Simulating GPS radio occultation using 3-D ray tracing

Numerical 3-D ray tracing techniques are commonly used for calculating the path of an electromagnetic signal in a medium specified by a refractive index that depends upon position. Numerical ray tracing is an important tool for applications of L-band frequency propagation such as GPS Radio Occultation (RO), where accurate and near real-time results are required. In this study, 3-D numerical ray tracing techniques are used to simulate GPS signals received by the Low Earth Orbit (LEO) satellites and to investigate their variability as a function of time and position due to the refractivity gradients in the ionosphere and the lower atmosphere. The GPS signal paths from the GPS to LEO satellites are simulated with an emphasis on the signal paths propagating through regions of the ionosphere where the refractive gradients are greatest. The effects of the Earth's magnetic field on the L-band RO propagation paths are also investigated.