Terrain Correction using SRTM 3sec and Uncheck Mask out areas without DEM


Using the Terrain-correction procedure with SRTM 3sec (Auto download), when i uncheck the option “Mask out areas without elevation” which values put in the results ?

Example if the pixel is sea with SRTM dem values equal -32000 (No Data), in this case the TC procedure which values put in the result ? because if i check this options, the TC put NaN otherwise what is the values ? 0.0 ? or the sames values of the pixel ? others values ?


Best Regards

In general, SRTM 3sec does not have data over the oceans. This option is provided to efficiently mask out ocean areas while terrain correcting. Values will become that bands no data value otherwise the pixel are terrain corrected with an elevation of 0 + the Earth gravitational model.
Note that usually inland water are not no data value and therefore are not masked out.

what is the value of the resolution of the dem srtm 3sec?

3 arc seconds is around 90m at the equator. It gets resampled by SNAP to the resolution of your source product.

ok thanks lveci

Hi Iveci,
Sorry for bothering you. I used the terrain-correction with SRTM 1 HGT, and check the option"mask out areas with elevation", but the result still has data over the oceans. Is there any solution to mask out? If not, should I do the “Back Geocoding” with SRTM 3 sec instead of SRTM 1 sec?
Really appreciate for you help :sweat_smile:

I had this same problem. I believe that the SRTM 1-arcsecond data has values of zero in the ocean, but SNAP does not use this to mask it out (v7). I found that I had to use the Raster->Masks->Land/Sea Mask function to mask out the ocean, but it only has the option to use the SRTM 3-arcsecond data for the masking so the coast is coarser than the 1-arcsecond data.