Tag Archives: snow

Ready, set, snow!

Chung-Chi Lin (ESA) & Dirk Schuettemeyer (ESA), 18 March 2013

At the end of February, teams from the Finnish Meteorological Institute (FMI), GAMMA Remote Sensing and the Swiss Avalanche Service (SLF) successfully carried out the SnowScat vertical profiling experiment in Sodankylä, Finland.

The experiment was conducted to gain deeper knowledge about the stratigraphy of snow. It is part of the activities of ESA’s CoReH2O (Cold Region Hydrology High-Resolution Observatory) candidate Earth Explorer 7 satellite.

The instrument worked perfectly during the experiment. The scientists were also happy since the data that were collected as they looked very representative.

Developed by GAMMA in Switzerland, the ‘SnowScat’ instrument is a fully polarimetric scatterometer, coherent stepped-frequency continuous wave radar that operates in the range of 9–18 GHz.

SnowScat has been used in the last four winters in Sodankylä and produced a wealth of data for analysing snow mass, snow structure and snow-pack morphology such as stratification, grain size and type.

Until this part of the campaign the instrument worked with a similar viewing geometry as a potential satellite. However, it was the time to change this to have a closer look at the layering of snow. This involved some basic construction to move the instrument around, as you can see below.

Preparing SnowScat as it snows. (ESA)

The campaign had good start since the weather and snow conditions at the time were rather favourable. The temperature rose to above freezing in the days preceding the experiment, causing partial surface melt. During the experiment, temperatures remained around freezing, so the hope was that some nice layering could be observed.

On the first day of the actual experiment, it snowed from the early morning until just after the mid-afternoon. It took the team the whole morning to set up SnowScat in these challenging conditions.  Initially, the team couldn’t mount a functioning laser pointer on SnowScat, which obtains a rough pointing knowledge of the instrument.

Nevertheless, the team used their creative skills to attached a string with a weight (actually it was a wrench) to determine the true vertical direction. The antennas of the instrument were then visually aligned with an accuracy of better than say half a degree. 

SnowScat with wrench. (ESA)

Owing to the heavy snowfall, there was a rapid accumulation of snow on the instrument. The meltwater dripped from SnowScat and created small indents in the surface of the snow on the ground. We don’t know yet what effect this will have on the SnowScat signatures.

On the second day, the sky was mostly clear, and it didn’t snow.

For the actual data acquisition, the extension beam was swung manually around a pivot point at back of the instrument. SnowScat was then operated at 11 different positions along an arc of approximately 2 m. 

The geometry is determined by the marks on the front-side railing as seen below. This string with the weight, i.e. the wrench turned out to be very useful, as it could be extended so that the weight was lowered at the end of the experiment to mark the nadir points on the snow surface for the snow-pit characterisation.

Snowpit team in action. (ESA)

At each horizontal position, SnowScat was operated at five elevation angles, from –2° to +2°.  At each elevation angle, it swept the maximum frequency range (9.5–17.5 GHz).  It was determined that the responses were not so sensitive with respect to the precise pointing around the vertical. 

At ±2°, the first peak became noticeably reduced, whereas the ground return remained comparable, which confirmed the assumption on the dominance of specular reflections from the snow surface and internal layers.

The team had to climb up the tower every time the extension beam was swung horizontally, but this helped to keep them warm! The first set of measurements from all the horizontal positions was completed by the end of the first day.

The same measurements were repeated in the morning of the second day.  So, we now have two complete sets of measurements with two slightly different snowpack conditions, one during snowfall on a partially melted/slightly refrozen surface and the other on fresh snow layered on refrozen snow.

SnowScat on tower with Sebastian (SLF) on left, Andreas (Gamma) in the middle, and Lin (ESA) on the right.

This is already an unique dataset in itself. To be able to really analyse the radar data and also be able to validate the data, the SLF team carried out some extensive in situ data sampling in the field of view of the instrument after the radar data acquisitions.

The different teams have returned home and started to analyse the data and can hopefully report on these measurements in detail soon.

 

SnowSAR in action!

