GNSS Augmentation using the VHF Data Exchange System (VDES)

There is an observed trend for the extent of sea ice in the Arctic to recede over recent years. Research by the Arctic Council and the Arctic Monitoring and Assessment Programme suggests that the Arctic Ocean could be largely free of sea ice in summer by earlier than mid-century, possibly as early as the late 2030s. Given these predictions, GNSS could be increasingly required to support maritime navigation for a growing number of ships over diverse Arctic regions. The safety of maritime navigation relies on the accuracy, integrity, availability and continuity of the navigation solution. At present, ground-based navigation augmentation systems are used to provide integrity and enhance the accuracy of GNSS-based positioning in major coastal and port areas of shipping around the world. Additionally, the provision of wide area maritime navigation augmentation services via Satellite-Based Augmentation Systems (SBAS) is gradually being developed. However, the geosynchronous satellites deployed by most existing SBAS are not visible at the high latitudes of the Arctic. The satellite component of the VHF Data Exchange System (VDES), currently being defined by the International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) and endorsed by the International Telecommunication Union (ITU) offers the potential to provide a data link capability for an Arctic GNSS augmentation system based on a number of possible satellite configuration options. This paper provides an overview of current and future GNSS and their augmentation systems and discusses their applicability to Arctic maritime navigation. Key technical characteristics of VDES are then described and two alternative navigation augmentation system architectures using VDES are proposed, each optimised for a different type of service: (i) an SBAS-type service providing near real-time integrity and correction data to maritime users in the Arctic; (ii) a store-and-forward type of service to deliver Integrity Support Messages (ISM) to users equipped with ARAIM (Advanced Receiver Autonomous Integrity Monitoring) enabled GNSS receivers. The system could also allow other data or messages to be conveyed, such as Maritime Safety Information, Virtual Aids to Navigation or ice charts. The availability of navigation augmentation services for Arctic waters could have significant economic impact for shipping and global trade, especially as the North Eastern Passage (including the Northern Sea Route over Russia) may become navigable all year round within a few decades. The proposed ARAIM ISM service also has the potential to benefit users in other parts of the world as the ISM data has global applicability.