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A new, freely-available digital elevation dataset born of international collaboration has the potential to improve the quality of Landsat and Sentinel satellite data, bolster interoperability across a wide range of satellite systems, and will offer immediate benefits to elevation modeling both within and outside the USGS.

Graphic of Copernicus GLO-30 DEM
Colorized display of the Copernicus DEM GLO-30 for the region of Krakow/Kielce (Courtesy Copernicus)

The Copernicus 30-meter global Digital Elevation Model (DEM), referred to as GLO-30, is now available online at no cost to users through the European Space Agency (ESA). DEM data characterize topography and can be used to correct geometric distortions that appear at higher elevations in data from land remote sensing satellites such as U.S. Landsat and European Copernicus Sentinel-2.

These elevation models are also used for a wide variety of studies related to elevation, with applications including coastal change monitoring and disaster planning, land management and erosion control studies and hydrologic modeling.

The European Commission (EC) agreed to help bear the cost of the multi-million Euro project based on the need for and value of consistent, high-quality global DEM data—a significant cost savings to the USGS had it decided to pursue the dataset on its own. The decision to proceed followed ongoing discussions between the EC and ESA with representatives from the USGS National Land Imaging (NLI) Program and the USGS Earth Resources Observation and Science (EROS) Center near Sioux Falls, SD, which began in spring of 2018.

The release of the new GLO-30 data signals the value of the Survey’s longstanding relationship with the EC and ESA and highlights the importance of its ongoing collaboration through the international Committee on Earth Observation Satellites (CEOS). The USGS chaired the 61-agency CEOS consortium in 2017 under the direction of former EROS Center Director Frank Kelly before handing off the reigns to the European Commission.

“The partnerships we’ve developed with ESA and with the European Commission really put this in motion,” said Steve Labahn of EROS, who heads up International Partnerships for the USGS. “We do this both bilaterally and through our multilateral CEOS engagements, where we’ve continued to have these same discussions.”

EROS Leads Evaluation of GLO-30 Utility

After the initial 2018 meeting, ESA moved to release its global Copernicus 90-meter DEM data (GLO-90) to the public but maintained restricted access to the higher-resolution GLO-30 dataset and its 10-meter DEM product over Europe. After a spring 2020 meeting, however, the USGS was asked to evaluate the potential benefits of a global 30-meter version of the dataset. The resulting report produced by EROS and NASA outlined the improved quality of the GLO-30 product over what was currently in use for Landsat data production.

The report also recognized the immediate value such a dataset would have for the science community, and its support to enhanced satellite interoperability worldwide in the coming years.

“The global availability of the Copernicus 30m DEM would assist numerous countries where a common baseline of elevation is key, such as coastal, hydrologic, ecologic, and climatic studies,” the April 2020 report concluded. “In particular, the Copernicus 30m DEM is expected to provide a much higher confidence in high-risk low elevation coastal zone delineation than other globally available DEMs today.”

The new DEM was not yet available for use with Landsat Collection 2, which will be released in the coming weeks, but Labahn expects the GLO-30 to be used in the production of Collection 3. Doing so would serve to further a goal shared by USGS, NASA, ESA, the EC and others in the remote sensing community at large of moving toward data processing schemes that ease the interoperability of civilian and commercial remote sensing satellite systems.

Collection 2 was reprocessed using the Copernicus Sentinel-2 Ground Reference Image (GRI) to more closely align Landsat and Sentinel-2 data on the ground. The use of GLO-30 DEM data as a common source for terrain correction will further improve that alignment, Labahn said, as well as offer a publicly available dataset for use by other systems such as the Indian Space Resource Organization (ISRO) Resoucesat-2/2A and commercial Earth observation companies.

“The reason GLO-30 is an improved solution is that it’s more consistent and of higher quality than any global DEM we’ve freely had access to before,” he said. “It’s a game changer.”

Immediate Application for GLO-30: Topographic Science

color graphic of Copernicus GLO-10, GLO-30, GLO-90 DEM
Copernicus DEM Instances EEA-10 (left), GLO-30 (upper right) and GLO-90 (lower right) (Courtesy Copernicus)

The new DEM data has more immediate value to scientists like Dean Gesch, who performs coastal vulnerability studies at EROS. Among other projects, Gesch leans on a variety of DEM sources for mapping projects that enable the modeling of sea-level rise impacts in low-lying areas. DEMs are also used to produce information on slope gradient and aspect (north or south)—factors that drive a wide variety of climatic, ecologic and hydrologic processes.

The newly-released DEM is an upgrade because it has better vertical accuracy, it’s globally consistent, and it’s newer than the most widely-used near-global DEM dataset, from the Shuttle Radar Topography Mission (SRTM). That dataset was collected in 2000 and first released in 2003. The total coverage of the SRTM data was limited by the Space Shuttle’s orbit – approximately 60˚N to 56˚S. By contrast, GLO-30 covers virtually all of the Earth’s landmass.

“As good as SRTM is, it’s getting long in the tooth now,” Gesch said. “It represents the state of the land’s surface, elevation-wise, in the year 2000. There’s no way around that. Elevation doesn’t change with the temporal frequency of land cover, but it does change. There are developments like open pit mining and road construction that change the topography.”

For modelers who feed elevation data into models on drainage, wetlands change, coastal inundation and the like, the improvements that will flow from the Copernicus DEM will mean more reliable results.

“Any model or study of a process that uses the GLO-30 DEM is going to have better data going in, so it’s going to have better results coming out,” Gesch said.

For the April evaluation of the GLO-30 DEM, Gesch looked at the data’s potential impact on studies that seek to define the Low Elevation Coastal Zone (LECZ), meaning areas 10 meters or less above sea level. Using a combination of newer, higher-resolution data can define such areas with 89 to nearly 100 percent confidence, whereas a combination of SRTM and other older sources returns results with confidence between 40 and 63 percent.

The evaluation concluded that the Copernicus DEM would return better results than any of the current freely-available global DEM data for the vulnerable LECZ.  

GLO-30 Release Carries on Tradition of Collaboration

Graphic of Copernicus GLO DEMs
Copernicus DEM data at three available spatial resolutions, from left: 10 meter, 30 meter, 90 meters (Courtesy Copernicus)

The new DEM data release is just the latest milestone for the international Earth observation partnerships long nurtured by the USGS. In 2010, following the adoption of the Landsat open data policy in 2008, the USGS worked through the Landsat Global Archive Consolidation (LGAC) project to repatriate data collected since the 1970s by ground stations operated by Europe into the Landsat Archive. Sentinel-2 data were added to the EROS Archive following an agreement with ESA that sought to improve Landsat and Sentinel data sharing and image calibration.

The transition of leadership duties in CEOS from the USGS to the EC further solidified an international commitment to improving data access, quality, and usability for the Earth observation community worldwide, Labahn said. The USGS will continue to work with the EC and CEOS membership to encourage the use of the GLO-30 DEM in Earth observation production and, consequently, improve interoperability across all products.

“It was through that partnership and leveraging our relationships with the (European) Commission and ESA that has enabled these significant accomplishments,” Labahn said.

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