It’s rare that an academic researcher gets to experience the life of a stunt pilot, but we found ourselves in more or less that position this past May, as we flew over the ice-covered fjords of southeast Greenland. It was exhilarating—and a little scary. We were riding in one of NASA’s research aircraft, a P-3 Orion turboprop, on which we had installed a special kind of radar for probing glacial ice. Although our equipment can work at higher altitudes, other science instruments needed to be flown low, over terrain so rugged that at times we came within a mere 30 meters of the ridges—near misses that our downward-looking radar measured for us while we peered out the window holding our breath.
Crisscrossing over this vast expanse of whiteness by air, you can easily forget that Greenland’s huge endowment of ice is slowly disappearing. The eight-times-larger Antarctic ice sheet appears to be shrinking, too, particularly around the periphery. These two areas hold 99 percent of the land-based ice on Earth, and as it melts, the water that runs off flows into the oceans, adding to their rising level. Meanwhile, most mountain glaciers, which contain the remaining 1 percent of the ice perched on land, are also retreating, further compounding an increasingly urgent problem. If sea level goes up by a meter over the next several decades, as many scientists suspect will happen, it will disrupt the lives of countless people around the world.
Will sea level really rise a meter? Or could it go even higher? And if so, how fast? Although the computer models of the ocean and atmosphere are good enough to gauge how much temperatures will likely climb over the next century, current ice-sheet models leave much room for improvement. In particular, they don’t account for many of the factors that are causing ice sheets to thin and sea level to rise.
One of the main problems is that these models lack important details about what’s going on where the ice meets the bedrock—whether the bottom of a particular locale is flat or sloping, whether there is liquid water lubricating the contact, that sort of thing. Those details in turn determine how quickly the ice will flow toward the sea.
The best way to get that information is by sending radio waves into the ice and examining the echoes. This can be done with downward-looking radar equipment that’s either towed over the ice or flown in aircraft, like the P-3 that carried us over Greenland.
The idea of using airborne and surface-based radar equipment to investigate polar ice sheets isn’t new. In fact, it’s many decades old. But we’re trying to bring such radars into the 21st century—a century that’s desperately in need of the insights that better radar surveys of these great accumulations of ice can provide.
The first inkling that radio might be useful for investigating ice sheets came during the 1930s, when the men working at the Little America base in Antarctica realized that snow and ice are transparent to radio waves. But it wasn’t until the late 1950s, after pilots reported that their radar altimeters were useless over ice, that electronics technician Amory Waite Jr. and others figured out how to use radar altimeters to measure the thickness of polar ice.
Over the next few decades, researchers from Canada, Denmark, the Soviet Union, the United Kingdom, and the United States devised various surface-based and airborne radars for probing ice. This equipment not only allowed scientists to map the bedrock hidden far below the thick ice sheets of Greenland and Antarctica, it also revealed internal layering within the ice, which can arise from the presence of air bubbles, density changes, liquid water, and even ancient dustings of the former ice surface with volcanic ash.