Oblique chirp sounding and modeling of ionospheric HF...

Oblique chirp sounding and modeling of ionospheric HF channel at paths of different length and orientation

G. G. Vertogradov, and V. G. Vertogradov

Rostov State University, Rostov-on-Don, Russia

Radiophysical Research Institute, Nizhny Novgorod, Russia

Abstract

[1] The results of systematic observations during 2005 of the main characteristics of HF propagation at a network of paths of oblique linear frequency modulation (LFM) sounding of the ionosphere are presented. The values of the maximum observed frequency (MOF) are calculated using the IRI 2001 model and the effective sunspot number W_eff. It is shown that the difference between the predicted and measured monthly mean values does not exceed 12%. It is found that at all propagation paths, quasiperiodic variations of MOF are almost always observed. The amplitude of the MOF variations in the daytime can reach 2 MHz. A spectral analysis of the MOF variations at the midlatitude paths Cyprus—Rostov-on-Don and Inskip—Rostov-on-Don is performed. It is shown that the spectra of the MOF fluctuations have a well-pronounced linear structure. The power of spectral components of MOF fluctuations is concentrated in the 20-90 min range. Analyzing the dynamics of motion of z-type features on a trace of the high-angle ray, the periods of traveling ionospheric disturbances (TID) are determined and found to be 15-30 min. It is found that the TID with such periods correlate well with the sunset and sunrise for the middle point of the path. Modeling of oblique sounding (OS) ionograms at the presence of TID is performed taking into account the procedure of LFM signal processing. On the basis of the comparison of the experimental and calculated data, parameters of middle-scale wave disturbances responsible for the formation of z-type features in OS ionograms are determined.

Received 20 January 2006; accepted 12 February 2007; published 11 May 2007.

Keywords: Ionospheric HF channel; Modeling of oblique sounding ionograms; Traveling ionospheric disturbances.

Index Terms: 0689 Electromagnetics: Wave propagation; 2487 Ionosphere: Wave propagation; 2435 Ionosphere: Ionospheric disturbances.