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December 8, 2012 Where's the Ice?

Ground Penetrating Radar (GPR) is one of the instruments being used during the 2012 season to determine the presence and depth of buried ice in areas of the Dry Valleys.

Photograph of Sean Mackay and GPR instrument
Sean Mackay prepares the Ground Penetrating Radar unit.

What is Ground Penetrating Radar (GPR)?

GPR is a geophysical technique that collects and records information about the subsurface without digging it up. GPR can detect underground water, rock structure, buried ruins and many other types of objects. A radio wave signal is shot directly at the ground by a transmitting antenna. This signal will travel through the ground until the material properties of the earth changes. When it comes across a different sort of object, some of the signal passes on and some of it is reflected back to a receiving antenna. The reflective portion is what is being measured. When the signal is reflected back, a computer measures how long it took to make the trip there and back. From this, the computer calculates how deep the buried object or change in underground material is. The GPR machine will be dragged back and forth over the ground, making thousands of measurements in an area. A computer puts these together to make a 2D model of the objects buried under the ground.

Diagram of Ground Penetrating Radar basics.
Diagram illustrating Ground Penetrating Radar basics.

Watch the video below to see Jackie and Sean using GPR in Upper Beacon Valley Antarctica. Notice the sound of the wind in Beacon Valley.

The printout below was supplied by Sean Mackay and illustrates the features interpreted from GPR data near the headwall of Mullins Glacier.

Interpreted Ground Penetrating Radar image.
Print out of Ground Penetrating Radar data highlighting interpreted features. Image provided courtesy of Sean Mackay.

A similar GPR technique using a radar instrument called the Mars SHAllow RADar sounder (SHARAD) is being used for subsurface investigations on Mars. SHARAD can identify liquid or frozen water in the first few hundreds of feet (up to 1 kilometer) of Mars' crust. Water, like high-density rock, is very conducting, and will have a very strong radar return. SHARAD probes the subsurface from the Mars Reconnaissance Orbiter using radar waves within a 15- to 25-megahertz frequency band to get the desired, high-depth penetration. In certain areas, radar properties are consistent with massive sub-surface water ice, and the results imply that these glaciers formed in a previous climate conducive to glaciation at middle latitudes.

Photos

Photograph of Sean Mackay and GPR instrument
Diagram of Ground Penetrating Radar basics.
Interpreted Ground Penetrating Radar image.

Video

Video

Details

Jacquelyn Hams's picture
Author: Jacquelyn Hams
Expedition: Buried Ice in Antarctica 2012
Location: Upper Beacon Valley, Dry Valleys, Antarctica