I'd like to get the weekly VHmean value to compare the threshold value.

I wrote the code with reference to other ones.

For example:
Google Earth Engine: cumulative iteration of weekly mean anomaly
Getting weekly mean composite in Google Earth Engine?

Here is my code.

var geometry = /* color: #00ffff */ee.Geometry.Polygon(
    [[[107.5334247704419, 16.553900323143303],
      [107.53325310906494, 16.544356397007547],
      [107.5268158074292, 16.540982999796455],
      [107.5264724846753, 16.53835006342529],
      [107.53505555352295, 16.540407048035554],
      [107.53574219903076, 16.534482872994197],
      [107.54200783928955, 16.536951301364418],
      [107.54278031548584, 16.54517916786569]]]);


var bsc1 = {

var sentinel_pre = ee.ImageCollection('COPERNICUS/S1_GRD')
              .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))
              .filter(ee.Filter.eq('instrumentMode', 'IW'))
              .filter(ee.Filter.eq('orbitProperties_pass', 'DESCENDING'))

var divideimage = function (year,week){
  var startDate = ee.Date.fromYMD(year,1,1);
  var endDate = ee.Date.fromYMD(year,12,31);

  var weekDifference = ee.Date(startDate)
                      .advance(1, 'week').millis()

  var weeks = ee.List.sequence(

  var getsentinel = function(date){
    var sentinel = sentinel_pre
    return sentinel;

  var dateMillis = weeks.get(week);

  var sentinel1_IC = function(dateMillis){
                     var date = ee.Date(dateMillis);
                     return getsentinel(date);
  return sentinel1_IC(dateMillis);

ee.Algorithms.If(divideimage(2017,42).get('VH') < -20

var image = function(year,week){
var condition = ee.Algorithms.If(divideimage(year,week) < -20



However, using this code, GEE returned "null" from


and both "1" and "0" from

ee.Algorithms.If(divideimage(2017,42).get('VH') < -20

Ideally, I'd like to get images when the VHmean value in the specific area
goes below the threshold value, and I expect to display the area red.

Now, I don't know why but I can display some images.

Could you tell me the reason of getting invalid values and revise my code?

  • Can you include the definition of the geometry object? May 2 at 16:06
  • Thank you for the comment! I added my geometry's information.
    – geefrog
    May 3 at 12:00
  • Please provide a complete, running script, with all used assets shared. Ideally, add a link to the code editor too (using the Get Link button). May 4 at 9:07
  • @DanielWiell, Thank you for the advice! I have updated my question. I know I should add my link, but I'm not familiar with privacy problem. So, I was wondering if you could use the written code...
    – geefrog
    May 4 at 12:12

1 Answer 1


I'm not completely clear what you're trying to do in your script, but divideimage() return an image. Calling get() on an image get you an image property. VH is not a property, it's a band, so you want to use select() instead.

You're also mixing up client-side and server-side operations with ee.Algorithms.If(divideimage(2017,42).get('VH') < -20. Read up on this here.

Maybe this script can give you some ideas how to approach your analysis.

var weeklyMean = calculateWeeklyMean(2017, 1, geometry)
var zeroOrOne = weeklyMean.lt(-20)
Map.addLayer(weeklyMean, {min: -30, max: 5}, 'weeklyMean')
Map.addLayer(zeroOrOne, {}, 'zeroOrOne')
Map.centerObject(geometry, 14)

function calculateWeeklyMean(year, week, geometry) {
  var date = ee.Date.fromYMD(year, 1, 1)
    .advance(ee.Number(week).subtract(1), 'weeks')
  return ee.ImageCollection('COPERNICUS/S1_GRD')
    .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))
    .filter(ee.Filter.eq('instrumentMode', 'IW'))
    .filter(ee.Filter.eq('orbitProperties_pass', 'DESCENDING'))
    // Hack so you get a masked image instead of a 0 band image 
    // when there is no imagery


  • Thank you for the wonderful answer! I have got the hint!
    – geefrog
    May 5 at 0:36
  • Oh, I'm sorry, but I'd also like to know the way to convert Image(from weeklyMean) into the Number of VH value...
    – geefrog
    May 5 at 2:06
  • You have different VH values for different pixels. Are you looking for the mean VH across all pixels in your area of interest? If so, that's reduceRegion() you want. May 5 at 4:12
  • Thank you so much! I'll try it!
    – geefrog
    May 5 at 8:43
  • I have complited my task! Thank you!
    – geefrog
    May 5 at 10:59

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