Despite the very slow progress of these surface vehicles, one of the major discoveries from the International Geophysical Year resulted from the recordings of these explosions. The scientists, bundled parkas, had to wait much longer than anticipated to record the echo from the ice sheet bottom. The reason: the ice was thicker than predicted. The East Antarctic Ice Sheet is up to 2.8 miles (4.5 kilometers) thick in places, enough ice to raise sea level globally 170 feet (52 meters) if it were to melt.
Driving over the ice sheet and setting off explosives every 50 miles is a slow process. Flying, even in a small airplane, is much faster. We will use two aircraft bristling with antennas and stuffed with instruments to collect new measurements of the ice sheet from the air, along with those taken from seismometers buried in the snow.
Mounted on the wings of the aircraft are eight antennas that transmit and receive 150 megahertz pulses to measure ice thickness. This radar system developed by the Center for Remote Sensing of Ice Sheets in Lawrence, Kan., has been developed specifically to image through the polar ice sheet. Similar to the seismic method, energy is transmitted through four of the antennas. The energy bounces back from the surface of the ice and the bottom of the ice sheet. We end up with thousands of measurements every second. This is a big improvement over 50 years ago when it took two to three days to measure ice thickness.
To get a better idea of the surface of the ice sheet, my colleague Michael Studinger has installed near-infrared laser mounted below the floor in the aircraft. Within the nitrogen- filled container, the laser fires at a revolving mirror. When the mirror spins, the laser is aimed first to one side of the aircraft then to the other, so that the laser measures the ice surface right below the aircraft and out to the side. When we accurately position the aircraft, the laser measures the distance to within 2 inches (5 centimeters)! Testing in the hall in our office, we can see people dashing in between rooms.
Along with the ice-thickness data, we want to understand the origin of the Gamburtsev Mountains. To do this, we need to decode the fundamental structure of the crust and lithosphere beneath. It will be years, maybe decades, before anyone drills into the Gamburtsev Mountains, so we will use gravity, magnetics and seismic velocities to remotely probe the subglacial terrains. The Earth's gravity field changes depending on the type of bedrock. A stronger gravity field means denser rock and a weaker gravity field means a less dense rock. An extremely accurate gravity meter will be mounted in the front of the aircraft. Measurements of variations in Earth's magnetic field will tell us about the nature of the underlying rocks. Some rocks are much more strongly magnetized than others. We will measure the changing magnetic field with cesium-based sensors mounted on the tip of the aircraft wings. Measurements of the magnetic field will tell us how magnetic the hidden rocks are.
The laser will measure the ice surface. The radar will measure the hidden topography. The gravity and magnetics will tell us about the makeup of the shallow part of the Earth—in general the crust. If we want to see deeper, we need a different method, A team lead by Doug Wiens from Washington University in St. Louis will install 26 seismometers spread hundreds of miles apart over the top of the Gamburtsev Mountains. Instead of shooting off explosives, the scientists will leave seismometers in place for months, recording distant earthquakes. These seismometers will be left in place for a year buried in the snow; they will be powered by the sun in the summer and by buried batteries through the long polar winter. The seismometers will record earthquakes from around the world to map the deeper structure beneath the mountain range. In the end, the seismic data will let us know how fast the energy from the global earthquakes travel and how warm or cold the Antarctic continent is at depths of hundreds of miles down.