Effect of an elevated M-inversion on radio wave propagation in a tropospheric waveguide

An attempt is made to develop a method for the analysis of transhorizon fields over the spherical earth in the case of a complex height dependence of the refractive index. The M-profile (where M is the refractive modulus) is assumed to have two inverted-gradient sections at essentially different heights. The field at the observation point can therefore be represented as a sum of normal modes peculiar to the surface ducting layer only and a set of rays reflected from the elevated M-inversion.