Tag Archives: DTU

Scientists head to the loneliest place on Earth for ESA missions

From Tȃnia (ESA-ESTEC), Noordwijk, the Netherlands

Over the next few weeks we will be carefully following two intrepid scientists as they carry out an extensive airborne campaign, called DOMECair, in the far reaches of Antarctica to support two ESA missions.

The reason why Steen Savstrup from the DTU National Space Institute and Daniel Steinhage from the Alfred Wegner Institute (AWI) have headed out to arguably the loneliest place on Earth is to collect measurements that will validate ESA’s SMOS and GOCE missions.

Concordia base is on East Antarctica’s polar plateau – about 3280 m above sea level and about 1000 km from the coast.

Not only will the harsh environment of East Antarctica’s polar plateau where summer temperatures drop to –40°C be challenging, but also the long flights over the vast expanse of nothing but ice will undoubtedly be tough. The plan is to fly across an area of 350×350 km centred at the Dome-C Italian –French base at Concordia, which is highlighted in the map above.

Planned flights for the DOMECair campaign. (ESA)

One of the photos that Daniel sent on his way out to Antarctica last week reminded me of just how far away and isolated Antarctica is, and made me smile at the same time. This photo of the boarding times at the airport in Cape Town lists Antarctica – the continent – as the destination, sitting rather oddly between the highly-populated cities of London–Heathrow and Amsterdam!

Outward bound – Antarctica the continent! (D. Steinhage)

Anyway, the guys have arrived safely and the plan is that they use two different instruments installed in the AWI’s Polar-6 airplane to take validation measurements. One instrument supports ESA’s Soil Moisture and Ocean Salinity (SMOS) mission. This is an instrument, called EMIRAD-2, is an L-band radiometer that is similar to that of SMOS, but from the aircraft gathers images at much higher resolution.

Measurements to support SMOS are already collected routinely from a tower at the station – previous entries on this blog describe its set up and purpose. However, since the instrument is fixed on a tower these measurements are taken of the same spot on the ice. Spatial variability of the L-band passive signal around DOME-C has not been measured to date so the impact of this variability on SMOS measurements cannot be properly assessed.

In addition, the spatial variability in L-band passive signals also impacts the cross-verification of SMOS measurements with parallel missions from other agencies such as the NASA AQUARIUS and SMAP missions over the same site. Quantifying and documenting the spatial variability is thus important to establish long-term cross-calibrated multi-mission L-band measurement timeseries.

The other instrument is the AWI Lacoste and Romberg air–sea gravimeter, which will take gravity gradient measurements over the ice to support ESA’s Gravity field and steady-state Ocean Circulation Explorer (GOCE) mission. These airborne gravity measurements can be propagated to the GOCE flight altitude and used to independently verify the satellite measurements of the local gravity gradients as well as to improve global and regional solutions to the gravity field models generated by the mission.

For the DOME-C area, airborne gravity measurements are sparse or non-existent and thus represent a gap in the required reference high-quality gravity anomaly maps.  Airborne gravity measurement such as those expected through DOMECAir will also contribute significantly to parallel initiatives by the science community such as AntGP to collect and generate a continent-wide high-resolution gravity reference map.

Importantly, this campaign will be the first time that measurements supporting two different missions will be collected at the same time.

The next blog entries will be from the team, but in the meantime we wish Daniel and Steen lots of luck as they start the campaign!

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.

It’s a wrap – airborne measurements of ice complete

From Henriette (DTU-Space), Denmark, 12 May

We ended our DTU-Space part of the CryoVEx campaign on 9 May. The Norlandair Twin Otter has flown about 85 hours, covering about 20 000 km. This is about the same distance as half way around the world at the equator.  The map below shows our flight tracks.

Twin Otter carrying ASIRAS (credits: M. Davidson)

We have been able to underfly several CryoSat passes. A few of them were in formation flight with the AWI Polar-5.

