Finnish Meteorological Institute (FMI) demonstrates a new service for the Baltic Sea: Baltic Sea landfast ice extent and thickness (BALFI). The service incudes maps of snow and ice thickness and ice deformation map on the landfast ice. The ice thickness map also shows the full extent of the landfast ice. The maps are based on three Baltic Sea products of the Copernicus Marine Environment Monitoring Service (CMEMS), SENTINEL-1 SAR imagery, and a sea ice thermodynamic model (called HIGHTSI) run at FMI.

For more details see http://nsdc.fmi.fi/services/Copernicus_Marine_Service/BALFI and menu tabs ‘Landfast ice extent’, ‘Snow and sea ice thickness’ and 'Sea ice deformation'.

The BALFI maps are generated daily during the Baltic Sea ice season (Nov/Dec to May), with areas of new SENTINEL-1 SAR image acquisitions updated.

The BALFI maps cover the whole Baltic Sea with a 500 m pixel size. They are in Mercator projection used in the Finnish Ice Service ice chart (see http://en.ilmatieteenlaitos.fi/ice-conditions).

The maps are visualized in the zoomable map window, and map data at mouse cursor location is shown under 'Pixel value' by clicking a mouse button. Snow and ice thickness are shown in cm. Color code of the selected ice information map is shown under 'Legend'.

The maps can be also downloaded in GeoTiff-format.

In the map window the raster format BALFI maps are shown over vector format geographic dataset (i.e. map). This geographic dataset has much better spatial resolution than the 500-m BALFI maps, and therefore, near coast there may be missing pixels (i.e. no-data areas) in the BALFI maps or pixels are slightly overlapping land. For small coastal areas without information in the BALFI maps, data from the nearest map pixels can be used. Over the land the maps show a pixel value of 250.

Estimation of the landfast ice extent is based on analysis of SENTINEL-1 SAR imagery daily mosaics from the last 15 days. Sea ice areas connected to land and which have not moved significantly during the last 15 days are classified as landfast ice. Therefore, the landfast ice extent map shows the average extent of the landfast ice during the past 15 days. The spatial resolution of the landfast ice extent map is 500 m.

In more detail, the estimation of the landfast ice extent is based on thresholding of temporal cross-correlation (TCC) median value between adjacent daily SAR mosaics from the past 15 days. The thresholding is performed separately for both HH and HV SAR polarization channels. To be classified as landfast ice the image pixel TCC median must be above a predefined threshold value and additionally the pixel must be connected to land (defined by a land mask) through other landfast ice pixels. The channel-wise (HH and HV) results are combined by a pixel-wise logical AND operator.

Sea ice thickness on landfast ice is extracted from the CMEMS Baltic Sea physics analysis and forecast model product (CMEMS identifier BALTICSEA_ANALYSIS_FORECAST_PHY_003_006). This model product provides forecasts for the physical conditions in the Baltic Sea, including sea ice concentration and thickness, see details at http://marine.copernicus.eu/services-portfolio/access-to-products/?option=com_csw&view=details&product_id=BALTICSEA_ANALYSIS_FORECAST_PHY_003_006.

The spatial grid of the model is 1 NM (1.85 km). Snow thickness over the landfast ice is estimated using a one-dimensional sea ice thermodynamic model (HIGHTSI) model run at FMI. The model is forced with ECMWF (European Centre for Medium-Range Weather Forecasts) numerical weather forecasting data. The HIGHTSI model data has a spatial grid of 0.0665 deg in longitude (7-8 km) and 0.133 deg in latitude (~14 km). The snow and ice thickness data are interpolated to the 500 m pixel size of the landfast ice extent map. It is noted that the snow and ice thickness maps show average thicknesses over a large area, and locally snow and ice thickness can vary a lot.

Sea ice deformation is estimated based on the cross-correlation between the HH and HV SAR image channels. The more deformed ice, the more distinguishable features (above the noise level) the SAR imagery has at both channels, resulting to an increasing inter-channel cross-correlation as a function of increasing deformation. The cross-correlation is computed between adjacent day mosaics, and the value corresponding to 10 percent of the ordered 15 day period values is used as the degree of deformation. The current scale is also from one (no deformation) to 255 (highly deformed). It is noted that the scale is a qualitative one, and it is not yet possible to link it to quantitative figures of sea ice deformation, like height of ice ridges.

The BALFI service has the following service disclaimer:

“The user of the products presented on this web portal is asked to bear in mind that ice conditions may change rapidly due to changes in weather conditions or in sea state. The products here do not foresee any such changes. The user is also asked to consider that there are other conditions that can hamper or prevent safe travel on the sea ice, like poor visibility or deep snow.”

“The service provider does not guarantee that the information contained in these web pages is faultless or that it is suitable for the intended purpose. Under no circumstances shall the service provider or its affiliates, partners, suppliers or licensors be responsible for any damages or losses that may be caused to the user due to use of this service or due to actions or decisions taken or made by the user on the basis of delivered or undelivered content. Furthermore, the service provider shall not be responsible for any claims presented against the user by third parties on the basis of such use, actions or decisions.”

Feedback on the BALFI portal and products can be send to balfi@fmi.fi

Coming soon.

The current day and also past maps can be downloaded in GeoTiff-format using wms and wcs from

https://data.nsdc.fmi.fi/geoserver/BALFI/wms

https://data.nsdc.fmi.fi/geoserver/BALFI/wcs

The Creative Commons Attribution 4.0 International license (CC BY 4.0) is applied for the BALFI products. An end–user is free to:

• Share – copy and redistribute the material in any medium or format.
• Adapt – remix, transform, and build upon the material for any purpose, even commercially.

FMI cannot revoke these freedoms as long as the end-user follow the license terms. For details see: https://creativecommons.org/licenses/by/4.0/legalcode