On a daily and weekly basis, the U.S. National Ice Center (USNIC) completes a detailed characterization of sea ice for the Arctic and Antarctic regions. Daily analysis includes analyzing ice information based on ice concentrations, separated into the Marginal Ice Zone (MIZ, area of ice concentrations 1 to 8 tenths) and Pack Ice region (ice concentration greater than 8 tenths). Whereas, weekly analysis includes ice information on both concentration, ice stage of development (ice type and general thickness) reported as partial concentrations, and identifying areas of land-fastened sea ice.
These analyses are performed using Geographic Information System (GIS) ESRI ArcMap software and a small selection of internal tools and scripts. For the USNIC daily analysis, the Arctic is broken into 3 regions while the Antarctic is done in 1. There are 40 individual Arctic regions and 13 individual Antarctic regions in our spatial database where ice occurs. These regions are divided up among a team of roughly a dozen trained and qualified sea ice analysts from a variety of scientific and military backgrounds each week. Some effort is made to keep analysts in consistent areas so that regional expertise may be developed.
To start an ice analysis, analysts begin by bringing in all the voluminous and varied data available to characterize sea ice over their regions. This data takes the form of imagery and ancillary data that is collected and cataloged by the USNIC IT department. The core imagery preferred by USNIC analysts is Synthetic Aperture Radar (SAR) due to its balance of resolution and swath width as well as the ability to penetrate clouds and display ice as a collection of floes, leads, and ridges rather than an ‘amorphous white mass’. Sentinel-1 satellites and Radarsat are typically the SAR platforms utilized. Visible imagery from VIIRS and MODIS plays an important role as well. Other visible imagery from GOES geostationary satellites is also available. The aforementioned image types are often grouped by analyst by date/time to ensure the most recent data is the primary imagery displayed. Other imagery comes into play in certain regions and times of year: Infrared imagery is available from various polar orbiters and is important when daylight is lacking. Passive microwave is used to infer motion of the ice pack but is not useful in characterizing the ice in detail. Ancillary data sources include winds, sea and air temperatures, surface pressure, and sea ice model output, though model output is only used as a last-resort basis for any analysis.
For the weekly ice analysis, it typically occurs Tuesday through Thursday. On Thursday, a quality control (QC) process occurs. An analyst not associated with the region uses the same ArcMap document and information to confirm the original analyst’s intentions. For example, someone completing the Bering region may be responsible for QCing the coast of Greenland. For daily ice analysis, it is completed everyday (even holidays) and is produced by a designated duty section for that week or weekend. Analysis is completed during morning hours, QC process is done by analysts within the duty section, and the goal is to wrap up before the afternoon in order to get all products derived from the analysis disseminated.
It is important to note the close relationship between the Canadian Ice Service (CIS) and the USNIC, that forms the North American Ice Service (NAIS). The two agencies coordinate and collaborate in many different ways. One of these ways is through the inclusion of CIS analysis information in USNIC weekly analyses. Over territorial Canadian waters as well as a portion of the American side of the Beaufort Sea, a USNIC analyst will import the Canadian analysis, which is created in a similar fashion to the USNIC analysis, into the USNIC database. This analyst will then check for the usually slight discrepancies between the two centers and massage these to create a unified hemispheric sea ice analysis.
Once an ice analysis is complete, there are numerous products that can be created, like: ice charts, GIS files, text support files, input into tailored support, and so on. Most products are hosted on our website and a more detailed description can be found in our Product Catalog.