The Baltic Sea is a shallow, semi-enclosed brackish water basin located in North Europe. Sea ice occurs there every winter, with the annual cover varying from 12 to 100%. There is a strong need for operational sea ice mapping due to intensive ship traffic assisted by 20–30 powerful icebreakers. Sea ice reports and charts are provided daily by ice services in all countries in the Baltic Sea area. In Finland and in Sweden, much effort is put into ice research in support of winter navigation [e.g., Leppdranta, 1986; Thompson, 1986].