Attenuation Of Radio Waves Research Articles

Centimeter and millimeter-wave radio signals attenuation in explosions

The mechanisms of centimetre and millimetre radio wave attenuation in the explosion area of chemical explosives are analyzed. It is shown that the dominant factor is the attenuation caused by absorption in finely dispersed solid explosion products. The results of experimental measurement of the attenuation factor, the area dimensions important for attenuation and the duration of its existence for wavelengths of 0.4, 0.8, 3 cm are presented. A comparison of experimental data with results of derivations is performed.

Attenuation and scintillation of radio waves in the Earth's atmosphere from radio occultation experiments on satellite‐to‐satellite links

A theoretical analysis of refractive loss of radio waves by the Earth's atmosphere in radio occultation measurements along the satellite‐to‐satellite line for various altitude profiles of the refractive index is given. Experimental results for refractive loss on the orbital spacecraft ‐ geostationary satellite link are presented. Theoretical calculations are compared with experimental data, and a conclusion is drawn that the signal amplitude during radio occultation is strongly dependent on the layered structure of the refractive index profile. Amplitude scintillations of centimeter (λ1 = 2 cm ) and decimeter (λ2 = 32 cm ) radio waves used in radio occultation experiments are described. Dependences of the rms value of the amplitude scintillations versus the minimum altitude of the ray line for the two above wavelength bands are presented. The frequency spectra of the log‐amplitude scintillations are analyzed together with the dependence of the rms amplitude on the wavelength. Experimental data are compared to the theory of scintillations in a turbulent atmosphere, and the altitude model of the structure constant of refractivity fluctuations is determined.

Computation of attenuation, phase rotation, and cross-polarization of radio waves due to rainfall in tropical regions

Computation of attenuation, phase rotation, and cross-polarization of radio waves due to rain in tropical regions using finite element method is the subject of this work. Computations are made of the forward-scattering amplitudes of oblate spheroidal raindrops at 20 and 30 GHz, assuming plane waves at normal incidence to the raindrop axis. The forward-scattering amplitudes are employed to obtain the required attenuation, phase rotation, and cross-polarization using the rainfall rate data for Nigeria, a tropical African country. The results obtained in this work compare with those existing in the open literature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Reduction of wave propagation loss by mesh in rectangular tunnels

The reduction of radio wave attenuation in rectangular tunnels is discussed. The attenuation of the dominant mode due to its field penetration into a lossy dielectric wall is reduced by means of the attachment of wire netting (mesh). First, a reflection coefficient from a mesh screen over a lossy surface is analytically evaluated. Then, based on a geometrical optical approach to the propagation model in tunnels, the attenuation of the dominant mode in a rectangular tunnel is derived using the reflection coefficient. The calculated attenuation constants are in good agreement with experimental ones obtained in a laboratory. Finally, the efficiency of attenuation reduction rate by the mesh shielding method is summarized as a function of spatial ratio of the mesh wire interval divided by the wavelength. It is shown that the efficiency of reduction rate by mesh is significant.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Attenuation and phase variation of millimeter and centimeter radio waves in a medium consisting of dry and wet dust particles

The attenuating and refracting properties of wet dust particles with sand and loam nuclei at wavelengths of about 0.1–10 cm are considered. Quantitative characteristics of radio-wave attenuation obtained for various models of homogeneous particles with effective permittivity are compared with an exact solution of the electrodynamic problem for two-layer particles (“sphere in envelope”). Radio-wave phase variations caused by the presence of dust formations in the medium are determined.

Constant Q attenuation of subsurface radar pulses

Q is a measure of the energy stored to the energy dissipated in a propagating wave and can be estimated from the ratio of attenuation and frequency. For seismic waves, Q has been found to be essentially independent of frequency. As a result, attenuation is an approximately linear function of frequency and the impulse response function of the earth. Hence, the distortion of a seismic pulse as it propagates can be described by a single parameter. Laboratory measurements show that the attenuation of radio waves in some geological materials can also be approximated by a linear function of frequency over the bandwidths of typical subsurface radar pulses. We define a new parameter Q* to describe the slope of this linear region. The impulse response of the transfer function for a given value of Q* differs from that of the same value of Q only in total amplitude. Thus the change of shape of a radar pulse as it travels through these materials can also be described by a single parameter. The constant Q* model successfully describes the distortion of radar pulses propagated through a laboratory water tank and through weathered granite in a borehole field study.

Rain Attenuation on Earth Space Path Over Shillong

The results on attenuation of radiowaves due to rain in the frequency range between 10 GHz and 400 GHz over earth space path for satellite communication over a tropical station, Shillong, is presented. Such results are derived by using the rain rate data obtained by a rapid response rain gauge and theoretical model for estimation of attenuation due to rain. The estimated results are compared with the results provided in CCIR texts. It is seen that the results on attenuation due to rain over tropical stations are underestimated by CCIR. The results provided in this paper may be used for estimating performance of satellite communication over north east region of India.

