E. S. Andreeva

Possibilities of the near‐space environment radio tomography

A number of radio tomography schemes of the ionosphere and near-space environment (Earths magnetosphere, plasmasphere, and protonosphere) are analyzed by utilizing multisatellite systems. A new approach to space-time tomography is proposed. It is shown that application of high orbital systems of Global Positioning System and Global Navigation Satellite System type with ground-based receivers is promising in the case of space-time tomography. Computer simulation results showed the possibility of realizing radio tomography of the near-space environment with the help of some multisatellite systems.

Radiotomographical Detection of Ionosphere Disturbances Caused by Ground Explosions

Long-lived local disturbances of the ionospheric density over the site of ground industrial explosions were detected by the ionosphere radiotomography method. It is assumed that the density anomalies arise because of the initiation of vortex motion in a neutral component after acoustic impulse passage.

Radiotomography and HF ray tracing of the artificially disturbed ionosphere above the Sura heating facility

We present the results of the radiotomographic imaging of the artificial ionospheric disturbances obtained in the recent experiments on the modification of the midlatitude ionosphere by powerful HF radiowaves carried out at the Sura heater. Radio transmissions from low orbital PARUS beacon satellites recorded at the specially installed network of three receiving sites were used for the remote sensing of the heated ionosphere. We discuss the possibility to generate acoustic-gravity waves (AGWs) with special regimes of ionospheric heating (with the square wave modulation of the effective radiated power at the frequency lower than or of the order of the Brunt-Vaisala frequency of the neutral atmosphere at ionospheric heights during several hours) and present radiotomographic images of the spatial structure of the disturbed volume of the ionosphere corresponding to the directivity pattern of the heater, as well as the spatial structure of the wave-like disturbances, which are possibly heating-induced AGWs, diverging from the heated area of the ionosphere. We also studied the HF propagation of the pumping wave through the reconstructed disturbed ionosphere above the Sura heater, showing the presence of heater-created, field-aligned irregularities that effectively serve as “artificial radio windows.”

Ionospheric Sounding and Tomography by GNSS

Studies of the ionosphere and the physics of the ionospheric processes rely on the knowledge of spatial distribution of the ionospheric plasma. Being the propagation medium for radio waves, the ionosphere significantly affects the performance of various navigation, location, and communication systems. Therefore, investigation into the structure of the ionosphere is of interest for many practical applications. Existing satellite navigation systems with corre‐ sponding ground receiving networks are suitable for sounding the ionosphere along different directions, and processing the data by tomographic methods, i.e. reconstructing the spatial distribution of the ionospheric electron density.

Sura Heating Facility Transmissions to the CASSIOPE/e-POP Satellite

Throughout a night-time pass of the CASSIOPE satellite at an altitude of about 1300 km above the Sura Heating Facility, transmission of O-mode radiation from Sura to the ePOP Radio Receiver Instrument on CASSIOPE was maintained. Also during this pass, continuous VHF/UHF transmission from the ePOP CERTO radio beacon to three coordinated ground receivers in the Sura vicinity was achieved. Tomography of the VHF/UHF received wave data based on total electron content permitted the two-dimensional distribution of ionospheric ambient electron plasma frequency fpe to be determined in the latitude-altitude space between Sura and CASSIOPE. foF2 values about 0.1 MHz above the Sura pump frequency of 4.3 MHz were measured by the tomography. We examine the question of whether the observations can be explained on the basis of classic propagation in a smooth ionosphere. Tracing of rays from Sura towards CASSIOPE orbital locations finds most rays reflected away from the topside by the patchy ionospheric structure in bottomside fpe. It is concluded that O-mode ducting in under-dense field-aligned irregularities is responsible for maintaining the transionospheric transmission across the 2-min pass. O-to-Z mode “radio-window” conversion in the F-region bottomside is not required to explain these data.

