Ionospheric mapping and radio tomography

Results of radio tomographic studies of the ionosphere in different latitudinal and longitudinal regions in the world under various solar and geophysical conditions are discussed. Modern methods of satellite ionospheric tomography are described (low orbital, LO, and high orbital, HO, radio tomography), advantages and limitations of these two techniques are compared. Examples of 2D LORT, 3D and 4D HORT ionospheric images are shown. Method of combined radio tomography involving both LORT and HORT and including elements of radio occultation (RO) technoque is considered. Results obtained with combined radio tomography are discussed.