Add date to an image collection to export to CSV

Question

I calculate the number of fires for a region and export the result to Google Drive as a CSV file, but I can't add the date to the image collection to export, it gives the following error:

ImageCollection (Error) Error in map(ID=2019001): Image.addBands, argument 'srcImg': Invalid type. Expected: Image. Actual: Date.

Here is the code:

// Load country shapefile 
var lsib = ee.FeatureCollection("USDOS/LSIB_SIMPLE/2017");
var vn_shape = lsib.filterMetadata('country_na', 'equals', 'Argentina');
print (vn_shape);


// Load fire counts image
var fire = ee.ImageCollection('FIRMS')
             .filterBounds(vn_shape)
             .filterDate('2019', '2020')
print(fire)

var scale = fire.first().projection().nominalScale();

// Filter fire with more than 50% confidence and add a new band representing areas where confidence of fire > 50%
var filterConfidence = function(image) {
  var line_number = image.select('line_number');
  var confidence = image.select('confidence');
  var conf_50 = confidence.gt(50).rename('confidence_50');
  var count_band = line_number.updateMask(conf_50).rename('count');
  // HERE IS THE PROBLEM!
  var date = image.date();          
  return image.addBands(count_band)
              .addBands(date);
};


var fire_conf = fire.map(filterConfidence);
print('fire_conf', fire_conf);

// Count for individual image.
var countIndividualImg = function(image) {
  var countObject = image.reduceRegion({
    reducer: ee.Reducer.countDistinct(),
    scale: scale,
    geometry: vn_shape,
    maxPixels: 1e9
  });
  return image.set(countObject);
};
var fire_ind_count = fire_conf.map(countIndividualImg);
print('fire_ind_count', fire_ind_count);
Export.table.toDrive({
  collection: fire_ind_count,
  description: 'FireCounts_gt50_conf',
  selectors:['count','date'],
  fileFormat: 'CSV'
});
print('Total fire count', fire_ind_count.aggregate_sum('count'));

Answer 1

One way to do it is to move the date calculation from the function filterConfidence to after the reducer function countIndividualImg, here is the code:

// Load country shapefile 
var lsib = ee.FeatureCollection("USDOS/LSIB_SIMPLE/2017");
var vn_shape = lsib.filterMetadata('country_na', 'equals', 'Argentina');
print (vn_shape);


// Load fire counts image
var fire = ee.ImageCollection('FIRMS')
             .filterBounds(vn_shape)
             .filterDate('2019', '2020')
print(fire)

var scale = fire.first().projection().nominalScale();

// Filter fire with more than 50% confidence and add a new band representing areas where confidence of fire > 50%
var filterConfidence = function(image) {
  var line_number = image.select('line_number');
  var confidence = image.select('confidence');
  var conf_50 = confidence.gt(50).rename('confidence_50');
  var count_band = line_number.updateMask(conf_50).rename('count');
  // 
  // I don't calculate the date here !!!
  // 
  return image.addBands(count_band);
};


var fire_conf = fire.map(filterConfidence);
print('fire_conf', fire_conf);

// Count for individual image.
var countIndividualImg = function(image) {
  var countObject = image.reduceRegion({
    reducer: ee.Reducer.countDistinct(),
    scale: scale,
    geometry: vn_shape,
    maxPixels: 1e9
  });
  // 
  // Add the date here
  // 
  return image.setMulti(countObject).set('date', image.date());
};

var fire_ind_count = fire_conf.map(countIndividualImg);
print('fire_ind_count', fire_ind_count);
Export.table.toDrive({
  collection: fire_ind_count,
  description: 'FireCounts_gt50_conf',
  selectors:['count','date'],
  fileFormat: 'CSV'
});
print('Total fire count', fire_ind_count.aggregate_sum('count'));