Ice Charts

The ice charts provide information on sea ice concentration, stage of development, and form. They are provided by the U.S. Ice Center on a weekly basis. The displayed parameters strictly follow the definitions by the World Meteorological Organization (WMO).

Utilizing ice charts offers a significant advantage due to their adherence to the highly standardized WMO and International Maritime Organization (IMO) Polar Code protocols. These standards ensure that the information provided is deemed 'official,' sourced directly from state offices mandated to deliver such data and verified by expert human ice analysts.

With IcySea, leveraging the Egg Code and the POLARIS risk index system becomes remarkably simplified and streamlined. Interpreting ice conditions and assessing risk levels is made intuitive and efficient through user-friendly interfaces. By simply clicking on a polygon within the ice charts, users can access the Egg Code alongside a clear written explanation detailing the specific type of ice represented by each code.

Applying the POLARIS risk index system

You can now customize your version of IcySea and add the ice class of your vessel via the settings menu. Based on the selected ice class of your ship and the specific ice conditions, the ice chart layer provides the option to display your ship's Polar Operational Limit Assessment Risk Indexing System (POLARIS) Risk Index Outcome (RIO) value alongside the other data layers in the IcySea map. These values reflect your ship's operational capabilities when navigating in ice-infested waters and were developed in association with the IMO's Polar Code in 2014. The risk index contains various Risk Index Values that correspond to different stages of sea ice development for each individual ice class.

Data sources and links

We are working towards including official ice charts from all national ice services. The current version of IcySea contains ice charts from the U.S. National Ice Center (USNIC) .

Interpretation guidelines

Sea ice concentration charts

The ice concentration charts provide polygons of uniform sea ice concentration. Sea ice concentration is given in tenths. A polygon showing e.g. 8-10 tenths indicates an area that is 80 to 100% covered by ice. The color coding does not provide information about the types of ice in the polygon area. This additional information is provided by the official Egg Code and more detailed explanations, which can be accessed by a 'Left Click' on the polygon of interest in IcySea (Fig. 1).

Sea ice concentration ice chart in IcySea — Figure 1: Screenshot of a sea ice concentration ice chart in IcySea (ice chart source: U.S. National Ice Center). 'Left Click' on a polygon opens the Egg Code and explanation window.

Stage of Development

The ice charts in IcySea also provide the option to switch from the Sea Ice Concentration to the Stage of Development (age) layer (Fig. 2). The Stage of Development charts are designed to indicate the age of the observed ice within the various polygons. The same polygons are used but with the color coding of the Stage of Development (age). Based on the partial concentrations of the observed ice, the Stage of Development layer shows the color code of the most extensive (highest concentration) partial ice type within the respective polygon. The 'Left Click' on the polygons accesses the Egg Code.

POLARIS Risk Index

The IMO Polar Operational Limit Assessment Risk Indexing System (POLARIS) Risk Index Outcome (RIO) is a value for the evaluation of risk of a ship operating in or planning to operate in ice-infested waters. The RIO evaluation is based on the prevailing ice conditions in the area of operation and the ice class of the ship operating in this area. POLARIS RIO values can fall into three categories, where ship characteristics and ice conditions determine the ship-specific range of these categories: 1) Normal operation, 2) Elevated risk and 3) Operation subject to special consideration (Fig. 3). Especially during the melt season ice can decay rapidly, which affects the RIO value for the individual ship in a melting and degraded ice environment. If navigators detect decaying sea ice they can select the 'Decayed ice conditions' feature within the POLARIS ice chart menu in IcySea. It is imperative to put great consideration into this assessment because selecting this option will recalculate the RIO for the new conditions and the ship's ice class. Regions that might have been indicated to be 'elevated risk' regions for your ship could be considered regions of 'normal operation' for your ship, so navigators need to be sure about the state of the ice in order to avoid navigating through risky areas.

Figure 3: Screenshot of a POLARIS RIO ice chart in IcySea (ice chart source: U.S. National Ice Center). The POLARIS ice chart in this example is customized for a vessel with ice class PC6, which is built for 'summer/autumn operation in medium first-year ice, which may include old ice inclusions'. 'Left Click' on a polygon opens the Egg Code and explanation window.

Egg Code

The Egg Code provides basic data concerning concentration, stage of development (age) and the form of the observed sea ice (floe size). With its oval form the Egg Code is able to indicate up to three ice types showing the partial concentration, stage of development and form of the thickest, second thickest and third thickest ice from left to right in three vertical levels (Fig. 4).

While the top value of the Egg Code describes the total concentration of all the ice in the respective polygon, the second level (C) provides partial concentrations of the thickest, second, and third thickest ice in tenths (from left to right). The third level (S) quantifies the stage of development of the thickest, second thickest, ... ice using a designated code (see Table 1).

Egg Code Table 1 — Table 1: Coding for the sea ice stage of development values shown in the official Egg Codes (taken from Environment and Climate Change Canada)

Lastly, the fourth level (F) provides information on the floe size (form) of the observed ice. F is given as a code as well with the respective floe sizes for each code given in Table 2.