Aspects of earth-space propagation impairments on low-angle paths

The prediction of propagation impairments for Earth-space paths at low angles is investigated. Estimates are required for many applications. The environments are complex, however, and reliable impairment estimation is difficult for such paths. Requirements to combine statistics of multiple effects into reliable overall representations of net impairment level introduce additional complications. Earth-space predictions are sometimes presumed to merge with terrestrial predictions as the path angle approaches zero, at least for physically well-founded models. Potential equivalence of low-angle Earth-space and terrestrial-path propagation models is explored here. The expectation of convergence for these link geometries appears to be unfounded in general.