Google Earth Engine – How to Download CSV of Dates from ImageCollection

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I need to download a CSV file containing the acquisition date of each Sentinel-2 image in a featureCollection. I filtered the following featureCollection:

var startDate = ee.Date('2020-01-01');
var endDate = startDate.advance(1, 'year');

var s2L2A_rawData = ee.ImageCollection("COPERNICUS/S2_SR_HARMONIZED")
                  .filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 100)
                  .filter(ee.Filter.inList('MGRS_TILE', ['30SYJ']))
                  .filterDate(startDate, endDate)
                  .filterBounds(geometry);

print('Sentinel-2 L2A raw data', s2L2A_rawData);

How can I download a CSV with the date of each image to work the data locally?

Best Answer

Here is a solution which extracts the 'sysem:time_end' property using aggregate_array, converts the list into a FeatureCollection and downloads it to Google Drive using Export.table.toDrive:

var startDate = ee.Date('2020-01-01');
var endDate = startDate.advance(1, 'year');

var s2L2A_rawData = ee.ImageCollection("COPERNICUS/S2_SR_HARMONIZED")
                  .filterMetadata('CLOUDY_PIXEL_PERCENTAGE', 'less_than', 100)
                  .filter(ee.Filter.inList('MGRS_TILE', ['30SYJ']))
                  .filterDate(startDate, endDate)
                  .filterBounds(geometry);

print('Sentinel-2 L2A raw data: ', s2L2A_rawData);

var property = 'system:time_end';
var dates = s2L2A_rawData.aggregate_array(property);

print('Sentinel-2 time serie dates: ', dates);

var dates_featureCollection = ee.FeatureCollection(dates
                                .map(function(element){
                                return ee.Feature(null,{property:element})}));

Export.table.toDrive({
  collection: dates_featureCollection,
  folder: 'Test_Folder',
  description:'dates',
  fileFormat: 'CSV'
});

Alternatively you can copy the values from dates list in GeoJSON format and paste it into your own text document, as shown in the image below:

Note that dates are stored in Unix Time.

Related Solutions

Google Earth Engine – How to Get Dates from an ImageCollection

The s1_dates variable isn't defined, but even if it was, you can't modify global variables inside mapped functions. You probably just want this:

dates = s1_collection_f.aggregate_array("system:time_start")

which is equivalent to this:

var dates = s1_collection
    .reduceColumns(ee.Reducer.toList(), ["system:time_start"])
    .get('list')

But, looking ahead, you probably didn't really want 361,000 separate acquisition times. You probably want at least distinct times, and more likely, distinct days (Y-M-D), in which case you need to convert the date somewhere along the way (it's in milliseconds). The easiest way to do that is to map a function over the images, returning a feature for each image containing just the formatted date. Then you can use distinct().

var dates = s1_collection_f
    .map(function(image) {
      return ee.Feature(null, {'date': image.date().format('YYYY-MM-dd')})
    })
    .distinct('date')
    .aggregate_array('date')

Google Earth Engine – Difference Between reduce(ee.Reducer.mean()) and mean() for ImageCollection

Did you look at the Earth Engine documentation for ImageCollection reductions?

For basic statistics like min, max, mean, etc., ImageCollection has shortcut methods like min(), max(), mean(), etc. They function in exactly the same way as calling reduce(), except the resultant band names will not have the name of the reducer appended.

In other words, the result is the same if you use .mean() or .reduce(ee.Reducer.mean()) but the latter method will append _mean to the band names.

Best Answer

Related Solutions

Google Earth Engine – How to Get Dates from an ImageCollection

Google Earth Engine – Difference Between reduce(ee.Reducer.mean()) and mean() for ImageCollection

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