How can I compute the harmonic instead of arithmetic mean for a series of images in Google Earth Engine? There is a build-in function to compute the arithmetic mean and median, but there is no harmonic/geometric mean available. I tried to build my own function by making use of the reduce function, but with this I did not succeed. Any ideas/examples on how to proceed?

1 Answer 1


This should be doable as follows:

// a random point on the map
var point = ee.Geometry.Point([-106.95381215107625, 39.46780712207983]);
// Make some constant images and put them together in a image collection
var list = ee.List([1,1,1, 2,2,2,3,4,5,5,6,6,6,6,7,7,8,9,9]);
var imageCol = ee.ImageCollection.fromImages(list.map(function(integer){
  return ee.Image.constant(integer).toInt();

// Calculate the harmonic mean based on: https://en.wikipedia.org/wiki/Harmonic_mean
var n = imageCol.size(); // number of observations (19)
var harmonicMean = imageCol.map(function(image){
  // Note that function image.pow() cannot handle 0 values
  return image.pow(-1);
print('harmonic mean image collection', 
        harmonicMean.reduceRegion('first', point, 1000).get('constant'));

// Calculate the harmonic mean based on: https://en.wikipedia.org/wiki/Harmonic_mean
    // All data points should be possitive
var geometricMean = imageCol.product().pow(ee.Number(1).divide(n));
print('geometric mean image collection', 
      geometricMean.reduceRegion('first', point, 1000).get('constant'));

According to Wikipedia, I checked how to calculate the harmonic and geometric mean. And according to this site, the outcomes coincide. Link to code.


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