[GIS] Google Earth Engine. How to get cloud cover score for each image in image collection

cloud covergoogle-earth-engine

I want to estimate cloud cover of each image in an image collection + would like to print out results for every image. I can see that cloud cover estimates are available for each image in their properties. But how to extract them to one table?

I am using this data:

//Load data collection
var l7r = ee.ImageCollection("LANDSAT/LE7_L1T")
.filter(ee.Filter.eq('WRS_PATH', 144))
.filter(ee.Filter.eq('WRS_ROW', 51));

Best Answer

I found this answer by Christoph in the Google Earth Engine Developers Forum (https://groups.google.com/forum/#!forum/google-earth-engine-developers).

var getCloudScores = function(img){
    //Get the cloud cover
    var value = ee.Image(img).get('CLOUD_COVER');
    return ee.Feature(null, {'score': value})
};

var results = landsat.map(getCloudScores);
print(Chart.feature.byFeature(results));

Or you can export data to drive:

// Export data to drive
Export.table.toDrive({
  collection: results, 
  description: 'File_Name',
  fileFormat: 'CSV'
});

Related Solutions

Counting Water Pixels in Landsat Collection using Google Earth Engine

It's going to be something like this:

var landsat8= ee.ImageCollection('LANDSAT/LC8_L1T_TOA').filterBounds(geometry)
var waterThreshold = 0; 

// water function:
var waterfunction = function(image){
  //add the NDWI band to the image
  var ndwi = image.normalizedDifference(['B3', 'B6']).rename('NDWI');
  //get pixels above the threshold
  var water01 = ndwi.gt(waterThreshold);
  //mask those pixels from the image
  image = image.updateMask(water01).addBands(ndwi);

  var area = ee.Image.pixelArea();
  var waterArea = water01.multiply(area).rename('waterArea');

  image = image.addBands(waterArea);

  var stats = waterArea.reduceRegion({
    reducer: ee.Reducer.sum(), 
    geometry: geometry, 
    scale: 30,
  });

  return image.set(stats);
};
var collection = landsat8.map(waterfunction);
print(collection);

var chart = ui.Chart.image.series({
  imageCollection: collection.select('waterArea'), 
  region: geometry, 
  reducer: ee.Reducer.sum(), 
  scale: 30,
});
print(chart);

I took the liberty of removing some redundant code from your function. Watch out for a reduction inside a map() for the reasons described here. Also, note that you may get no pixels in the result (waterArea=0) if the region overlaps the image footprint, but no valid pixels.

Landsat – How to Apply a Cloud Filter to Landsat8 Collection in Google Earth Engine

You need to check how Image.reduceRegion works. From documentation:

reduceRegion(reducer, geometry, scale, crs, crsTransform, bestEffort, maxPixels, tileScale)

Apply a reducer to all the pixels in a specific region. Either the reducer must have the same number of inputs as the input image has bands, or it must have a single input and will be repeated for each band. Returns a dictionary of the reducer's outputs.

Arguments:

this:image (Image): The image to reduce.

reducer (Reducer): The reducer to apply.

geometry (Geometry, default: null): The region over which to reduce data. Defaults to the footprint of the image's first band.

...

maxPixels (Long, default: 10000000): The maximum number of pixels to reduce.

Change this argument to avoid this error message:

var cloudiness = cloud.reduceRegion({
reducer: 'mean', 
geometry: S_sudan, 
scale: 30,
maxPixels: 1e10
});

Best Answer

Related Solutions

Counting Water Pixels in Landsat Collection using Google Earth Engine

Landsat – How to Apply a Cloud Filter to Landsat8 Collection in Google Earth Engine

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