How to import an external DEM into SNAP?

[ABraun]

@carantes

I did the download of DEM from ALOS images from VERTEX website (12.5m of spatial resolutuion). Is it not correct?

Unfortunately, this data not really offers a spatial resolution of 12.5 meter. For most parts of the world, the DEM contained in ALOS products fom Vertex is just SRTM data (30 m) which was up-sampled to a pixel size of 12.5 m. Please have a look here:

Difference between using a dem of 30m and 90 m to INSAR

that is a quite popular misconception. Although the DEMs delivered with the ALOS RTC files have a pixel size of 12.5 meters, they are mostly just up-sampled DEMs from SRTM to match the spatial resolution of the input data (ALOS PALSAR with 12.5 meters in this case) [grafik] Source : https://www.asf.alaska.edu/asf-tutorials/dem-information/ So the quality is not better than any SRTM which is automatically downloded by SNAP (SRTM 1 ArcSec). You can use it right away. If the quality is not suf…

So, to answer your question: If you select SRTM 1Sec (AutoDownload), you already have the best quality which is freely available. I suggest to directly use it (instead of an external DEM, unless its quality is really better) to avoid unneccessary resampling.