Category Archives: CryoSat

Swapping summer for winter for ESA’s CryoSat mission

Stefan Hendricks (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research) 8 October 2013

There aren’t many chances to do field work on polar sea ice in the depths of winter, and even fewer opportunities in Antarctica.

Polarstern in Antarctic winter (Stefan Hendricks, Alfred Wegner Institute)

The Antarctic Winter Ecosystem & Climate Study (AWECS) of the German Polarstern Research Icebreaker, however, provided such an occasion.

Pancake Ice (Stefan Hendricks, Alfred Wegner Institute)

Our voyage from Cape Town, South Africa, to our main working area in the Weddell Sea in Antarctica and back to Punta Arenas in Chile took nine weeks. We were in ice-covered areas from mid-June to early August, mid-winter in Antarctica – and dark for much of the time.

Working in the polar night and in a storm (Stefan Hendricks, Alfred Wegner Institute)

One of the goals of the campaign, called CryoVex, was to look at how ESA’s CryoSat mission can be used to understand the thickness of sea ice in Antarctica. The extent of the sea ice here in winter is currently more than normal, which could be linked to changing atmospheric patterns.

This is in contrast to what we are seeing in the Arctic where there is a trend towards declining sea-ice extent in the summer. CryoSat is showing that ice continues to thin.

Airborne sea-thickness measurements with the EM-Bird (Stefan Hendricks, Alfred Wegner Institute)

Sea-ice thickness data for Antarctica, which covers a larger area than Arctic sea ice, is also necessary to understand and potentially predict the future behavior of the ice.

To achieve sea-ice thickness retrieval with CryoSat, we have to understand the complex remote-sensing signature of snow on Antarctic sea ice and what it means for the range measurements of the CryoSat’s SIRAL radar altimeter.

Studies of snow properties (Stefan Hendricks, Alfred Wegner Institute)

Therefore, swapping our northern hemisphere’s summer for winter in the southern hemisphere we sailed with Polarstern to Antarctica to study the properties of snow, its evolution in winter and to measure sea-ice freeboard and thickness for later validation of CryoSat data.

The validation activities continue with another Polarstern cruise-leg from August to October and an aircraft experiment in November at the Antarctic Peninsula. This specifically looks at how the satellite radar penetrates the snow overlying the sea ice.

Snow crystal (Stefan Hendricks, Alfred Wegner Institute)

In the beginning of the cruise in mid-June we observed the main sea-ice growth phase of winter.

Sea ice in Antarctic very often forms as pancakes owing to the ever-present ocean swell. These pancakes solidify with time and get increasingly covered with snow.

Ice station (Stefan Hendricks, Alfred Wegner Institute)

Since there is more snow fall in Antarctica then in the Arctic, the snow can push the ice surface 10–20 cm below the water layer.

This means wet shoes and complications when interpreting CryoSat range retrievals.

We measured snow depth and stratigraphy, freeboard and thickness at several ice stations where Polarstern was anchored to an ice floe. This had to happen in the dark and often in stormy conditions and we were grateful for the wind shadow and the lights of the ship.

Ocean heat (Stefan Hendricks, Alfred Wegner Institute)

In the short hours of daylight and twilight, we used our onboard helicopters to obtain the regional sea-ice thickness distribution by our airborne sensor, the EM-Bird.

Aurora Australis (Stefan Hendricks, Alfred Wegner Institute)

We have to understand the impact of the snow layer on the Antarctic sea-ice thickness retrieval with CryoSat first, but this data will serve as a benchmark for a possible sea-ice thickness data product.

Check out the AWI website for more information about the campaign.

On to Station Nord

From Indridi, Sine & Henriette (DTU Space), on the way to Thule Airbase, 29 April

Continuing our campaign to validate CryoSat, the last days of April were busy. We flew over the Austfonna ice cap on Svalbard to measure Kongsvegen Glacier and the sea ice in Fram Strait on the way to Station Nord, the most northeasterly habited point in Greenland, and we underflew CryoSat t over the sea ice north of Greenland.

Ice cap meets the sea

At the Austfonna ice cap the ground team from University of Oslo and Norwegian Polar Institute had put up five corner reflectors prior to the flight. These are used as a reference point to validate the penetration of the radar signal in the upper layers of the ice cap, and to check the timing of the ASIRAS radar.

We had fairly good weather conditions over the ice cap with just a few low clouds in the west and northwest. Although the laser scanner doesn’t penetrate through clouds, the cover was rather thin and data was gathered over most of the flight lines. The ASIRAS radar does see through clouds so radar surveying was done for all the lines.

