FRAM – High North Research Center for Climate and Environment

Digital edition 2023

Satellites and drones for sea ice and iceberg mapping

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

Parked between two gigantic icebergs, the expedition stopped for a full day and a night of work on the sea ice in cold but calm weather on 1 May 2022. Note level sea ice between smaller and larger ridges, young ice forming behind the ship, and open water in the distance. Photo: Maritime Robotics

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.

The radar signal coming from satellites passes through the snow lying on top of the sea ice. Depending on the properties of the snow cover, the radar signal may be altered and harder to interpret. Careful study of the characteristics of the snow – the number and thickness of snow layers, the different snow crystal types and grain sizes, temperature, density, and salinity of the snow cover – allows more confident interpretation of satellite data. Photos: CIRFA and Sebastian Gerland / Norwegian Polar Institute (bottom left)

The expedition

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.

Colleagues from France joined the expedition and used a tomographic ground-based radar that was positioned on the sea ice and operates at the same microwave radar frequency as satellite radars (C-band). This method allows us to study the ability of microwave signals to penetrate through various snow and ice surfaces. These measurements, combined with in situ snow and ice data, can tell where the echoes come from by locating the scattering centres. Photo: Sebastian Gerland / Norwegian Polar Institute

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.

Drones equipped with cameras (optical, infrared, thermal) or radars can scout for difficult ice conditions and other obstacles ahead of the ship that are ambiguous in other navigation information, or can identify interesting sites to visit. Drone images also help connect satellite remote sensing products with in situ sea ice observations. With high-resolution data acquisitions but a limited spatial range, drones are an ideal tool to quantify types and extent of different sea ice classes, icebergs, and open water, and for situational awareness within about one kilometre around and ahead of the ship. For scale, the 100-metre long ship RV Kronprins Haakon can be seen on the right side of the photomosaic. Photomosaic: Maritime Robotics. Drone photo: Sebastian Gerland / Norwegian Polar Institute

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.

To measure surface roughness, the snow lying on top of the sea ice was carefully removed and a laser instrument was used to determine how smooth the ice surface was. The geometrical roughness of an ice surface tells us about its ability to backscatter radar signals, i.e. whether it looks bright or dark in a SAR satellite scene. Surface roughness measurements were done with a red laser profiler mounted on a 1.8 m long frame. The surface roughness, together with the internal microstructure of snow and ice, provides a complete ground truth data set for understanding radar scattering. Photo: Andrea Schneider / UiT The Arctic University of Norway

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 ScanSAR RADARSAT-2 satellite scene (300 km x 300 km) showing the central part of the research area in the western Fram Strait. The image nicely displays how the brightness varies, with the brightest areas being deformed first- or multi-year ice, the grey areas level and less deformed first year sea ice, and the darkest areas smooth newly formed ice and open water. Two polynyas, appearing dark in the upper left of the image, with new ice and open water, caught our interest and were visited with the ship and drones. West and north of them was fast ice, held in place by grounded icebergs, while east of them the sea ice was drifting. Data for the image shown were provided by NSC/KSAT under the Norwegian–Canadian RADARSAT agreement 2022. RADARSAT-2 data and products are copyright of MDA Geospatial Services Inc. 2022, all rights reserved. RADARSAT is an official mark of the Canadian Space Agency.

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.

Further reading

Cirfa website

Cruise report

About CIRFA:

CIRFA stands for Centre for Integrated Remote Sensing and Forecasting for Arctic Operations. It is a so-called Centre for Research-based Innovation (SFI) funded by the Research Council of Norway in 2015. CIRFA is hosted by UiT The Arctic University of Norway in Tromsø and has seven research and eight industry partners.

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