From Alex Coccia (MetaSensing), 8 March 2013

In the last week of February, the final European SnowSAR campaign for this winter in was accomplished. The campaign falls within the AlpSAR project supporting the preparations for ESA’s CoReH2O (Cold Region Hydrology High-Resolution Observatory) candidate Earth Explorer 7 satellite.

This latest campaign follows two other SnowSAR experiments that took place in November 2012 and January 2013, all in the same area ofAustria.

One of the three sites used for SnowSAR acquisitions. The Mittelbergferner, glacier in the Ötztal Alps. (MetaSensing)

The breathtaking landscape of the European Alps around the Austrian–Italian border was the setting for operations.Innsbruckairport is the base of operations for the MetaSensing team operating the SnowSAR instrument.

It’s not an easy life for the pilots of the Cessna 208 Grand Caravan though, which hosted the measuring system, as Innsbruckairport is renowned for having a difficult approach because of the surrounding high mountains.

Cessna 208 at Innsbruck airport, the base of operations for the MetaSensing team. (MetaSensing)

Flying the tracks for the SnowSAR acquisition isn’t a trivial task either, especially when clouds tend to hide the mountain tops.

Aerial view of the Austrian Alps. (MetaSensing)

Despite the challenges, the SnowSAR campaign was successful with data being acquired over each of the three chosen sites, from 1000 m up to and above 3000 m above ground.

SnowSAR point of view on the alpine panorama. Dual frequency, dual polarisation X- and Ku- band radar. (MetaSensing)

The image below was acquired at Ku-band, VH pol, over the Leutasch site in November 2012. On the right, corner reflectors deployed for radiometric calibration purposes can be seen.

Example of SnowSAR image. (MetaSensing)

Although the field campaign is over, there is no time to relax. The data recently acquired are now being checked and pre-processed. Preliminary SnowSAR images from the November and January campaigns are also being released.

And, the SnowSAR instrument is already on its way toCanadafor the next stage of the campaign. Stay tuned!

 

 

Battling Arctic conditions for SnowSAR

From Chris Derksen (Environment Canada)  Inuvik, Canada

Although the schedule for the final preparations was very tight, activities are proceeding well for a SnowSAR flight in Canada.

Peter Toose and Arvids Silis stop for a break while en route from Inuvik to the study site. (Environment Canada)

Over the past week, scientists from Environment Canada have been in the field near Inuvik, in the Northwest Territories. As expected, the environment near Inuvik in December has posed some challenges – the Sun does not rise above the horizon at any point in the day, so between 11:00 and 16:00 it’s just twilight. Temperatures have been very cold, not climbing above –30°C and reaching as low as –38°C.

In spite of these conditions, measurements are proceeding well – Lidar scans to determine snow depth along large snow drift features are complete. Transects of snow depth, density, snow stratigraphy and grain size, and surface roughness are ongoing.

Alex Coccia from MetaSensing preparing to setup a calibration target for the SnowSAR. (Environment Canada)

The scientists are based in a small cabin approximately 50 km from Inuvik, which provides them with quick snowmobile access to the study area. They are enjoying the rustic lifestyle!

Arvids Silis from Environment Canada preparing to take measurements with a ‘magnaprobe’ – an automatic snow depth measuring device equipped with a GPS. (Environment Canada)

The Cessna-208 aircraft arrived in Inuvik from Norman Wells yesterday afternoon. The rear baggage doors were removed in the evening, and replaced with specially designed doors that will house the SnowSAR instrument. Installation of the SAR is planned for this morning, and if weather conditions cooperate, the science flight will be conducted this afternoon.

The campaign supports the development of ESA's CoReH2O candidate Earth Explorer mission.

Things hotting up for measuring snow mass

From Dirk (ESA), 3 December 2012

A few weeks ago we kicked off a series of campaigns to hopefully provide high-quality airborne data for the development of ESA's CoReH2O candidate Earth Explorer mission. This mission is currently undergoing feasibility study.

