Modeling signal amplitude of ground-based GPS occultation in marine tropospheric ducts

The propagation characteristics of Global Positioning System (GPS) signals at very low elevation angles are frequently affected by tropospheric refraction as the satellite rises or sets at the horizon. Previous research indicated that the signal can be used to detect normal and surface-based duct refractive conditions. Using reciprocity, we develop a model to predict ground-based GPS occultation signal propagation in the presence of marine tropospheric ducts. To involve the effects of refraction, sea surface impedance, roughness, and the Earth’s curvature, the parabolic equation (PE) method is adopted in the low atmosphere. In implementing the PE numerically using the split-step discrete mixed Fourier transform algorithm, we propose a new approach of utilizing the relationship between the impedance coefficient and the reflection coefficient to modeling the right-hand circularly polarized GPS signal. The refraction effects from the top of the PE region to the satellite are modeled by ray tracing technique. Data measured by a ground-based receiver are presented and compared to the model under normal and duct refraction conditions, which show the validity of the propagation model in ground-based GPS occultation events. Potential applications of the ground-based occultation signal are also discussed.