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Helicopter flies instrument over ice.
Photo Credit: Peter Rejcek
A helicopter flies the HEM bird over the Sea Ice Runway earlier this month. The HEM bird, used by New Zealand scientists to determine sea ice thickness, employs a technique called electromagnetic induction, along with a laser altimeter, to make the measurement.

Additional safety check

New Zealand helps USAP test EM technique to determine Sea Ice Runway thickness

An instrument used by New Zealand scientists and their collaborators to study sea ice in the polar regions may prove to be a useful piece of technology to save time and labor for the U.S. Antarctic Program (USAP) External U.S. government site.

During a windy day in early December, a helicopter carrying what appeared to be a torpedo with a cone in the back and dangling vertical about 50 feet below the chopper, swept across the sea ice near the USAP’s McMurdo Station External U.S. government site.

The benign torpedo-shaped instrument is called the HEM bird. It creates a magnetic field around itself that generates a small electric current in the conductive saltwater below to form a second magnetic field, as part of a method known as electromagnetic induction to measure the distance to the bottom of the sea ice.

People depart big plane.
Photo Credit: Jean Varner/Antarctic Photo Library
Passengers disembark from a C-17 on the Sea Ice Runway.

An altimeter aboard the helicopter concurrently shoots a laser down to measure the distance between the New Zealand A-Star and the sea ice surface. The difference between the distance of the electromagnetic fields created by the HEM bird and the measurement from the laser altimeter provides an estimate for the thickness of the sea ice.

During the test, the helicopter flew low down the flagged Sea Ice Runway External U.S. government site before banking away and making a turn above McMurdo Station, with the cloud-shrouded Erebus volcano External Non-U.S. government site in the distance. Soon it made another pass across the Sea Ice Runway, which had just been decommissioned a couple days earlier as air operations moved to Pegasus Airfield External U.S. government site on the permanent McMurdo Ice Shelf about 14 miles away.

Only last week, huge wheeled aircraft like the U.S. Air Force’s C-17 Globemaster III External Non-U.S. government site had used that same swath of ice – not much thicker than the tallest NBA player – as a runway for landings and takeoffs.

Each year personnel at McMurdo Station build a temporary runway on the sea ice for aircraft to use during October and November, in support of the summer field season for researchers.

The Sea Ice Runway requires constant monitoring to ensure the safety of people and aircraft. A professional surveyor periodically takes temperature and thickness measurements across the groomed ice runway, which is 10,000 feet long and 200 feet wide with a 1,000-foot overrun.

Buildings and planes sit on ice in front of mountain range.
Photo Credit: Peter Rejcek/Antarctic Photo Library
The Sea Ice Runway in 2011.

“One guy, or even a lot of guys, can only do so many spot measurements. We’ve wondered for a long time about the variability [of the ice] – not that we don’t think that we’re safe and that we’re not doing it the right way – but it’s another check,” explained Maggie Knuth, Operations manager for Antarctic Infrastructure and Logistics External U.S. government site in the National Science Foundation’s Division of Polar Programs External U.S. government site.

Knuth said NSF approached Antarctica New Zealand External Non-U.S. government site about doing a test run across the Sea Ice Runway to test the viability of the technology. The EM system is also available in a ground-based platform that would allow an instrument package to be dragged by sled across the ice, according to Knuth.

“This was an opportunity to work with [Antarctica New Zealand] and collaborate,” she said. “The idea is to get away from the labor needed to constantly check it.”

The thickness of the Sea Ice Runway – as much as 95 inches in some places this season – determines how heavy a plane can be loaded and how long it can remain parked in one location, according to Knuth, an engineer formerly with the U.S. Army Cold Regions Research and Engineering Laboratory (CRREL) External U.S. government site.

“This is to preserve the sea ice,” she explained. “You can have local deflection.”

The Sea Ice Runway is usually constructed in roughly the same place, within a couple of miles of McMurdo Station. It takes about six to eight weeks to prepare depending on ice conditions, according to Gary Cardullo, airfield manager for the USAP.

Air operations usually shift to Pegasus Airfield by the end of November while ice conditions between the sea ice and ice shelf transition are still good, she said. Later in the summer, the sea ice will usually melt and blow out of McMurdo Sound, to be replaced by open water.

“The Sea Ice Runway was in great shape this year. They did a great job,” Knuth said.

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