Feature: Arctic Thaw

Measuring Change

Leveraging the Moment

by | 4.9.2012 at 3:24pm
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gravity check

Jim Cochran setting up the portable gravimeter next to the tie station. (Photo by M. Turrin)

Time takes on a new meaning in the field. Every moment is compressed in order to gain maximum yield. Applying human accounting, field time is limited by available resources, personnel, and funds, while using nature’s accounting the limits shift to windows of weather, and seasonality for ice phenomena. In the field both human and nature can conspire for or against you. A seasoned field crew learns to take advantage of every break from the planned work schedule to rethink, refine and reprogram their instruments and data collection.

After four days of intense commitment on the part of the flight crew, and the NASA and Wallops teams, the plane has traversed over 4450 miles round trip, spent two days under repair and will arrive back within hours. While the instrument teams await the return of the P-3 they work through data, check on equipment and ensure that all systems remain ready to begin as soon as IceBridge flights resume.

Lamont’s teams are responsible for the gravity and magnetics equipment. Gravity and magnetics are windows to the geology beneath the ice. The gravity measures density telling us of changes in structure or material beneath the ice sheet which result in a change in gravitational attraction or pull. Gravity is useful for locating changes but magnetics helps us ‘see’ more of what is under the ice, distinguishing between the low magnetic strength of soft mounds of sediment, to high magnetic strength of volcanic basalts. Understanding the Earth below is important in predicting future glacial movement and speed.

Magnetic Station

Beth Burton from the USGS checks that the base station for the magnetometer is functioning smoothly. (Photo by M. Turrin)

The magnetics base station has been visited to be sure it is intact, solar panels cleared of snow, and is recording data on the background magnetics from the Earth’s magnetic field. Collecting this data is essential since the plane magnetometer measures not only the geology beneath the plane as it flies, but the total magnetic field which includes changes in the Earthʼs field through the day. Collecting the background field allows us to back this out of the final readings to better understand the true signature of the geology beneath.

The gravity team also has a base station. They use this station, as well as a series of values that have been taken around Kangerlussuaq, as tie points for their data. Today is an opportunity to tie the readings to an absolute gravity reading by the Danish Geodynamics Department National Survey & Cadastre. A portable instrument will be used to collect readings at both the absolute survey point and the base station location. Gravity instruments are temperature sensitive so each is heated to an optimal temperature and must be kept at this range. The portable instrument has an internal heater and after several attempts it is clear the heater is not functioning correctly and will not allow the team to collect the tie in. The attempt will have to be revisited at some point in the future. For the immediate future, however, we hope to be back in the air flying tomorrow!

Gravimeter tie in

Jim Cochran checking the gravimeter readings on the Kangerlussuaq airstrip with the snow dusted walls of the Russell Fjord behind. (Photo by M. Turrin)

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