Earthquake Prediction Research Using Radio Tomography of the Ionosphere

Under development since its invention in 1990 as an ancillary application of ionospheric radio-tomography (RT), a new earthquake (EQ) prediction system is being evaluated. It has already been deployed along the United States West Coast, from Vancouver in Canada to San Diego in Southern California, and is currently undergoing Beta testing. This Chapter addresses RT–EQ prediction concepts, the underlying RT theory, evolution and implementation, and a few examples of the Beta test system’s performance. This work is an investigation of EQ precursors, which we hope will lead to an operational system. The current system provides a foundation and the tools to study ionospheric effects linked to conditions in the Earth’s crust prior to major earthquakes. Progress toward a fully operational system will require several more years of data acquisition and analysis.

HF ray tracing of the artificially disturbed ionosphere above Sura heating facility

We present the results of high-frequency (HF) ray tracing of a pumping wave in an artificially disturbed ionosphere above the Sura heating facility applying parameters that are reconstructed using the radiotomography (RT) approach with the signals of the Parus and CASSIOPE beacon satellites. We also discuss the possibility of generating atmospheric gravity waves (AGWs) with special regimes of ionospheric heating and present the examples of such structures in radiotomographic reconstructions.

Assessing the degree of ionospheric perturbation from radio tomographic data

The methods are suggested for constructing the ionospheric perturbation indices (IPIs) from the empirical electron density distributions retrieved by the ionospheric radio tomography (RT). The indices take into account the specificity of the low- and high-orbiting (LO and HO) RT data, their spatio-temporal resolution and coverage. We consider and analyze various schemes of IPIs construction, calculate the correlation between the IPIs and geomagnetic Kp index, identify the indices that are most sensitive to the geomagnetic activity factor.

Estimation of sea level variations with GPS/GLONASS-reflectometry technique

In the present paper we study GNSS - reflectometry methods for estimation of sea level variations using a single GNSSreceiver, which are based on the multipath propagation effects caused by the reflection of navigational signals from the sea surface. Such multipath propagation results in the appearance of the interference pattern in the Signal-to-Noise Ratio (SNR) of GNSS signals at small satellite elevation angles, which parameters are determined by the wavelength of the navigational signal and height of the antenna phase center above the reflecting sea surface. In current work we used GPS and GLONASS signals and measurements at two working frequencies of both systems to study sea level variations which almost doubles the amount of observations compared to GPS-only tide gauge. For UNAVCO sc02 station and collocated Friday Harbor NOAA tide gauge we show good agreement between GNSS-reflectometry and traditional mareograph sea level data.

Modeling the problem of low-orbital satellite UV-tomography of the ionosphere

The results of modeling the direct and inverse problems of low-orbital satellite ultraviolet (UV) tomography of the ionospheric 135.6 OI volume emission rate are presented. The direct problem was solved with the orbital geometry of DMSP block 5D3 satellites with SSUSI and SSULI UV spectrographs among the other payloads, the real operating parameters of these instruments (the scan rate and the interval of scan angles), and the set of the model distributions of the volume emission rate that contain irregularities on various scales. The solution of the direct problem yields the radiation intensities in the 135.6 nm line, which is used as the input data for reconstructing the initial (prototype) model distributions of the volume emission rates. The obtained system of linear equations (SLE) was solved using the Algebraic Reconstruction Technique (ART) and Simultaneous Iterative Reconstructive Technique (SIRT) algorithms, which are highly efficient in problems of the low-orbit radio tomography of the ionosphere. It is shown that the initial model distribution can be successively reconstructed if one takes the non-negativity condition of the solution into account, uses weighting functions to decrease the solution in the regions where it is known to be a priori small, and applies inter-iteration smoothing to eliminate the effects of the approximation errors. Here, the averaging parameters should decrease in the course of the iterations. With these constraints fulfilled, the computational costs of the ART- and SIRT-based solutions are similar, while the reconstruction error is approximately 6%. The influence of random errors and bias in the data on the results of the reconstruction is explored. It is shown that with a given error level of the initial data the parameters of the reconstruction algorithms can be adjusted in such a way as to efficiently suppress the influence of the noise with a relative amplitude of 2–3% on the solution.