24 Apr 2026

 

As sea ice continues to succumb to the climate crisis, measuring its decline with precision has never been more urgent. To meet this challenge, the European Space Agency is developing three new Copernicus satellites, each employing distinct but complementary techniques to monitor this fragile component of the Earth system.

To ensure the data from these new satellites are razor-sharp, an international team of hardy scientists is now out on the Arctic sea ice braving the cold and flying above to collect critical in situ measurements.

 

The Copernicus Expansion Missions Sea Ice Experiment focuses on three upcoming missions: Copernicus Imaging Microwave Radiometer (CIMR), Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) and Copernicus Radar Observing System for Europe at L-band (ROSE-L).

These are three of six Copernicus Sentinel Expansion missions that ESA is building for Copernicus – the Earth observation component of the European Union’s Space programme. Using different observing techniques and addressing a broad range of applications, this new suite of six missions will respond to EU policy priorities and gaps in Copernicus user needs, and expand the current capabilities of the current Sentinel missions.

Building state-of-the-art satellites cannot be achieved through scientific studies, laboratory experiments or engineering work in cleanrooms alone. It also requires field campaigns, where scientists and engineers test airborne and ground-based versions of satellite instruments under real environmental conditions to validate measurement techniques, assess instrument performance and refine retrieval algorithms.

These field campaigns provide a critical bridge between instrument design and a satellite working perfectly in space, even if a new measuring instrument is based on proven heritage missions.

By collecting observations in the field and comparing them with airborne measurements and existing satellite data, researchers can calibrate sensors, improve data products and reduce uncertainties before launch.

For the CIMR, CRISTAL and ROSE-L missions, which each measure sea ice properties, among other variables, in different ways, this groundwork is especially important.

Properties such as snow depth and snow salinity, ice thickness and surface roughness are all part of the Earth system and are changing rapidly in the polar regions in response to the climate crisis – and these important parameters remain challenging to measure accurately from space.

This is why scientists from numerous institutes including, for example, the University of Calgary, the Technical University of Denmark, the Alfred Wegener Institute, NASA and ESA are currently out in the Arctic for the six-week Copernicus Expansion Missions Sea Ice Experiment.

Through coordinated measurements on the ice and from the air, the teams are collecting critical data to improve CIMR, CRISTAL and ROSE-L’s retrieval methods and help ensure these important upcoming satellites deliver accurate and reliable observations of the polar environment.

This kind of field campaign is not for the faint hearted – it is an extremely harsh environment, and changeable. Based largely in Cambridge Bay, Nunavut, in the Canadian Arctic, the hardy scientists involved are having to head out onto the sea ice and brave freezing temperatures, fierce winds and very long days.

Instruments have had to be installed on the sea ice to take coordinated measurements with aircraft flying above – and where possible, these aircraft under fly satellites such as ESA’s CryoSat, Copernicus Sentinel-3 and NASA’s ICESat orbiting above.

In addition, helicopters are being used to transport teams and equipment to the more remote measurement target sites.

ESA Campaign Scientist, Tania Casal, said, “The campaign is a major undertaking, involving a large team of dedicated and highly driven scientists. The setup builds on the successful Multidisciplinary drifting Observatory for the Study of Arctic Climate MOSAiC experiment, adapting the framework for a new and equally ambitious objective.”

This campaign focuses on first-year sea ice, specifically conditions where saline layers remain preserved at the base of the snow layer – an important but poorly observed feature influencing microwave scattering, snow–ice interactions and satellite retrieval performances.

Unlike MOSAiC which set on drifting sea ice, the aim here is to take measurements in a stable ice setting where ice motion would not interfere with repeated observations and controlled experiments.

For this reason, Cambridge Bay provides an ideal location, offering representative first-year ice together with logistical accessibility.

Dr Casal continued, “We are collecting an exceptionally comprehensive suite of measurements, integrating extensive ground-based and airborne observations during satellite overpasses. Ground observations include scatterometer measurements, snow pit surveys, magna probe transects, snow micro pen profiles and numerous complementary geophysical and snow characterisation techniques.

“These in situ datasets are being paired with airborne observations from laser and radar altimeters, snow radars and electromagnetic systems, providing detailed information on snow depth, ice thickness, surface roughness, and subsurface structure.

“Crucially, these measurements are being acquired beneath the ground tracks of CryoSat, ICESat-2, and Sentinel-3, for example, enabling direct comparison between field observations, airborne remote sensing and satellite retrievals.”

By linking measurements made on the ground, from aircraft and from space, the campaign is helping to sharpen the performance of CIMR, CRISTAL and ROSE-L before they are launched, reducing uncertainties and strengthening confidence in the data they will deliver.

 

[Image]

(A) Copernicus Sentinel Expansion Missions

(B) Arctic campaign tracks

(C) Arctic sea-ice extent

(D) Radar view of Arctic sea ice captured by Sentinel-1