The DEM problem¶
One of the main goals of rgitools is to provide not only aggregated statistics (hypsometry), but also a local topography map for each single glacier in the RGI.
Unfortunately, there is no gap-free and freely available global DEM to date. For most regions we can rely on a number of sources, which all have their own issues. Here is the list currently supported by OGGM/rgitools:
- the Shuttle Radar Topography Mission (SRTM) 90m Digital Elevation Database v4.1 freely available for all locations in the [60°S; 60°N] range
- the Greenland Mapping Project (GIMP) Digital Elevation Model covering Greenland (for RGI region 05)
- the Radarsat Antarctic Mapping Project (RAMP) Digital Elevation Model, Version 2 covering the Antarctic continent (for RGI region 19 with the exception of the peripheral islands)
- the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER GDEM) Global Digital Elevation Model Version 2 covering the entire globe. (password protected for license issues)
- the Viewfinder Panoramas DEM3 products, a global DEM based on various of the above listed sources, manually merged and corrected.
- the TanDEM-X 90m DEM, newly released and covering the entire globe. (password protected for license issues)
- the Arctic DEM newly released in version 7 and covering the northern latitudes at various resolutions (we picked 100m for a start).
In theory, this should be enough data. In practice, none of the solutions above is 100% satisfying. We didn’t do a thorough assesment yet, but you can have a look at the following examples:
TODO: examples in Antarctica
We have to keep in mind that any kind of glacier bed estimate inversion or glacier simulation based on ice-dynamics cannot deal with artefacts. Therefore, robust and gap-free datasets are much preferred over more accurate but incomplete DEMS. Furthermore, the concurrent timing of the glacier outline with the DEM is another important criterion, as shown by the Columbia example.
Altogether, we are confident in: - SRTM for all latitudes below 60° N and S - GIMP for Greenland - RAMP for Antarctica (but the peripheral Islands are an issue)
For everything else, more investigation is needed. DEM3 offers the stability and timeliness that TanDEM-X and ArcticDEM cannot offer (yet), and is the current default in OGGM.