Terrain setup and how to use DEM calculations in SEAMCAT simulation
Chapter content:
How to setup system and simulation using digital terrain in SEAMCAT and run simulations
How to inspect results of simulation using digital terrain in SEAMCAT
How to use Terrain profile Tool
How to use Propagation Model Test Tool
How to use EPP 15 to extract terrain data of simulation using digital terrain in SEAMCAT
How to use EPP 1 to extract Geo coordinates and propagation loss of simulation using digital terrain in SEAMCAT
How to download SRTM files on website https://earthexplorer.usgs.gov´
Where to find and how to download ASTER GeoTIFF files
Note on void filling method in SEAMCAT
Pre-requisites
Download / installation of SEAMCAT version supporting DEM / SEM (5.4.3A4 or later)
SEAMCAT terrain reader supports:
SRTM 1-Arc second (30 m) version 2 and version 3 in bil format
SRTM 3-Arc second (90m) version 2 raster data in bil format
SRTM 1-Arc second (30 m) version 3 GeoTIFF in tif format
ASTER GeoTIFF in tif format
Other GeoTIFF formats ending with dem.tif, 1arc_v3.tif
Terrain tiles needed for the area of interest have to be downloaded (e.g. using USGS earth explorer, or elsewhere – see information on acquiring the data bellow) and put in Folder reachable to SEAMCAT (could be also on cloud)
How to use Propagation Model Test Tool
Select propagation models to test
Set up propagation model specific settings
For propagation model using terrain select check box Use Terrain Profile Data
Set up Control panel settings
For Terrain – select Terrain Settings and there Select Start Geo coordinate, raster and Azimuth in deg
Inspect results – See below comparison of Free space, ITU-R P.452-16 with and without terrain
How to use EPP 15 to extract terrain data of simulation using digital terrain in SEAMCAT
EPP 15 enable SEAMCAT to collect geographic coordinates of Tx and Rx, calculated basic transmission loss and terrain profile. These values are collected for last event for all links in the simulation event: Victim system links, Interfering system links and Interfering links and exported to files.
Collected values are:
Frequency (MHz)
Distance (km)
Pathloss (dB)
Tx Latitude and Longitude (degree)
Rx Latitude and Longitude (degree)
Terrain profiles (m / km)
EPP 15 user interface:
UI gives explanation of values collected and enables user to determine for which category of links in SEAMCAT simulation wishes to collect values. UI is consistent with settings used for some other EPPs (e.g. EPP 1, EPP11, etc.).
EPP 15 Results:
EPP15 results are available in the Results section grouped by type of the link
By clicking link type group, user gets detailed results of collected values giving type of value and unique identifier of link (same as in Event results display). Here is example of values collected for generic system victim system link
When selecting Terrain profiles section for selected type of link user get all terrain profiles and can select terrain profile of interest to get display of height – distance profile and can export it in external file.
How to use EPP 1 to extract Geo coordinates and propagation loss of simulation using digital terrain in SEAMCAT
EPP1 can be added to simulation and used for collecting or inspecting some of the intermediate results like geo positions and path loss calculated in the simulation
In the EPP 1 settings you need to select for which type of link to collect values
Results are available under Results
Below you can find some examples of use of the EPP1 results
In Results section you can inspect these collected values by type of the link
Compare vector tool can be used to compare vectors (e.g. propagation loss for different links)
Vector scatter tool can be used to inspect scatter plot of the positions of the points in the Geo coordinates
How to download SRTM files on website https://earthexplorer.usgs.gov
Create new account - Register profile
How to find and download files in EarthExplorer
In EarthExplorer Zoom map on the area of interest for DEM files download
Under first tab – Search Criteria – select Polygon and Use Map
Under DataSets Tab select Digital Elevation – SRTM – SRTM 1 Arc-Second Global
Click Results to get resulting list
In the Results tab select file you want to download
For download select bil type of file
There is option for bulk download of many files, but it downloads not just bil but other formats
Definition of files naming and format:
https://lta.cr.usgs.gov/DD/srtm.html#entity_id
Entity ID
Field Definition: This field describes the naming convention of each tile.
