The results of modeling the conditions of propagation of LF-MF radio waves over the impedance structure "thick ice - sea" in the Arctic Ocean are presented. To calculate the electromagnetic field of the two-layer structure “thick ice-sea”, the applicability regions of impedance boundary conditions for a vertically polarized wave depending on the thickness of the ice are determined. Methods of calculating the ground wave field tension on high-latitude impedance paths with an ice thickness of 2-9 meters are considered. The results are necessary for calculating the attenuation function W and the field level E of radio waves.
In the lower atmosphere, the deviation of the trajectory of radio waves occurs due to the variability of the refraction of air with height. The vertical profile of the refractive index substantially depends on the geographical position, altitude and time of year of observation. The refractive properties of the troposphere and tropospheric delays of signals in different seasons of the year are considered at polar points of observation Murmansk, Wiese Island, Norilsk, Tiksi and Yakutsk. Altitude meteorological data is determined by launching radiosondes or selected on the NOAA remote sensing site. Knowing the vertical gradient of the refractive index is the basis for calculating the angles of refraction and the true distance to the object, which can be located above the level of the troposphere. The possibility of using the GPS measurement method to study the refractive effects of the troposphere without taking into account meteorological data is shown.
The field of the ground wave which is created by a vertical electric dipole above an inhomogeneous surface of the Earth is considered. For inhomogeneous radio paths, the calculation of the attenuation function of the ground wave field is proposed to be performed by the method of the Feinberg’s integral equation, which takes into account the underlying medium in the form of a multi-sectional impedance path. This method allows performing calculations in the LF-MF ranges of radio waves over long paths with relatively "poor" conductivity of the medium. In the initial homogeneous section of the radio path, the attenuation function is calculated according to the model of a “flat” Earth surface using Sommerfeld's formulas. The values of the attenuation function of the ground wave field over permafrost radio paths in the North-East of Russia are calculated.
For calculations of the electromagnetic field over the two-layer structure “thick ice-sea”, the areas of applicability of the impedance boundary conditions for a vertically polarized wave in the range of 0.01 ˗ 120 MHz are determined. Seven models of ice cover are considered. The ice thickness varied from 2 to 9 m. Results are needed to calculate the attenuation function W and the field level in the LF-MF-HF range of radio waves.
For calculations of the electromagnetic field of the two-layer "thin ice-sea" structure, the areas of applicability of the impedance boundary conditions are determined depending on the thickness of the ice and the angle of incidence of the vertically polarized wave. Results are needed to calculate the attenuation function W and the radio wave field level. It is shown that for the "thin ice-sea" structure, taking into account the dependence of surface impedance on the angle of incidence is important for over-the-horizon radar systems in the HF range of radio waves. In the VHF range for ice 80 cm thick, frequency bands are identified in which impedance boundary conditions are applicable.
Propagation conditions of radio waves over the “ice-sea” structure with a highly inductive impedance are often more favorable than over a clear sea due to the appearance of a surface electromagnetic wave. Numerical calculation algorithms for various radio wave propagation path models have been developed. The method of making prognostic maps of the surface impedance of the “ice-sea” structure according to the ice situation maps for the Arctic Ocean (AO) in different seasons of the year is considered. A formula is proposed for converting the spatial dependence of the ice thickness into the spatial dependence of the surface impedance at a fixed frequency in VLF-LF-MF ranges. Calculations of surface impedance for various types of sea ice are presented.
KEYWORDS: Solar processes, Interference (communication), Signal attenuation, Radio propagation, Global Positioning System, Antennas, Atmospheric sciences, Electromagnetism, Navigation systems, Receivers
Diurnal variations of radio noise intensity (14.88 kHz) registered in Yakutsk in June 2009-2014 is 10 dB, March - 9 dB, September - 8.7 dB, December - 7.3 dB. Diurnal variations of intensity of radio station VLF signals, radio noise intensity and the number of lightning discharges in Yakutsk are compared. VLF noise variations in summer 5-10 UT defined local thunderstorm activity. The period 11-20 UT for receiving radio noise defined distant thunderstorm cells in Western Siberia, the territory between Hinggan, Buretsky and Stanovoy mountaines. Radio signals from these areas propagate in similar paths like signals Novosibirsk and Khabarovsk navaid stations. The attenuation variations from a solar activity minimum to the maximum are estimated. Taking into account the changes of propagation attenuation of 1.2 dB (signal Khabarovsk) from a minimum to a maximum of solar activity in July, the power of VLF radio noise at a minimum on 7.6 dB greater than at solar activity maximum.
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