Waiting in the Wings

News

By Ashley Thompson
Winter 2011

The 2010 Antarctic Operation Ice Bridge (OIB) campaign was expected, in large part, to mirror the 2009 mission. The home base, Puntas Arenas, remained the same. The same key players were at the helm. The same plane, NASA’s DC-8, would again zig-zag and swoop over carefully charted flight paths, again loaded with CReSIS’ unique suite of radars and other crucial instruments. Mornings would be filled with the same 5 a.m. coffee-chugging as the weary scientists geared up for 12 hours of flying from the tip of Chile to specific regions in Antarctica and back. With any luck, the days would consist of the same predictable fluidity that keeps these creatures of habit sane and satisfied during grueling fieldwork.

Glacier

Photo 1: View of a Transantarctic mountain glacier from the DC-8. Credit: Sarah DeWitt, NASA GSFC.

A repeat of 2009 was what the research team hoped for. That year, two-thirds of the days in Chile brought agreeable weather, which meant packing in as many flights as possible. Researchers found themselves asking when they’d ever get a break.

In 2010, however, a different sense of desperation took place. “This time around, we just kept asking, ‘When are we going to be able to fly?’” said Ben Panzer, a CReSIS electrical engineering PhD student who participated in the 2009 and 2010 campaigns. “2009 and 2010 were definitely two extremes in what you expect when doing research in Antarctica.”

Indeed, 2010 brought a barrage of low-pressure systems that pummeled the Antarctic Peninsula. Windows of ideal flying conditions occurred sparingly. Operations were grounded up to six days at a time. During what would have been luxurious downtime the previous year, the science and engineering teams tinkered with GPS alignment, improved algorithms, took brief sanity breaks on the beach, and did a whole lot of laundry.

“Weather is always an issue in Antarctica, but usually we can sneak flights in between storm systems,” said Michael Studinger, project scientist for OIB at NASA. “This year, they just came one right after another.” The team would gather around anxiously to watch the animated WRF model, which is used to predict weather conditions (such as visibility and wind speed) in the next six to 12 hours. Groans abounded as the screen showed system after system lining up to snowball (no pun intended) the region.

Flights

Photo 2: A screenshot of all 10 flights flown during Operation IceBridge's Antarctic 2010 campaign. Credit: Michael Studinger

Despite uncooperative weather and a slew of other roadblocks (stomach viruses, shipment delays, and minor aircraft malfunctions), the OIB team completed 10 of its projected 12 flight paths and logged 115 hours of flight time, totaling some 40,000 miles of flying. Among its most impressive accomplishments was the completion of the 86 degree arc over the South Pole, a high-altitude path begun during one of the 2009missions. The 86-degree arc precisely matches ICESat-I’s previous paths, meaning data can be closely compared.

KU sent six professors, students, and staff members to Puntas Arenas for the third consecutive year of airborne study of Antarctica. Dr. Carl Leuschen, Dr. Fernano Rodriguez-Moralez, Ben Panzer, Dan Hellebust, Daniel Garcia-Gomez, and Dr. John Paden, (along with Chad Brown, from Indiana University’s PolarGRID team) took part in the NASA-sponsored OIB campaign, the largest airborne survey ever of Earth’s precarious polar regions. The program aims to bridge the gap between NASA’s now-faded ICESat-I satellite and the launch of ICESat-II, not expected to occur until 2015. Until then, bi-annual trips to the poles (Antarctica in the fall, the Arctic in the spring) are in store for NASA polar researchers and their affiliates. ICESat-I produced 3D maps of these crucial polar ice sheets using laser altimetry radar. Though highly sensitive and advanced, certain ice sheet characteristics are more accurately monitored using a bevy of complementary systems mounted in the DC-8, which provides highly detailed data on near-surface internal layers, ice sheet thickness, and snow accumulation on sea ice, among other properties.

As in 2009, the DC-8 was transformed into a state-of-the-art airborne laboratory, mounted with the trifecta of CReSIS radar systems: the Snow radar, the Ku Band Altimeter radar, and the depth-penetrating MCORDS (Multichannel Coherent Radar Depth Sounder) system. This year, all three boasted off-season improvements that were designed to increase the sensitivity of the radar or software systems.

