Tag Archives: POLARIS

IceSAR campaign heads north

From Klaus Scipal (ESA), Greenland, 7 June

As part of the IceSAR 2012 campaign, Jørgen Dall and Anders Kusk from DTU and I headed up north yesterday to fly the Polaris system over the K-transect on Russell Glacier in southwest Greenland. This is near Kangerlussuaq, 67° N, just inside the Arctic Circle.

Assembling and installing Polaris

Assembling and installing Polaris

The campaign supports the evaluation of the Biomass candidate Earth Explorer mission. It may sound a little strange that a mission designed to measure forests properties in the Tropics will also be used to map glaciers and ice sheets.

This is thanks to the unique Biomass instrument and mission concept, which is based on using a very long wavelength (P-band) quad pol SAR, designed to acquire interferometric measurements of Earth’s surface.

Heading north to Akureyri

IceSAR 2012 will provide, for the first time, evidence that these observations can provide precious information on ice velocity and ice subsurface characteristics. We are going to do this by taking measurements with the airborne Polaris P-band system, which is configured in such a way that it is similar to the Biomass concept.

This trip is particularly special because we are not only flying over Greenland, but also decided to stopover in Iceland to join forces with our colleagues from NASA to map parts of the Hofjökull and Langjökull ice caps with the Polaris system.

Getting to Iceland is easy. From Amsterdam, it takes three hours by plane to Reykjavik. In Reykjavik, we changed plane to travel on to Akureyri on the north coast. Akureyri is the second largest city in Iceland and the base of Norland Air, which provides the planes for most of our campaigns far north.

Cloudy conditions in Iceland for this week

In Iceland, we coordinate our flights with the NASA UAVSAR team, who are carrying out a larger campaign to map the Hofjökull and Langjökull ice caps. The UAVSAR team will map the entire Hofjökull and Langjökull ice caps multiple times in the 12-day campaign. Since we only have one day in Iceland and a swath width 4–6 times smaller than that of the UAVSAR, our Polaris system can only cover a very small part of the ice caps. However, the P-band data acquired by Polaris will be an invaluable dataset to better understand features seen in the UAVSAR data.

A day in Iceland

A day in Iceland

Mark Simons from NASA expects a higher sensitivity to changes of the dielectric constants with P-band. This data together with UAVSARs L-band data could provide a better understanding of a recently observed change in the dielectric properties of the ice sheets during the melt season. Mark is also interested in Polaris sounder data for comparison.

Today, we are spending  all our time to assemble the instruments and install them on the plane. As we have to start at 04:00  on 8June everything has to be ready and tested this afternoon. The tight schedule and just one day in Iceland does not allow time for any problems. We will also meet with the pilots and discuss the flight schedules.

Just two days ago, Mark told us of  an unusual surface mudflow over one of the glaciers that indicates that there is a pulse of water coming up to the surface from the bed. Apparently, nobody has seen anything like this before. It could mean that the ice is particularly thin there. Having Polaris sounding measurements over this spot could be fascinating so we’ll try to adapt our flight lines accordingly.

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.

POLARIS system

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.

POLARIS antenna

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.