In April and May 2022, Norway’s first ship-based Arctic research expedition with a focus on satellite remote sensing of floating ice visited the western Fram Strait and East Greenland waters to collect ground truth data for the validation of satellite remote sensing products.
By: Torbjørn Eltoft and Andrea Schneider // UiT The Arctic University of Norway, Sebastian Gerland // Norwegian Polar Institute
With marine areas more than five times as large as the land area and its long coastline, Norway has a strong focus on the marine environment and securing its sustainable development. Norway also has deliberate ambitions of keeping maritime activities safe. This ambition in itself and the challenging Arctic nature require specialised tools for situational awareness and decision-making support.
The Centre for Integrated Remote Sensing and Forecasting for Arctic Operations (CIRFA), a centre for research-based innovation, has the goal to improve knowledge and provide technologies for environmental monitoring and forecasting in response to the needs of users of Arctic waters.
The methods that CIRFA scientists are developing aim at improving remote sensing and forecasting technologies. CIRFA’s “innovative toolbox” contains products based on satellite data and models such as weather forecasts, drift models, and automatic sea ice maps as well as drone sensors and – not least – experience and knowledge from on-ice-fieldwork.
Starting from Longyearbyen, the Norwegian ice-class research vessel Kronprins Haakon reached the landfast (i.e. stationary) sea ice in the western Fram Strait, the so-called Norske Øer Ice Barrier, after four days of sailing. The expedition’s main goal was to collect ground-truth data for validating remote sensing products for sea ice, icebergs, and ocean, that have been developed by CIRFA since its start in 2015. The science team consisted of 33 scientists and engineers from Norwegian and French CIRFA partners. With its well-equipped laboratories, helicopter deck, and hangars, RV Kronprins Haakon is an ideal platform to perform the planned sea ice, iceberg, and ocean studies, and make observations related to satellite remote sensing. In addition, several synergetic projects with Fram Centre partners addressed changes in sea ice and ocean.
Data collection across wide scales
CIRFA’s research focuses on analysis of synthetic aperture radar (SAR) data. SARs are imaging radars, which from altitudes of 600-700 km, can provide metre-resolution images of Earth’s surface. They are key tools for monitoring sea ice and studying how it changes in a warmer Arctic climate, because they can “see” through clouds and are unaffected by light conditions. They do not display colours or optical brightness, but nonetheless provide information about surface roughness and electromagnetic surface properties.
The validation of sea ice remote sensing products will tell us more about how accurate and reliable their information is. To retrieve ground-truth data at a multitude of spatial scales, the CIRFA team collected data and samples with surface information ranging in scale from micrometres, inferred from snow pits and sea ice coring sites, to kilometres, inferred from transects and drone data. In addition, autonomous sensors were deployed in sea ice and ocean to reveal sea ice and ocean changes and dynamics.
The roughness of the sea ice surface has a major influence on SAR images: a smooth ice surface will look dark, whereas a rough surface will look bright. Likewise, temperature, density, salinity, and internal microscopic structure of snow and ice affect the scattering and attenuation of radar signals inside these media, and hence influence the amount and quality of information that the radar signals carry back to the satellite.
Snow and sea ice also have different electrical properties that are determined by their microstructure and the fractional mixture of ice, water, brine, and enclosed air. All these parameters were measured during stops in the ice. A laser roughness profiler was used to reveal surface topography characteristics, and analysis of snow pit measurements and ice cores tells us about the physical properties of snow and sea ice.
Validation of satellite remote sensing requires that the ground-based measurements are geographically co-located with satellite acquisitions and coincide in time. During the expedition, this was regularly achieved, thanks to detailed planning and communication between the field and land teams. A whole suite of satellite images was acquired, including scenes from the European Space Agency, Sentinel-1 and the Canadian RADARSAT-2 satellites.
The combined ground truth and satellite measurements will allow future studies to address important research questions in Arctic remote sensing and development of new technologies. The European Space Agency supported parts of the fieldwork since the ground truth data and subsequent analysis have direct relevance for its ongoing and upcoming missions.
A tool box for safe activity at sea
At the intersection between research and industry, CIRFA is developing a new “innovative toolbox” to detect, analyse, and predict ocean surface conditions. Elements from this toolbox may be chosen or adapted depending on the task at hand, the situation, and weather conditions. Selected tools may contribute to increased situational awareness, operational support, and environmental monitoring in the daily work of industrial actors in icy waters.