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SEA ICE THICKNESS CHARTS
Routine ice charts published by the national ice services in WMO ice symbols are showing ice conditions in 2-25 km scale. For users at sea this resolution is too rough be used in ice navigation. In order to provide information in ship's scale automatic ice thickness charts are published by the Finnish Meteorological Institute (FMI). The algorithm, which combines SAR data and ground truth, provides ice thickness information in 500 m resolution. The products are provided operationally and available to users shortly after SAR data is available. The mean level ice thickness estimates given in the traditional ice chart by Finnish Ice Service are compiled by an ice analyst from many sources including drilling measurements near coastline, systematic field observations provided by the staff of icebreakers and other ships at sea and ice growth estimates yielded by ice models. SAR images with a wide coverage are used to produce spatially more accurate ice thickness charts than the routine ice charts. An ice thickness chart is operationally produced after a SAR image has been received, using the latest available ice chart as an input. Then the ice field boundaries are refined, the thinnest and the thickest ice areas inside each ice chart segment are identified on the basis of the SAR signal statistics. The resulting thickness chart is then color coded according to the ice thickness based navigation restrictions. The spatial accuracy of the resulting ice thickness charts as well as routine ice charts has been analyzed using the electromagnetic induction based ice thickness measurements. The performed analysis has shown more accurate results for ice thickness charts. Currently, the ice thickness chart can use RADARSAT-1 ScanSAR Wide Mode images and ENVISAT ASAR Wide Swath images as its input image. Baltic Sea Ice Seasons The Baltic Sea freezes annually. The maximum annual ice extent occurs between January and March, when ice covers from 12 % to 100 % of the Baltic Sea, the average being 52 %. On average there occurs ice cover at latitude of Stockholm in every second winter. Ice season lasts from weeks in the south up to seven months in the north. The ice in the Baltic Sea occurs as fast ice and drift ice. Fast ice exists in coastal archipelago areas. Drift ice has a dynamic nature being forced by winds and currents. Ridges and brash ice are the most significant obstructions to navigation in the Baltic Sea. Powerful, ice-strengthened vessels can break through thick level ice, but they are not capable of navigating through ridges and heavy brash ice barriers without icebreaker assistance. Ice dynamics cause high pressure in the ice field and can be dangerous to the vessels and may cause time delays up to several days. Baltic Sea Marine Traffic The two most heavily trafficed waterways in the word, where seasonal sea ice plays an important role in navigation, are Gulf of St. Lawrence in Canada and the Baltic Sea in Europe. In Gulf of St. Lawrence some 180 million tons of goods are transported annually. The total cargo turnover in the Baltic Sea in is about 700 million tons, some 40% of which occurs during winter. In Finland almost 90% of foreign trade is transported by sea. Annual turnover in 2004 was 95 million tons. During the winter months there are more than 25,000 port-calls in Finnish harbours transporting about 40 million tons of goods. The marine transportation has increased worldwide. In Finland it has increased in 1995-2004 by 34%. In the Baltic Sea e.g. in 2001 the number of vessels sailed in the Gulf of Finland was 38,000; in 2015 this is expected to rose into 53,000 vessels. Russian oil export is growing rapidly. In 2002, 76 million tons of oil was transported through Gulf of Finland, in 2005 will be 125 million tons, and by 2015 there is expected to transport more than 300-400 million tons. Winter navigation is made possible by the use of icebreakers, ice-strengthened vessels and by restricting navigation. Navigation is restricted by closing half of the harbours for the winter and giving assistance only to vessels suitable for ice navigation. Under normal conditions the sailing time from the ice-edge to e.g. the northern Bothnian Bay is one day (400 nautical miles), but under severe conditions it can extend to nearly one week. End Users Finnish Maritime Administration, Finland
(www.fma.fi)
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