RECOMMENDATION ITU-R P.834-3 - Effects of tropospheric refraction on radiowave propagation 1 Ray bending 2 Effective Earth radius 3 Modified refractive index 4 Apparent boresight angle on slant paths 4.1 Introduction 4.2 Visibility of space station 4.3 Estimation of the apparent elevation angle 4.4 Summary of calculations 4.5 Measured results of apparent boresight angle 5 Beam spreading on slant paths 6 Effective radio path length and its variations 7 Propagation in ducting layers 7.1 Influence of elevation angle 7.2 Minimum trapping frequency