An Evaluation of WAAS to Meet Maritime Navigation Requirements in Canadian Waters

Abstract

Currently, mariners navigating in Canadian waters use a Ground-Based Augmentation System (GBAS) which provides differential corrections and integrity monitoring of the Global Positioning System (GPS) in order to improve their position accuracy and their trust in GPS. Since 1994, the Canadian Coast Guard (CCG) has been providing a GBAS in the form of a Differential GPS broadcast service. This service, called DGPS, consists of 19 land-based DGPS sites installed across Canada. The service is currently only provided south of latitude 60°N in collaboration with the United States Coast Guard (USCG). Before embarking on a recapitalization program of its 24-year old DGPS and given that the USCG is progressively shutting down its National Differential GPS (NDGPS) sites, the CCG is evaluating various options for the future of its own aged DGPS network. One of these options is to propose a space-based augmentation system (SBAS) called the Wide Area Augmentation System (WAAS) as an alternative to DGPS. It has emerged as a reliable and precise source of GNSS corrections. Although originally developed by the US Federal Aviation Administration (FAA) for civil aviation, WAAS has proven to be a reliable option for marine navigation as well. At first glance, with an equivalent performance, this option seems to be a workable solution. Before going further, a confirmation is needed to ensure that navigation using WAAS is safe in Canadian waters, including in the Arctic. With the continued expansion and improvement of WAAS (i.e. additional satellites, additional frequencies), the CCG is evaluating if either the current or the next generation of WAAS could be an acceptable alternative to DGPS performance in Canadian waters including in the Arctic. This paper describes the evaluation undertaken by the authors for the CCG to determine the expected accuracy, integrity, and availability of WAAS throughout Canadian waters, both north and south of 60°N. Models for both current and future WAAS systems have been created in STKO and simulations run to develop coverage and accuracy plots for all of Canada. The paper describes the various constellations and settings used to set up the models. These simulations show that the current WAAS provides acceptable accuracy and integrity throughout most of Canada, but not the higher latitudes. Improvements and additions to WAAS in the future will enable maritime navigation requirements to be met in all areas, even the higher latitudes. In either case, the WAAS aviation integrity model could be extended to maritime usage to provide a better indication of system performance to the mariner.