Self‐scattering of a powerful HF radio wave on stimulated ionospheric turbulence

Abstract

An analysis is presented of high‐frequency (HF) signals from the European Incoherent Scatter HF ionospheric modification transmitter received during 26–30 October 2002 at three sites, two in Europe and one in Antarctica. Two components with different characteristics (“mirror‐reflected” and “scattered”) were observed in the signal spectra. The mirror‐reflected component can be associated with radiation through the side lobes of the transmitting antenna thus bypassing the modified volume on its way to the receiving sites. In contrast, the scattered component was radiated through the main antenna beam and then scattered by pump‐induced ionospheric irregularities above the heater. As a result, variations in the scattered component signal intensity and Doppler frequency shifts (DFS) recorded at the greatly separated sites showed a high level of correlation. It is shown that the Doppler frequency variations can be associated with variations in the plasma density and/or physical motion velocities of stimulated inhomogeneities within the volume common to all propagation paths. Analysis of Doppler frequency shifts at greatly separated sites would allow identifying the mechanism responsible for the self‐scattering effect. In the case of DFSs due to motion of the pump‐induced scatterers it would be also possible to reconstruct the full velocity vector of the inhomogeneities.

HF wave scattering by field‐aligned plasma irregularities considering refraction in the ionosphere

“…This would suggest that in the presence of several ionospheric layers (e.g., E and F ), a certain fraction of the scattered wave energy can be captured by the interlayer ionospheric waveguide. Since such waveguide propagation is characterized by a very small attenuation, it is quite plausible that this mechanism supported the super long distance propagation of the EISCAT signals observed in the “self‐scattering” experiment [ Zalizovski et al ., ]. The potential of exciting the ionospheric interlayer waveguide by the aspect‐sensitive scattered HF signals requires greater investigation.…”

“…The above analysis supports the mechanism of the “self‐scattering effect” that was suggested by Zalizovsky et al . [] for the explanation of their experimental results of monitoring the EISCAT transmission at three remote locations (SPB, RAO, and UAS). Recall that during the experiment the variations of the Doppler frequency shifts recorded at all the sites were almost identical.…”

“…Since the scattering region guiding the signals into the interlayer duct channel for propagation into different directions is the same, it is plausible to expect that the variations of the Doppler frequency shifts and signal amplitudes recorded at greatly dispersed receive sites will be very similar, as was observed during the “self‐scattering” experiment reported by Zalizovski et al . [].…”

“…Thus, the aspect‐sensitive scatter mechanism can explain the “self‐scattering effect” which was observed using the EISCAT transmission by Zalizovsky et al . []. Therefore, there exists the potential for the practical applications in HF communication, although further studies are required for a more reliable assessment.…”

“…Such effect was apparently first experimentally discovered by Zalizovsky et al . [] using the European Incoherent Scatter (EISCAT) HF heater (Tromso, Norway) and was given the name “self‐scattering effect.” In their experiment, the EISCAT transmission was monitored at three greatly dispersed receiving sites: at the Ukrainian Antarctic station “Akademik Vernadsky” (UAS); at the Radio Astronomical Observatory of the IRA NASU (RAO) near Kharkov, Ukraine; and near Sankt‐Petersburg, Russia (SPB). Typically, the received signals contained two characteristic spectral components.…”