I have a raw "Path Image" RADARSAT image as a CEOS file, which is by default not georeferenced and in units of Digital Numbers (DN). I'm trying to convert it to a projected geotiff in units of backscatter intensity (sigma-nought), but I've hit a wall in terms of the workflow in ENVI.

Converting the raw image to backscatter intensity is simple enough using the "Sigma Nought Calibration" Tool in ENVI, but it requires a DEM to be the same spatial extent and pixel size as the CEOS file - but I'm not sure how to get the DEM to match the spatial extent and pixel size of an non-georeferenced RADARSAT CEOS file.

I tried to project the CEOS file first, so I could match it to an existing DEM geotiff, but once it is georeferenced it is no longer recognized as a RADARSAT file and cannot be used in the Sigma Nought Calibration tool in ENVI. Further, I manually tried to project the DEM to what coordinate system I believe the CEOS raw RADARSAT is in (WGS84), but they didn't get even close to matching spatial extents. After that, I matched the DEM to the spatial extent and pixel size of the projected (WGS84 UTM17N) RADARSAT - but of course since it was projected, it didn't match the spatial extent of the raw CEOS file, and couldn't be used.

Short of just manually geo-referencing the DEM to the unprojected RADARSAT CEOS file, I'm not sure how to proceed and would love some guidance. How can I get a DEM to match the spatial extent/pixel size of a non-georeferenced CEOS file?

  • I think the real problem is that path image isn't going to have even sized pixels, so reprojection is non-trivial. I'd suggest trying to get a map image instead, if possible. – BradHards Aug 3 '17 at 1:58
  • I have a map image of the same scene, but the geotiff path images don't have the Metadata contained in a CEOS header file, and so they can't be used in ENVI to calculate sigma nought. I'm half thinking of converting to beta nought, which doesn't require a DEM, then manually calculating the conversion to sigma nought. But that still wouldn't produce a georeferenced file.. – Italianhiker Aug 3 '17 at 2:19

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