We flew six lines of high priority and expect to have hit four out of the five corner reflectors several times. Two hits were confirmed in the air on the realtime radar display. This is possible as the radar response shows a very characteristic circular shape above the ice surface when flying over the reflector, see the capture below. Along a few lines we surveyed all the way to the open water where the ice cap gives way to the sea as the photo at the top shows.

Radar response to corner reflector

After this flight we packed our gear and headed towards Station Nord. On route from Longyearbyen to Greenland we were able to survey Kongsvegen glacier, and the sea ice in the Fram strait.

Konsvegen Glacier (H. Skourup)

As our survey altitude is about 300 m, from time to time we get a glimpse of the Arctic fauna from above. This time we were lucky to see group of whales in a pond of open water in the ice pack. Unfortunately we do not have any pictures, as even whales are only a few pixels wide in images taken from this altitude.

Sea ice

We landed at Station Nord at 14:08 UTC. Fortunately, the personal at the station were willing to support another flight, as this was the only chance to have an underflight of CryoSat over the sea ice north of Greenland. We only had time for a quick lunch, as we had to take off again at 15:40 because we wanted to rendezvous with CryoSat at 16:40 on a flight line about an hour from the station. We succeeded in surveying the line between 16:00 and 18:00 UTC where we ‘met’ CryoSat at 82N 52.6 15W 29.2 at 16:40:20, see photo of navigation screen.

Navigation screen

Another successful day. The next main task will be the flight over Devon Island, we’re crossing our fingers for nice weather!

A very first peek at the outcome of the sea-ice flights for CryoVex 2012

Malcolm (ESA), Noordwijk, NL, 27 April

I thought I would dedicate today’s entry to data processing. Data processing is the often the overlooked aspect of campaigns. Long after the excitement of the aircraft taking to the skies, the satellite passing over top and the breath-taking views of polar regions, the actual processing of the large volumes of data collected during a typical campaign require time, skill and dedication. Nonetheless, the key to the success of any campaign lies in the skilled processing and interpretation of the data, and the new insight and scientific results it brings.

CryoVex campaign results from 2 April 2012

So, today I’m pleased to show some very first results from 2 April 2sea-ice campaign. All credit should go to my ESA colleagues Marco Fornari and Thomas Armitage, and Henriette Skourup from DTU who made it possible. Marco for instance was able to wade into the huge stream of data CryoSat produces each day, pluck out precisely the orbit on 2 April over the Arctic Ocean, which was underflown both by ESA and NASA aircraft. Using his expertise and favourite laptop he then processed the raw data, turning the numbers into meaningful information such as radar echo shapes and distance estimates.

CryoSat radar echoes

Enter Henriette from DTU, a steadfast member of the campaign team, who performed similar processing feats with the airborne laser data collected from her plane on that day. The final steps, putting everything together were done by Thomas, who skilfully combined measurements from CryoSat taken from 700 km above Earth with those from the airborne instruments taken only a few hundred meters above the ice – providing us with a first and most intriguing insight into some of the basic science questions surrounding the mission.

CryoSat crossing and a lead (green cross) visible in the airborne laser data

I finish with a remarkable illustration of the result. The plot at the top shows both laser height measurements from the airplane (the grey dots) and CryoSat data (the green and red crosses). The green crosses correspond to CryoSat measurements of sea ice and red crosses areas of thin ice or open water (called leads).

Notice how the laser measurement 10–20 cm ‘hover’ above the CryoSat green crosses. The difference is most likely due to a layer of snow lying on top of the sea ice. The laser bounces of this surface whereas the CryoSat radar signal penetrates deeper into the snowpack and, hence, gives a lower reading. By carefully studying these differences scientists are not only able to determine the amount of snow on the ice, which could be interesting for climate studies for instance, but also make adjustments in the CryoSat data to improve the accuracy of the thickness maps it generates. Studying these differences and ensuring that the maps are accurate is at the core of CryoSat validation activities.

Even more interestingly perhaps, notice the difference between the CryoSat radar echoes on sea ice (green crosses) and thin ice or water (red crosses). These are only 20 cm apart yet CryoSat is able to detect the difference 700 km away. Since the 20 cm represent the height of the ice above water, and knowing that for floating ice about 9/10ths of the ice lies below water, we now know thanks to all the efforts that the ice thickness on that day and along this particular track was approximately 2 metres thick.

Lead in the sea ice seen from the aircraft

Svalbard: first impressions

From Tommaso (ESA), Svalbard, 25 April

ESA’s CryoSat mission manager, Tommaso Parinello, is on campaign in Svalbard to take part in the continuing efforts to validate CryoSat. He shares his first impressions of the Arctic as he waits for the DTU team to arrive.

