DGPS and WAAS Maritime Accuracy and Availability Studies

Gregory Johnson, Richard Hartnett and Peter Swaszek

Abstract:	The Coast Guard currently operates a maritime differential GPS service consisting of two control centers and over 85 remote broadcast sites. This service broadcasts GPS correction information on marine radiobeacon frequencies to improve the accuracy and integrity of GPS. The stated accuracy is 10 meters in all coverage areas with typical accuracy much better than this. However, to date there has been no known quantitative analysis of the absolute accuracy possible in a post-SA environment. The Federal Aviation Administration (FAA) has developed an alternative system for augmenting the GPS system called WAAS or Wide Area Augmentation System. This system transmits corrections from one or more geostationary satellites that can also act as additional pseudo-GPS signals to provide an additional pseudorange for position solutions. This system was developed for aeronautical users, but could theoretically be used by maritime users as well; however, to date no definitive study has been done of availability for a maritime user. With sponsorship from the Coast Guard C2CEN, the Coast Guard Academy has undertaken a study of the Accuracy and Availability of DGPS and WAAS in a harbor environment. The goal of this study is to determine DGPS beacon and WAAS coverage (signal strength and availability) and absolute accuracy in certain harbor areas. The testing consists of two segments: static and kinematic. The static testing consists of an equipment suite designed to collect DGPS signals from 4 different beacons, WAAS GPS, and unaugmented GPS at a fixed location. The Continuously Operated Reference Stations (CORS) network is used to post-process the GPS information for each fixed location to provide a highly accurate ground truth position that is used to calculate statistics on the error in the DGPS and WAAS positions. Data is collected at multiple locations to investigate the accuracy as a function of distance from the beacon. The kinematic testing consists of a suite of equipment installed on a vessel to collect DGPS beacon and WAAS signal strengths as the vessel traverses the harbor area. Using post-processing with CORS sites, analysis of the kinematic position accuracy is also conducted. This paper presents data collected in New York, Miami, Houston, and San Francisco harbor areas as well as data collected along the Eastern Seaboard. DGPS and WAAS coverage will be presented within the various harbors. Statistics on the DGPS and WAAS position errors are also presented for each beacon tracked, and at each location around the harbors.
Published in:	Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004) June 7 - 9, 2004 Dayton Marriott Hotel Dayton, OH
Pages:	741 - 753
Cite this article:	Johnson, Gregory, Hartnett, Richard, Swaszek, Peter, "DGPS and WAAS Maritime Accuracy and Availability Studies," Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004), Dayton, OH, June 2004, pp. 741-753.
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