A review of tropospheric refraction effects on Earth-to-satellite systems

Abnormal refractivity gradients may cause radio waves to be trapped within tropospheric layers, thus producing regions through which the waves do not pass called radio holes. For some locations and for many applications, refractive corrections based on the surface refractivity are adequate for elevation angles above a few degrees. However, new systems which operate at elevation angles near the horizon often require improved accuracies. Techniques for obtaining these improved corrections are reviewed.