Radar views of permanent ice for climate research – DLR research flights over Greenland
The Greenland ice sheet is, in places, more than three kilometres thick and a crucial feature in climate modelling. Scientists of the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR), together with colleagues from ETH Zurich (Eidgenössische Technische Hochschule Zürich), are currently conducting tests of new radar imaging methods in a research flight campaign over Greenland initiated by the Microwaves and Radar Institute in cooperation with the Danish Defence Acquisition and Logistics Organization (DALO). These methods shall provide information about three-dimensional snow and ice conditions at depths of up to 50 metres. "In the long term, it should be possible to determine the impact of climate change on the internal stratification of snow, firn (partially compacted snow) and ice," explains Irena Hajnsek, Project Manager of the ARCTIC15 campaign. This is interesting to, for example, investigate how much water from the snow that melts on the surface freezes again during infiltration and thus does not contribute to sea level rise. This effect is considered to be insufficiently addressed in current climate models, as stated in a recent report issued by the Intergovernmental Panel on Climate Change (IPCC).
Flights over crevasses and summits
The Aircraft Supported Synthetic Aperture Radar (Flugzeuggestütztes Radar mit Synthetischer Apertur; F-SAR) is installed on the DLR Do 228-212 research aircraft D-CFFU. The aircraft will fly over each of five study areas in southern Greenland several times during the approximately six-week campaign, which lasts until the end of May. "Flying over Greenland's permanent ice is something special," says DLR pilot Thomas van Marwick. "The vast distances between landing facilities and the sometimes extreme weather conditions must be carefully taken into account." The crew on board the DLR Flight Operations (FB) are flying, amongst other places, over areas along the coast where the ice sheet transforms into large glaciers and fissures as well as over the southern highlands, where the highest point, the South Dome, is found. The flights usually last between four and five hours; on the longer routes they sometimes include stopovers for refuelling.
Beneath the surface
"This new radar technology will enable us to, in the future, recognise the various types of ice and snow from the air or from space," says Campaign Manager Ralf Horn from the DLR Microwaves and Radar Institute. "Different types of ice reflect the radar signals differently and the DLR F-SAR is able to detect these differences – sometimes at depths of up to 50 metres." The ice covering Greenland reveals varying structures, depending on the region being examined. The central and high-altitude areas experience hardly any snowmelt in the summer, forming a firn layer tens of metres in thickness, which is converted to ice by the pressure of the overlying layers. In contrast, exposed ice is found near the coast; it has low snow cover only in the winter. An examination of the depth of the ice is, at the same time, a glimpse of the climate over the last few decades, because successive ice layers have formed over the years.
Hard fieldwork at the beginning
Before the flight campaign began, the remote areas on the ground were explored, radar reflectors were installed, and the snow, firn and ice were examined by hand. For this purpose, DLR researchers used a chartered aircraft capable of landing on snow. During the five- to six-hour stays, sometimes at temperatures below minus 25 degrees Celsius and strong winds, a ground radar system, on loan from the Alfred Wegener Institute, and a snow probe were used. "These were the toughest and most exciting working conditions that I have experienced in my career so far," says DLR researcher Georg Fischer, who organised the expedition and implemented it with two colleagues from DLR and ETH Zurich.
After returning from Greenland, on the basis of this research campaign, the researchers plan to develop new methods for snow and ice analysis, which will then be applied to the data gained from future satellite missions such as Tandem-L. This is expected to enable the use of a new method for examining variations in glaciers and ice sheets being observed from space, and will allow coverage information to be generated. At present, this can only be determined in select locations through complex expeditions.
All the research is being carried out as part of the Helmholtz Alliance 'Remote Sensing and Earth System Dynamics' programme.
The researchers report on their adventurous scientific expedition in Greenland in the DLR Blog.