Downloading Shuttle Radar Topography Mission (SRTM) data using QGIS
One of the key components of geospatial analysis is digital elevation model (DEM) data, which provides information about the height and slope of the earth’s surface.
The Shuttle Radar Topography Mission (SRTM) is a NASA mission that has provided high-resolution global DEM data, and with the right tools, it is possible to download and use this data for free.
Further reading: the difference between DEM, DTM, and DSM
In this blog post, we will guide you through the process of downloading SRTM DEM data using the popular open-source software QGIS.
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Step-by-step instructions for downloading SRTM digital elevation model data using QGIS:
- Install QGIS software on your computer.
- Open QGIS and click on the “Plugins” menu on the top toolbar.
- Select “Manage and Install Plugins” from the dropdown menu.
- In the “Search” bar, type “SRTM Downloader” and select the plugin from the list of results.
- Click on the “Install plugin” button to install the SRTM Downloader plugin.
- Once the installation is complete, click on the “Web” menu on the top toolbar and select “Quick Map Services”.
- In the “Search” bar, type “OpenStreetMap” and select the “OSM Standard” option.
- Change the coordinate reference system of the data frame to EPSG:4326 (WGS 1984) by clicking on the “Project” menu on the top toolbar, selecting “Properties” and then selecting “CRS”. Select EPSG:4326 from the list and click “OK”.
- Zoom in to the area for which you want to download the SRTM data using the “Zoom In” tool.
- Click on the “SRTM Downloader” icon on the toolbar to open the plugin.
- Select the “Use canvas extent” option to specify the boundaries of the area you want to download.
- Click on the “Download Now” button to start the download process.
- Enter your NASA Earthdata login credentials (or create a new account if you don’t have one) when prompted.
- Wait for the download process to complete. The downloaded tiles will be added to your workspace as separate layers.
- To merge multiple tiles into one raster file, click on the “Raster” menu on the top toolbar and select “Miscellaneous”. Choose the “Merge” tool, select the input layers you want to merge, and click “Run”. The merged raster file will be added as a new layer to your workspace.
- To save the merged raster file, right-click on the layer and select “Export” > “Save As”. Choose the file format and location, and click “OK”.
That’s it! You have successfully downloaded SRTM digital elevation model data using QGIS.
Shuttle Radar Topography Mission (SRTM) and the data you just downloaded
The Shuttle Radar Topography Mission (SRTM) was a collaborative project between the National Aeronautics and Space Administration (NASA) and the National Geospatial-Intelligence Agency (NGA), with participation from the German Aerospace Center (DLR) and the Italian Space Agency (ASI). The primary goal of the mission was to create high-resolution, near-global digital elevation models (DEMs) of Earth’s land surface.
The mission was carried out from February 11 to February 22, 2000, using the space shuttle Endeavour on its STS-99 mission. The SRTM payload consisted of a specially modified radar system known as C-band Synthetic Aperture Radar (C-SAR) and an X-band Synthetic Aperture Radar (X-SAR). The C-SAR was operated by NASA, while the X-SAR was a joint effort between DLR and ASI.
The radar systems functioned by sending out microwave signals that bounced off the Earth’s surface and were then received by the shuttle’s antennas. The differences in the time it took for the radar signal to return, as well as the phase difference between the transmitted and received signals, were used to calculate the elevation of the Earth’s surface.
The SRTM utilized a technique called interferometry, in which two radar antennas were mounted on the shuttle, one at the end of a 60-meter (200-foot) mast and the other on the shuttle itself. The large baseline between the two antennas allowed the system to measure height differences with great precision, resulting in high-resolution elevation data.
The mission covered the majority of Earth’s land surface between 60 degrees North latitude and 56 degrees South latitude, which includes about 80% of the Earth’s total landmass. This coverage encompasses most of the world’s inhabited areas and major landforms. The elevation data collected by the SRTM was processed into DEMs with a horizontal resolution of 1 arc-second (approximately 30 meters) for the United States and 3 arc-seconds (approximately 90 meters) for the rest of the world.