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I have used this code https://www.gears-lab.com/intro_rs_lab8/ in order to learn and practice my SAR-1 skills. I have created an almost similar code, but few things are not clear to me regard this code. In the end of the code, I am supposed to display in RGB 3 different layers. How does it work? I get only one image, so what is the meaning of display each one of them as RGB in one image?

  1. When I use the inspector in order to check the values I gave in the RGB stack (seasonal stack) I have "layer" that not suppose to be there- VV. That confuses me even more- why don't I get the 3 layers I stack together? (vv1,vv2, and vv3)

enter image description here

I would say this relates to the first question. of how it displays 3 images as 3 different band in one image.

This is the code I used, it has error with the VH for a reason I don't know yet

var geometry=geometry2;
// Filter the collection for the VV product from the descending track
var collectionVV = ee.ImageCollection('COPERNICUS/S1_GRD')
    .filter(ee.Filter.eq('instrumentMode', 'IW'))
    .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VV'))
    .filter(ee.Filter.eq('orbitProperties_pass', 'DESCENDING'))
    .filterBounds(geometry)
    .select(['VV']);
print(collectionVV);

// Filter the collection for the VH product from the descending track
var collectionVH = ee.ImageCollection('COPERNICUS/S1_GRD')
    .filter(ee.Filter.eq('instrumentMode', 'IW'))
    .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))
    .filter(ee.Filter.eq('orbitProperties_pass', 'DESCENDING'))
    .filterBounds(geometry)
    .select(['VH']);
print(collectionVH);

Map.centerObject(geometry);

var clippedVV=collectionVV.map(function(im){ 
   return im.clip(geometry);
}); 

var clippedVH=collectionVH.map(function(im){ 
   return im.clip(geometry);
}); 




var VV = clippedVV.median();
var VH= clippedVH.median();

// Adding the VV layer to the map
//Map.addLayer(VV, {min: -30, max: -1}, 'VV');
//Map.addLayer(VH,{min:-30, max:-1}, 'VH');

// Create a 3 band stack by selecting from different periods (months) for VV

var VV1 = ee.Image(clippedVV.filterDate('2017-10-01', '2017-11-30').median());
var VV2 = ee.Image(clippedVV.filterDate('2017-12-01', '2018-12-31').median());
var VV3 = ee.Image(clippedVV.filterDate('2019-01-01', '2019-02-28').median());

// Create a 3 band stack by selecting from different periods (months) for VH

var VH1 = ee.Image(clippedVH.filterDate('2017-10-01', '2017-11-30').median());
var VH2 = ee.Image(clippedVH.filterDate('2017-12-01', '2018-12-31').median());
var VH3 = ee.Image(clippedVH.filterDate('2019-01-01', '2018-02-28').median());
//Add to map
Map.addLayer(VV1.addBands(VV2).addBands(VV3), {min: -30, max: -1}, 'Season compositeVV');
Map.addLayer(VH1.addBands(VH2).addBands(VH3), {min: -30, max: -1}, 'Season compositeVH');

Map.addLayer(VV1,{min:-30,max:-1},'Season composite inly vv1');
Map.addLayer(VV2,{min:-30,max:-1},'Season composite inly vv2');
Map.addLayer(VV3,{min:-30,max:-1},'Season composite inly vv3');
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Looks like you want to explore the image.visualize() function. For example, you can create an imageCollection with your Images of interest, then convert that collection into a single Image with 3 bands. The visualize() function allows you to assign those bands to RGB values:

// convert images to Collection
var myCol = ee.ImageCollection.fromImages([VV1,VV2,VV3]); 
// convert to 3-band image
var myColBands = myCol.toBands();
// Visualize using min and max parameters from code above
var myColViz = myColBands.visualize({min:-30, max:1});
// Add to map
Map.addLayer(myColViz,{},"myColViz");
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  • 1
    You can avoid converting to ImageCollection and back to Image by using the ee.Image.cat() function. var myColBands = ee.Image.cat(VV1, VV2, VV3); – Justin Braaten Nov 11 '19 at 0:20
  • Thaks for your answer, but there is something I am still bot sure about. If I convert those images into image collections and then display it in RGB, then how does it decided which value will get which color? each pixel has 3 values (one from each image), so then how is it decided what will be the value ? – Reut Nov 14 '19 at 9:07
  • Use the Bands argument as per documentation: developers.google.com/earth-engine/image_visualization – JepsonNomad Nov 14 '19 at 16:58

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