An empirical model of ionospheric scintillation at high latitudes
University of New Brunswick
Trans-ionospheric radio signals experience both amplitude and phase variations as they propagate through a turbulent ionosphere, this phenomenon is known as scintillation. As a result of these fluctuations, GPS receivers lose track of signals and consequently induce positioning and navigational errors. Therefore, there is a need to study scintillation and their causes in order to not only resolve the navigational problem but in addition develop analytical and numerical radio propagation models. This thesis presents the work that has been done to develop an empirical model of ionospheric scintillation at high latitudes. In this study, GPS L1 signals were recorded and characterized using the Canadian High Arctic Ionospheric Network (CHAIN).We developed new indices to quantify scintillation and the chaoticity of the turbulent ionosphere. More particularly, we used the multi-fractal aspect of the scintillating GPS signal to compute the corresponding wavelet-based entropy and fractal dimension. These indices were used to construct scintillation maps in the geomagnetic domain. It has been found that the chaoticity of the scintillating signal exhibits a dependence on geomagnetic conditions and a seasonal cycle, suggesting the possibility to quantify the ionospheric turbulence using the proposed indices. In the second part of the thesis, a simulator of the trans-ionospheric channel was developed. The model takes into account the case of strong scintillation, where the amplitude fluctuations start to build up inside the ionospheric slab. The features of the power spectra of the observed scintillation events were reproduced: it has been found that the amplitude fluctuations are characterized by a power spectral density that obeys a power law with a break down at the Fresnel scale. The phase, on the other hand, does not exhibit a breakdown of the power law, which is in agreement with the observations.