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I'm trying to make an annual composite of Landsat 5 data for a region of interest in Google Earth Engine but what I end up with is hazy and cloudy. I've tried filtering for haze and clouds but still get both in my final version.

The code I have written is below

 roi =
ee.Geometry.Polygon(
    [[[-70.94315884724863, -13.228382487713638],
      [-68.53715298787363, -13.228382487713638],
      [-68.53715298787363, -12.022330477798716],
      [-70.94315884724863, -12.022330477798716],
      [-70.94315884724863, -13.228382487713638]]]);
var clouds = function(image) {
 var qa = image.select('pixel_qa');
 var cloud = qa.bitwiseAnd(1 << 5)
              .and(qa.bitwiseAnd(1 << 7))
              .or(qa.bitwiseAnd(1 << 3));
 var mask2 = image.mask().reduce(ee.Reducer.min());
 return image.updateMask(cloud.not()).updateMask(mask2);
};

function lsHazeMask(image) { 
var mask = image.select('sr_atmos_opacity').lte(300);
return image.updateMask(mask);
}

var jsonCoordString = roi.toGeoJSON();

for (var start_year = 1986; start_year <= 1990; start_year++)
{
var startDate = ee.Date.fromYMD(start_year,01,01);
var sr = ee.ImageCollection(ls5SR).filter(ee.Filter.bounds(roi)).filter(ee.Filter.calendarRange(6,9,'month')).filterMetadata('CLOUD_COVER', 'less_than', 30).filter(ee.Filter.date(startDate,startDate.advance(1,'year')));
sr = sr.map(clouds);
sr = sr.map(lsHazeMask);
sr = sr.reduce(ee.Reducer.median());

Map.addLayer(sr.select([2,1,0]).clip(roi),{min: [0,0,0], max: [2000,2000,2000]},'puerto'+start_year);
}

2 Answers 2

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You will need to extend the date range for the composites. You just have 2-3 images in each composite. That is insufficient to make a correct median image composite.

You can check the number of images which a pixel is made of using the count reducer:

var srCount = sr.select([0]).reduce(ee.Reducer.count());
Map.addLayer(srCount.clip(roi),{min: 0, max: 20},'puertoCount'+start_year);

https://code.earthengine.google.com/735dc190d389a949a6814b06190ba094

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  • thank you for this! I found that if I allowed images from the full year - it was shockingly even cloudier and worse quality throughout. But maybe combining this with @Daniel Weill's comment will help
    – Rachel
    Apr 16, 2020 at 17:58
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The pixel_qa band for Landsat 5 can be a bit hit-and-miss. You might want to complement this band with some cloud scoring algorithm. Here is an example of an implementation. It's quite aggressive and will mask out much of built-up areas, while still not getting all haze. So, room for improvements. Like @Kuik points out, you will certainly get better results if you include more imagery.

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  • thank you for this! I will try to implement the cloud scoring algorithm. I ended up with so few images because if I let it pull from the whole year (Tropical forest so basically super cloudy most days of October - May) then the resulting image was 100% clouds, so narrowing the dates let me get at least some land cover haha. But maybe this cloud algorithm you've linked will help me get around this and then I can use the full year's dates. :)
    – Rachel
    Apr 16, 2020 at 18:00

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