08-04','2025-08-04');
var longRain2017Filter = ee.Filter.date('2025-08-04','2025-08-04');
var shortRain2017Filter = ee.Filter.date('2025-08-04','2025-08-04');
var longRain2018Filter = ee.Filter.date('2025-08-04','2025-08-04');

var allSeasonsFilter = ee.Filter.or(longRain2016Filter, shortRain2016Filter, longRain2017Filter, shortRain2017Filter, longRain2018Filter); // Create joint Filter

var allSeasons = s2.filter(allSeasonsFilter); //apply Filter to ImageCollection