Available sources of DEM - DTM data
DTM (bare terrain) models are very hard to find. Usually, they use some form of post processing of DSM data using some other data sources and methodologies to eliminate artefacts on top of bare terrain form DSM models.
FABDEM (Forest And Buildings removed Copernicus DEM)
The University of Bristol has combined forces with Bristol-based flood modelling company Fathom to launch FABDEM. Initially designed to create a more accurate, detailed data set for flood modelling, landslide modelling and location analysis, the GIS applications for FABDEM could be very useful for SEAMCAT users as source of DTM data.
FABDEM is the first global DEM with forests and buildings removed at a 30 m resolution making it “bare Earth” Digital Terrain Model DTM. The dataset is available between 60° S and 80° N at 1 arc second (∼30 m) grid spacing. FABDEM v.1.2 is an update of original version v.1.0 and is freely available at [2]:
The original source of DSM data for FABDEM is from new Copernicus GLO-30 (COPDEM30), which is intended to become the ‘gold standard’ for global DEMs. They have used machine learning correction algorithm to remove buildings and forests from the Copernicus Digital Elevation Model to produce a global DTM map at 1 arc second (∼30 m) grid spacing.
Training of correction algorithm was done on a unique set of reference elevation data from 12 countries, covering a wide range of climate zones and urban extents. Hence, this approach has much wider applicability compared to the previous DEMs trained on data from a single country.
Authors elaborate that method applied reduces mean absolute vertical error in built-up areas from 1.61 to 1.12 m, and in forests from 5.15 to 2.88 m. The new elevation map is more accurate than existing global elevation maps and will strengthen applications and models where high quality global terrain information is required [3].
Figure describes in general the workflow process for creating FABDEM DTM from Copernicus DEM model.
FABDEM DTM data are stored in 1 deg x 1 deg raster tiles in GeoTIFF format. The lower left coordinate is used for tile naming. On the web page it is possible to download the whole data set (which is around 296.7 GiB), and there are also prepacked zip files 10 deg x 10 deg each containing approximately 100 DEM tiles.
Data is available under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0) license which is a non-commercial open license.
The key features of this license are listed as follows:
Attribution (BY): You must give appropriate credit to the creator, provide a link to the license, and indicate if changes were made;
NonCommercial (NC): You may not use the material for commercial purposes;
ShareAlike (SA): If you remix, transform, or build upon the material, you must distribute your contributions under the same license as the original.
This license allows to share, copy, and redistribute the material in any medium or format.
Sonny's LiDAR digital terrain models of EUROPE
STG considered freely available DTM and DLU raster data and identified a database of Digital Terrain Model for Europe that is freely available from a private, non-commercial website https://sonny.4lima.de/ .
The data are based on precise LiDAR elevation sources that have been collected using the Airborne Laser scanning (ALS) method. The database contains two types of DTM data:
HGT files with 1” and 3” horizontal resolution and 1 m vertical resolution (aligned to SRTM grid);
GeoTIFF files with 20 m and 30 m horizontal resolution and 0.1 m vertical resolution.
Analysing the hgt DTM elevation data available on the website, it was identified that files are provided for geographical area of Europe and organised in tiles. From the webpage, the user can download hgt files, either country by country or for the whole Europe.
The 1" and 3" models are split into several 1 x 1° files in the file format of the SRTM datasets (.hgt files). Their horizontal resolution is ca. 20 x 30 m (1") and ca. 60 x 90 m (3"), and their vertical resolution is 1 m. Because of their finer grid the 1"-DTMs are more precise than the 3"-DTMs but on the other hand also much larger. For the alpine countries Austria and Switzerland even finer models (0.5") are available.
GeoTIFF DTM elevation files are provided for geographical area of Europe and files are organized country by country. This is non-typical setting of files which determined some of issues in implementation.
Their horizontal resolution is 20 x 20 m (20m) and 50 x 50 m (50m), and their vertical resolution is 0.1 m. Because of their finer grid the 20m-DTMs are more precise than the 50m-DTMs but on the other hand also much larger regarding download- and file sizes. For the alpine countries Austria and Switzerland there are available finer models (0.5" and 10m).
The corresponding DTM file readers and other related functionalities have been implemented in SEAMCAT and the DTM models can be used in the simulations, EPPs and tools (see doc STG(24)25, STG(24)26R1).
The Sonny's website seems to be a valuable source of DTM data. However, in addition to being limited only to Europe, other limitations include possible license terms issues, the web site is private, the precision of obtained data and errors of the post processing are not fully clear, etc.
DTM hgt files are downloaded from open-source repositories:
DTM GeoTIFF files are downloaded from open-source repositories: