Jim Cochran, Geophysicist, Lamont-Doherty Earth Observatory
ICE Bridge scientists gathering at NASA’s Dryden Flight Research Center (DFRC) in Palmdale, CA for our upcoming Greenland mission were greeted in true California style. We were awakened by a magnitude 4.4 earthquake in the middle of the night! Although small by California standards the event was centered only about 35 miles south of Palmdale at Pico Rivera and we definitely felt the effects.
I represent one part of the Lamont-Doherty team who will participate in this second leg of the ICE Bridge mission with NASA. While the first phase of ICE Bridge imaged sea ice and ice shelves in West Antarctica, this phase will focus North on Greenland fjords and Arctic sea ice. For a Greenland campaign it may seem odd to travel from New York to California and then on to Greenland, but the DC-8 plane to be used in the first half of the campaign is based at NASA’s DFRC in Palmdale. The scientists are here for mandatory safety training and a science test flight.
A 6:30 AM trip to the hangar shows off the desert sunrise spreading a beautiful red glow across the sky over the mountains. Two huge hangers looming up out of the flat desert dominate the research center. They house our DC-8 along side the Boeing 747 modified to carry a 2.5-meter telescope used for Sofia (Stratospheric Observatory for Infrared Astronomy). By 8 AM we were in the air for a six-hour flight to test and calibrate the instrument. I am responsible for the gravimeter which will be used to measure the Earth’s gravity field to estimate how deep the water ice beneath the ice. The test flight gives us a chance to be sure the instrument is working properly.
The first several hours we fly over the ocean, first up at 40,000 feet to calibrate LVIS (Laser Vegetation Imaging Sensor), a scanning laser altimeter, which will measure the surface elevation of the ice sheet, and then down at 1000 feet above the water to test other instruments. We do a little bit of actual science by using LVIS to map a portion of the San Andreas Fault. The very detailed high-resolution map produced can be compared to similar maps made later to find out how deformation is distributed along the fault. The last two hours of the flight are spent flying repeat runs over the Mohave desert at 1500 feet above the ground, well below the height of the mountains on either side of us.
Next we’ll pack up gear for Thule and load it onto the plane.This means packing up the two GPS stations that we had set up near the runway.The GPS stations are a key part of our equipment.They are used to do what is called differential GPS, a technique to increase the accuracy and precision of the GPS measurements made on the airplane.This is very important since we use the GPS to calculate not only the plane’s positions but also its accelerations.We will need to remove these accelerations from the gravimeter accelerations to determine the actual gravity measures.