Which function is correct for cloud masking

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I was writing a function to mask cloudy pixels of the Sentinel-2 data.

Function 1:

function cloudMask(image) {
  var qa = image.select('QA60');
  var cloudBitMask = 1 << 10; ###
  var cirrusBitMask = 1 << 11; ###
  var mask = qa.bitwiseAnd(cloudBitMask).eq(0).and(
             qa.bitwiseAnd(cirrusBitMask).eq(0));
  return image.updateMask(mask).divide(10000);
}

Function 2:

function cloudMask(image) {
  var qa = image.select('QA60');
  var cloudBitMask = Math.pow(2, 10); ###
  var cirrusBitMask = Math.pow(2, 11); ###
  var mask = qa.bitwiseAnd(cloudBitMask).eq(0).and(
             qa.bitwiseAnd(cirrusBitMask).eq(0));
  return image.updateMask(mask).divide(10000);
}

Which function is correct? The difference between two functions is that how cloudBitMask and cirrusBitMask are defined.

google-earth-engine mask
1 Answers

Both functions are correct as they are doing exactly the same thing. Either 1 << 10 or Math.pow(2, 10) will result in a number with a value of 1024.

As we usually use both opaque cloud and cirrus cloud for cloud masking, I suggest keeping the code short and clear as below:

function cloudMask(image) {
    var qa = image.select('QA60');
    var allCloudBitMask = (1 << 10) + (1 << 11);
    var mask = qa.bitwiseAnd(allCloudBitMask).eq(0);
    return image.updateMask(mask);
}
user_84176310
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