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Physical mechanisms associated with long‐range propagation of the signals from ionospheric heating experiments
Author(s) -
Zabotin Nikolay A.,
Zavorotny Valery U.,
Rietveld Michael T.
Publication year - 2014
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1002/2014rs005573
Subject(s) - ionosphere , narrowband , scattering , computational physics , antenna (radio) , physics , optics , beam (structure) , wideband , range (aeronautics) , signal (programming language) , doppler effect , backscatter (email) , acoustics , geophysics , materials science , telecommunications , wireless , computer science , astronomy , composite material , programming language
Long‐range propagation of heater‐produced signals has been studied in experiments with the European Incoherent Scatter Scientific Association ionospheric heating facility and with several globally distributed receiving sites by Zalizovski et al . [2009]. Two distinctive components were present in the signals' spectra, and these can be attributed to two modes of propagation of the signals. One of the components is narrowband and stable; it obviously can be associated with the multihop ionospheric propagation of HF waves radiated by the side lobes of the heater's antenna array. Prominent features of the second component are its wider spectral band (up to few tens of hertz) and strong variations in the average Doppler frequency shift and in the power, which in many cases were synchronous at the different receiving sites. These effects are most likely produced by the ionospheric scattering and dynamics within the heater's main beam. The tricky part is to explain how a portion of the HF energy contained in the relatively narrow main beam of the heater is redirected toward the remote receiving locations. We suggest a robust mechanism explaining the long‐range propagation of the wideband component of the heater‐generated signal based on the theory of scattering from rough surfaces. This mechanism preserves all the observed properties of the remote signals. We show that mountain relief in the vicinity of the heater plays the role of the rough surface causing almost isotropic scattering of the heater's main beam after it is reflected by the ionosphere. Multiple scattering by natural and artificial field‐aligned irregularities in the ionospheric layer may be related to the ground‐scattered remote signals through its role in spatial redistribution of the heater's radiation.