Format:
SRTM3N35E089V1
SRTM = Dataset designator
1 or 3 (1 = 1 arc-second coverage, 3 = 3 arc-second global coverage)
N or S (N = North, S = South hemisphere)
Next two characters indicate lower left corner Latitude
E or W (E = East, W = West hemisphere)
Next three characters indicate lower left corner Longitude
V1, 2, or 3 (1 = SRTM Non-Void Filled, 2 = SRTM Void Filled, 3 = 1 Arc-Second Global)
Where to find and how to download ASTER GeoTIFF files
ASTER files are provided in GeoTiff format and only available for 1 Arc-Sec resolution (30 m). ASTER stands for Advanced Spaceborne Thermal Emission and Reflection Radiometer done by the Ministry of Economy, Trade, and Industry (METI) of Japan and the United States National Aeronautics and Space Administration (NASA).
Aster data tiles can be found here:
NASA provides a tool EarthData Search, with the help of which maps in ASTER Global Digital Elevation Model V003 (1 Arc-Sec, 30 m resolution) can be downloaded. A registration is necessary to open an EarthData account, but the “EOSDIS data are openly available to all and free of charge except where governed by international agreements.”
Link to EarthData Web site
Another tool that provides ASTER GDEM freely and without a need for registration is from the Japan Space Systems web page (also only Model V003).
Note: When downloading files from Japan Space Systems ASTER GDEM there will be 2 subfolders with different files – GeoTIFF DEM fiels are the files ending with dem.tif
Link to ASTER GDEM Web Site
Format of file name:
ASTGTMV003_XXXXXXX_dem.tif
Field Definition: This field describes the naming convention of each tile.
Format:
ASTGTMV003_N45E015_dem.tif
ASTGTM = Dataset designator
V003 = version of source data
N or S (N = North, S = South hemisphere)
Next two characters indicate lower left corner Latitude
E or W (E = East, W = West hemisphere)
Next three characters indicate lower left corner Longitude
dem = designation for DEM data
Explanation of the format:
Geospatial World, “GeoTIFF – A standard image file format for GIS applications,” Online:
https://www.geospatialworld.net/article/geotiff-a-standard-image-file-format-for-gis-applications/
NASA Earth Data, “GeoTIFF File Format,” 'Online:
https://cdn.earthdata.nasa.gov/conduit/upload/12430/ESDS-RFC-040v1.1.pdf
Open Geospatial Consortium, “OGC GeoTIFF standard,” 2019, Online:
http://docs.opengeospatial.org/is/19-008r4/19-008r4.html
Adobe, “TIFF,” Revision 6, 1992. Online:
https://www.adobe.io/content/dam/udp/en/open/standards/tiff/TIFF6.pdf
Aware Systems, «TIFF File Format,» Online:
https://www.awaresystems.be/imaging/tiff.html
Note on void filling method in SEAMCAT
Global SRTM 1-Aec Sec data are not void filled in regions outside the United States. In that respect some tiles contain voids where height data is not defined1.
According to the US Geological Society2,
“SRTM Void Filled elevation data are the result of additional processing to address areas of missing data or voids in the SRTM Non-Void Filled collection. The voids occur in areas where the initial processing did not meet quality specifications. Since SRTM data are one of the most widely used elevation data sources, the NGA filled the voids using interpolation algorithms in conjunction with other sources of elevation data. The resolution for SRTM Void Filled data is 1 arc-second for the United States and 3 arc-seconds for global coverage.”
Voids shown with red colour in one tile
To avoid presenting voids in the extracted profile, SEAMCAT uses method to fill the void data in the profile with the last “valid height”. Note is added to the Terrain profile tool and PMP explaining this method.
1 It is observed that voids in general occurs in mountainous areas where there are big changes in height in short distance or water surfaces.