HR: 08:30h
AN: G51D-03 INVITED    [Abstracts]
TI: Mitigation of Ionospheric Effects on DGPS and WADGPS Operations
AU: * Skone, S
EM: sskone@geomatics.ucalgary.ca
AF: University of Calgary, Department of Geomatics Engineering 2500 University Dr. N.W., Calgary, AB T2N 1N4, Canada
AB: Under high levels of ionospheric activity, significant degradations in differential GPS (DGPS) and wide area DGPS (WADGPS) positioning accuracies can occur. DGPS and WADGPS methods are employed for many applications and millions of users. Examples include marine DGPS services, land applications (such as transportation monitoring, fleet management and emergency response) and commercial aviation. In previous studies for the North American sector, DGPS and WADGPS positioning errors were observed to increase by factors of 10-30 under increased ionospheric activity. In particular, gradients of up to 50 ppm are associated with a feature known as storm enhanced density (SED). This feature is a localized enhancement of total electron content (TEC) extending northwest through the mid-latitudes. Positioning errors of 20 m or more have persisted for hours during such events. Specific WADGPS services include the Satellite-Based Augmentation Systems (SBAS) WAAS and EGNOS. The WAAS has been designed for commercial aviation in the United States; EGNOS operates in a similar manner for the European sector. In this presentation, DGPS, WAAS and EGNOS capabilities are assessed under severe ionosphere events. The horizontal and vertical positioning accuracies are determined throughout North America and Europe during such events using available data from existing GPS networks (IGS and CORS). All DGPS baselines of length 100-200 km are processed; one station of the baseline is designated as reference and the other as remote user. Differential corrections are computed for the reference and applied at the remote user location. DGPS positioning solutions are generated for hundreds of baselines simultaneously in this manner to derive full spatial statistics of positioning accuracies. WADGPS positioning solutions are also generated for the same set of remote user stations using archived WAAS and EGNOS messages, and computing and applying localized corrections. An extensive study is conducted using data representative of a range of ionospheric conditions, including three major geomagnetic storm events. Under enhanced ionospheric activity, the WADGPS positioning errors can be as large as 25-30 m, and typically exceed those for single baseline DGPS. Methods of mitigating the larger positioning errors are proposed, with specifications for reference network densities and update intervals required. Space weather warning products designed for navigation applications are also introduced for the GNSS user community.
DE: 1200 GEODESY AND GRAVITY
SC: Geodesy [G]
MN: 2007 Fall Meeting