Satellite Advances, NSF Computation Power Rapid Mapping of Earth's Surface
By Ken Chiacchia and Tiffany Jolley
New satellite technologies have completely changed the game in mapping and geographical data gathering, reducing costs and placing a new emphasis on time series and timeliness in general, according to Paul Morin, director of the Polar Geospatial Center at the University of Minnesota.
In the second plenary session of the PEARC conference in New Orleans on July 12, Morin described how access to the DigitalGlobe satellite constellation, the NSF XSEDE network of supercomputing centers and the Blue Waters supercomputer at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign have enabled his group to map Antarctica—an area of 5.4 million square miles, compared with the 3.7 million square miles of the "lower 48" United States—at 1-meter resolution in two years. Nine months later, then-president Barack Obama announced a joint White House initiative involving the NSF and the National Geospatial Intelligence Agency (NGIA) in which Morin's group mapped a similar area in the Arctic including the entire state of Alaska in two years.
"If I wrote this story in a single proposal I wouldn't have been able to write [any proposals] afterward," Morin said. "It's that absurd." But the leaps in technology have made what used to be multi-decadal mapping projects—when they could be done at all—into annual events, with even more frequent updates soon to come.
The inaugural Practice and Experience in Advanced Research Computing (PEARC) conference—with the theme Sustainability, Success and Impact—stresses key objectives for those who manage, develop and use advanced research computing throughout the U.S. and the world. Organizations supporting this new HPC conference include the Advancing Research Computing on Campuses: Best Practices Workshop (ARCC), the Extreme Science and Engineering Development Environment (XSEDE), the Science Gateways Community Institute, the Campus Research Computing (CaRC) Consortium, the Advanced CyberInfrastructure Research and Education Facilitators (ACI-REF) consortium, the National Center for Supercomputing Applications' Blue Waters project, ESnet, Open Science Grid, Compute Canada, the EGI Foundation, the Coalition for Academic Scientific Computation (CASC) and Internet2.
Follow the Poop
One project made possible with the DigitalGlobe constellation—a set of Hubble-like multispectral orbiting telescopes "pointed the other way"—was a University of Minnesota census of emperor penguin populations in Antarctica.
"What's the first thing you do if you get access to a bunch of sub-meter-resolution [orbital telescopes covering] Antarctica?" Morin asked. "You point them at penguins."
Thanks in part to a lack of predators the birds over-winter on the ice, huddling in colonies for warmth. Historically these colonies were discovered by accident: Morin's project enabled the first continent-wide survey to find and estimate the population size of all the colonies.
The researchers realized that they had a relatively easy way to spot the colonies in the DigitalGlobe imagery: Because the penguins eat beta-carotene-rich krill, their excrement stains the ice red.
"You can identify their location by looking for poo," Morin said. The project enabled the first complete population count of emperor penguins: 595,000 birds, +14%
"We started to realize we were onto something," he added. His group began to wonder if they could leverage the sub-meter-resolution, multispectral, stereo view of the constellation's WorldView I, II and III satellites to derive the topography of the Antarctic, and later the Arctic. One challenge, he knew, would be finding the computational power to extract topographic data from the stereo images in a reasonable amount of time. He found his answer at the NSF and the NGIA.
"We proposed to a science agency and a combat support agency that we were going to map the topography of 30 degrees of the globe in 24 months."
Blue Waters on the Ice
Morin and his collaborators found themselves in the middle of a seismic shift in topographic technology.
"Eight years ago, people were doing [this] from the ground," with a combination of land-based surveys and accurate but expensive LIDAR mapping from aircraft, he said. These methods made sense in places where population and industrial density made the cost worthwhile. But it had left the Antarctic and Arctic largely unmapped.
Deriving topographic information from the photographs posed a computational problem well beyond the capabilities of a campus cluster. The group did initial computations at the Ohio Supercomputer Center, but needed to expand for the final data analysis. In 2014 XSEDE Project Director John Towns offered XSEDE's help in tackling the massive scale of data that would come from an array of satellites collecting topographic images. From 2014 to 2015, Morin used XSEDE resources, most notably Gordon at San Diego Supercomputer Center and XSEDE's Extended Collaborative Support Service to carry out his initial computations. XSEDE then helped his group acquire an allocation on Blue Waters, an NSF-funded Cray Inc. system at Illinois and NCSA with 49,000 CPUs and a peak performance of 13.3 petaflops.
Collecting the equivalent area of California daily, a now-expanded group of subject experts made use of the polar-orbiting satellites and Blue Waters to derive elevation data. They completed a higher-resolution map of Alaska—the earlier version of which had taken the U.S. Geological Survey 50 years—in a year. While the initial images are licensed for U.S. government use only, the group was able to release the resulting topographic data for public use.
Thanks to the one-meter resolution of their initial analysis, the group quickly found they could identify many man-made structures on the surface. They could also spot vegetation changes such as clearcutting. They could even quantify vegetation regrowth after replanting.
"We're watching individual trees growing here."
Another set of images he showed in his PEARC17 presentation were before-and-after topographic maps of Nuugaatsiaq, Greenland, which was devastated by a tsunami last month. The Greenland government is using the images, which show both human structures and the landslide that caused the 10-meter tsunami, to plan recovery efforts.
The activity of the regions' ice sheets was a striking example of the technology's capabilities.
"Ice is a mineral that flows," Morin said, and so the new topographic data offer much more frequent information about ice-sheet changes driven by climate change than previously available. "We not only have an image of the ice but we know exactly how high it is."
Morin also showed an image of the Larsen Ice Shelf revealing a crack that had appeared in the glacier. The real news, though, was that the crack—which created an iceberg the size of the big island of Hawaii—was less than 24 hours old. It had appeared sometime after midnight on July 12.
"We [now] have better topography for Siberia than we have for Montana," he noted.
While the large, high-resolution satellites have already transformed the field, innovations are already coming that could create another shift, Morin said.
"This is not your father's topography," he noted. "Everything has changed; everything is time sensitive; everything is on demand." In an interview later that morning, he added, "XSEDE, Blue Waters and NSF have changed how earth science happens now."
One advance won't require new technology: just a little more time. While the current topographic dataset is at 1-meter resolution, the data can go tighter with more computation. The satellite images actually have a 30-centimeter resolution, which would allow for the project to shift from imaging objects the size of automobiles to those the size of a coffee table.
At that point, he said, "instead of [just the] presence or absence of trees we'll be able to tell what species of tree. It doesn't take recollection of imagery; it just takes reprocessing."
The new, massive constellation of CubeSats such as the Planet company's toaster-sized Dove satellites now being launched promises an even more disruptive advance. A swarm of these satellites will provide much more frequent coverage of the entire Earth's surface than possible with the large telescopes.
"The quality isn't as good, but right now we're talking about coverage," Morin said. His group's work has taken advantage of a system that allows mapping of a major portion of the Earth in a year. "What happens when we have monthly coverage?"
Feature image caption: Buildings in Juneau, Alaska, as shown in the University of Minnesota topographic survey of the Arctic region. The airport runway can be seen at the bottom.
Ken Chiacchia, Senior Science Writer, Pittsburgh Supercomputing Center
Tiffany Jolley Strategic Content Specialist, National Center for Supercomputing Applications