Service Interruption

The NSIDC Web site and data services are currently having intermittent problems and may be unavailable. We are working to restore these services as soon as possible and apologize for any inconvenience this may cause. Please contact NSIDC User Services for assistance.

Tetherless World Constellation SSIII is supported by NSF


Semantic Sea Ice Interoperability Initiative

SSIII Ontologies


The SSIII is developing a detailed, yet broad, sea ice ontology linked to relevant marine, polar, atmospheric, and global ontologies and semantic services. Our overall goal is to improve the interoperability, usefulness, and understanding of Arctic sea ice data using Semantic Web approaches and technologies. The Semantic Web approach exposes, shares, and connects pieces of data through the use of unique identifiers and standardized protocols for describing data. This linked data approach is combined with knowledge models formalized in ontologies to develop sophisticated applications that can help you find, process, integrate, and analyze information. An ontology can be described as "a formal, explicit [machine-readable] description of concepts in a domain of discourse." In this case, our domain is sea ice and its relations to the Arctic system.

SSIII Ontology Browser

The SSIII Ontology Browser is an easy way to explore our ontologies. The ontologies are listed in a main horizontal navigation bar across the top of the Web page. A pull-down menu on the left-hand side of the Web page populates after you have chosen an ontology from the main horizontal nav bar. A Find Tool on the right-hand side of the Web page helps you explore the ontology browser.

Ontology Types

Currently, SSIII has seven Ontology types: sea ice, seaice concentration, seaice development, seaice form, ice of land origin, egg code, and Sea Ice Grid (SIGRID), also called SIGRID-3, since this ontology describes a data format that has been through three updates. SSIII recognizes the existing operational use of the egg code and SIGRID-3 at National Ice Centers around the world. We hope that eventually these ontologies can aid the creation and reuse of operational sea ice charts. We have also worked to ensure our ontologies use terminology from the World Meteorological Organization (WMO) Sea Ice Nomenclature.

Egg Code

On sea ice charts, refer to Figure 2, sea ice parameters are represented by symbols with accompanying numbers giving the values of the sea ice parameters. The symbols varied depending on what nation was compiling the sea ice chart until the 1980s, when an international standard called the egg code was developed by the WMO. The egg code, which gets its name from the shape of the symbol used to embody the WMO standard sea ice information, is now used for most sea ice charts. Refer to Figure 1. Scientists and sea travelers use the egg code to describe ice conditions around the world. The egg code describes sea ice concentration (amount of the sea surface that is covered in ice), stage of development (thickness), and form of ice (floe size) for a given area.

The letters in the egg code describe the parameters such as sea ice concentration, thickness, and size. The numbers in the egg code, inserted by people who observe the sea ice directly from ships or aircraft, or indirectly through remote sensing images, represent the stages of the sea ice development such as thickness, type, size, and concentration. Technicians print ice-code ovals on top of ice maps, and captains use the egg code to avoid thick ice and find the best way to get where they're going. Egg codes are also used for lake ice in large bodies of fresh water. The U.S. National Ice Center Web site has a more detailed explanation of the egg code.

egg code

Figure 1. The WMO System for Sea Ice Symbology, a.k.a. the Egg Code


SIGRID is an alphanumeric coding of ice chart information originally obtained by overlaying a grid on the original paper chart and encoding the ice information in each grid cell. SIGRID-3 evolved from earlier SIGRID formats and incorporates much of their content. The SIGRID-3 format is a WMO standard shape file format for sharing and archiving ice chart information. A chart encoded in SIGRID-3 has two main components: the chart information itself in shape file format, and metadata describing the chart.

SIGRID encodes the information in each egg as illustrated by the following example:

WMO egg code chart

Figure 2. NIC sea ice chart showing the egg code. The numbers in the egg give total concentration, usually as a range; partial concentration of the first, second, and third thickest ice; stage of development of the first, second, and third thickest ice; and other information such as form, if available.

Web Ontology Language

The Web Ontology Language (OWL) is one of a family of knowledge representation languages for authoring ontologies. The languages are characterized by formal semantics and a variety of serializations for the Semantic Web. OWL is endorsed by the World Wide Web Consortium (W3C) and has attracted academic, medical, and commercial interest.

Our sea ice ontologies use OWL, and they are available in two formats: OWL/XML files and OWL Manchester Syntax files. Refer to Table 1. The OWL files can be encoded in Resource Description Framework (RDF). RDF is a standard model for data interchange on the Web. RDF has features that facilitate data merging even if the underlying schemas differ, and it specifically supports the evolution of schemas over time without requiring all the data consumers to be changed (W3C Semantic Web,, accessed 1/2012). The RDF is a family of W3C specifications originally designed as a metadata data model. It has come to be used as a general method for conceptual description or modeling of information that is implemented in Web resources, using a variety of syntax formats (Wikipedia, _Framework, accessed 1/2012).

Version Information

Our sea ice ontologies were updated to Version 2 in 2013 to incorporate user comments from the WMO. This upgrade also makes it possible for NSIDC to create open linked data for Sigrid-3 formatted data sets. NSIDC will be using the data set Canadian Ice Service Arctic Regional Sea Ice Charts in SIGRID-3 Format as our test case. We will use the Virtuoso Triplestore to store the data and develop a simple user query and access interface as a first experiment with open linked data. We hope to have this service available sometime within the next year.

Table 1. SSIII Ontologies
Ontology Type Ontology PURL Link Manchester Ontology Syntax File Link
Seaice trunk/ontology/seaice.omn
Seaice Concentration trunk/ontology/seaice-concentration.omn
Seaice Development trunk/ontology/seaice-development.omn
Seaice Form trunk/ontology/seaice-form.omn
Ice of Land Origin
Sigrid-3 trunk/ontology/sigrid3.omn
Egg Code trunk/ontology/egg.omn