Viacheslav E. Kunitsyn

Some features of the equatorial anomaly revealed by ionospheric tomography

The equatorial anomaly in ionization density has been imaged using the computerized ionospheric tomography technique applied to data from a low-latitude ionospheric tomography network. Examples of images representative of typical conditions during equinox and low solar flux are presented and shown to exhibit some characteristic features which have not been observed directly previously. The EA core, comprising the highest density region of the EA, is shown to exhibit a characteristic structure and asymmetry. These characteristics are quantified using measures of the ionospheric slab thickness and altitude, and they are discussed in light of the fountain mechanism which is responsible for formation of the EA.

Statistical Radio Tomography of a Randomly Inhomogeneous Ionosphere

Very often the ionosphere contains large volumes filled with a great number of electron density irregularities of different sizes. This is typical of equatorial and polar regions, especially in the nighttime. Of course, in such cases, reconstruction of separate realizations of the disturbed dynamic ionosphere makes little sense, and of more interest is reconstruction of the statistical parameters of a turbulent randomly inhomogeneous ionosphere, such as the correlation function or the spectrum of electron density fluctuations. The statistical approach is explicitly informative of the structure of a disturbed ionosphere. It allows studying generation mechanisms of the irregularities and their effect on propagating radio signals. A randomly inhomogeneous ionospheric plasma causes fluctuations or scintillations in the radio waves coming through the ionosphere. Getting rid of such scintillations is a problem of greatest importance in radio location and communication systems. Separation in time and space of the receiving systems and signal coding schemes helps to weaken the influence of scintillations, but design of such schemes requires information about the statistical parameters of electron density irregularities.

Ionosphere: Structure and Basic Methods for Radio Sounding and Monitoring

The term “ionosphere” for defining the ionized shells encircling Earth was introduced by V. Watt in 1929. The hypothesis that a conducting region should exist in the upper atmosphere was first advanced at the end of the nineteenth century first by B. Stewart and then by A. Schuster [Schuster, 1889] to explain diurnal variations of the geomagnetic field. However, this hypothesis became widespread only after Heaviside and Kennely explained in 1902 the propagation of radio waves over large distances. The existence of ionized regions in the upper atmosphere was directly proved in the 1920s. Of greatest importance was the invention of the pulse ionospheric station by G. Breit and M. Tuve [Breit and Tuve, 1926], who were the first to carry out radio probing of the ionosphere. In Russia, the first results in this field were obtained by M.V. Shuleykin [Shuleykin, 1923] who inferred from studying the operation of broadcasting stations that a radio wave exists that comes from above to Earth’s surface. He calculated the reflection height as 260 km.

Ray Radio Tomography

The problems of ray radio tomography of large-scale structures are usually formulated as follows: to recover the structure of some ionospheric region from linear integrals measured along a series of rays intersecting this region. Since the sizes of large-scale irregularities, both natural (such as, e.g., the ionospheric trough) and artificial (spacecraft traces, technological emissions), are of the order of dozens to thousands of kilometers, diffraction effects can be neglected in VLF/UHF probing.

Further Development of Tomographic Methods

In the previous chapters, various modifications of radio tomography with ground-based receiving systems have been discussed. The use of satellite-borne receiving systems makes it possible to sound the ionosphere in the satellite-to-satellite direction and allows obtaining information about the ionosphere over a set of quasi-tangential rays. In particular, nowadays, most promising for ionospheric and atmospheric investigations are the systems mounted in low-and middle-orbiting satellites that receive radio signals from navigational systems such as GPS/GLONASS.

Diffraction Radio Tomography of Ionospheric Irregularities

In forward scattering, the definition of the linear integrals q z (ρ, ω) (3.21) from the complex potential q(r,ω) reduces the ISP to the problem of tomographic reconstruction, i.e., the problem of reconstructing an object from its projections. Achievements in X-ray tomography in recent decades have been responsible for the intense development of tomographic techniques for recovering the structure of nonuniform objects. Reconstruction algorithms applied in practical X-ray tomography are based on a rectilinear approximation of ray trajectories. Mathematically, such problems are reduced to reconstruction of the damping function or the refraction coefficient from the set of linear integrals, i.e., to reconstructing the object from its projections of smaller dimensions. X-ray radiation has been followed for tomographic purposes by practically all of the known kinds of radiation and waves. In tomographic studies using optical, ultrasound, radio, microwaves and other kinds of waves, linear ray approximation does not often lead to good results. Therefore, in recent years, the reconstruction methods making use of refraction and diffraction effects have been developing intensively, and a special term — diffraction tomography — has come into being.

Inverse Scattering Problems

As shown in Sect. 1.2, for high sounding frequencies, vector equation (1.11) splits up into three scalar equations, and it is sufficient to consider the equation for one component of the field

Study of GNSS-measured ionospheric total electron content variations generated by powerful HF-heating

\Delta E + {k^2}\varepsilon \left( {r,k} \right)E = 0