Radiophysical Measurements Research Articles

GEORADAR AND RADIOIMPEDANCE DIAGNOSTICS OF THE SELENGA RIVER WATER AREA

The relevance of the work is determined by the fact that no radiowave methods have ever been used to study the water areas of rivers and lakes and their geoelectric sections within the Baikal natural territory (BNT) in winter time. The purpose of the research is to determine the electrical and geometric characteristics of the layered medium "ice – water – bottom soil" and the ice cover of the Selenga River on the BNT in the VLF-LF and VHF radio wave bands according to the data of instrumental radiophysical measurements by GPR and radio impedance methods, including the determination of the structure of the ice crossings over the Selenga River. Using the Selenga River as an example, consideration has been given to the results of combining VLF-LF and VHF methods of electromagnetic diagnostics of a layered medium in a wide range of radio waves (from tens of kilohertz to units of gigahertz). Radio impedance profiling and sounding in the VLF-LF bands with the IPI-300 equipment made it possible to determine the sub-bottom structure of the soil from the change in impedance and geoelectric section. GPR in the VHF band made it possible to differentiate the fine structure of the Selenga River in winter by thickness of snow, ice and water. The sounding involved the use of georadar "Oko-2" with antenna units "Triton" (central frequency 50 MHz), AB-400 (central frequency 400 MHz), AB-700 (central frequency 700 MHz), and AB-1700 (central frequency 1700 MHz). The thickness of ice of the road crossing in the Mostovoy microdistrict of Ulan-Ude city was 0.5–1.2 m – 0.1–0.2 m thicker than that beyond the road crossing. It was found that the presence of snow cover beyond the road crossing prevents the ice mass from freezing. Calibration sounding of ice with borehole drilling yielded ice dielectric constant ε=3.17. The specific electrical resistance (SER) of water from boreholes is 71–74 Ohm·m at a temperature of 1 °C. The methods used complement each other and provide a quantitative description of the object of research. The integration of various methods of radio wave diagnostics provides more detailed information on the structure of the layered medium "ice – water – bottom soil". The obtained results and the developed methods of radio impedance and GPR sounding and profiling of an inhomogeneously layered underlying environment in winter time can be used in engineering and geological surveys in the eastern and northern regions of Russia.

Modeling of the Lower Ionosphere During Solar X‐Ray Flares of Different Classes

AbstractThis study presents the results obtained from modeling the lower ionosphere response to C‐, M‐ and X‐class solar X‐ray flares. This model is based on a 5‐component scheme for the ionization‐recombination cycle of the ionospheric D‐region. Input parameters for the plasma‐chemical model under different heliogeophysical conditions corresponding to selected X‐ray flares were determined by using data received from the AURA, SDO, and GOES satellites. Verification of the obtained results was carried out with use of ground‐based radiophysical measurements taken at the geophysical observatory Mikhnevo. The results obtained from a comparison of the calculated and experimental radio wave amplitude variations along six European very low frequency (VLF) paths show that the average normalized root mean square error is ∼7%, 14%, and 18% for C‐, M‐, and X‐class flares, respectively. Qualitative and quantitative analysis of the verification results for the VLF signal amplitude show good predictive capability of the model built for describing weak and moderate ionospheric disturbances.

Preface

This issue of the journal is dedicated to the scientific and applied research presented at the 8 International Conference «Actual Trends in Radiophysics».The conference was held on October 1–4, 2019 in Tomsk (Russia).The conference is organized by:• The Russian Foundation for Basic Research.• National Research Tomsk State University.• Center for collective use “Centre of radiophysical measurements, diagnosis and research of parameters of natural and artificial materials” of TSU.• Radiovision Ltd. Tomsk, Russia.List of Conference Sections, Committee, Program Committee, Organizing Committee are available in this pdf.

Relationships between the Structure of Convective Clouds and Lightning Frequency Derived from Radiophysical Measurements

The results of simultaneous radar, radiometric, and lightning location measurements are analyzed to reveal interrelations between the characteristics of electric discharges and the parameters of a cumulonimbus cloud developing near Saint Petersburg. The dependences of the cloud electric activity on the radar characteristics as well as on the parameters derived from the Meteosat SEVIRI radiometer measurements are considered. It is found that lightning frequency highly correlates with the volume of supercooled cloud regions with high values of reflectivity. An increase in the lightning frequency occurs about 20 minutes after the moment when supercooled cloud volumes with reflectivity above 35–55 dBZ reach the maximum values. The maximum precipitation flux precedes the maximum lightning frequency.

