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I am interested at looking at Sentinel 1 imagery from Alaska. However when I pull up my images they seem to have 'streaking' (elongation of the pixels in the direction of the slopes). I think this is from the terrain correction done by google that takes foreshortened GRD images and stretches them to match the DEM.

Is this actually what is causing this? Is there a way to re-project or smooth this data to make this streaking less obvious?

// Region of Interest
var roi = ee.Geometry.Point(-149.4758, 68.1294);
Map.setCenter(-149.4758, 68.1294, 13);

// Load Sentinel-1 C-band SAR Ground Range collection (log scaling, VV co-polar)
var collection = ee.ImageCollection('COPERNICUS/S1_GRD')
.filterBounds(roi)
.filterDate('2019-10-01', '2019-11-12')
.filterMetadata('resolution_meters', 'equals' , 10)
.select('VV')
;

// Filter by date
var before = collection.filterDate('2019-10-21', '2019-10-23')
.first();

Map.addLayer(before, {min: -18, max:10}, 'October 22nd',0);

var kernel = ee.Kernel.circle({
  radius: 2, units: 'pixels', magnitude: 1
});

// Smooth the image by convolving with the kernel
var beforeS = before.convolve(kernel);

Map.addLayer(beforeS, {min: -18, max:10}, 'Smoothed Oct 22nd',0);
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Yes, this is the result of imperfect terrain correction. Terrain flattening should do a better job, and we plan to investigate applying TF to S1 instead of terrain correcrt

  • Thanks for the clarification. Is there a good method to terrain correct on GEE that I could apply to the images to reduce this affect? Or would I need to use the Sentinel1_GRD_Float images and try to terrain flatten in that collection? – ZachK Nov 13 '19 at 23:29
  • Terrain correction ideally has to be done by us using the S1 toolbox before ingestion. I'm going to look at this soon. – Simon Ilyushchenko Nov 15 '19 at 2:43
  • Additionally do you know if GEE is looking in to using the arctic DEM for this instead of the current DEM for upper latitudes? pgc.umn.edu/data/arcticdem – ZachK Nov 25 '19 at 16:36
  • I see you already asked this question at the S1 toolobox forum:forum.step.esa.int/t/… We need the toolbox to support the arctic DEM. – Simon Ilyushchenko Nov 26 '19 at 18:10
  • Isn't this streaking caused by foreshortening from the steeper terrain? How would terrain flattening give any different result? This seems like it might just be how radar images that are terrain corrected are going to look since you have to stretch the foreshortened pixels? – ZachK Dec 1 '19 at 1:18

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