Global DEMs at OpenTopography

Global DEMs from OpenTopography

Guth and Kane (Transactions in GIS, 2021) suggest that Copernicus is the best choice among these. ALOS World 3D would be the second choice.

DEM and its properties	OpenTopography Metdata and location to start download Pick link for the data set you want	Precision	File numbers and size for complete data set	Notes
Copernicus DEM	OT.032021.4326.1	Float	26,440 files, 550 GB	Resampled to same arc second spacing in x and y if you select by box, which changes the data characteristics. Some countries missing for political reasons. Goes farther north than SRTM and NASADEM.
ALOS World 3D AW3D30 v 3.2:	OT.112016.4326.2	Integer	23,997 files, 220 GB	Not void filled. They have the averaged data from the 5 m source; JAXA also has median
NASDADEM	OT.032021.4326.2	Integer	14,251 files, 128 GB	HGT files, stored as TIFF here
SRTM v3:	OT.042013.4326.1	Integer	14,280 files, 125 GB	Unclear which 3" version they have (middle or average)
USGS 1" 3DEP/NED merged with DEMs from Canada and Mexico	OT.012021.4269.2			Terrible choice for name, since it is not just USGS but international. Perhaps not surprisingly, this has disappeared without explanation that I can find.
Global Multi-Resolution Topography and bathymetry	OTGMRT.112016.4326.1
SRTM 15+ (land/ocean merge; the 15 arc second resolution is about 450 m)	OTSRTM.122019.4326.1

Graphical interface option in browser
- Pick a region that includes what you want. It is better to get too much rather than not enough and then having to come back.
- Open the Global Data Tab and choose the data set and the resolution for those that have 1" and 3" data. Get the geoid version for the Vertical datum unless you are absolutely sure you want the ellipsoid version. If there is any chance you might get both, store them differently as the downloads do not indicate the vertical datum.
- If you are having problems with the graphical selection, you can manually select the coordinates. You can use the Bounding box that covers the area you want.
- You do not need a hillshade (uncheck the option) since the GIS can easily create.
- The limit is 450,000 square km.
- Keep the default Geotiff format.
- Download will be a tar.gz file, which is a Unix format you can decompress in MICRODEM. You can have the program delete the compressed file. The file will be in a sub-directory in the folder where the tar.gz file was.
- If you let the download change the file name, say by adding " (1)" because there is another download with the same name, you will have to manually untar the result from the un-gzip (so don't let Windows rename).
- File will be named "output_srtm", so you must keep track of which version you got. The metadata has the data spacing, but not the vertical datum. Considering renaming the final TIF file with the geographic region and the Vertical datu selected.
Raster bulk downloads use AWS command line
- This gets the complete data set, so be ready for some serious bandwidth and hard disk requirements
- I suspect you could figure out how to get just the area you want, which is left as an exercis for the curious student.

You must have GDAL installed, via OSGEO4W, to use the DEMs in MICRODEM.

The grids use -9999 for missing data without indicating this in the Geotiff header. You should mark it missing on Import/Export, or editing the grid, if the color scheme is distorted by the invalid large negative elevations.

DEM results will be in tar.gz (Unix) compressed file. Compress/Decompress option in MICRODEM will use decompress with 7-Zip without bothering you with the details. If you do multiple downloads you must segregate them in different directories, as they decompress with the same names and some of the decompressions will fail.

General instructions for Open Topography

Key Global Regional DEMs

Last revision 20/7/2021