bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric delay fluctuations with scale sizes greater than one kilometer, observed with a radio interferometer array
Authors: Hamaker J. P.
Published: February 2008

The Westerbork radio telescope samples the wavefront from a radio source at 10 equidistant points over a 1300 m baseline. Observing frequencies are 0.6, 1.4, and 5.0 GHz. When observing a point source, the instrument senses the distortion of the wavefront resulting from atmospheric inhomogeneities. It is found that irregularities with sizes larger than the array predominate. In many cases they are seen to move over the array at speeds characteristic of tropospheric winds. Their effect can be described by a parabolic phase variation with position, the coefficients of which fluctuate with time. A number of examples illustrate the widely varying character the time dependences may exhibit. Analysis of a large number of observations shows diurnal and seasonal variations in the intensity of the fluctuations similar to those found by other workers and generally interpreted as indicating a tropospheric origin. The fact that the 1.4 GHz fluctuations are about twice as strong as those at 5.0 GHz is in disagreement with such an interpretation. Analysis of more observational material will be needed to resolve this matter.
Some perspectives on research into the biological response to non‐ionizing electromagnetic radiation
Authors: Sharp Joseph C.
Published: February 2008

Research on biological effects of RF radiation has undergone a turbulent series of swings in the United States during the last three decades. A peak of activity during the Tri‐Service era of the late 1950s and early 1960s was followed by a nadir—in 1965, not a single federal agency was supporting research in the area. The resurgence of research during the past decade—13 federal agencies or departments are now annually supporting a multi‐million dollar effort—is examined in the light of two related projects involving NASA: the proposed Space Power Station (SPS) and the Search for Extraterrestrial Intelligence (SETI). Interwoven in the complex of technological, economic, and political considerations that affect both projects is the eventuation of a new pragmatism—a moral retrenchment—that the author sees as a potential decline in the national spirit of outreach and enterprise. In the entirely justifiable search for bread and energy, the US may also be pursuing a course that starves and chills its national soul.
Approximate expressions for horizontal electric dipole (HED) quasi‐static range propagation within a conducting slab
Authors: Bannister Peter R. , Dube Rene L.
Published: February 2008

Approximate expressions for the ac quasi‐static fields produced by a horizontal electric dipole (HED) antenna located within a conducting slab have been derived by employing finitely conducting earth image theory techniques. Asymptotic results have also been obtained by applying the quasi‐near approximation to the basic Sommerfeld integrals. The resulting approximations agree with previously derived numerical integration results. The resulting expressions are particularly applicable to short‐range electromagnetic propagation in a shallow sea.
Low‐frequency radiation from an electric dipole in an isotropic plasma
Authors: Singh Nagendra
Published: February 2008

Low‐frequency radiation characteristics of an electric dipole antenna in an isotropic plasma with warm electrons and cold ions are studied. The electron distribution function is approximated by the multiple water‐bag model. The current distribution on the antenna is calculated by solving a boundary‐value problem. It is found that at low frequencies (ω ≲ ωpi, ωpi being the ion‐plasma frequency), the propagation constant for the current wave on an infinitely long wire is approximately (ω/ωpe)2λd−1 where ωpe is the plasma frequency and λd is the Debye length. At very low frequency (ω ≪ ωpi), the dipole resistance R varies as (l/λd)2 × (ω/ωpe)4 × (M/m)5/2, where l is the half length of the dipole and M and m are respectively the ion and electron masses. When ωpi. < ω ≪ ωp, the resistance is the same as previously reported in the literature; R ∝ (l/λd)−l. At the frequency ω = ωpi, the dipole impedance has a resonance; the dipole is inductive for ω < ωpi and it is capacitive for ωpi < ω ≪ ωpe.
ULF/ELF electromagnetic fields generated above a sea of finite depth by a submerged vertically‐directed harmonic magnetic dipole
Authors: Fraser‐Smith A. C. , Bubenik D. M.
Published: February 2008

