Exporting MERRA2 image with Google Earth Engine with same resolution

Question

I am trying to extract MERRA2 columnar dust data from Google Earth Engine for a specific range of dates. I have to download it as daily data so I have converted it from hourly to daily. The image's resolution is 69375 meters * 55000 meters (As mentioned in the GEE catalog). However, when I download it through GEE, the resulting image doesn't have the same resolution. Here's my code for exporting the entire images (which I visualized in ArcGIS)

var dust = ee.ImageCollection('NASA/GSFC/MERRA/aer/2')
               .select('DUCMASS')
               // clip to your study area
               .map(function(image) {return image.clip(table)});
              
              
      var startDate = ee.Date('2009-06-18')
      var endDate = ee.Date('2009-06-28')

      var numberOfDays = endDate.difference(startDate, 'days')
      var daily = ee.ImageCollection(
      ee.List.sequence(0, numberOfDays.subtract(1))
      .map(function (dayOffset) {
        var start = startDate.advance(dayOffset, 'days')
        var end = start.advance(1, 'days')
         return dust
         .filterDate(start, end)
        .mean()
        .set('system:time_start', start.millis());
         })
         )
      Map.addLayer(daily.first().select(0), {
    min: 0,
    max: 1,
     palette: ['001137', '01abab', 'e7eb05', '620500'],
      });
   var merged = daily.toBands();
  Export.image.toDrive({ 
   image: merged,
   description: 'dust',
     region: table,
     });

Can anyone suggest how to tackle this issue?

Answer 1

You only need following lines en your code for exporting entire images with desired resolution:

.
.
.
var scale = dust.first().projection().nominalScale();
.
.
.
      .reproject('EPSG:4326', null, scale)
.
.
.

Complete code looks as follows:

var dust = ee.ImageCollection('NASA/GSFC/MERRA/aer/2')
               .select('DUCMASS')
               // clip to your study area
               .map(function(image) {return image.clip(table)});

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

print("scale", scale);

var startDate = ee.Date('2009-06-18');
var endDate = ee.Date('2009-06-28');

var numberOfDays = endDate.difference(startDate, 'days');

var daily = ee.ImageCollection(ee.List.sequence(0, numberOfDays.subtract(1))
  .map(function (dayOffset) {
        var start = startDate.advance(dayOffset, 'days');
        var end = start.advance(1, 'days');
         return dust
         .filterDate(start, end)
         .mean()
         .reproject('EPSG:4326', null, scale)
         .set('system:time_start', start.millis());
        })
      );

scale = daily.first().projection().nominalScale();

print("scale", scale);
      
Map.addLayer(daily.first().select(0), imageVisParam, 'DUCMASS');
Map.centerObject(table, 7);
   
var merged = daily.toBands();

Export.image.toDrive({ 
   image: merged,
   description: 'dust',
   region: table,
});

Before including above lines, composite daily images have a resolution of 111319. However, when above code is running, it can be corroborated in following picture that both resolutions are identical.

By the way, I used an arbitrary table geometry in USA because your table is not available.