On the Possibility of Bistatic HF Ionospheric Sounding by Exact Time Signals

Characteristics of high-frequency signals that propagated between the RWM radio station (Moscow region, Russia) and Radio Astronomical Observatory (Kharkiv region, Ukraine) at frequencies above the maximum usable frequency on direct path were investigated. The Doppler frequency shifts and group delay of individual components were investigated for the multimode signal received with the nondirectional antenna. The azimuthal dependence of received signal power was measured by a highly directive antenna. It is shown that the electromagnetic energy propagated between the transmitting and receiving points through several different paths, which differed in length, position and time of existence. An explanation of the group delay of individual modes and their existence time is proposed. It is shown that the main component of the received signal power is determined by the oblique back scatter sounding from the south-east and by scattering on the edge of the aurora oval during geomagnetic disturbances.