Ionospheric scintillation in GNSS signals: a tool for earth observation
(English) This PhD thesis is intended to study ionospheric scintillation and its relationship with some of its sources, in particular the observed correlation between the ionospheric perturbation and the lithosphere. However, before addressing this topic, some simulators and models have been develop...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2024 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/694491 |
| Acceso en línea: | http://hdl.handle.net/10803/694491 https://dx.doi.org/10.5821/dissertation-2117-429981 |
| Access Level: | acceso abierto |
| Palabra clave: | Àrees temàtiques de la UPC::Enginyeria de la telecomunicació 621.3 - Enginyeria elèctrica. Electrotècnia. Telecomunicacions 55 - Geologia. Meteorologia |
| Sumario: | (English) This PhD thesis is intended to study ionospheric scintillation and its relationship with some of its sources, in particular the observed correlation between the ionospheric perturbation and the lithosphere. However, before addressing this topic, some simulators and models have been developed. A trans-ionospheric ray tracer has been developed in this thesis in order to simulate the effects of an electromagnetic wave traveling through the Earth's ionosphere. It consists of an updated version of an old algorithm that has been provided with the most recent models of the ionospheric density, geomagnetic field, and atmospheric composition, in addition to a model for equatorial plasma bubbles.Ionospheric scintillation is the term used to describe a phenomenon affecting electromagnetic waves traveling through the ionosphere which suffer from rapid changes in its intensity and phase. It is motivated by the turbulent electron density fluctuations within the ionosphere in different temporal and spatial scales. Ionospheric scintillation is more probable to occur in equatorial regions after the sunset, and in polar regions, but it is highly related to external perturbations from the space weather. Its complex behavior is studied by mathematical models such us the Rino's model, which uses a phase screen to derive the phase and intensity changes of the waves crossing it. This model is capable of estimating the scintillation indices ($S_4$, and $\sigma_\phi$) for any ray geometry, but it needs some inputs characterizing the ionospheric conditions. These inputs refer to the intensity and spectral distribution of the fluctuations ($C_kL$, and $q$), and its shape and velocity. The WBMOD model is one of the climatological models widely utilized to provide the ionospheric scintillation parameters globally as a function of the date, time, location, and geomagnetic/solar conditions. However, this model is not freely available. The work presented in this PhD thesis is the development of an approximated twin model of WBMOD based on neural networks trained with available WBMOD data. Ionospheric scintillation can be estimated from GNSS signals, through different techniques. First, by direct measurement of the GNSS signal in ground stations. Second, by using the GNSS Reflectometry technique, which senses from LEO satellites the wave reflected over the ocean. Third, by employing the GNSS radio occultation technique, which studies the signal coming from GNSS satellites near the horizon, crossing the ionosphere tangentially. These three techniques together allow a wider coverage of the Earth, particularly, over regions where the traditional ground stations do not exist, i.e. oceans. Many studies in the last decades have evidenced a coupling between the lithosphere, the atmosphere, and the ionosphere, the so-called LAIC. These studies report changes in the ionosphere total electron content, perturbation in the magnetic field, or detection of extremely low frequency radiation, among other phenomena, both before and after seismic events. In this thesis, the relationship between the ionospheric scintillation detected by the three methods mentioned before, and seismic events has been studied, focusing on the precursory signatures. For this, a preliminary study to assess the effectiveness of the GNSS Reflectometry to detect ionospheric scintillation has been performed using CYGNSS GNSS-R data. Finally, this PhD thesis presents the statistical study on the relationship between ionospheric scintillation anomalies and earthquakes globally, and in a second step, related to the localized seismic activity produced by a volcanic eruption in La Palma in 2021. The results of these parts found a small signature of the ionospheric scintillation anomalies as earthquake's precursory signals. However, this evidence is so small that it does not allow its straightforward use as an early alarm system for seismic activity. |
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