Polar Handymen Take on GNET Summer Helicopter Maintenance Flying rocks, 100-mile-an-hour winds, curious wildlife and careful logistics planning were just some of the issues a small team of scientists led by the Technical University of Denmark (DTU) had to address this summer while conducting maintenance operations at GNET (Greenland GPS Network) sites in Greenland.
GNET is a network of ruggedized instruments, most of which were installed with NSF funding between 2007 and 2009, around Greenland’s coast for measurements that help scientists monitor the state of the ice sheet.
“This is the first time we’ve actually done a concentrated ‘We need to go here for maintenance’ effort.” Mike Willis, a scientist based at Cornell University, said. “That was largely because we hadn’t visited some of the sites since they were first installed in 2007.”
This summer’s helicopter maintenance team led by Finn Bo Madsen of DTU’s National Space Institute tackled everything from installing new hardware, improving reliability of communications, to repairing damage caused by extreme winds and polar bears.
Over the two-week maintenance mission, Madsen and his team—a fellow scientist and a helicopter pilot—visited 11 sites on the southeast coast of Greenland covering 800 km and racking up 30 hours of flying time.
Prepping for site visits requires a lot of foresight and planning. Greenland’s rugged geography and sparse population added unique challenges. With 630 km separating Greenland’s two closest towns on the east coast, striking the right balance between fuel, equipment and personnel was critical for safe helicopter navigation.
“The helicopter has a finite limit for take-off weight. The more equipment you want to bring, the less fuel the helicopter can carry and thereby the shorter range in miles the helicopter will have,” Madsen explained. “So if we bring lots of equipment, we need places to stop to refuel the helicopter on the ground. In Greenland there are usually long distances between cities or settlements with refueling opportunities, so often we need to deploy our own caches of fuel drums in the field.”
Once the helicopter was packed to capacity and fueled, the team was off to the GNET sites.
When the team arrived at a site that hadn't produced data or sent out contacts in several years, they were not sure what to expect. In many cases the fixes were fairly simple— retrieve the stored data, replace any damaged communication equipment, test to ensure proper operation, then fly on to the next one. But other station repairs were more challenging.
“There’s a hell of a lot of MacGyvering with this project,” Willis joked. “Everything is standardized and kind of just fits together and works, but when you’ve landed at a place that’s been blown apart and you don’t necessarily have all the tools or all the things to fix it, you have to sit there and ask, ‘What can I do to make this work until the next time someone can get here?”
Earth, Wind, and Animals
At two locations, the GNET units were completely blown over by strong, localized winds that sweep off the ice. In some cases these katabatic winds can exceed 100-miles-per-hour, yielding more than enough strength to overturn up to 2,700 pounds of equipment.
“When the remains of a hurricane [spin] off the south coast of Greenland, it basically sucks all the air off the plateau. A couple of the sites were blown a few feet from where they should have been. The aluminum frames looked as though a kid picked them [up], crumpled them up like a piece of paper and threw them back on the ground.” Willis said.
At another site, near the Humboldt Glacier in northwest Greenland, polar bears were responsible for the damage. Although in 2007 care was taken to install the sites far from known polar bear breeding grounds and high traffic areas, every now and then an inquisitive polar bear comes across the equipment.
“We have seen one station attacked by curious polar bears that may have rubbed their backs on the monument, been chewing on cables or have given the equipment a thorough pounding with their paws.” Madsen said. “We repaired a station that had been badly beaten up by a polar bear and three days later we lost communications – probably because the bears returned.” Madsen plans to go back to the polar bear-damaged site in mid-September with some new tricks up his sleeve to reinforce the structures.
Overall, the maintenance visits found that most stations were operating normally. These stations received planned upgrades to ensure continuing reliability. The communications system at three sites had problems that were remedied, and the maintenance team recovered data stored on the GPS receivers. At two heavily damaged stations, data were recovered and the sites were rebuilt as best as possible.
The GNET Project
GNET is an international, collaborative effort whose U.S. effort is funded by the National Science Foundation and led by Dr. Mike Bevis at the Ohio State University. It involves partners at the Technical University of Denmark, the University of Luxembourg and Cornell University. The network consists of 56 rugged GPS units stationed along Greenland’s coast that measure “post-glacial rebound.” Ten of these stations existed prior to the establishment of GNET, while 46 new stations were installed between 2007 and 2009. Over the next two to three years, GNET will measure the vertical movement of Greenland’s crust in response to ice mass gain or loss. The results will also help scientists correct satellite measurements of the Greenland Ice Sheet, like those collected by the GRACE gravity mission, that give a broader picture of ongoing ice changes.
“We’ve got two signals that we’re looking at: a ‘big picture’ one that allows us to correct satellite measurements and get an overall picture of the state of health of the ice sheet and one, which is more local, that tells us what is happening in the neighborhood of the GPS systems,” Willis explained.
An international group of scientists began installing GNET in 2007. A fully equipped GNET station consists of enclosures containing 12 to 24 batteries, an aluminium mast bolted to solid bedrock carrying a GPS antenna housed in a domed structure called a radome, and an electronic control board containing a GPS receiver and an Iridium modem.
Fueled By Alternative Energy
Southern stations that get more sunlight are powered by batteries and two to four solar panels attached to a specially designed lightweight metal frame. Northern stations incorporate the same design and also include small wind generators that provide additional power during the long, dark high-Arctic winter. Data are downloaded daily by Internet where available, and via Iridium satellite modem at more remote locations.
Needless to say, the GNET equipment was designed to withstand extreme environmental conditions. But not even the most durable devices can escape completely unscathed by Greenland’s weather conditions and curious wildlife inhabitants.
To ensure continued performance of a large network such as GNET, maintenance is essential. Next year, the GNET field season will be led by Ohio State University with support from DTU and UNAVCO. Despite occasional damage to the equipment the GNET stations are performing well, delivering a data return of more than 80 percent.
For more information about the GNET project, visit: www.polenet.org—Alicia Clarke