Faraday polarization fluctuations of VHF geostationary satellite signals near the geomagnetic equator

Abstract

A two-slope power law spectrum for the equatorial F region irregularities has been introduced in the theory of Faraday polarization fluctuations (FPF) in place of a single-slope power law spectrum. The break scale length, at which the transition from a shallow to a steep slope in the irregularity power spectrum occurs, is found to play an important role in determining the strength of FPF. Analysis of Faraday rotation data for 40- and 140-MHz linearly polarized signals transmitted from the geostationary satellite ATS6 and received at the equatorial station Ootacamund (magnetic dip 6° N) yielded the following results: (1) FPF for the 140-MHz signal is negligible (< |ΔΩ|²>1/2 « 0.1 rad) although the quadrature components from which the Faraday rotation angle Ω is derived show large fluctuations in the event of strong amplitude scintillations; (2) there is appreciable FPF (< |ΔΩ|²>1/2 ≥ 0.1 rad) for the 40-MHz signal in these cases, which is explained on the basis of the two-component nature of the irregularity power spectrum.