IceSAR: April flights
From Jørgen Dall and Anders Kusk (DTU Space), Kangerlussuaq, 22 April
From Thursday to Saturday (19–21 April), a Twin Otter aircraft was flown over the K-transect, a line starting at the Russell outlet glacier near Kangerlussuaq and stretching some 150 km into the ice sheet. The Twin Otter carried a radar called POLARIS, developed for ESA by the Technical University of Denmark. Asa Tania’s earlier post mentioned, the objective was to assess one of the secondary objectives of ESA’s Biomass Earth Explorer candidate mission: ice mapping.
The direction of the antenna pattern can be steered by means of electronic beamforming, and looked to the left, to the right and straight down with POLARIS configured as a SAR and as an ice sounder.
The SAR data must be acquired from altitudes up to 20 000 ft, and since the Twin Otter is not pressurised, we emptied several of the white oxygen bottles seen in the picture.
Twin Otter cabit at 20 000 ft
With a few meters precision, the pilots repeated the same tracks over and over again, carefully following the variation of the ice surface elevation.
Two weeks from now, these exact tracks will be repeated to measure the motion of the ice during this period. One of the primary parameters to be measured with POLARIS is the ice velocity, and the K-transect excels by offering in situ measurements from several permanent GPS receivers.
Prior to the campaign, two 2-metre radar reflectors were lifted by helicopter onto the ice sheet and deployed by scientists from the Institute for Marine and Atmospheric research Utrecht (IMAU). Assisted by the helpful staff from the local Air Greenland ground services team, we deployed a third reflector on firm ground in Kangerlussuaq. These reflectors will help calibrate the POLARIS system and combine data from multiple tracks.
IceSAR ready to fly in Greenland
From Tania (ESA), Kangerlussuaq, 20 April
It is perhaps somewhat ironic that the P-band imaging SAR designed for forest biomass mapping on the Earth Explorer candidate mission Biomass could also provide unique information on ice sheets in the cryosphere. However, a number of scientific studies have shown that long-wavelength P-band radar images to map forest biomass, may also be highly useful to monitor ice movement on ice caps.
Even more tantalisingly, since P-band radar penetrates into the snow surface much more than other radar frequencies, images from Biomass could potentially provide a glimpse of ice structures beneath the surface.
So, enter ESA campaigns to test and document this potential !
This weekend, for the first time a new airborne P-band imaging radar instrument developed for ESA by the Danish Technical University (DTU) will take to the skies above the Greenland ice sheet. Making use of the same sturdy Twin-Otter plane used recently in the CryoSat CryoVEx campaign in northern Canada, the instrument appropriately called Polaris will fly multiple lines straight out of Kangerlussuaq onto the nearby ice sheet for several days.
Interestingly, this will mark only the first of three flight sessions over the same area, spaced about 20–30 days apart. By cleverly combining the images collected during each session, scientists hope to illustrate the potential of the Biomass mission to monitor ice movement at continent scales, for instance across Antarctica.
Pushing technology and current radar processing techniques to its limits, scientists from DTU and the Politecnico di Milano participating in the campaign are also hoping to demonstrate 3D subsurface mapping at P-band.
For the moment, however, the team and aircraft are assembling today in Kangerlussuaq, Greenland and getting ready for the flights during the next few days. The sky is blue and very little snow remains on the ground. The coming days promise to be interesting.