Seasonal averages time series of an area

Question

I want to calculate seasonal variations of LST over some years

what I have so far is monthly average but can't make seasons out of those months !!

here is my code

var LandsatLST = require('users/sofiaermida/landsat_smw_lst:modules/Landsat_LST.js')
var geometry = ee.Geometry.Rectangle( 32.96780026,28.39841527,32.97560417,28.40330991);
var satellite = 'L7';
var date_start = '2000-01-01';
var date_end = '2021-12-30';
var use_ndvi = true;
var LandsatColl = LandsatLST.collection(satellite, date_start, date_end, geometry, use_ndvi)
var LandsatColl = LandsatColl.select("LST")
//#convert to Celsius
var LandsatColl = LandsatColl.map(function(img) {
  return img
    .subtract(273.15)
    .copyProperties(img, ['system:time_start']);
});

var years = ee.List.sequence(2000, 2021);
var months = ee.List.sequence(1, 12);

var yrMo = ee.ImageCollection.fromImages(
  years.map(function (y) {
   return months.map(function (m) {
            return LandsatColl
              .filter(ee.Filter.calendarRange(y, y, 'year'))
              .filter(ee.Filter.calendarRange(m, m, 'month'))
              .mean()
              .set('Month', m)
              .set('year',y)
               .copyProperties(LandsatColl, ['system:time_start']);
        });
    }).flatten());

I want to filter the image collection by seasonal average, I tried :

  var seasons = ee.List([[1,3], [4,6], [7,9],[10,12]])
  var createSeasonComposites = function(months) {
  var startMonth = ee.List(months).get(0)
  var endMonth = ee.List(months).get(1)
  var monthFilter = ee.Filter.calendarRange(startMonth, endMonth, 'month')
  var seasonFiltered = yrMo.filter(monthFilter)
  var composite = seasonFiltered.mean()
  return composite
}
var compositeList = seasons.map(createSeasonComposites)

print(compositeList,"seasons")

but the ee.Filter.calendarRange() doesn't work in my case due to the absence of timestamps which I tried to add but failed ?!

Any help how to make the seasonal averages ?

Answer 1

You can't copyProperties like this when you work on an image collection inside your yrMo mapped function. The approach seems to be working, here is a suggestion to get the timestamp property working working:

 var timestamp = ee.Image(subset.first()).get('system:time_start')

But you end up with another problem, namely seasons/year combinations without images. So in the link below I show you the examples it works for to copy the timestamp property:

https://code.earthengine.google.com/eadf4867626f2625d48f4283722140e6