Modelling tropospheric ducting effects on VHF/UHF propagation

The application of the parabolic equation method to range-independent and range-dependent tropospheric propagation modelling problems is demonstrated. The parabolic equation is an approximation to the Helmholtz wave equation which allows progressive calculation of the propagated electromagnetic field as solution is stepped out in range. The solution method described is derived from a technique developed by R.H. Hardin and F.D. Tappert (1973) for application to underwater acoustics problems. This split step Fourier solution involves the discretization of the field with respect to height and the use of the fast Fourier transform at successive range points. The solution is stable, with errors being dependent on wavenumber, range step size, and the gradients of refractive index with respect to height and range. Advantages of this method over other methods used to evaluate the effects of ducting layers on tropospheric propagation are discussed