Ionospheric Threat Parameterization for Local Area Global-Positioning-System-Based Aircraft Landing Systems

Abstract

Observations of extreme spatial rates of change of ionospheric electron content and the characterization strategy for mitigation applied by the U.S. local area augmentation system are shown. During extreme ionospheric activity, the gradient suffered by a global navigation satellite system user a few kilometers away from a ground reference station may reach as high as 425 mm of delay (at the GPS L1 frequency) per km of user separation. The method of data analysis that produced these results is described, and a threat space that parameterizes these possible threats to user integrity is defined. Certain configurations of user, reference station, global navigation satellite system satellite, and ionospheric storm-enhanced density may inhibit detection of the anomalous ionosphere by the reference station. Nomenclature B = satellite clock bias, m b = receiver clock bias, m D = ionospheric threat model maximum ionospheric delay, m f1 = 1575.42 MHz, GPS L1 frequency f2 = 1227.60 MHz, GPS L2 frequency g = spatial rate of change of ionospheric delay, also known as slope or gradient, mm=km