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I am working on a project using the Sentinel 1 GRD product in Google Earth Engine and I have found a couple examples of missing data, apparently in swath overlaps in the descending orbit. This is not the issue discussed here and explained on the GEE developers forum. It is a much larger gap and does not appear to be the product of the terrain correction as explained for that other issue.

This gap seems to persist regardless of year changes in the date range or polarization. The gap is resolved by changing the orbit filter param from 'DESCENDING' to 'ASCENDING', presumably because of the different swaths or by increasing the date range. I get that increasing the date range increases revisits and thus coverage but is this then just a byproduct of the orbital geometry? ie it takes more than the standard temporal repeat to image that area? I am just trying to understand where this data gap is coming from. Code example:


var geometry = ee.Geometry.Polygon(
    [[[-123.79472413785096, 46.20720039434629],
          [-123.79472413785096, 42.40398120362418],
          [-117.19194093472596, 42.40398120362418],
          [-117.19194093472596, 46.20720039434629]]], null, false)
    
var filtered = ee.ImageCollection('COPERNICUS/S1_GRD').filterDate('2019-01-01','2019-04-30')
    .filterBounds(geometry)
    .filter(ee.Filter.eq('orbitProperties_pass', 'DESCENDING'))
    .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VH'))
    .filter(ee.Filter.listContains('transmitterReceiverPolarisation', 'VV'))
    .filter(ee.Filter.eq('instrumentMode', 'IW'))
    .select(["VV","VH"])
    
print(filtered)
var filtered_mean = filtered.mean()
print(filtered_mean)
Map.addLayer(filtered_mean.select('VH'),{min:-25,max:1},'filtered')

You can view an example here: https://code.earthengine.google.com/26556660c352fb25b98ac80667298959

brobertsp
  • 71
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0 Answers0