On the dependence of scintillation on GPS signal propagation geometry

Abstract

A detailed investigation on the dependence of amplitude and phase scintillation indices on the Magnetic Field Aligned Angle (MFAA) is conducted using six years of data from nine stations of the Canadian High Arctic Network (CHAIN) distributed along a wide range of geographical latitudes ranging between 56:65°–73:004°, making the study the first of its kind to look into the geometrical dependence of scintillation from a statistical point of view. The results indicate that both the scintillation indices show a gradual increase when the MFAA approaches zero. This happens when the satellite link is parallel to the magnetic field line vector and indicates the presence of field aligned irregularities which are elongated along the field vector. Comparisons to previous studies on this subject was also conducted and is shown to contradict what other studies had previously found on the nature of the dependence of scintillation indices upon elevation and azimuth angles of the satellite. It is shown that the scintillation producing irregularities are field aligned, i.e. elongated in the direction of the magnetic field and not perpendicular to the field as some previous studies had concluded. It is also observed that the higher dependence of σø as compared to the S[subscript 4] index on the propagation geometry of GPS satellite signals is due to refractive contributions induced on the signal phase as a result of improper detrending of the carrier phase. It is shown that this refractive puctuation in σø could be removed if one properly detrends the phase of the signal by taking into account the dynamic nature of the Fresnel frequency at high latitudes.