Is there a simple way to get sentinel-1 GRD data on a longitude-latitude-grid using SNAP? I guess I could create a lon-lat-grid first and use the collocate function, but is there a better way?
2 Answers
Over land:
- Range Doppler Terrain Correction: Select WGS84 (DD) as projection and a good DEM (SRTM 1Sec AutoDownload)
Over ocean:
- Ellipsois correction: Select WGS84 (DD) as projection.
Then proceed with:
- Band Maths: Create two bands named longitude and latitude (disable the 'virtual band' option) with these expressions: $x and $y respectively. This will write the coordinate of each pixel into a new band.
Figured out how to do it (this is very basic functionality, but I write it anyway in case someone is as confused as I was). I'm definitely not an expert, but this worked for me.
Two steps, though I'm not sure if the second step is necessary
Apply a correction: Radar-> Geometric -> Ellipsoid Correction -> Average Height Range-Doppler (or whatever correction that suits your purpose)
Reproject: Raster -> Geometric -> Reprojection. In the window that opens, select the reprojection tab and make sure that the projection is Lat/Lon.
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1Radar data is geometrically distorted by topography, so the Range Doppler Terrain Correction will give you more precise results. Also, the Reprojection seems redundant to me, because you can define WGS84 (DD) as output coordinate reference system already in the previous step.– AndyBJun 4, 2021 at 5:55
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@AndyB That is only true for land data right? I worked with ocean/sea ice data. But I should clarify that– bluppJun 4, 2021 at 6:01
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yes, that changes some things, I'll edit my answer. I just think the resampling unnecessarily alters the original pixel values.– AndyBJun 4, 2021 at 6:06