ИСТИНА

The satellite radio tomography (RT) of the ionosphere is an efficient method for electron density imaging in the different geographical regions of the world under different space weather conditions. In this work, we used two modifications of the radio tomographic methods: first - low orbiting radio tomography (LORT), which relies on the coherent transmission of previous generation navigational satellites like Parus/TRANSIT received at the chains of the receivers located along satellite passes, thus providing 2D height-latitude crossections of the ionosphere; second - high orbiting radio tomography (HORT) based on GNSS signals processing at global and regional receiving networks capable to reconstruct 4D spatio-temporal electron density distributions in the ionosphere. We used LORT and HORT methods to study ionospheric disturbances both in European sector along Svalbard - Murmansk - Moscow line and American sector along Cordova- Gakona-Delta line during famous Halloween Storm 2003. We show the comparison of obtained tomographic crossections with IRI model data and study the peculiarities of the formation of ray trajectories of HF radio waves in real and model ionosphere under the geometric optics of inhomogeneous anisotropic media approximation. We show significant differences in ray patterns of HF radiowaves even for undisturbed geomagnetic conditions especially in the regions of significant spatial gradients of electron density, i.e., in main ionospheric trough region. The ray trajectories may strongly differ by the size of the receivers radio shadow, the length of the one-hop trace, and other parameters. Besides, in some cases the IRI model is not capable to predict the HF channeling up to the heights of the outer ionosphere and different focusing and caustic structures which are observed in the RT imaging data. These results can be of significant interest for physics of the ionosphere and for practical HF communication applications.