Dissertation

A New Method of Measuring Atmospheric Refractivity

Lewis, Oliver Scott

2025

Overview

This thesis explores a new source of atmospheric refractivity information by measuring the refraction of radio transmissions broadcast by commercial aircraft. Detailed measurements of atmospheric humidity in the lower atmosphere are currently difficult and expensive to obtain. For this reason, there is interest in the development of low-cost, high-volume opportunistic technologies to acquire measurements of tropospheric humidity. The angle-of-arrival (AoA) of the 1090 MHz Automatic Dependent Surveillance-Broadcast (ADS-B) radio transmission can be measured using vertically-orientated, two-element interferometers. Atmospheric refraction is strongly influenced by changes in humidity, and refractivity observations have proved to be an effective source of humidity information for numerical weather prediction models. This thesis shows the derivation of novel inversion algorithms to retrieve refractivity structure from AoA measurements using gradient-free and adjoint-based techniques. The initial experimental results from a prototype interferometer installed on the Clee Hill weather radar tower in Shropshire, United Kingdom are shown. The inversion algorithms are applied to observational data and vertical profiles of refractivity were retrieved. The principal sources of observational uncertainties and methods to mitigate their impacts were explored through simulations and experiments. The observations obtained were significantly impacted by multipath contamination, where multiple signals from the same source mutually interfere at the receiver. Variations in atmospheric refractivity structure on mesoscale (∼10-100 km) and ∼15-minute spatial and temporal scales respectively were detected with the prototype ADS-B interferometer. The proposed technique is relatively low cost (∼€10k), requiring off the shelf equipment and making use of freely available software. The results from this thesis encourage further exploration and research into this new remote sensing technique. Future work would benefit from simulated and real assimilation experiments using observational data.

• Publisher: ProQuest Dissertations & Theses
• Subject: Aircraft / Altitude / Astronomy / Astrophysics / Atmosphere / Data assimilation / Geometry / Humidity / Interferometry / Physics / Receivers & amplifiers
• ISBN: 9798290629056