PRINCIPLES OF CORRECTION OF THE IONOSPHERE MODEL WITH DEVELOPMENT OF SOFTWARE-ALGORITHMIC SUPPORT FOR EVALUATION OF MAXIMUM ACHIEVABLE CAPACITY OF HF-RADIO CHANNEL

The article outlines the principles of correction of the ionosphere model in real time. These principles are based on the tabulation of mathematically complex (integrated physical and empirical) models on the section of a particular path (cross section) with sufficiently fine space grid, for development of effective reinstating algorithm for the cross section, for adjustment of values of the model in the grid points, according to informative value of used radio physical measurements performed in real time, for utilization of graphical display of the cross section structure of the model for the purpose of ensuring effective actions of the operator related to optimization of the parameters of the correction mode.

Examples for the importance of radiophysical measurements in clinical phototherapy

Optimal UV therapy requires regular surveillance of the variables that influence therapeutic success. In daily practice, phototherapy equipment is often operated with an attitude of "autocontrol." This implies that thorough control measurements of the emission spectra and calibration of UV fluences are not routinely performed. For both quality control and patient safety, it is essential to regularly check whether a UV source is providing the right target spectrum with the correct dose to the skin. We have exemplarily taken three UV sources currently used in clinical practice and performed radiophysical measurements, i. e. determined emission spectra, radiation output and correctness of dose calculation. All three sources revealed either a largely inhomogeneous distribution pattern of radiation intensity, variation of radiation intensity over time or insufficient filtering of the UV lamp emission spectrum. Furthermore the dose calculation procedures had to be revised because of significant differences between the estimated and the administered UV doses. Radiophysical measurement of all UV-equipment in clinical use is a simple and effective way to improve the safety and reliability of phototherapy. Such measurements help to uncover technical flaws in radiation sources and prevent unnecessary side effects and UV exposure risks for the patient.

Ionosphere as a natural detector for investigations of solar EUV flux variations

It is proposed a method to determine solar EUV fluxes on the basis of data of ionospheric E-layer critical frequency measurements and of ionospheric activity index calculations. A new solar activity index was elaborated on the base of improved ionization theory in ionospheric E-region. It makes possible to carry out independent estimations of EUV fluxes and reciprocal calibration of EUV measurements, using information on ionospheric E-layer as data of the global natural detector of EUV emission. It is shown, that variations of the upper atmosphere temperature and density does not influence the instrumentation indications, and EUV flux responsible for E-layer ionization, can be determined due to E-layer critical frequency measurements. The new index may serve as a quantitative measure of EUV emission, at least, in lines 97.7 and 102.6 nm. Every mid-latitude ionospheric station may serve as a device for measurements of index – “equivalent flux” of EUV. Calibration error of this index is defined by a low error of radiophysical measurements of critical frequencies and is equal to ∼7%. The index allows also to investigate long-term variations and to expand a temporal range of research. The L α flux for almost four cycles of solar activity was calculated due to Slough and Chilton stations data. It is shown that variations of EUV fluxes approximately correspond to the main tendency of activity increase in the period from the 20-th to the 23-day cycle. Analysis of ionospheric index reveals an absence of noticeable long-term trends of EUV emission during 1957–2003 period. Use of this index allows to eliminate contradiction between EUV intensities observed onboard SME and UARS satellites, because fluxes in minima between the 21 and 22 cycles (SME epoch) and between the 22 and 23 cycles (a UARS epoch) are practically identical. In general all EUV cycles are similar to each other and it was not found a significant emission trend.

The season peculiarities of behaviour of the long-term temperature trends in the middle atmosphere on the mid-latitudes

On the basis of rocket, nightglow and radiophysical measurements at heights of 25–110 km in middle latitudes the seasonal variations of the long-term temperature trends at various altitude levels are determined. At heights of 25–87 km the trends are mainly negative within all year. Only in winter period in middle and upper stratosphere the trend within several months becomes positive. At heights of 92–93 km the trend is very close to zero throughout the year. In summer period the altitude of zero trend extends downward to heights of 82–85 km, where the noctilucent clouds are usually observed. At heights of 95–110 km the trends are positive all year round. Mean annual height distribution of the temperature trend shows long-term cooling at atmospheric heights between 25 and 90 km, leading to a systematic subsidence of the upper atmospheric layers.

Quasi-biennial response of the upper atmospheric temperature on the same variations of the solar activity

On the basis of the data of the emission and radiophysical measurements some regularities of quasi-biennial oscillation (QBO) of the atmospheric temperature at heights of the mesopause and lower thermosphere are investigated. It is shown, that they are closely connected with quasi-biennial variations of solar activity and form within the limits of a cycle of solar activity the fading wave train of fluctuations. Such behaviour of the wave train can be good described by the Airy function. The wave train arises during an ending of previous cycle of solar activity. Within the maximum of solar activity the period of fluctuations is ∼38 months and linearly ( r = m 0.98) decreases up to ∼21 months to the end of a 11-year cycle.

Analysis of ice conditions in arctic regions according to data of radiophysical measurements by the “Okean-01” satellite

Analysis of ice conditions in arctic regions according to data of radiophysical measurements by the “Okean-01” satellite