Generalized force method for point-to-point ray tracing in anisotropic ionosphere: Implementation and applications to NeQuick2 and IGRF13 models

The generalized force method, previously developed for an isotropic inhomogeneous ionosphere, exploits the knowledge about the character of the extrema of the phase distance—where high ionospheric rays correspond to minima and low rays to saddle points—to systematically find all relevant rays between fixed points, thereby enabling efficient global point-to-point ray tracing. In this article, the generalized force approach is extended to magneto-active, anisotropic ionosphere by locating minima and saddle points of a more general phase distance functional where trial functions include both the candidate ray path geometry and the orientation of the wavefront. For both O and X modes, the rays are found using an optimization algorithm guided by the generalized force whose definition depends on the ray type. The generalized force method, implemented in the form of computer software, is applied to problems of oblique sounding in realistic ionosphere described by NeQuick2 and IGRF13 models. The results of the ionogram simulations demonstrate the method's ability to solve routine problems of ionospheric ray tracing and show its potential in solving various inverse problems, as well as in verifying and correcting models of the ionosphere.