A HF ionospheric propagation model using analytic ray tracing

A method to approximate horizontal gradients when using analytic ray tracing is presented. This method involves automatically tilting the modelled ionospheric profile by displacing the Earth´s centre. This method is applied to a grid point ionospheric model which consists of a known ionospheric model coupled with real-time ionospheric measurements at a number of locations. Thus, the grid point ionospheric model is a real-time ionospheric model and together with the tilting method, is useful in a number of applications. Analytic ray tracing results incorporating the tilting method and the grid point ionospheric model are presented. In order to demonstrate the effectiveness of this analytic approach the results are compared with those obtained using the numerical ray tracing package HIRT (homing-in ray tracing) Norman et al., [1994] over the same region