Variation of radio refraction in the lower atmosphere

Measurements of the variation of the incident angle were made on several line-of-sight paths, together with the simultaneous observation of the refractive index gradient of the atmosphere. Statistics of incident angle variation and
M
-gradient and their relations were analyzed. Radio refraction is dependent on the atmospheric layer thickness in which radio waves are propagated. Considering the controlling layer thickness, a method of predicting refraction variation is presented for arbitrary radio paths and meteorological conditions. The measurements of the incident angle were found to agree well with the estimated refraction.