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Greater than the sum of its parts: airborne multi-instrument sea-ice observations

Sea ice thickness Science Arctic

The way sea-ice thickness is currently calculated from satellite altimeter data must be improved. The airborne data presented in our recently published study are only the first step in finding new ways to tackle this issue.

Background

Satellite altimeters measure how much the sea-ice surface floats above the water level. This parameter is called freeboard and it is further converted into sea-ice thickness. This calculation requires information about how much snow there is on top of the sea-ice layer and about the density of sea ice. Density depends primarily on two factors: how old the ice is and if the ice has been deformed. In young ice, there are small pockets of salty sea water that make it denser, whereas in older, multi-year ice the pockets have been replaced by air bubbles, which decreases the overall density. Winds and ocean currents deform sea ice by pushing ice floes against each other piling up blocks of ice into thick pressure ridges. Between the blocks from the lowest one of the ridge keel to the highest one of the sail, there are big gaps filled with sea water below the water line and with air above the water line when looking at a vertical column of sea ice. Measuring sea-ice density accurately is therefore difficult and traditionally requires coring or cutting out pieces of ice, which is why observations are sparse.

Measuring ice density on the fly

During the airborne AWI IceBird winter campaigns over the western Arctic Ocean in April 2017 and 2019, we measured sea-ice thickness, snow depth, and freeboard from our research aircraft Polar 5 and 6 using three sensors: an electromagnetic induction sounding device (EM-Bird), a microwave radar, and a laser scanner (Fig. 1). IceBird campaigns are currently the only effort of regular airborne sea-ice observations worldwide and the first of its kind capable of measuring snow depth, sea-ice thickness, and freeboard at the same time. From these three parameters, we can calculate sea-ice density (Fig. 2). From the more than 3000 km of airborne survey data collected, we can derive new up-to-date estimates and parameterisations for sea-ice density.

A way forward

The way sea-ice thickness is currently calculated from satellite altimeter data can and must be improved to gain improved and more accurate observations. But even with new sea-ice density estimates, trade-offs are still necessary: snow depth is not measured directly but often taken from monthly climatologies or modelled. Future satellite missions (such as CRISTAL, planned launch in 2027) will be much better than what we have today, but sea-ice density will still remain as a crucial parameter. It is important to understand why density values are what they are and how they may evolve in the future. During the last decades in the warming climate, the Arctic sea ice has become younger on average (less multi-year ice) that is more prone to deformation – both factors affect sea-ice density. The airborne data presented in our recently published study are only the first step in finding new ways to tackle this issue, as traditional methods have become insufficient.

Publications

  • Jutila, A., Hendricks, S., Ricker, R., von Albedyll, L., Krumpen, T., and Haas, C.: Retrieval and parameterisation of sea-ice bulk density from airborne multi-sensor measurements, The Cryosphere, 16, 259–275, doi.org/10.5194/tc-16-259-2022, 2022.
  • Jutila, A., King, J., Paden, J., Ricker, R., Hendricks, S., Polashenski, C., Helm, V., Binder, T., and Haas, C.: High-Resolution Snow Depth on Arctic Sea Ice From Low-Altitude Airborne Microwave Radar Data, IEEE Transactions on Geoscience and Remote Sensing, 60, 4300716, doi.org/10.1109/TGRS.2021.3063756, 2022.

Data sets

  • Jutila, A., Hendricks, S., Ricker, R., von Albedyll, L., Haas, C.: Airborne sea ice parameters during the PAMARCMIP2017 campaign in the Arctic Ocean, Version 1, PANGAEA, doi.org/10.1594/PANGAEA.933883, 2021.
  • Jutila, A., Hendricks, S., Ricker, R., von Albedyll, L., Haas, C.: Airborne sea ice parameters during the IceBird Winter 2019 campaign in the Arctic Ocean, Version 1, PANGAEA, doi.org/10.1594/PANGAEA.933912, 2021.
  • Jutila, A., King, J., Ricker, R., Hendricks, S., Helm, V., Binder, T., Herber, A.: Airborne snow depth on sea ice during the PAMARCMIP2017 campaign in the Arctic Ocean, Version 1, PANGAEA, doi.org/10.1594/PANGAEA.932668, 2021.
  • Jutila, A., King, J., Ricker, R., Hendricks, S., Helm, V., Binder, T.: Airborne high-altitude snow depth on sea ice during aircraft flight P6_211_RESURV79_2018_1804100301, Version 1, PANGAEA, doi.org/10.1594/PANGAEA.932702, 2021.
  • Jutila, A., King, J., Ricker, R., Hendricks, S., Helm, V., Binder, T., Haas, C.: Airborne snow depth on sea ice during the IceBird Winter 2019 campaign in the Arctic Ocean, Version 1, PANGAEA, doi.org/10.1594/PANGAEA.932790, 2021.

Contact

  • Arttu Jutila
    Arttu Jutila is a doctoral candidate in the AWI’s Sea Ice Physics section. For his dissertation, that he will be defending soon, he studied the snow layer on top of sea ice using ground-based and airborne microwave radars.
  • Dr. Stefan Hendricks

Questions

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Research aircraft Polar 5 being prepared for a survey flight.

Research aircraft Polar 5 being prepared for a survey flight at Alert, Ellesmere Island, Canada, in 2017 (Photo: Alfred Wegener Institut / AWI).