Ground truth at -20°C: A day in the life on the CEMSIE campaign
23rd June 2026
“Getting your hands out of your gloves to operate a touchscreen, tighten screws, or peer at snow crystals through a handheld magnifying lens. All while wearing multiple layers and ensuring not to expose your hands for too long, was probably the hardest part of the work” says Alicia Fallows, a CPOM affiliated PhD researcher at UCL who spent ten days at the The Copernicus Expansion Missions Sea Ice Experiment (CEMSIE) campaign in Cambridge Bay, Canada in April 2026.
With temperatures ranging from -5°C to -20°C and colder still with wind chill, dressed for the elements in heavy fieldwork gear, and long days capturing and recording vital data fieldwork can be an exhausting experience. Despite this, Alicia was keen to get back out on the ice every day. As part of a team made up mostly of Early Career researchers, “everyone was enthusiastic, willing to help each other, and was genuinely excited to be there!”
Snow on sea ice in a warming Arctic
The Arctic is warming faster than the global average and this is impacting Arctic sea ice. A 2024 CPOM UCL study found that Arctic sea ice in coastal regions may be thinning up to twice as fast as previously thought.
Satellites offer the only means of observing sea ice at scale, but the accuracy of retrievals depends on how well we understand what they are measuring.
Sea ice, and the snowpack sitting on top of it, remains one of the most challenging components of the cryosphere to characterise accurately because sea ice and snow are both changeable, and this impacts our ability to accurately retrieve sea ice properties from satellite observations.
As snow depth, density, salinity and microstructure all potentially influence microwave scattering signatures, uncertainties remain in satellite retrievals. We need to ensure the methods and assumptions we use to retrieve information about sea ice from space are correct.
The CEMSIE campaign – what it is and why it’s important
The CEMSIE campaign aims to reduce those uncertainties ahead of the launch of the ESA missions CIMR, CRISTAL and ROSE-L, bringing together scientists from a range of institutions across Canada and Europe to collect in-situ measurements to improve the retrieval methods used by the future missions.
Cambridge Bay offers stable, representative first-year sea ice (the ice that forms each winter and melts each summer) in conditions that are accessible for the large, multi-week campaign. Unlike sea ice that drifts with ocean currents, the ice here remains in the same place, allowing for repeated measurements at the same location.
An average day in the CEMSIE camp
Over 6 weeks, teams of researchers including Alicia, collected daily measurements of snowpack and sea ice properties – information that will directly inform instrument development for CIMR, CRISTAL and ROSE-L. Tasks were rotated so everyone got a chance to experience using different technologies.
“One person might manage the scatterometers, turning on each radar, putting on the generators, and initiating the scans via a laptop. Another would take on the main snow pit: a full day’s work in itself, involving a wide array of instruments to measure snow properties.
For example, we took density measurements and assessed the specific surface area of the snow using various instruments. Salinity was measured from bagged snow samples. All data was carefully recorded on a standardised snow pit sheet. Other regular tasks included taking ice cores and ice thickness measurements every few days, and setting up the passive radiometers – which needed to be switched on and configured each morning.”
Overnight temperatures can fall dramatically, possibly producing measurably different radar returns from the snow, so team members could also volunteer to work overnight to capture diurnal variations in the snowpack, keeping the scatterometers running and measuring temperature changes in the pack by digging snowpits.
Once back at camp, after unpacking, cleaning and drying the equipment, and having dinner (made by whoever was on a ‘rest day’) the work was still not over, and the team could find themselves working late into the evening.
“After dinner, there was always a team meeting, which could run until eight or nine in the evening sharing successes, challenges, and planning for the next day. After that, there was usually data to upload, field notes to digitise, and lab measurements to begin before they piled up. Most nights, we wouldn’t be done until ten or eleven. Then it was straight to sleep, and up to do it all again. We did find an evening for a team film night!”
While there, Alicia captured a typical day in the life of an Early Career researcher at CEMSIE in a 90 second video. For best view, open to full screen.
Aside from the daily campaign tasks, Alicia also got the opportunity to go on a full site transect (a circuit of approximately two kilometres around the camp) using additional instruments like the magnaprobe, which you push down into the snow to measure depth, as well as an excursion to an area with dramatic ice ridging. Supported by colleagues, she also got the chance to complete her own experiment supporting her PhD research into a process called flooding, which occurs when seawater infiltrates into the snowpack.
“I dug down to the sea ice surface and artificially created a flooding event – pumping seawater into a channel cut into the ice, effectively creating a small, contained pool. I then dug a series of snow pits at increasing distances from the flood site to track how far the water moved through the snow. We also set up one of the passive microwave instruments beside the site to monitor any changes in the radar return as the water spread. It was a genuinely exciting set of experiments to run!”
What is Copernicus and CRISTAL?
Copernicus is the Earth observation component of the European Union’s Space Programme, led by the European Commission (EC) and implemented in partnership with the European Space Agency (ESA). ESA develops and manages the space element, which is built around the Sentinel satellite missions and provides open-access data to support understanding and mitigation planning of the effects of climate change.
The Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) mission is due to be launched in 2027, equipped with a dual-frequency Interferometric Radar altimeter for Ice and Snow (IRIS) and a passive microwave radiometer, satellite instruments similar to the in-situ devices used by Alicia and the other researchers. This data can be compared to current ice EO missions, CryoSat-2, Sentinel-3 and ICESat-2 and inform instrument design with CRISTAL.
Alicia’s day-in-the-life film offers a window into what ground truth looks like in practice – very long days, keeping instruments running in sub-zero temperatures, and carefully recording data before the next task begins. For the early career researchers, the campaign delivers on three fronts: rigorous contributions to pre-launch validation for future space missions, invaluable field data to support their own research, and networking with international colleagues in a unique environment.
Most importantly, the campaign will mean more accurate retrievals and increasingly robust assessments of sea ice, and better-informed planning for future ice behaviour in a warming planet.
Alicia Fallows is based at UCL in the Department of Earth Sciences, and was supported to attend the CEMSIE fieldwork campaign by Julienne Stroeve and CEMSIE. Her PhD is funded by the London NERC DTP.
The CEMSIE campaign is funded by the European Space Agency SUPFIX-Polar funding call.
With thanks to the Canadian High Arctic Research Station (CHARS) facilities and support.
