Investigation of the Fresnel Scale From Ionospheric Scintillation Spectra

Trans-ionospheric radio signals recorded on the ground exhibit random amplitude and phase fluctuations attributed to irregularities in the ionospheric electron density. Studying the ground-based measurements of trans-ionospheric radio signals can contribute to understanding plasma instability mechanisms leading to the development of ionospheric structures. In this regard, radio signals emitted from satellites, making up the Global Positioning System (GPS), and recorded by the Canadian High Arctic Ionospheric Network (CHAIN) GPS receivers, are analyzed to study the physical signatures of both amplitude and phase fluctuations. The current ionospheric scintillation paradigm posits that amplitude fluctuations arise from diffraction caused by Fresnel scale ionospheric structures, while refraction is responsible for signal phase variations. The amplitude power spectrum profile consistently displays a rollover frequency, which is not equal to the Fresnel frequency under the Taylor hypothesis. Phase screen theory is used to investigate this phenomenon further and identify an empirical relation between the rollover and Fresnel frequencies. Notably, we have found that the rollover frequency is consistently smaller than the Fresnel frequency. Furthermore, the Fresnel frequency extracted from two-component phase spectra tends to be larger than the rollover frequency. Based on our results, we have concluded that the identified Fresnel frequencies are directly linked to the ionospheric irregularities causing scintillation.