Something’s going on in the arctic

09.01.16 -

by Barbara Jewett

Where Fido does the business is probably not your most pressing thought right now. Yet innocuous actions take on epic importance when your life relies on clean surface water from a Greenlandic lake sitting on permafrost. Such is life in the Arctic.

In Greenland, where the bulk of the country a sheet of ice, keeping fresh water sources free of contaminants is vital. But defining boundaries around watersheds was a challenging task, until now.

Paul Morin, head of the University of Minnesota's Polar Geospatial Center (PGC), and his ArcticDEM project collaborators from Ohio State and Cornell universities, are using the Blue Waters supercomputer at the National Center for Supercomputing Applications (NCSA) to create digital elevation models, or DEMs, that are swiftly changing what we know about the Arctic. A DEM is just what the name implies—a computer-generated 3D topographic map that shows the height of everything on the earth's surface.

"People think the Arctic as these uninhabitable places, but they're not. People live there. There are places we go in Antarctica where we actually can get a Wi-Fi signal," says Morin. However, he notes, the regions are fragile ecosystems, especially Arctic, "so any time we can do work without being there is a good thing."

In the case of Greenland, the country prohibits anything being placed inside a watershed area so as to protect the potable water sources for the island's more than 72,000 residents. But determining watershed boundaries in remote areas has been difficult as the existing DEM's weren't quite good enough. Using the new, more detailed maps Morin's team generated on Blue Waters enabled the delineation of watersheds for about 50 villages in less than a month.

The current uniform DEM for the Arctic DEMs is at a resolution of a kilometer and it has a vertical accuracy of sometimes hundreds of meters. ArcticDEM's will have a horizontal resolution of 4 meters with an error of less than 2 meters.

"It's amazing," says Morin of the satellite imagery the project's using. Each day the DigitalGlobe satellites collect the area equivalent of California in the Arctic. Over a period of a week PGC can receive up to 30 TB of data. That's where the Blue Waters supercomputer comes in.

"We can't live without Blue Waters now," he emphatically adds. "The supercomputer itself, the tools the Blue Waters team developed, the techniques they've come up with in using this hardware…Blue Waters is changing the way digital terrain is made and that is changing how science is done in the Arctic."

Why create Arctic DEMs

The ArticDEM project was established, says Morin, to create the first high-resolution, high-quality (<5 meter posting), and openly distributed set of DEMs of all Arctic landmasses above 60 degree N to help scientists understand and measure the rapid, ongoing changes to the Arctic landscape resulting from climate change and human use. This includes all of Greenland, all of Alaska, and the Russian Kamchatka Peninsula.

The goal is to complete Alaska by the end of 2016 and the entire Arctic region in 2017, within the two-year term of the U.S. chairmanship of the Arctic Council. The resulting DEMs will be made freely available to researchers, governments and the public.

How it is done

The traditional way of creating a DEM is to fly an airplane over a region, take pictures or shoot lasers from the air. The logistics of the remote operation of an airplane, the speed it flies and weather all make this a self-limiting way to collect data over a large area.

Satellites, on the other hand, continuously orbit the earth from pole to pole. So the National Geospacial Intelligence Agency (NGA) and the National Science Foundation (NSF) are leading a public-private collaboration. Using NGA-provided data from commercial satellites owned and operated by Colorado-based DigitalGlobe, Inc., the ArcticDEM project feeds the data into Blue Waters to create the digital elevation models. Morin says collaborators developed software to automate the processes.

"It is automatic and is high quality no matter what the terrain. The satellite is so well located that we can produce terrain just from the metadata without any human input. The software takes parts of two images, tries to predict where one pixel is on the other, manipulates to minimize error, and creates a new image. And it does this for 20 trillion data points," he says with a laugh.

The team began by producing Alaska and then proceeded to other regions in the Arctic. As of June, much of Alaska has been processed to 2 meter (6 foot) resolution, the rest of the arctic has been done to 8 meter (26 feet) resolution.

Morin says they use the 8m data to figure out where the good imagery is, the images that produce clearly usable elevation, and the ones that don't. Next, they do an analysis of where the holes are. These holes can be caused by clouds, by severe shadows, or open water. The solution is to keep acquiring imagery of those missing areas on subsequent satellite orbits and processing them on Blue Waters. As new imagery is acquired it will be processed into DEMs that will fill holes and be compared to earlier data. This both improves the overall elevation data and identifies topographic change.

"This is quite an astounding thing to be producing topography for 30 degrees of the globe with supercomputers and 1-foot resolution satellites," says Morin. "I've never seen anything like it."

Observing changes

The high-resolution maps allow scientists to identify changes in the landscape by comparing images from different time periods. For instance, in one area in Siberia when researchers compared images from November 2012 and June 2015 they could see that an access road had been made and trees clearcut from several areas. In fact, the data was so accurate that they've been able to document melting ice caps. The Vavilov Ice Cap off the coast of Siberia lost ice at the rate of 0.04 cubic kilometers per year between 1984 and 2012. Between 2013 and 2016, the mass loss has increased to 0.045 cubic kilometers per year, mostly since August 2015.

"The surface is currently dropping at a rate of 30 centimeters per day; a foot per day! And we are seeing that with Blue Waters," says Morin.

"We are really pleased to be pulling this off so quickly," he continues. "This project took vision. Vision at NSF, vision at NGA, and vision from everybody on the Blue Waters project. It is one of the key data sets in the earth sciences. My collaborator on ArcticDEM at Ohio State, Ian Howat, just got funded to do Antarctica. So we're going to have topography of 98 percent of the ice on earth in two years."

National Science Foundation

Blue Waters is supported by the National Science Foundation through awards ACI-0725070 and ACI-1238993.