A four-person research group achieved the largest Antarctic expedition since the 1950s. Back then, the Commonwealth Trans-Antarctic Expedition led by Sir Edmund Hillary and Sir Vivian Fuchs successfully crossed the Antarctic via the South Pole for the first time. During this year’s Antarctic summer a team from Antarctica New Zealand, a government agency, found a way across an unknown section of the Ross ice shelf, an ice region the size of France. Crucial information for determining the route was supplied by the German Aerospace Center (DLR) using data from the TerraSAR-X radar satellite. The successful traverse was part of the "Ross Ice Shelf Project", which is investigating how the ice shelf reacts to global warming.
Crevasses are the largest threat to safety when crossing an ice shelf. Glacier cracks can be hidden under the snow cover and extend down to sea level. "Without the TerraSAR-X data it would be like walking blind through a minefield. In the past, optical images were consulted, which are basically only photographs taken from space. With the help of radar images cracks can now be mapped much better and more reliably", explains Dana Floricioiu of DLR’s Earth Observation Center. The radar satellite operated by DLR in Oberpfaffenhofen can see through clouds and dry snow with its radar instrument, thus making hidden cracks visible.
While Sir Hillary and Sir Fuchs used aerial reconnaissance in their day, the current expedition team could make use of TerraSAR-X data and the expertise of the mission team in Oberpfaffenhofen. The problem was to find a safe route through unknown terrain and across a total of 1,000 kilometres of ice shelf—and it could be accomplished: "Without satellite data it would be impossible, or require a great deal of luck, to avoid encountering crevasses. With such data, we only had to deviate once from the planned route ", says expedition member Dan Price of the University of Canterbury in Christchurch, New Zeeland.
Hidden structures in ice and snow
Because microwaves penetrate snow and ice, the TerraSAR-X sensors react sensitively to physical features near the surface, such as the moisture and roughness of the imaged areas. The satellite records in so-called "X band", at a frequency of 9.65 gigahertz, and is a valuable tool for spatially extensive investigations of subtle ice and snow structures. Characteristics like flow lines and cracks can be monitored in detail and used to study the flow dynamics of glaciers and ice streams. The radar instrument also has different recording modes, so fine details at high resolution can be mapped as well as large overviews.
The use of satellite images certainly paid off in the field. "In these monotonous surroundings completely without structures we could always use the radar images to precisely determine where we were", explains Price. Radar analysis using TerraSAR-X data also revealed that some of the ice mass is no longer anchored on the seabed, but is beginning to break loose—the Ross ice shelf is floating. The exact grounding line could be determined at DLR as part of the ESA "Antarctic Ice Sheet CCI" project.
On the successful traverse of the southernmost part of Earth the expedition team could identify places for drilling through the ice shelf to obtain information about the ice, the ocean and the sediments on the ocean floor. Next year over 60 tons of material are to be transported from Scott Base to Siple Coast using the newly established route — 1,000 kilometers across the Ross Ice Shelf.
Research potential of Tandem-L
With the earth observation missions TerraSAR-X and TanDEM-X Germany has accumulated unique, globally-acknowledged expertise in the area of radar remote sensing. The "Tandem L" mission proposal is intended to strengthen it further. The goal is to image Earth’s land mass on a weekly basis. The imaging technology of the Tandem-L mission should set new standards in earth observation. The data, with their high temporal and spatial resolution, could provide unique access to the sensitive polar regions and provide urgently required information to environmental and climate researchers for monitoring ice dynamics and structure. A research-policy-related evaluation of the mission proposal is in progress. A decision about the realisation of Tandem-L is anticipated at mid-year.