Tomographic Methods for Studying the Upper Atmosphere and Near-Earth Space: Current State and Development Prospects

The review examines the physical and mathematical formulations of the tomography problem in relation to remote sensing of the atmosphere and near-Earth space. Special attention is given to ionospheric sensing using satellite beacon signals from low-orbit (Parus/Transit/Cassiope, etc.), medium-orbit, and high-orbit (GPS/GLONASS and new global satellite navigation systems) satellites. The capabilities and limitations of 2D low-orbit and 4D high-orbit ionospheric radio tomography methods are discussed, along with the results of radiotomographic reconstructions of electron density distribution at various latitudes under both natural and artificial disturbances. A separate focus is placed on studying small-scale ionospheric irregularities based on satellite signal amplitude scintillation data, as well as challenges in implementing such sensing schemes at high latitudes using GPS/GLONASS signals. Besides, the prospects of tomographic systems for upper atmosphere sensing are discussed, considering the significant reduction in the number of low-orbit satellites, the potential installation of satellite beacons on new platforms (CubeSat), and the use of radio tomography methods in ultraviolet tomography of the upper atmosphere. The first results obtained using the dual-frequency (150/400 MHz) coherent signal transmitter MAYAK onboard the satellites of the Russian “Ionosphere” project are presented.