We have visited five main validation sites, circled in red on the map: Devon ice cap, Austfonna ice cap, the EGIG line Greenland interior, as well as sea ice north of Alert and sea ice around Svalbard in the Fram strait with our colleagues down on the ice below.

Flight tracks from DTU Twin Otter carrying ASIRAS (credits: H. Skourup)

It has been a pleasure to working with all those involved and I want to thank everybody for the great collaboration and excellent timing.

As you may have already have noticed, the corner reflectors are giving very valuable information of the radar penetration depth.

The updated version of the ASIRAS radar has a realtime display so we can see whether we have hit the reflector as we fly over. This demands very precise navigation as the reflector has to be within 10 m of the aircraft track.

Thanks to our highly-skilled air crew we only missed 2 or 3 reflectors out of 45 passes.

For our part, the airborne campaign has been a success, and we have now a collection of unique measurements to work with.

Mapping sea ice up close with ASIRAS

From Malcolm (ESA), Alert, 16 April

Henriette on the Twin Otter monitoring the sensing instruments (credits: M. Davidson)

As an ESA campaign coordinator, I sometimes fly along with airborne scientists and observe how data are collected and how the different instruments on the plane are run. This part of my work has always been fascinating and of great value in understanding how to run campaigns together with participants.

Today, I was a guest on the Norlandair Twin Otter at Alert, Canada, carrying the CryoSat airborne simulator ASIRAS. Its cramped interior is packed with instruments and, thankfully, the odd seat for the scientists operating the instruments.

In the past few days, the ASIRAS team members – guided by their friendly and experienced scientist Henriette Skourup from Danish Technical University – have been showing off what the instrument can bring to validation for CryoSat.

Sea ice close to northern shore of Ellesmere Island (credits: M. Davidson)

With the help of good weather, ASIRAS has already flown an impressive 2300 km in three days. All three of the ground test sites have already been 'imaged' by ASIRAS. This is good news to the ground team who have been painstakingly measuring snow and ice properties and can now look forward to ASIRAS data over their site to make comparisons.

I’m particularly impressed with the precision with which the flights over the test sites where made. High-precision flights over the ground sites are difficult to execute, but crucial to the success of the campaign.

ASIRAS radar signature from corner reflector below (credits: M. Davidson)

ASIRAS needs to pass within 5 m of the corner reflectors that were earlier carefully erected by the ground teams to ensure that airborne and ground data can be properly compared later on. During the campaign, the pilots and scientists running ASIRAS on-board the Twin Otter have come through with flying colours, 'nailing' several passes over each site to within a few meters – no mean feat!

The clear ASIRAS signatures of the corner reflectors studied quickly after each flight show how incredibly good the data is.

Indridi keeping a check on ASIRAS (credits: M. Davidson)

The image on the left is for the techies out there - it shows the spectacular ASIRAS radar signature from a corner reflector below. The well-formed hyperbola in the middle highlights both teh quality of the measurement and the proximity of the plane to the position of the reflector.

Another spectacular 'first' that comes to my mind, has been the tandem underflight of a CryoSat track of ASIRAS on the Norlandair Twin Otter and the EM-Bird on board the Basler aircraft all the way up to 86° North, only 4° from the North Pole.

 Together – separated by only a minute or two – the two aircraft and their precious scientific crew carefully flew directly underneath the track of the CryoSat satellite orbiting at 7km/s overhead. To accomplish this feat, the pilots of both planes needed to keep in constant visual contact, as well as carefully follow the track laid down by CryoSat.

ASIRAS passes as seen by GPS (credits: M. Davidson)

The result of their efforts is a unique opportunity to bring together the ice-thickness measurements by EM-Bird and the high- and low-resolution radar altimetry of ASIRAS and CryoSat, respectively. This has resulted in a terrific chance to cross-compare all three measurements.

All in all, ASIRAS – the workhorse of CryoSat validation – guided by experts, Henriette and Indridi from DTU, has been showing its mettle and taken this campaign huge leap forward.