Results

Photo 3: Initial results from the MCoRDS radar, collected from an altitude of about 30,000 feet (9,000 m) above the surface from the DC-8 aircraft in November 2010.Credit: CReSIS

Changes made to the Snow radar, which measures snow accumulation on sea ice, were of particular importance. Its transmit and receive antennas were repositioned under the wings instead of in a fairing structure under the belly of the plane. Prior to departure, NASA designed radar-transparent panels on which to mount the antennas. Increasing the amount of space between each antenna enhances radar sensitivity. Panzer, who ran both the Snow and Ku Band Altimeter radars during the flights, said this modification had been in the works since the 2009 campaign.

“When you are constantly receiving and sending signals like we are, you ideally desire 70 db of isolation. We managed to get 75 db of isolation on this trip,” Panzer said.

Because the antennas were previously constricted to the fairing structure under the belly of the plane, they sat only eight inches from one another, thus increasing the signal’s clutter and noise, Leuschen explained. “We should see the quality of the Snow data improve greatly.” Increasing the radar sensitivity will also result in smaller error bars.

The CReSIS team also doubled the bandwidth of the Ku-Band Altimeter radar, increasing from 2 GHz to 4 GHz, which increased measurement resolution. The radar worked in conjunction with NASA’s airborne topographic mapper (ATM) to measure surface thickness of sea ice.

MCORDS received heady tune-ups and software upgrades after Antarctica 2009. Though it couldn’t employ the groundbreaking 15-element array that debuted in Greenland last May (DC-8 planes do not have the under-wing capabilities to be fitted with as many antennas as the P-3 aircraft), it operated with improved dynamic range and sensitivity. Using five antennas (see diagram for placement) and eight channels, MCORDS multiplexed its way to new heights.

Antenna placement

Photo 4: Diagram showing MCORDS antenna placement. Credit: CReSIS

“The previous system required that the antennas be divided between transmit and receive,” said assistant research professor John Paden, who was charged with processing all MCORDS data in the field. “The new system employs transmit-receive switches that allow an antenna to be used for both transmitting and receiving.”

The 2010 MCORDS was also able to simultaneously run high- and low-gain channels. Low-gain channels avoid saturating the receiver with radar echoes that bounce off the ice surface and lead to signal distortion; this can occur when using only high-gain channels. The team also increased the pulse repetition frequency that the radar sent to its target, which accounted for receiving 50 percent more energy from the target.

In the MCORDS’ case, that target may lie three kilometers beneath the ice’s surface. These important improvements, along with software upgrades, culminated in the very first successful sounding of the South Pole bedrock at high altitudes (35,000 feet, to be exact). The system operated alongside NASA’s Laser Vegetation Imaging Sensor (LVIS) and the ATM.

Flight Path

Photo 5: The flight path arc around the South Pole at a distance of 240 miles. Credit: Rick Auld, United States Air Force.

Along with measuring the relatively understudied South Pole region, the DC-8 duplicated several sea-ice runs from 2009. Interestingly, a projected flight path in the BellingshausenSea had to be changed last minute due to unexpected shifts in the sea ice’s location. The planned route would have had the crew zig-zagging over open water, which is of little interest to OIB. The pilots and researchers quickly modified their flight path in order to measure the ever-changing sea ice. Using GPS technology, comparisons from last year’s data, and data from ICESat-I, scientists will then be able to get a clearer picture of the sometimes unpredictable nature of sea ice, which is heavily influenced by the Earth’s warmer, rising seas.

The crew also managed three flights over the ever-important Pine Island glacier to compare data from previous years. Pine Island, in Panzer’s words, is “the rock star” of Antarctic ice streams because of its rapidly accelerating flow and thinning. Pine Island comprises 10 percent of the massive West Antarctic Ice Sheet (WAIS), which is roughly the size of the western United States.

Data from all the flights were processed in the field within 24 hours of touch-down. However, once back stateside, the crew began reprocessing to include trajectory data from GPS units and the ATM, as well applying advanced signal processing algorithms. For the MCORDS system, whose terabytes upon terabytes of data is being processed at Indiana University, a complete, refined data product is due by June 1.

By that time, the OIB and CReSIS teams will have likely returned from their northern counterpart adventure of charting the precarious Arctic glaciers and sea ice. Deployment is set for mid-March 2011. New upgrades to the radar systems will be revealed, that much is certain. The rest is but a guessing game, as the weather promises to be a mercurial presence once again.