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I am working with MODIS-NDVI data (MODIS/006/MOD13Q1) in Google Earth Engine. I have a script which exports each image in the image collection for given area and time period. I need to upgrade script which will composite band by years to have a single file for each year. Later, I need to export them Google Drive. Could anyone please assist me on upgrading below shown code?

var col = ee.ImageCollection("MODIS/006/MOD13Q1")
    .select("NDVI")
    .filterDate("2000-01-01","2018-06-01");


var ExportCol = function(col, folder, scale, type,
                         nimg, maxPixels, region) {
    type = type || "float";
    nimg = nimg || 500;

    var colList = col.toList(nimg);
    var n = colList.size().getInfo();

    for (var i = 0; i < n; i++) {
      var img = ee.Image(colList.get(i));
      var id = img.id().getInfo();

      var imgtype = {"float":img.toFloat(), 
                     "byte":img.toByte(), 
                     "int":img.toInt(),
                     "double":img.toDouble()
                    }

      Export.image.toDrive({
        image:imgtype[type],
        description: id,
        folder: folder,
        fileNamePrefix: id,
        region: studyarea2,
        scale: scale,
        maxPixels: maxPixels})
    }
  }

  ExportCol(col, "NDVI_MODIS_NKz_KZ", 250);
  • What kind of composite are you aiming for - the mean value for each band and year? – Kersten Jun 22 '18 at 11:40
  • I would like to stack all layer in one year to single file like a bands and to be able export the stacked layers as single file – Sarvarbek Eltazarov Jun 22 '18 at 13:43
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try this code: https://code.earthengine.google.com/9052c17efac7990cf1c5449654186d08

Script:

var col = ee.ImageCollection("MODIS/006/MOD13Q1")
    .select("NDVI")
    .filterDate("2000-01-01","2018-06-01");

// Functions to stack colletion series into image bands  

var stackCollection = function(collection) {
  var first = ee.Image(collection.first()).select([]);
  var appendBands = function(image, previous) 
  {return ee.Image(previous).addBands(image);};
  return ee.Image(collection.iterate(appendBands, first));};

// Function to generate mask for each Scene.

var getSceneMask = function(scene) {
  var dateString = ee.Date(scene.get('system:time_start')).format('yyyy-MM-dd');
  var mask = scene.select('NDVI').gt(-9999).updateMask(ee.Image(1));
  return mask.rename(dateString);};

//Stacked mask for collection

var MaskCol = stackCollection(col.map(getSceneMask));

// Generate a datelist for collection 

var datelist = ee.List(MaskCol.bandNames()).map(function(date){return ee.Date(date).format('yyyy-MM-dd')});

print(datelist)

// Stack bands and rename by date  

var ndvi_stacked = stackCollection(col.select('NDVI')).divide(10000).rename(datelist);

Map.addLayer(ndvi_stacked,{min:-1,max:1},'ndvi_stacked');

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