A numerical integration technique is used to compute the amplitudes of the quasi‐static electromagnetic fields produced on and above the surface of a sea of finite depth by a submerged vertically‐directed harmonic magnetic dipole. The purpose of these computations is to determine the conditions under which an electrically conducting sea floor can produce significant changes in the fields, as compared with the fields produced on and above an infinitely deep sea, for frequencies in the ULF/lower‐ELF bands (frequencies less than 300 Hz). It is shown that even a comparatively highly conducting sea floor (conductivity σƒ ∼ 0.4 mho/m) can produce substantial changes in the field amplitudes for certain source‐receiver configurations and that alterations of two orders of magnitude or more can occur in the amplitudes on the sea surface for smaller values of σƒ. The changes generally become smaller as the altitude of the receiver is increased, but even at altitudes equal to ten sea water skin depths (10 δ) the field quantities may be doubled by the presence of a sea floor. As might be expected, the sea floor effects are most marked in seas that are electrically shallow, i.e., for seas that are only a few skin depths deep. The largest changes are produced when the VMD is within 1 δ of the sea floor, and there is essentially no sea floor effect when the VMD is more than 3 δ above the floor.
Detection of traveling ionospheric disturbances with auroral zone incoherent scatter radar
Authors: Pinger Wayne H.
Published: February 2008

A technique for the study of traveling ionospheric disturbances has been developed using the incoherent scatter radar at Chatanika, Alaska. Using one wave event, the technique is employed to compute the period of oscillation (36.5 min), southward velocity (208 m sec−1), and power profile. A possible source event for the traveling ionospheric disturbance has been identified as being a filamentary auroral arc moving southward toward Chatanika.
Duct propagation of localized radio‐frequency fields along an inhomogeneous magnetoplasma column
Authors: Ohnuma T. , Gonfalone A.
Published: February 2008

Duct propagation of localized radio‐frequency fields, namely resonance cones, in the higher density plasma region is confirmed experimentally in an inhomogeneous magnetoplasma column. The localized rf‐fields with multi‐reflections at the plasma boundary are confirmed experimentally to construct the Trivelpiece‐Gould mode.
A review of recent observations of equatorial scintillations and their relationship to current theories of F region irregularity generation
Authors: Basu Sunanda , Kelley M. C.
Published: February 2008

Our understanding of transionospheric radio wave propagation problems associated with irregularities in the nighttime equatorial F region has grown enormously in the past few years. This has been achieved by making coordinated phase and amplitude scintillations from a host of geostationary and orbiting satellites and multitechnique irregularity measurements. The variety of supporting measurements include radar backscatter, in situ irregularity observations by rockets and satellites, and airglow and ionosonde observations aboard aircraft. Because of the great volume of work in this field the scope of the present review is limited to a description of these recent coordinated observations and a discussion of the relevant theories of irregularity generation. An attempt is then made to explain some aspects of equatorial scintillations on the basis of these new theoretical developments.
Turbulence and waves in the optically clear planetary boundary layer resolved by dual‐Doppler radars
Authors: Doviak Richard J. , Berger Myron
Published: February 2008

Dual Doppler radars provide a unique method to resolve the spatial structure of planetary boundary layer (PBL) air motions. Both the wave and turbulent fluctuations of air in the convectively unstable PBL are revealed from synthesis of the Doppler velocities of echoes (from the atmosphere's intrinsic scatterers) returned to two spaced (40 km) radars. The smaller turbulent scales follow closely the two‐thirds law‐of‐similarity theory, whereas the observed 4‐km wave is compared with those from theoretical models. Power spectra derived from Fourier space analysis of Doppler‐synthesized wind are compared to those obtained from time‐space conversion of Fourier time analysis applied to wind measurements on a 500‐m tower. It is shown that turbulent eddies move with the mean wind and maintain an identity for nearly 60 min. Larger wind variance is observed in the cross‐wind component than in the along‐wind component. Error variances are in agreement with estimates from theoretical studies. Comparisons of refractive index structure constants Cn2 deduced by radar and aircraft are within 1 dB.
Depolarization of a 50‐MHz radio wave backscattered from the middle atmosphere
Authors: Wakasugi K. , Kato S. , Fukao S.
Published: February 2008

Depolarization properties from the middle atmosphere, which refer to the change in polarization of radio waves, are investigated by using the high‐powered 50‐MHz radar at Jicamarca (12.0°S, 76.9°W). The echoes of the pulses transmitted alternately in right and left circular polarizations are received simultaneously by two receivers of each polarization. Small depolarization is generally observed at the altitude of 70–80 km in the mesosphere and in the stratosphere, suggesting the dominance of stable atmospheric structures. On the other hand, echoes with large depolarizations dominate the altitude of 80–90 km. The depolarization of the mesospheric scattering varies with a period of more than 10 min and shows a marked negative correlation with the echo power. In the stratosphere the fluctuation time is quite different from that in the mesosphere. The stratospheric echo power varies by 10–30 dB within a period of several to several tens of seconds and shows a close negative correlation with the depolarization. However, no correlation is observed in the period of the order of 10 min.
Irregular variations in the global distribution of total electron content
Authors: Kane R. P.
Published: February 2008

