Oblique Sounding and Modeling of the Ionospheric HF Channel |
| |
Authors: | GG Vertogradov VP Uryadov VG Vertogradov |
| |
Institution: | (1) Rostov State University, Rostov-on-Don, Russia;(2) Radiophysical Research Institute, Nizhny Novgorod, Russia |
| |
Abstract: | We present the results of experimental studies of the distance-frequency and amplitude-frequency characteristics of the ionospheric
HF channel on mid-latitude paths of oblique chirp sounding. It is shown that the maximum observed frequencies (MOFs) are subject
to short-period variations with the quasi-periods from 30 min to 2 h.The amplitude of the MOF variations reaches 2 MHz and
can increase up to 5–8 MHz on the Cyprus—Rostov-on-Don one-hop path in the sunrise-sunset time. It is established that the
MOF fluctuations are accompanied by pronounced “cusp” features occurring in the upper rays and moving with time to the region
of shorter delays, i.e., from lower to higher frequencies. The amplitude-frequency characteristics of individual propagation
modes undergo deep fluctuations (up to 20–30 dB)whose quasi-period and depth depend on the frequency. It is shown that the
appearance of fluctuations is caused by interference of the unresolved rays within the limits of one propagation mode. Based
on the modeling, it is shown that “cusps” in oblique-sounding ionograms are due to the influence of traveling ionospheric
disturbances (TIDs). The TID parameters are estimated. It is shown that conditions of the formation of “ cusps” in the distance-frequency
characteristics depend on the TID amplitude, the wavelength of the disturbance wave, and the direction of its phase front
with respect to the propagation path. The effect of quasi-regular frequency modulation of the Pedersen mode with a period
of 250–300 kHz on the Cyprus-Rostov-on-Don chirp-sounding path is found. Altitude stratification of the ionosphere near the
F-layer maximum, which is responsible for the focusing and defocusing of the Pedersen mode, is estimated. It is established
that the stratification scale amounts to approximately 200–250 m.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 6, pp.455–471, June 2005. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|