Refractivity Retrievals Using Interferometry of Aircraft Radio Transmissions: First Results and Potential for Future Experiments

The first results from a prototype Automatic Dependent Surveillance-Broadcast (ADS-B) interferometer are presented. The novel method aims to provide high-volume, low-cost refractivity information through the use of interferometry to measure the incident angle of arrival (AoA) of ADS-B radio transmissions routinely broadcast by commercial aircraft. The AoA is combined with the reported aircraft position (encoded inside the ADS-B) to compute the total bending of radio signals due to atmospheric refraction. The bending is highly sensitive to changes in the refractivity structure, which provides important information concerning the spatial and temporal variability of water vapour in the lower atmosphere. The method addresses a gap in high-density observations of refractivity in the lower atmosphere. The sensitivity of observations to spatial and temporal variations in refractivity are demonstrated and the opportunities for future observation campaigns are suggested.