Getting to Svalbard from Europe is reasonably easy. From Oslo, it takes three hours by plane. Landing in Longbyearbyen, the administrative centre of the archipelago, offers a view of the KSAT satellite acquisition station on the right and of the Adventfjorden on the left. At this time of year and at this latitude, the sea is almost free of ice.

Arriving in Svalbard

While the aircraft was aligning with the runway, I could see the dome of the CryoSat transponder in the distance. It is smaller than the other domes, but quite recognizable. You should imagine that inside these big ‘golf balls’, huge antennas rotate to track the different satellites, including those of ESA.

I have promised myself to visit the station and the CryoSat transponder, before leaving the islands, time permitting.

As soon as we disembarked, I was captivated by the beautiful white mountains that are partly reflected in the blue cold sea on the other side of the fiord. Being used to continental Europe and in particular to the Italian landscape, I found this marvellous view breath-taking.

Svalbard

Instantly, you really get the feeling of having arrived at the top of the world and you suddenly realise that you have to have guts to live here, especially when the weather is so extreme – though not the case when we landed. It was only –2°C, but due to a fresh easterly, it felt colder.

Quite soon after leaving the airport, you become aware that although Longyearbyne is made of a small number of colourful houses scattered in an area of several hectares, it truly is a modern town with first class facilities and shops that somehow contrast with the first impression.

Svalbard

Soon after arriving at the Hotel, Henriette and her team from DTU, informed me that they were still in Constable Point (West Coast of Greenland) waiting for the aircraft to undergo routine checks. The aircraft and the instruments were going to be used the next day for our measurements over the west coast of Svalbard and over the north-east glacier of Austfonna. Unfortunately, this would have delayed their arrival in town. Bad luck.

The rest of the afternoon was spent checking the equipment, plans for the next day and replying to a few emails that were in the inbox that deserved my attention.

Over the Greenland ice cap to Alert

Malcolm (ESA), Alert, 2 April

On Friday I was picked-up by the DTU team at Qaanaaq airport with their workhorse Twin Otter plane. It was a beautiful sunny day and we put it to good use. Instead of flying to Alert along the coasts of Greenland and Canada, we headed directly up onto the Greenland ice cap then turned north and flew along a CryoSat track acquired on the previous day.

The transition from the glacier and onto the Greenland ice cap (left part of the photo). The plane is flying at about 300 m.

The transition from sea level to the ice cap itself is spectacular, often consisting of a succession of deeply crevassed glacier fronts. The ice cap itself is much less so, especially after a few hours of flying since, apart from some patterns owing to snow drift, it is mostly featureless.

Still, it inspires awe in terms of its sheer size and extent, and it is easy to get a mental picture of the mind-boggling amount of water locked up in the ice below.

The Canadian military base Alert at the northern trip of Ellesmere island.

We finally made it to the military base of Alert, Canada on Friday evening where the teams have now spent two days analysing the data acquired so far and making plans for today (Monday).

Rene Forsberg from DTU making a GPS position measurement beneath a corner reflector placed at the end of the runway on Sunday.

Three, or maybe four, planes filled with scientific sensors to measure ice conditions below will head to a meeting point slightly to the east of the Alert base and then collectively head north as CryoSat crosses high above them. Conditions are cold (–27°C) and clear, which is perfect. More to follow - but the plane is waiting !

The temperature this morning as we prepare for the joint ESA and NASA flights.

First CryoSat underflight – a perspective from the Twin Otter

From Rene Forsberg (DTU-Space), Alert, 1 April

Twin-Otter aircraft at Alert, northern Canada

The ESA Norlandair Twin-Otter, which we are responsible for during the ESA CryoVEx campaign, is equipped with a CryoSat-like radar called ASIRAS and a laser scanner. Last Thursday, we flew over the Arctic sea-ice on a 5-hr mission starting from our Alert home base at the northern tip of Canada.

Flight tracks of the two aircraft, with times in decimal hours

By taking off quickly early in the crisp cold Arctic morning we reached the CryoSat track at about 8:25 local time, which is within two minutes of the overhead pass of CryoSat satellite more than 600 km above. That morning the NASA IceBridge P-3 aircraft also underflew the same track, six minutes ahead of our plane. As they fly much faster we could not catch up – but this was not our goal. We know that by combining radar, laser and optical data from both aircraft missions today we will gain both valuable information on sea-ice thickness and conditions below and a better understanding of how CryoSat measures ice thickness from space.

