Integrating Regional Ice Charts and Copernicus Sea Ice Products for Navigation Risk in Alaskan Waters

TL;DR

This study addresses the challenge of accurately representing Arctic sea ice for safe navigation by comparing Copernicus satellite ice concentration data with high-resolution ASIP ice charts around Alaska from 2010–2025. It introduces a spatial alignment on a UTM tiling grid, harmonizes disparate data formats, and uses a discrepancy metric and residuals to quantify differences, followed by a EOF analysis to identify shared physical variability modes. The operational relevance is demonstrated by applying AIS-based POLARIS risk assessments, showing that about 36% of ice-affected AIS observations fall into elevated-risk categories, underscoring the importance of regional charts for risk-informed decision making. The results show that while Copernicus captures large-scale ice patterns, it underestimates nearshore and marginal ice-zone concentrations, especially during melt seasons, whereas ASIP provides finer-scale detail that enhances navigational risk modeling when integrated with satellite data.

Abstract

As climate change continues to reshape marginal ice zones in the Arctic, accurate and reliable sea ice data are critical for ensuring maritime safety. This study compares regional ice charts from the Alaska Sea Ice Program with satellite derived Copernicus sea ice concentration data to evaluate spatial and temporal discrepancies in ice representation across Alaskan waters from January 2010 to March 2025. Daily Arctic Sea Ice Program polygons were aligned with Copernicus grid points in a common UTM framework, and residuals were computed to quantify systematic differences. Results show that Copernicus consistently underestimates ice concentration relative to Arctic Sea Ice Program, particularly in nearshore and marginal ice zones affected by land-spillover and mixed-pixel effects such as those observed in Cook Inlet. Empirical Orthogonal Function analysis shows that both datasets capture the same dominant physical modes of sea ice variability, with the first mode representing the annual freeze thaw cycle and the second reflecting marginal ice-zone dynamics. To assess operational implications, vessel Automatic Identification System data were combined with Alaska Sea Ice Program ice charts using the IACS POLARIS Risk Index Outcome framework. Approximately 36 percent of AIS observations within ice affected waters corresponded to negative Risk Index Outcome values, indicating that vessels frequently operated under elevated-risk conditions. These findings demonstrate that regional charts and Copernicus provide complementary capabilities that together enable more accurate and operationally meaningful Arctic navigation and risk assessments.

Figures (15)

• Figure 1: Temporal and spatial coverage of the two main data sources. The top bar shows Copernicus sea‐ice products (Arctic‐wide) from January 2010 through March 2025, with a dashed line at 2017 marking the transition from AMSR‐E/AMSR2 to SSMIS sensors. The bottom bar shows ASIP regional ice charts around Alaska (SIGRID‐3/WMO formats), daily from June 2014 through March 2025.
• Figure 2: Flowchart of the methodology illustrating major steps. A large arrow indicates the iterative or cyclic nature of the process.
• Figure 3: ASIP ice chart with UTM zones and AIS data overlaid for August 18th, 2018. Vessel types (filled circles) include Cargo (yellow), Fishing (brown), Not Available (gray), Other (white), Passenger (purple), Pleasure Craft/Sailing (green), Tanker (red), Tug Tow (orange), and Unknown (black). In terms of ice concentration, red indicates 7--10 tenths (70%--100%), orange indicates 5--7 tenths (50%--70%), yellow indicates 3--5 tenths (30%--50%), green indicates 1--3 tenths (10%--30%), blue indicates 0--1 tenths (<10%), gray indicates landfast ice (100%), and black indicates no ice (0%).
• Figure 4: A visual representation of the Alaskan seas and oceans and how they are defined relative to the Copernicus grid. The colors presented for the seas in this figure are the same used in subsequent figures
• Figure 5: Aggregate Monthly Average errors between the ASIP Ice Charts and Copernicus Sea Ice Concentration for the months of December (top left), January (top right), February (bottom left), and March (bottom right). The warmer colors are points when the ice charts show a higher average ice concentration than Copernicus, and the cooler colors indicate the inverse. The Black indicates points that are undefined in the ice charts, and the grey dots represent where the 2 sources agree.