Spectral broadening and phase scintillation measurements using interplanetary spacecraft radio links during the peak of solar cycle 23

Abstract

[1] When an interplanetary spacecraft is in a solar superior conjunction configuration, the received radio signals are degraded by several effects that generally increase in magnitude as the angle between the spacecraft and the Sun (Sun-Earth-Probe or SEP angle) decreases as viewed by a terrestrial tracking station. During periods of quiescent solar activity, phase scintillation and spectral broadening follow well-defined trends as a function of solar impact distance (SEP angle) and link frequency. During active solar periods, the magnitudes of these effects increase above background levels predicted by the quiet period models. Several such events were observed during the solar superior conjunction of the Cassini spacecraft during the peak of solar cycle 23 in May 2000. Pronounced features in the spectral broadening data above the quiet background appear to be associated with Coronal Mass Ejections (CMEs), and last for extended periods of time ranging from $30 min to $4 h. These features are coincident with periods of increased activity seen in the region of the spacecraft signal source on coronal white light images, and tend to be related or matched with EIT flare events and possibly long-duration flare events seen in satellite X-ray data. Several such features were captured in the May 2000 Cassini solar conjunction phase scintillation and spectral broadening data at X band (8.4 GHz) and Ka band (32 GHz) radio frequencies, and are presented here. Such characterizations are beneficial in understanding the impact of such events in future interplanetary communication scenarios during solar conjunction periods.

A 1.1-1.9 GHz SETI SURVEY OF THEKEPLERFIELD. I. A SEARCH FOR NARROW-BAND EMISSION FROM SELECT TARGETS

“…Woo (2007) presents an assimilation of phase scintillation and spectral broadening observations of the S-band (2.3 GHz) carrier on Pioneer and Helios spacecrafts at solar impact distances up to 200 R (adapted from Woo 1978), and find a roughly R −9/5 dependence for spectral broadening past R ∼ 10 R . A variety of models and observations suggest that the electron density fluctuations in the solar wind follow an approximate power law density spectrum, with a mean index very close to the Kolmogorov value of 5/3 (Morabito 2009 and references therein), allowing these results to be extrapolated based on ∆ν broad scaling as ν −6/5 . Scaling based on the results in Woo (2007), we calculate a spectral broadening contribution from the IPM of approximately:…”

“…The strength of these effects depend largely on the solar impact distance R, or line-of-sight solar separation angle, but significant longitudinal and temporal (e.g. the solar cycle and coronal mass ejections) variations occur as well (Morabito 2009). Woo (2007) presents an assimilation of phase scintillation and spectral broadening observations of the S-band (2.3 GHz) carrier on Pioneer and Helios spacecrafts at solar impact distances up to 200 R (adapted from Woo 1978), and find a roughly R −9/5 dependence for spectral broadening past R ∼ 10 R .…”

Plasma Motions and Compressive Wave Energetics in the Solar Corona and Solar Wind from Radio Wave Scattering Observations

“…The collective Compton scattering from electron density fluctuations (e.g., Akhiezer et al 1958;Dougherty & Farley 1960;Bingham et al 2003) that are moving or oscillating perpendicular to the direction of wave propagation can, however, lead to an inelastic change in the wavenumber and hence frequency broadening (that is normally a small fraction of the observed frequency). Doppler broadening of radio waves from spacecraft has been extensively studied to diagnose the expansion of the solar wind (e.g., Woo 1978), and moving density irregularities have also been analyzed via observations of interplanetary scintillations (e.g., Woo & Gazis 1993;Woo 1996;Morabito 2009;Mejia-Ambriz et al 2015). The spectral width of the radio wave signal, or the strength of scintillation, is proportional to the speed of the density irregularity weighted by the amplitude of the density fluctuation.…”