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?