Internal reflection in the troposphere and propagation well beyond the horizon

Abstract

A simple estimate of the feeble internal reflection from the normal troposphere explains remarkably well long puzzling fields well beyond the horizon throughout the VHF and microwave spectrum. Even in the absence of ducts, the continuous decrease with height of the index of refraction under gravitational influence makes the troposphere an inhomogeneous continuously stratified medium. The effective earth's radius notion allows for the refractive effect of this inhomogeneity in calculating the diffracted field beyond the horizon, but not for internal reflections. A bilinear model for the index profile of the normal atmosphere gives modes with db/mi attenuation rates in approximate agreement with the experimental one of roughly 1/7 db/mi at 50,400 and 3000 Mc. To a considerable extent, the internal reflection idea obviates the need for hypothesizing omnipresent atmospheric turbulence up to heights of several miles in the troposphere, a phenomenon once erroneously thought also to cause "angel" echoes on radars.