Example of quick-look data showing the height of the sea ice in the GPS coordinate system. Red colours are ridges, and blue areas thinner ice.

The joint experiment was a great success in cooperation and execution, with a nearly perfect alignment of aircraft and satellite, blessed with excellent weather (no clouds or wind, and a minimal sea-ice drift). The instruments on the ESA aircraft all functioned well, in spite of the low temperatures during the morning takeoff (–35°C). The cold has already provided some challenges during the flight to Alert across northern Greenland to the small (but resolute and able) DTU-Space team participating in CryoVEx 2012.

The figures above show some examples of the tracks of the two aircraft, with the NASA and ESA flights in red and black. The ESA aircraft repeated the measurements along the 500-km line flying out and back at two different elevations. By taking two looks at the same ice below we hope to be able to estimate sea-ice drift. An example image of ice freeboard (how far the ice extends above the water surface) as measured from our plane is also shown.

Arctic sea-ice

The photo of the sea ice taken from the plane that morning will give you an idea of what it looks like out there. The ice is several meters thick, but changing frequently to thinner leads (cracks between ice floes) and thicker ridges.

DTU-Space crew: Henriette Skourup,Arne Vestergaard Olesenand Rene Forsberg

100 years on … the spirit of international collaboration and our polar regions

From Michael (NASA), the Arctic, 29 March

Today marks the centennial of Sir Robert Falcon’s death on the Ross Ice Shelf on March 29, 1912. There are many commemorative events taking place around the world today to remember the scientific accomplishments of the Terra Nova Expedition. The most prominent of all events is a National Service of Commemoration for Captain Scott and the Pole Party at St. Paul's Cathedral in London, with our own Seelye Martin participating as a guest of honor. In 2008, I had the privilege to visit Captain Scott's historic Terra Nova Hut on Cape Evans in Antarctica, and the geographic South Pole, where the National Science Foundation has installed a sign with Scott’s famous quote. It took my breath away.

One hundred years later we launch two aircraft from different locations and meet up over the Arctic Ocean on a track that has been flown shortly before by a spacecraft more than 600 km above us.

Today's flight plan

A lot has changed to say the least, but nevertheless operating in remote polar regions remains a challenge even today, with the safety and success depending on extremely experienced and skilled members of the aircrew and instrument teams that excel in meeting this challenge every day. Today’s polar research is driven by a spirit of international collaboration and today’s flight is a fine example of what can be accomplished when many nations and organizations team up instead of competing with each other. Recognizing the enormous accomplishments of the early polar explorers we dedicate today’s mission to the members of the Terra Nova Expedition who died in Antarctica 100 years ago.

Ellesmere Island at start of our CryoVEx survey (M. Studinger)

The first part of today’s mission was a joint survey with the European Space Agency’s CryoVEx campaign. The plan was to fly three aircraft and CryoSat-2 within hours on the same satellite orbit. In addition to the P-3 (N426NA), the Technical University of Denmark (DTU Space) has chartered a DHC-6-300 Twin Otter (TF-POF) from Norlandair and has installed a laser scanner and ASIRAS, which is the airborne version of SIRAL, the radar that flies on the CryoSat-2 spacecraft. We had also planned to have a Basler BT-67 (DC-3) aircraft, ‘Polar 5’ (C-GAWI) from the Alfred Wegener Institute in Germany, participate in the joint flight. The Polar 5 is equipped with an EM-31 bird for measuring sea ice thickness, an airborne laser scanner, and nadir looking video and camera systems. Unfortunately, there was a technical issue with the EM-31 bird that could not be resolved in time for the flight and the Polar 5 did not participate on today’s CryoVEx flight.

One of the many refrozen leads we saw today (mosiac from Eric Fraim)

The choreography of events we had developed worked out perfectly. We had excellent weather in the survey area, which was an incredible help. We only have two orbits per day that are inside the temporary SAR mode mask of CryoSat-2 north of Alert (see map) and selected the early morning orbit that was flown by the spacecraft at 11:31 Zulu. The P-3 took off from Thule as soon as the airfield opened at 11:00 Z. At 12:12 Z we were close to Alert and heard on the radio that the Norlandair Twin Otter was taxiing. N426NA reached the start of the survey line at the coast of Ellesmere Island at 12:18 Z with TF-POF close behind us. The timing worked out perfectly – a job well done by everyone involved. At 13:16 Z we reached the end of the CryoSat survey line and turned towards waypoint RK04 of the ZigZag West mission plan. At 17:05 Z we reached the end of the survey line at waypoint NTSW and started climbing for the transit back to Thule.

It was a perfect day.