On the simplified expression of realistic raindrop shapes

AbstractThe Pruppacher‐and‐Pitter (PP) raindrop model has been well accepted as a realistically distorted raindrop model. To employ this model for the investigation of radio wave attenuation by rain requires tedious numerical calculations. In this Letter a simple mathematical formula is used to simplify and improve the expression of the nonaxisymmetric distorted raindrop shapes, enabling the scattered field by rain to be derived analytically. The coefficients in the formula are determined for different raindrop sizes by translating the polar coordinates vertically and fitting the shapes of the Pruppacher‐and‐Pitter‐form raindrops to the shapes discussed in this Letter. Using the least‐squares method, a general expression for the coefficients in terms of the raindrop sizes is obtained. A comparison of the raindrop shapes obtained from the Pruppacher and Fitter expression and the expression in this Letter demonstrates the validity of the simplified formula for realistically distorted raindrops. © 1994 John Wiley &amp; Sons, Inc.

Measurements and predictions of attenuation and scatter of microwave signals by trees

A set of propagation measurements was conducted at a uniformly planted apple orchard to determine the attenuation of radio waves at 11.2 GHz with increasing foliage depth in the signal path. Measurements were also made to examine the level of scattered signals emerging from such media into free space (backscattering) and its dependence on the angular direction of the receiving antenna. Measurements were conducted over the same path in April where the trees were without leaves and in July where the trees were in full leaf. In support of the experimental study, a theoretical model based on the theory of radiative energy transfer for attenuation and scatter predictions was used to assist in interpreting the experimental results. The model considers a plane wave incident from an air halfspace upon the plane interface with a vegetation halfspace. The vegetation medium is treated as a statistically homogeneous random medium of discrete, lossy scatterers. A comparison of experimental results and theoretical predictions is also presented.

Correlation of millimeter-band radio-wave attenuation in cloud and rain parts of cloud-rain system

The experimentally detected difference by a factor of two or more of the autocorrelation times of millimeter-wave attenuation in the rain and cloud parts of a cloud-rain system is examined. In cases of moderate to heavy rain, the measured autocorrelation time of millimeter-wave attenuation in the cloud part of the system is greater by a factor of two than that in the rain for a given degree of cloudiness. In the case of drizzle, the measured relationship is inverted: the attenuation autocorrelation time in the rain part exceeds that in the cloud part by a factor of two. Specific realizations are used; the problem of estimation of the average correlation-time relationships, which is required for prolonged measurement periods, is not posed; nevertheless, the need for its formulation follows from the results considered here. The physical meaning of the results is that the horizontal spatial heterogeneities of moderate to heavy rain are smaller than those of drizzle and greater than those of the clouds from which the given rain falls.

Rain Rate Measurements with 10 Seconds Integration Time for Microwave Attenuation Studies

The rain rate distributions deduced from rapid response rain gauge measurements over different locations in India are presented in this paper from the point of view microwave attenuation by rain. Based on the simultaneous observations of rain fall rate measured by rain gauges having integration times 10 seconds and 15 minutes, a power law has been obtained. The extension of rain cells deduced from radiowave attenuation data is found to be dependent on rain rate.

On the reduction of wave propagation loss in tunnels

The reduction of radio wave attenuation in two-dimensional tunnels is discussed. The attenuation of the dominant mode due to its field penetration into the lossy dielectric side wall is reduced by means of the attachment of periodically aligned metallic strips on the wall surface. The electric field distributions in tunnels with and without strips are illustrated to show the effect on the attenuation characteristics. The efficiency of attenuation reduction rate by the metallic-wall stripping method is summarized. The calculation results based on the boundary element analysis are verified by a laboratory experiment.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radio wave propagation through rain forests of India

A radio wave attenuation measurement survey program was undertaken for the tropical rain forests of India. Measurements were taken at frequencies from 50 to 800 MHz, for antenna heights from 1.5 to 16.5 m above the ground with both horizontally and vertically polarized emissions, and at various separation distances varying from 40 to 4000 m. There were 96 combinations of system parameters for each selected distance between transmitting and receiving locations. In addition to the copolar measurements, cross-polar measurements were carried out to study cross-polar phenomenon in the presence of vegetation. The results of the studies are discussed, covering scatter of the data, lack of homogeneity of the foliage, variation in foliage proximity of the antenna, scattering of radio waves, effect of antenna beamwidth, effect of changes in wind velocity, frequency and polarization dependence of the basic transmission loss, seasonal variation of the loss, effect of climate and type of vegetation, foliage loss, specific attenuation, and effect of increased antenna height in the forest. An empirical model derived from these measurements is proposed. >

Attenuation and reflection of radio waves by a melting layer of precipitation

Attenuation and reflection of a melting layer are calculated using a meteorological model. The model employs a new scheme for the calculation of the dielectric properties of melting ice particles with densities ranging from those of loose snow to hail, and a new scheme for calculating the melting rate is employed. The input parameters are derived from high resolution Doppler radar data and provide a data set for statistical analysis. Statistical relations were derived for attenuation in the melting layer based on measurements made with a surface rain gauge, a radar (with and without a polarisation facility), and a lower frequency satellite link. It was found that the specific attenuation of melting snow surpasses the value of rain because of the larger size and particle number density during melting, the attenuation within the melting layer increasing with its reflection. In stratiform precipitation, the attenuation in the melting layer is found to increase only slightly with frequency. The reflection in the melting layer decreases with the frequency of the radio waves in such a way that a bright band is only observed for frequencies below 20 GHz.

