Mapping with MODIS

 

Using the detailed, near-real-time imagery that appeared on his computer screen each day, Stone detoured the ships through the gap between what seemed to be the safer, predictably lodged icebergs B-15K and C-16, neither of which had moved in the past 3 years.

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  C-16 bathymetry
 

“To everyone’s surprise, C-16 began to move slightly the afternoon of January 8, and by January 11 was moving in earnest, making the prospect of a blocked shipping channel a real concern,” says Jessica Walker, GIS analyst with Raytheon Polar Services, to whom the task of tracking the icebergs in the MODIS imagery fell. “C-16 sometimes barreled forward,” she says. “After 3 years of not moving, it jumped 7.5 kilometers north about the same time as the ships were moving in fuel and supplies.”

Walker had been making regular animations of B-15A, which was hurtling towards the Drygalski Ice Tongue, the floating extension of the David Glacier over the Ross Sea, on a direct collision course. A direct collision between the largest moving object on the planet and a roughly 75-kilometer-long spit of ice could make for an exciting show, a demolition derby on a gargantuan scale. “Everyone wanted to see the collision and wanted to document it,” says Walker. “I couldn’t even go to the coffee house without someone asking me about the iceberg. It was neat being able to provide critical information of such a significant event.”

 

Bathymetry data outline the contours of the sea floor around the C-16 and B-15K icebergs. Since the icebergs were most likely to move along the deep channels, the bathymetry helped the U.S. Antarctic Program predict where the icebergs might drift and where it would be safest to cut the shipping channel through the ice. Image by Jesse Allen, Earth Observatory, based on data from Jeff Schmaltz (MODIS Rapid Response Team), Jessica Walker (Raytheon Polar Services) and Fred Davey (Institute of Geophysical & Nuclear Sciences Ltd.)

  B-15A edge
 

A countdown to collision ensued, but B-15A defied predictions and ground to a halt mere kilometers from the ice tongue. Bathymetry information overlaid on the MODIS images showed exactly why the iceberg had stopped; it was grounded. The bathymetry images also explained why the iceberg later rotated and drifted into deeper waters in the Ross Sea, sideswiping the tip of the ice tongue as it went. The massive berg was following the deeper channels of the sea. “When you look at the image, you realize it was the only way the iceberg could move,” says Walker.

Despite the anticlimax of B-15A’s movements, Walker’s practice at making animations and bathymetry images now stood her in good stead as she turned to track C-16, a much larger operational concern. The bathymetry maps showed a shallow shoal to the west of the shifting iceberg, which she hoped would keep the berg out of the shipping channel.

The Coast Guard, whose icebreakers were keeping the channel clear, began to watch the MODIS imagery closely. “The captains were concerned that C-16 would rotate in and close off the channel. They worried that it would be hard to get their ships out,” says Stone. The captain of a Russian icebreaker hesitated to enter the channel at all. Stone brought the MODIS images to the ship to reassure the caption that the ship’s crew could watch the icebergs’ movements daily. “I don’t know if he used the images, but he brought his ship through the channel to McMurdo,” says Stone.

 

The B-15 iceberg was already a navigational concern when Josh Landis photographed it on a November 2000 excursion. GIS specialist Jessica Walker combined satellite images with underwater topographic data to predict the movements of one of the giant iceberg’s largest pieces, B-15A, as it moved toward a collision with an ice tongue in the Ross Sea. The analysis was good practice for predicting the movements of other icebergs in the shipping route to McMurdo Station. (Photo courtesy Josh Landis, National Science Foundation, AWS/AMRC Photo Gallery)