Performance Evaluation of the Wide Area Augmentation System for Ionospheric Storm Events

Abstract

Abstract.One of the greatest challenges in developing accurate and reliable satellite-based augmentation systems (SBAS) is modeling of ionospheric effects. Wide area GPS networks are generally sparse (station spacings of 500-1000 km), and ionosphere models can suffer degraded performance in regions where large spatial gradients in total electron content (TEC) exist. Of particular concern for Wide Area Augmentation System (WAAS) users is the feature called storm enhanced density, which is associated with large TEC gradients at mid-latitudes. This effect is a significant source of error in the WAAS correction models. The Canadian GPS Network for Ionosphere Monitoring (CANGIM) consists of three GPS reference stations in western Canada, augmented by two additional sites in the northern United States. In addition to measures of ionospheric activity, WAAS messages are collected continuously at these sites and decoded (post-mission) at University of Calgary. Localization schemes have been developed to compute WAAS ionosphere corrections for any location in North America. In this paper, performance of the broadcast WAAS ionosphere model is quantified through comparison with truth data from over 400 GPS reference stations in North America. WAAS ionosphere model accuracies throughout North America are evaluated for intense storm events, and compared with WAAS Grid Ionosphere Vertical Error (GIVE) bounds. Limitations in the WAAS ionosphere model are identified for enhanced ionospheric activity and, in particular, the storm enhanced density phenomenon.

On the generation/decay of the storm‐enhanced density plumes: Role of the convection flow and field‐aligned ion flow

“…Such large TEC gradients may have a profound impact on radio communication and navigation systems [Ledvina et al, 2002;Doherty et al, 2004;Skone et al, 2004;Coster and Skone, 2009;Sun et al, 2013] and therefore motivate continued study of the SED/trough evolution and generation mechanisms.…”

Ionospheric research and space weather services

“…Firstly, because ionosphere models can suffer degraded performance in regions where large spatial gradients in TEC exist. Secondly, because the observed feature of storm-enhanced density, associated with large TEC gradients at mid-latitudes, is a significant source of error in the SBAS correction models (Skone et al, 2004). It is therefore reasonable to conclude that such conditions can be specified successfully by space weather forecasting techniques based on real-time data availability in conjunction with mathematical algorithms to extrapolate to near-future conditions (Wilkinson, 2006).…”

TEC response at two equatorial stations in the African sector to geomagnetic storms

“…Large magnetic storms with Dst < À100 nT have been found to cause intense ultra-high frequency (UHF) scintillation in the Wide Area Augmentation System (WAAS) which is to provide GPS based navigation to aircraft. For instance, Skone et al (2004) observed large WAAS errors in the region of strong electron density enhancement during the October and November, 2003 geomagnetic storms. Geomagnetic storms of different magnitudes (based on magnetic indices such Kp and Dst) have been observed to produce different effects on TEC at different latitudes.…”