A statistical analysis of the Fresnel frequency of ionospheric scintillation in the high latitude region using a piecewise fitting technique.
University of New Brunswick
Changes in electron density in the ionosphere affect the refractive index of the medium and as a result can affect the amplitude and phase of a trans-ionospheric radio wave. For an L-band signal, such as that used in the Global Positioning System (GPS), large-scale changes in electron density will cause purely refractive changes in the signal, while smaller scale structures may induce diffractive changes. Disturbances that cause these diffractive changes are called ionospheric scintillation. Refractive changes to a signal are deterministic and are therefore mitigatable, whereas diffractive changes are stochastic. In order to differentiate between these effects, it is important to determine the Fresnel frequency, the threshold frequency in which diffraction can affect the signal. The Fresnel frequency depends upon the frequency of the trans-ionospheric wave, the relative height of the ionospheric inhomogeneity to the receiver, as well as the relative drift speed between the wave source and ionospheric irregularity relative to the receiver. In this thesis, an automated technique to determine the appropriate Fresnel Frequencies of a given scintillation event will be discussed. To determine the values, the technique uses a piecewise linear regression with dynamic breakpoints to fit the frequency spectra of the amplitude of a signal. Using this method, 3 years worth of scintillation data from three different stations from CHAIN has been used to take a statistical look at the Fresnel frequencies using numerous scintillation events. The resulting data suggest that the Fresnel frequencies are dynamic in the high latitude region and do indeed range well above the 0.1 Hz detrending frequency.