The campaigns are built around an airborne synthetic aperture radar (SAR) called SnowSAR, which measures in the X- and Ku-band frequencies. The instrument was developed by Metasensing NL. It is used to simulate the instrument that could be carried on the CoReH2O satellite.  

The major goal of these campaigns  is to map and monitor the mass of seasonal snow over different surfaces in the Austrian Alps and in Inuvik, Canada. This is done by using the SAR carried on an aircraft and also taking measurements on ground. The fact that these campaigns can be conducted is thanks to co-funding from national bodies in Austria, Canada and the US and because everyone involved is willing to work on very flexible schedules.

Campaigns such as these always pose logistical challenges. The first, in this case, was a question of instrument availability. Since there was only one instrument available, and had to come up with a plan on how to ship the instrument between the Netherlands, Austria and Canada in the winter period.  

In October, the instrument was shipped to Canada and installed in a Cessna C-208 aircraft. For this purpose one of the doors was modified, which also involved ground and flight tests to ensure the aircraft’s airworthiness.

Cessna 208 with adapted door so that the instrument could be fitted.

The procedure went smoothly thanks to the efforts of the team in Canada and Metasensing. After a week in Canada we were able to ship the instrument back to the Netherlands and start the preparations for the flights in Austria.

In the meantime, the ground teams in Innsbruck, Austria, had prepared for the related ground measurements.

Checking temperature sensors, drilled into the ice of Mittelbergferner glacier in preparation for the AlpSAR campaign. (ENVEO)

We scheduled the first flight in Austria for the week starting 19 November. The aircraft had arrived two days earlier and the crew carried out the first test flights. Everything seemed to be perfect, including the weather and we planned the first real flight to go ahead on the Tuesday.

Early Tuesday morning, the ground teams left to make measurements in different valleys, including an Alpine glacier.

Snow pit on Mittelbergferner glacier – to measure vertical profiles of snow density, grain size and structure, and snow temperature. (ENVEO)

The aircraft took off but the crew realised very quickly that the Global Positioning System on board wasn’t working properly. So, they had to return to the airport and tried to fix the problem. It turned out that the GPS had to be replaced. The crew shipped in a new GPS unit on the same day and  installed it on the Wednesday morning. After some checks on ground the aircraft took off again and took all the measurements needed for the day.

In the evening, we all met and everyone was really pleased that everything worked on the ground and on the aircraft. There was even some time to visit the Christmas market in Innsbruck on Thursday morning before packing up.

We met again on Friday to ship the instrument to Canada, which should arrived by 11 December to perform measurements in Inuvik.

The ground teams in Canada are now preparing and facing up to the challenge of working in the dark and in temperatures around down to –30°C.

Over the coming months we will keep you updated on progress and also let the different teams introduce themselves.

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!

NASA IceBridge – clear but bumpy over southeast Greenland

From Michael (NASA) Greenland ice sheet, 11 April

Gyldenlove glacier, Greenland (credits: M. Studinger)

On April 11, NASA's IceBridge campaign finally got the clear weather necessary to fly over glaciers in southeast Greenland. Typically, this area is shrouded in cloud, but strong winds from the Greenland ice sheet can clear the cloud – but these winds and the rugged coastal topography cause a lot of air turbulence. So, with clear skies came winds of up to 70 knots, which made for a bumpy ride over the calving front of glaciers such as Gyldenlove seen here.

Despite the difficult conditions we were able to survey all planned glaciers in the cloud-free area south of 65N. The amount of windblown snow was extreme and often reduced visibility for flight operations. Today’s data will be a good dataset to evaluate the potential impact of windblown snow for ICESat-2 laser altimeter measurements.

Wind-blown snow over Greenland (credits: M. Studinger)

NASA's IceBridge, is an airborne campaign to monitor polar ice. As part of their campaign, NASA is taking part in joint flights with ESA planes, overflights of European ground sites and underflights of CryoSat.

By cooperating in collecting a huge and varied airborne dataset a better understanding of the data from ESA's CryoSat and NASA's ICESat missions will be achieved.

Post adapted from Michael Studinger's 11 April Operation IceBridge flight report.