A numerical study of tropospheric ducting at HF

In this paper, path loss calculations for frequencies between 4 and 32 MHz are compared with Hansen's recent measurements on a 235-km over-ocean southern California path. The calculations involve standard waveguide theory along with available radiosonde data and show convincingly that signal enhancement, relative to that expected on the basis of ground wave theory, observed on frequencies greater than 20 MHz was due to superrefractive environments.