Comparison of Ray Tracing through Ionospheric Models

A comparison of ray tracing predictions for transionospheric electromagnetic wave refraction and group delays through ionospheric models is presented. Impacted applications include over-the-horizon RADAR, high frequency communications, direction finding, and satellite communications. The ionospheric models used are version 2.1 of Utah State University's Global Assimilation of Ionospheric Measurements (USU GAIM) model and the 2001 version of the International Reference Ionosphere (IRI) model. In order to provide ray tracing results applicable to satellite communications for satellites at geosynchronous orbit (GEO), a third ionospheric model is used to extend the sub-2000-km USU GAIM and IRI ionospheric specifications to 36540 km in altitude. The third model is based on an assumption of diffusive equilibrium for ion species above 2000 km. The ray-tracing code used is an updated implementation of the Jones-Stephenson ray-tracing algorithm provided by L. J. Nickisch and Mark A. Hausman. Ray-tracing predictions of signal refraction and group delay are given for paths between Goldstone Deep Space Observatory near Barstow, California, and the PanAmSat Galaxy 1R satellite. Results are given for varying frequency between 11MHz to 1GHz, varying time of day between 0600 and 1700 Pacific Standard Time on 1 November 2004, and varying signal transmission elevation angle.