More pictures are here:

http://michaelstudinger.smugmug.com/

New CryoSat ice campaign kicks-off up north

From Malcolm (ESA), Kangerlussuaq, Greenland, 28 March

On-route to the high Arctic

After months of preparation and hundreds or even maybe even a thousand emails, the 2012 CryoSat Validation Experiment otherwise known as ‘CryoVEx 2012’ finally kicks-off this week across the Arctic.

Together with NASA colleagues and participating scientists from the USA, Canada and Europe, some remarkable airborne flights are planned later this week and early the week after.

One of the highlights could come as early as tomorrow when the CryoSat satellite will pass over the Arctic Ocean from the north at about 7 km per second and pass almost directly over the Canadian military base Alert located at the northern tip of Ellesmere island. This provides an ideal occasion to fly directly under the satellite and collect valuable data from the onboard instruments on the real ice-conditions and ice thickness beneath both plane and satellite.

For the moment, however, I’m in Greenland still travelling to the campaign location. Reaching the isolated Alert base is itself a challenge and typically takes two to three days or more, albeit through some interesting and spectacular landscapes.

Landing in the main port of entry into Greenland – Kangerlussuaq – I was greeted appropriately by a snow storm as you can see in the picture of the ferry plane between Europe and Greenland. If all goes well I’ll be in Alert tonight or tomorrow evening. In the Arctic, however, you never know as weather can change quickly. Let’s see!

Antarctic expedition checks CryoSat down-under

From campaign team (UTAS/AAD/AWI), East Antarctica, 10 December

Skidoo and corner reflector (credits: UTAS–J. Beardsley)

Next week marks 100 years since Roald Amundsen reached the South Pole. As a team of scientists brave the Antarctic to validate data from ESA’s CryoSat mission, it’s hard to imagine what these first intrepid explorers would have thought of today’s advances in polar science.

Read the full article about this challenging Antarctic campaign on ESA's Campaigns web page: http://www.esa.int/esaLP/SEMHXD5XPVG_LPcampaigns_0.html

The end of a remarkable Arctic campaign

ESA's CryoSat Validation Manager in the field (credits: M. Davidson)

From Malcolm (ESA), NL, 13 May

While there are still several teams on the ground finishing off their measurements, the successful ASIRAS flight over T15 on the Greenland ice cap this past Monday following the royal visit on Sunday marks the official end of the ESA CryoVEx campaign for 2011.

This has been a remarkable campaign in many ways. One element that comes to my mind is the sheer size of the effort. At times, we have had up to 50 scientists working on land ice or on sea ice across the Arctic, taking dedicated measurements from the air and on the ground – all contributing to CryoSat validation.

In addition to a ship or two lodged in the sea ice supporting teams on the ice, there were occasions during the campaign when up to four planes were in the air at the same time moving across the ice like a performance of aerial ballet making coordinated measurements of ice conditions below.

Icebreaker KV Svalbard (credits: A. Renner)

It was fantastic to see, for instance on April 15, the combined flights of the NASA IceBridge team, the DTU-team and their Norlandair Twin Otter with ASIRAS on-board and the AWI Polar-5 with EM-Bird coming together.

Polar-5 towing the EM-Bird over ice (credits: C. Haas)

Another personal highlight was my visit to T15 this past Sunday with high-ranking representatives from ESA, University College London, WWF-Netherlands, Oil and Gas Industry and the Dutch Royal Family.

HRH Prince Willem-Alexander of the Netherlands (right) being met by Santiago de la Peña on the Greenland ice cap (credits: V. Liebig)

It provided a unique opportunity to illustrate vividly on-site the scientific goals of the CryoSat mission and environment that the satellite is now measuring so precisely from space.

It also highlighted the role of ground and airborne measurements in ensuring that the maps generated by CryoSat will be of unprecedented accuracy. These ensure a better monitoring of changing polar ice conditions and provide a better understanding of long-term trends.

NASA P-3 aircraft (credits: NASA/IceBridge)

The fact that the campaign worked out so well is a tribute to the dedication of the CryoVEx teams and their efforts in the field, and to the excellent collaboration and coordination between ESA, NASA, airborne and ground teams.

Henriette Skourup monitoring ASIRAS on the Twin Otter (credits: M. Davidson)

Lastly, the first-ever ESA blog for a campaign – maintained by our indefatigable Honora Rider – provided the opportunity for all participants to share their work and experiences on the ice.

I would like to thank all my ESA colleagues and campaign participants for your contribution and for your hard work. The next steps in analysing the data and putting the results together should be very exciting and valuable indeed.

I sign off with a few photos containing some of the highlights of the CryoVEx campaign.