High‐Intensity Rainfall Rate Determination from Tipping‐Bucket Rain Gauge Data

AbstractHigh rainfall rates have a major impact on agriculture through runoff, erosion, and surface crusting and on other industries through sedimentation, failure of dams, and attenuation of radio waves. Traditional techniques used to measure and record rainfall have produced event totals or hourly rates. These are unsuitable for studying short‐term impacts in brief storms (e.g., 27 mm in 30 min). The objective of this work was to develop an analytical procedure to provide millimeter per minute resolution in rainfall rate from short‐term, tipping‐bucket, rain gauge data. Counts of tips in 1‐min intervals were assembled into an array of accumulated rainfall over time during an event. A cubic spline was fitted to the accumulated rainfall curve and then differentiated to yield the rate curve. Four synthetic rainfall patterns were used to test the technique by matching original and reconstructed curves. Regression of reconstructed rates on input rates resulted in 9 ranging from 0.989 to 0.996. When applied to field data from 8 events (total: 209.5 mm) in July 1984 and 6 events (total: 139 mm) in July 1985, the technique described rainfall rate as a smooth, continuous function of time. This characteristic improves the suitability of the data for input to models of infiltration and runoff that adapt time steps to overcome numerical instability under rapidly changing conditions.

Attenuation in melting layer of precipitation

A model of the melting layer is employed on radar measurements to simulate the attenuation of radio waves at 12, 20 and 30 GHz. The attenuation in the melting layer is simulated to be slightly larger than that of rain with the same path length and precipitation intensity. The result appears to depend on the maximum reflectivity in the melting layer.

Peculiarities of the development and saturation of artificial ionospheric turbulence during a high-power disturbing transmission

The peculiarities of the wide-band anomalous attenuation of radio waves reflected in a region of the ionosphere disturbed by a high-power pumping wave are investigated experimentally. It is shown that saturation of the anomalous attenuation sets with an increase in the radiation power: its intensity and time of development are stabilized. This indicates the saturation of the magnitude and spectrum of small-scale artificial inhomogeneities responsible for the effect of anomalous attenuation. The weakening of this effect in the process of development of large-scale artificial inhomogeneities is described. The results of an investigation of the initial stage of self-action of a high-power radio wave under the conditions of cyclic operation of the high-power transmitter are given.

The winter anomaly as seen in the propagation of low frequency 40 kHz radio waves

An analysis of propagation data for LF 40 kHz radio waves shows that the field strength of the sky wave is enhanced during day-time on winter anomaly days (WAD), in striking contrast to the severe attenuation of HF radio waves. This peculiar enhancement of the field strength may be ascribed to an increase in the reflection coefficient. The analysis also demonstrates that the reflection height is lower on WAD, which seems to be associated with enhancements of ionization in the D-region. Moreover, it was found that WAD are characterized by an earlier occurrence in the morning and a delayed occurrence in the evening of pronounced interference maxima and minima, respectively.

Large-scale Cherenkov detectors in ocean, atmosphere and ice

Theoretical and experimental problems related to deep underwater muon and neutrino detection by Cherenkov optical radiation from muons and cascades from muons and neutrinos in ≳ 10 7 m 3 setups (DUMAND project) are considered. The possibilities for searching for high-energy neutrinos, magnetic monopoles and supersymmetric particles in underwater experiments are pointed out. The prospects for creating radio muon and neutrino detector “hearing through” a volume of 10 9–10 11 m 3 in ice massifs with a small decimetric radiowave attenuation are discussed. Ground-base detection of Cherenkov radioemission by extensive air shower (EAS) in the energy range ≳ 10 19–10 20 eV and detection of cascades produced by neutrinos (muons) underground near the Earth's surface by radio-emission entering the atmosphere are considered. For underwater registration of transition (Cherenkov) radioemission of electron-photon or hadron cascades from muons and neutrinos, a system of thin dielectric waveguides can be used. Estimations show that Cherenkov radio detectors in ice can register fluxes of cosmic electron antineutrinos with energies close to the resonance energy E res ≈ 6 × 10 15 eV (reaction ν e + e − → W − → hadrons ), while radio detectors in ice and atmosphere can register fluxes of neutrinos with E ν ∼ 10 18–10 19 eV.

MEASUREMENT OF THE DIELECTRIC CONSTANT OF SLURRIES IN PIPES†

The dielectric constant and the ionic conductivity are measured for a slurry flowing in a conducting pipe. These properties are determined from a measurement of the wavelength, frequency and attenuation of radio waves propagating inside the pipe. A mixing model is used to infer the solids fraction of the slurry.