Second-order ionospheric effects on satellite radio occultation observations and their impact on atmospheric studies

This dissertation describes the development of first-of-a-kind mathematical models that both quantify higher-order ionospheric effects and their impact on Global Positioning System radio occultation (GPS/RO) data products. We develop new and innovative models to: a) remove the second-order ionospheric effect from Total Electron Content (TEC) estimations; b) quantify the second-order ionospheric delay in GPS/RO signal propagation using the Faraday phenomenon; c) quantify the vertical distribution of the first- and second-order ionospheric residual effects on GPS/RO data products; and d) retrieve improved atmospheric water vapour profiles. For the first time we combine GPS/RO measurements with space-based gravity missions to characterize the response of the GPS/RO-derived atmospheric parameters to the Earth's gravity anomalies.;the water vapour pressure. Further studies reveal that the second-order ionospheric residual effect increases non-linearly with solar variability, oscillating between +/-3 mm (at Rz12=2) and +/-15 mm (at Rz12=114), whereas its value increases with increasing latitude. The first-order ionospheric residual effect arising from the geometrical splitting of the dual-frequency GPS radiowave signals is ∼2-3 orders of magnitude smaller than the second-order ionospheric residual effect, with the potential of increasing in magnitude at high solar activity. A series of sensitivity studies show that the LEO velocity uncertainties affect the GPS/RO bending angle accuracy more than the Doppler shift uncertainties. Finally, we find that the Earth's gravity anomalies can introduce negative systematic biases on the atmospheric temperature profiles of up to ∼0.5 K close to the Earth's surface. This dissertation demonstrates the simplicity, innovation, effectiveness and importance of our proposed mathematical models on the future of GPS/RO atmospheric remote sensing.;Independently, we implement these mathematical models in a new GPS/RO processing software package to investigate, for the first time, the impact of higher-order ionospheric residual effects on ionospheric and atmospheric products. We observe that under low solar activity, the second-order ionospheric residual effect introduces: a) slowly varying positive systematic biases of ∼1-3 TECU on TEC estimations as function of occultation time; b) maximum negative systematic biases of ∼0.35 N-units on atmospheric refractivity close to the Earth's surface; c) negative systematic biases of ∼0.5 K close to the Earth's surface, which decrease with altitude and above 26 km become positive, peaking at ∼2.0 K at 50 km and d) negative systematic biases of ∼0.08 mbar on...