Description: The SIGRID-3 vector archive format is one of the World Meteorological Organization (WMO) standards for archiving digital ice charts in the Global Digital Sea Ice Data Bank (GDSIDB). The WMO ice chart archiving formats are the Sea Ice Grid (SIGRID) format developed in 1981 and formalized in 1989 and its successor SIGRID-2. The National Ice Center digital Ice Analysis charts (Hemispheric, Regional and Daily are encoded in SIGRID-3 and have two main components: the shapefile containing the Ice Analysis ice information (ice polygons and related attributes) and the metadata describing the Ice Analysis data under the SIGRID-3 format.
The National Ice Center legacy ice data set contains hemispheric spatial data files from 1972 through 2004 inclusive. Regional Spatial data files of the traditional "seas"(ex Beaufort Sea) have been available since 1997. Legacy data are available in various formats from the National Snow and Ice Data Center in Boulder, Colorado ( http://nsidc.org/ ). Legacy Great Lakes charts are available from the Great Lakes Environmental Research Laboratory in Ann Arbor, Michigan ( http://www.glerl.noaa.gov/ ). Currently (October, 2006), spatial data files are available for each hemisphere, and for each sub-regional area, of which there are approximately 62. The ice analyses for each sea or sub-sea are also available in a jpeg format. They represent the ice conditions for the week in which they are published. Data for the analyses can go back 96 hours from when they are completed. They are dated with the week they are published. They are based on an analysis and integration of all available data on ice conditions, including weather and oceanographic information, visual observations from shore, ship and aircraft, airborne radar, satellite imagery and climatological information. The Regional Ice Analyses describe areas of differing ice conditions using the WMO ice observing standards, and indicate where significant changes in the amount, stage of development and form of the predominant ice types have occurred. The Regional Ice Analyses for all of the Northern and Southern Hemisphere Seas are produced every other week. The analyses for the Bering, Chukchi, Beaufort, Arctic Basin (High Arctic), Northern East Greenland, Barents, Kara and White Seas and the Cook Inlet are produced at least weekly. The Ross Sea is produced weekly during Austral Summer navigation season. The Chesapeake and Delaware Bay areas are produced weekly when there is ice. The analyses for the Great Lakes (when there is ice and in collaboration with the Canadian Ice Service), the Bering Sea, the Cook Inlet and the Chukchi and Beaufort Seas are produced twice per week when there is an ice edge present. The National Ice Center also produced daily ice edges in text format for both the Northern and Southern Hemispheres.