Serendipity, Satellites, and Sea Ice
Martin Jeffries got a surprise present recently, literally out of the blue. More exactly, it came through the blue sky: it was a satellite image captured by Landsat 5 of his particular research stamping grounds in the Canadian High Arctic.
Jeffries' glaciology research has led him several times into the high-latitude seas off Canada to study ice islands (flat-topped icebergs) and the ice shelves off northern Ellesmere Island. (That's north indeed---greater than 80 degrees north latitude, closer to the pole than any part of Alaska.) When he's not on the ice itself, he studies it remotely; as a research associate professor with the Alaska Synthetic Aperture Radar Facility (ASF) at the Geophysical Institute, he helps interpret satellite images of the ice-covered polar sea.
Yet his field and office interests had never exactly coincided until very recently. While testing a new system, two ASF technicians came up with nearly cloudless images of unfamiliar icy terrain. But it wasn't unfamiliar to Jeffries; to him, it was like seeing the face of an old friend from an unfamiliar angle.
Simply listed, the features sound exotic: they included the ice caps of Ellesmere and Axel Heiberg islands, multiple glaciers, the Milne and the Alfred-Ernest ice shelves, and the multiyear ice fringe attached to the islands' northern coasts. The images revealed as well some effects of mountain barriers and gradients in wind and weather on cloud cover and sea ice condltlons.
Everything visible on the images is sensitive to global change factors. "This demonstra-tion of Landsat capability to provide images from so far north means that we now have another tool to study environmental changes there," Jeffries explained. That can have immediate importance for the management of Canada's Ellesmere Island National Park Reserve and longer-term significance for researchers watching for symptoms of global warming.
The arrival of good images surprised the experts because Landsat is the kind of satellite that can deliver data only to a line-of-sight receiving station. No station had been in position to pick up information Landsat gathered above that portion of the Canadian High Arctic until 1989. Then, the institute's Quick-Look Project for Landsat images was relocated so that the project could use the new ASF antenna atop the Elvey Building, home base for the Geophysical Institute. That antenna stands eight stories above the highest ground on the University of Alaska Fairbanks campus; it has turned out to be just high enough to be line-of-sight for Landsat data covering a new portion of the Arctic.
Not that the now-available satellite images will remove the need for Jeffries to get out on the ice. It's still necessary to find what's called "ground truth," even when ground plays little part in the matter. The floating ice shelves on which Jeffries concentrates his efforts sometimes ground locally to the sea floor, but generally their land attachment ends at the shore.
"Antarctica's huge ice shelves derive primarily from glaciers," Jeffries said, "while those from Ellesmere are built up also from sea ice. One ice shelf, the West Ward Hunt, has thick layers of sea ice---up to 20 meters of it. By studying ice cores from Hobson's Choice Ice Island, which calved in 1982-83 from the East Ward Hunt Ice Shelf, we found that it contained no sea ice. Probably it was melted off by relatively warm fresh water during warm climatic intervals. However, it looks as if fresh water has actually been freezing to the bottom of the vast Ward Hunt Ice Shelf during the last 30 or 40 years."
That sort of complexity isn't easy to explain solely through studying satellite images. You have to get out there and risk freezing vital appurtenances while gathering ground truth.
Although such activity still appeals to Jeffries, he will not soon be returning to the ice shelves of Ellesmere. Instead, he's going south; his next search for ground truth will be on Antarctica' s icy edges.
