Collaboration Advances Elevation Mapping
USGS EROS and NGTOC work together to map a 1-meter Digital Elevation Model for a watershed
We can know a place pretty well and still learn something from a map of it. A map showing terrain elevation including rivers and streams, for example, indicates where heavy rainfall will flow or new construction of structures, bridges and roads would be most suitable.
The U.S. Geological Survey (USGS) has more than 140 years of experience mapping elevation, a key ingredient to topographic maps. Methods and accuracy are continually improving, as a new collaboration among USGS scientists reveals.
The Earth Resources Observation and Science (EROS) Center and the National Geospatial Technical Operations Center (NGTOC) make maps with different methods and purposes, but they have found value in sharing expertise. Their ability to collaborate has strengthened in recent years since they were brought together to comprise the USGS National Geospatial Directorate. In September 2024, the centers celebrated the completion of an elevation mapping prototype project that was enhanced by the involvement of both as they helped and learned from each other.
As part of its mission to provide national topographic information, the USGS National Geospatial Program (NGP) oversees the 3D Elevation Program (3DEP) and the 3D Hydrography Program (3DHP). The NGP challenged the National Geospatial Directorate, as its primary operational provider, to come up with a process that could relatively quickly provide new 1-meter seamless Digital Elevation Model (DEM) data for the nation as input to derive all new 3DHP surface water data and to support myriad other requirements of a broad range of users.
Digital Elevation Models (DEMs) rely on lidar data to generate a 3D view of elevation for lidar collection projects. Lidar (light detection and ranging) is a method of remote sensing that uses a laser to transmit pulses of light to the ground that then reflect back. Travel time for the light is used to determine the distance between the laser scanner—in an airplane or drone, for example—and the ground.
These lidar projects are combined to create a seamless, continuous model of the terrain surface for the United States. A seamless model allows scientists and other analysts to do large-scale assessments and planning for any area, regardless of the original boundaries of the individual projects.
Figuring Out How to Approach a Big Goal
The resolution for the currently available national seamless DEM is 10 meters. When NGTOC received the request to create a prototype 1-meter seamless DEM for a watershed, USGS Senior GIS Applied Researcher Barry Miller started exploring methods to make it happen.
Miller faced some challenges. This DEM area would contain 10 times the detail of the currently available seamless DEM, and it would need to blend, in a consistent way, the vertical and horizontal data from several lidar collection datasets that varied by year, from 2013 to 2020. The production method also had to be expandable to a seamless nationwide dataset. And the prototype had a firm deadline: the end of September 2024.
Miller decided to look to EROS for help as well. EROS is well known as the USGS center that archives and distributes Landsat satellite imagery, but it also performs science using a variety of remote sensing data and had a key role in producing the precursor to 3DEP, the now retired National Elevation Dataset (NED). Current elevation work at EROS focuses on coastal areas and takes into consideration both land elevation and water depth for the Coastal National Elevation Database (CoNED) Applications Project, with support from NGTOC.
The watershed selected for the prototype was the Lower Androscoggin watershed, a hilly, forested, 2,200-square-mile area in part of Maine and New Hampshire that contains numerous lakes, rivers and towns. While lidar coverage already existed for the entire area, it came from five different data projects that needed to be merged to make a seamless product.
That blending process presents a technical challenge, even when all the project data comes from lidar. The data first must be transformed horizontally (pinpointing location) to meet the same standards, and then vertically (determining elevation above sea level). It’s no easy feat if some of the data available was obtained earlier through less accurate methods than more recent data. An algorithm helps bring the older vertical data up to the newer standards.
That’s where collaboration has become key. NGTOC has easy access to elevation data onsite and a lot of experience with automation and producing a large volume of data quickly. EROS, meanwhile, has significant experience from the CoNED project in figuring out how to integrate differing datasets in coastal areas including shoreline topography with water depth, or bathymetry.
Collaboration Helped Meet the Deadline
Miller’s research into a method to use for producing the prototype led him to seek out geographer and GIS analyst William (Matt) Cushing at EROS to learn more about a tool Cushing created for transforming disparate vertical datasets for use in CoNED.
“NGTOC has the experience in putting out this kind of volume and managing that level of elevation data, which is a different beast than Landsat, what this center focuses on,” Cushing said. “But on the CoNED end, we bring in the asset of understanding and integrating datasets. That’s where it made sense to meld the two together.”
Miller and Cushing have been working to integrate software code bases used at each center to use Cushing’s tool for blending datasets in the future. Because of the short timeframe for the prototype, a less customized method was used with code supplied by Cushing for the vertical data transformation.
“The data was better quality than I expected. I was pleasantly surprised with how well they lined up,” Miller said.
When the prototype had been completed, it needed to be published as a data release through the USGS digital repository ScienceBase by the end of September, and collaboration came in handy again. Miller didn’t have extensive experience with that process, which tends to be more automated for his other work, but Cushing and others at EROS did—Jeff Danielson, a physical geographer who leads CoNED, and Jeff Irwin, a geographer who helps assess lidar accuracy for the 3D Elevation Program.
For several intense days, Miller, Danielson, Irwin and Cushing forged through all of the review, metadata and data-access steps necessary to release the prototype data. And on September 26, they celebrated the release.
‘We’re Better Working Together’
Miller and Cushing’s collaboration continues as an example of the complementary strengths that David Brostuen, director of the National Geospatial Directorate, wants to take advantage of.
“These two centers have different missions. One thing they have in common is mapping the nation. EROS maps the nation with Landsat data and with land cover data. NGTOC maps the nation with a variety of other national data layers to produce topographic maps,” Brostuen said. “It just makes sense wherever possible to bring the remote sensing expertise that EROS has together with the geospatial expertise that NGTOC has to see where we can produce new products and services. This is one example of that, but there could be a lot more.”
EROS Director Pete Doucette agrees that this project made sense to bring together both centers. “Advancing the development of next generation elevation products was the most constructive place to start with our partnership.”
NGTOC Director Kimberly Mantey, who previously worked on elevation projects herself, is excited to see a seamless 1-meter product come together after a dozen years or more of talking about the concept. And having worked with Jeff Danielson and others at EROS in the past, she praises the teamwork for this accomplishment.
“We’re better working together. We’ve achieved something in this year that I think a lot of people weren’t sure was going to happen. And it wasn’t only achieved, it was achieved with smiles on people's faces,” Mantey said. “We can lean on the strengths of each center to make great things. USGS exists to do good science for the public and do good science for each other.”
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