The Spatial and Temporal Variations in Ionospheric Range Delay

Patricia H. Doherty and Paul J. Gendron, Robert Loh,David N. Anderson

Abstract:	In this study, we present statistics of the temporal variations in ionospheric range delay recorded at several locations in the continental US, Canada, Alaska and Hawaii. The measurements, recorded in 1993 and 1996, were obtained from the International GPS Geodynamics Service (IGS) network, managed by the Jet Propulsion Laboratory. These statistics are based on the rate of change in range delay for particular times of day at each receiver location. Since these measurements cover only solar moderate to minimum conditions, we augment the statistics on the temporal variations with a historic database of ionospheric measurements of VHF signals from geostationary satellites of opportunity. In addition, we will provide insight to the magnitude and locations of significant spatial gradients in ionospheric range delay. This analysis in intended to provide a characterization of ionospheric variations that will be encountered in the Federal Aviation Administration’s (FAA) operational Wide Area Augmentation System (WAAS). The WAAS system is intended to support en-route and precision approach flight operations. An important factor in the operational system will be the accuracy of the vertical ionospheric delay estimates that will be provided to a user aircraft in a satellite broadcast message. These estimates of vertical ionospheric delay will be based on slant dual-frequency GPS measurements of ionospheric range delay made at 24 reference stations (21 in the continental US, 1 in Hawaii, 1 in Alaska and 1 in Puerto Rico). Historically, the ionosphere has proved to be extremely variable in nature. Its behavior is a function of geographic location, local time, season, geomagnetic activity and solar activity. In the continental US, measurements of ionospheric range delay at midday can range from less than 2 meters at solar minimum to nearly 20 meters at solar maximum. In Hawaii, daytime observances of range delay as high as 30 meters have been recorded during a solar maximum period.
Published in:	Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997) September 16 - 19, 1997 Kansas City, MO
Pages:	231 - 240
Cite this article:	Doherty, Patricia H., Gendron, Paul J., Loh, Robert, Anderson, David N., "The Spatial and Temporal Variations in Ionospheric Range Delay," Proceedings of the 10th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1997), Kansas City, MO, September 1997, pp. 231-240.
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