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Gravimeter

AIRGrav gravimeter aboard a NASA airborne laboratory(NASA P-3B and DC-8; UTIG BT-67)

The gravimeter measures the shape of seawater-filled cavities at the edge of some major fast-moving glaciers. Data about the amount of water under ice fills in a crucial gap in knowledge related to calving and melting of glaciers. Water has less mass than rock and thus exhibits a lower gravitational pull, meaning that the gravimeter can show what lies under the ice. The AIRGrav gravimeter, developed by Sander Geophysics (www.sgl.com), uses several sensitive gyroscopes to keep the instrument orientation stable. Accelerometers measure the force of gravity from the Earth below while GPS is used to record, and then remove, the motion of the aircraft.

More details on the AIRGrav system can be found here:http://www.sgl.com/Gravity.html

The University of Texas Institute for Geophysics’ (UTIG) obtains gravimeters for its surveys through leases or partnerships with other agencies.
Gravimeter data showing bedrock and sub-ice water near the Thwaites Glacier, Antarctica.

 
Ice on Antarctica's Ellsworth Mountains, 10/22/2012 Ice on the Ellsworth Mountains in Antarctica as seen from the IceBridge DC-8 on Oct. 22, 2012. The Ellsworth Mountains are home to Antarctica’s highest point, Vinson Massif (16,050 ft / 4,892 m). Credit: NASA / James Yungel