Ground-to-Air Tropospheric Mapping Function for Elevation Angles Below Three Degrees

We propose a new mapping function for ground-to-air radio links. We validated the mapping function using the data from numerical weather model over an entire year, by comparing it with the mapping function estimated with ray-tracing the refractivity profile of the troposphere (i.e. the space traversed by the ground-to-air radio link). Two asymptotic expansions are derived, that model the tropospheric delay for the entire range of elevation angles from zenith down to 0.5?.