IcySea Sea-Ice Concentration Information

Sea-ice concentration is a low-resolution information layer for strategic planning purposes and to assist the interpretation of Sentinel-1 radar images. It is updated several times a day, automatically created and therefore to be used with care. Each pixel covers an area of 6.25 x 6.25 km². Colours refer to the fractional area in percent (%) which is covered with ice. For a correct use of the sea-ice concentration layer the following guidelines should be considered:

The 10% Rule

Sea-ice concentration below ~10% is not resolved by the sensor. I.e. a region showing no sea-ice concentration can still have enough ice floes remaining a significant navigational hazard.

Photograph from KPH of loose ice concentration — **Sea-ice floes in the Hinlopen Strait in May 2018:** It is possible that this ice situation appears as open water on the sea-ice concentration information layer.

Comparison SIC and S1 layer — **Comparison between sea-ice concentration and Sentinel-1 image:** Although the sea-ice concentration layer shows open water (upper image), on the Sentinel-1 scene (lower image), same time and place, individual smaller ice fields are identifiable.

The Coastal Bias

Close to the coast the sea-ice concentration is overestimated due to the influence of land You can best see this by looking on the Norwegian coast, which never has ice. The sea-ice concentration you see close to the Norwegian coast is the expected error for all coasts.

No Ice Types

Sea-ice concentration does not indicate the type of ice. A 100% ice cover might be old multi-year ice, first-year ice or even a thin refrozen ice layer only. To clarify this, use additional radar images and/or ice charts, if available.

Check the Timestamp

When you compare sea-ice concentration with a satellite image, be aware of the different time stamps. The time-stamp of the current sea-ice concentration layer is shown in the lower left corner in red letters just above the colour code legend. Usually sea-ice concentration is the newest layer.

Atmospheric Bias

Large atmospheric cyclones influence the measurements as well. Sometimes you see large areas indicating a sea-ice concentration of about 20-30 % in the middle of the open ocean. This is very likely an error due to a cyclone.

Cyclone bias — **Atmospheric bias:** The shown medium ice concentrations in the middle of the open ocean is very unlikely to be sea-ice, but an atmospheric distortion of the measurement due to a cyclone.

Physical Background of the Data

The sea-ice concentration data layer is an automatically generated product on the basis of satellite based passive microwave measurements provided by the Japanese Space Exploration Agency's (JAXA) AMSR2 sensor of the GCOM-W mission. The GCOM-W satellite circulates the earth 14.5 times a day (=14.5 revolutions per day). Due to its polar orbit, it crosses the poles during every revolution. The AMSR-E sensor records the passive microwave radiation on a stripe of 1450 km width (so called swath width). The data are thankfully provided by JAXA after every revolution, which enables so-called swath updates several times a day. The physical parameters of the GCOM-W mission are available here.

SIC updates — **Daily updates of the sea-ice concentration layer:** The number of updates of the sea-ice concentration layer per day depends on the latitude, the further north, the more often it is updated. The Svalbard archipelago is being updated 6 to 8 times a day.

The Sea-ice Concentration Algorithm

The conversion from passive microwave data to sea-ice concentration uses the ARTIST sea-ice algorithm from Spreen et al. (2008).