The day‐to‐day variability of daytime total electron content (TEC) at several locations is compared to that at the mid‐latitude station Hamilton for quiet as well as disturbed days in 1969. It is noticed that all these changes are seldom parallel. Sometimes, large north‐south gradients are noticed, while at other times, TEC seems to pile up on either side (latitudinally) of Hamilton. On some occasions, TEC at the southern hemisphere mid‐latitude is smaller than that at Hamilton for several consecutive days. It is concluded that TEC changes, at different latitudes, are neither parallel nor antiparallel in any consistent way, and large‐scale random movements and/or long‐lasting TEC changes, probably due to height variations, are indicated. If these are due to neutral winds, large‐scale vagaries of neutral winds during quiet as well as disturbed periods (but more so during the latter) are indicated.
A new interpretation of the VLF impedance measurements of island slot antennas
Authors: Barr R.
Published: February 2008

It was first suggested by Morgan in 1960 that an island might serve as a naturally resonant VLF slot antenna. However, theoretical studies by Galejs and Staras suggest that the principal current path would not be, as hoped, the ocean looping around the ends of the island. Rather the current would be confined to a region of the order of 1 skin depth radius centered on the conductor coupling the VLF power to the island. This is in conflict with the recent observations of Morgan, who claims to have observed resonances in the impedance of Deception Island. It is suggested here that these resonances are in fact resonances of the transmission lines used to connect power to the island. A similar explanation is also offered for the peninsula resonances observed by Gould. With this interpretation the experimental data on island antennas is fully in agreement with the current theoretical predictions of Galejs and Staras.
Comment [on ‘A new interpretation of the VLF impedance measurements of island slot antennas’ by R. Barr]
Authors: Morgan M. G.
Published: February 2008

The contention by Wait (1979) and Barr (1980) that the resonance at 9.5 kHz observed at the input to the Deception Island feed line (Morgan, 1979) was due merely to reduced phase velocity on the feed line is disputed. Greatly reduced phase velocity occurs only when a line is buried or laid on smooth earth, but the line at Deception Island was laid over very rough and steep terrain, and a resonance at 60 kHz demonstrated that the phase velocity on the line was essentially that of free space.
Theories for radio ground wave transmission over a multisection path
Authors: Wait James R.
Published: February 2008

Two analytical methods for treating electromagnetic wave transmission over a multisection curved earth are compared. In the first method, the integral equation is reduced such as to yield sums of residue terms that turn out to be identical in form to the result obtained by a mode‐matching procedure. The approximations employed are similar only to the extent that waves reflected from the separation boundaries are neglected.
Computations of the transmission and reflection scattering coefficients in an irregular spheroidal model of the earth‐ionosphere waveguide
Authors: Bahar E.
Published: February 2008

By using a full‐wave approach, the electromagnetic fields are computed along the propagation path in an irregular spheroidal model of the earth‐ionosphere waveguide. The transmission and reflection scattering coefficients that characterized mode coupling in the perturbed region are shown to satisfy reciprocity. A method is also developed to solve accurately the modal equation in the perturbed waveguide. The advantages of exciting the earth‐detached mode to minimize the effects of mode interference are also discussed.
Electron loss coefficients at 80 km from a simplified positive ion model
Authors: Prasad B. S. N. , Mohanty S.
Published: February 2008

Experimental electron densities for a mid‐latitude station and a simplified positive ion model consisting of O2+, NO+ and their respective cluster ions are used in analyzing the normal day ion production and loss processes at 80 km for solar zenith angles 45° to 75°. Effective recombination coefficient and positive ion relative composition are calculated and compared with the experimental results. For a satisfactory agreement, the NO density is taken as 1.6 X 106 cm−3, which is about an order of magnitude less than the generally accepted value from rocket studies. It is also shown here that q ∝ [e] is not valid at 80 km.
On the temporal coherence loss of strongly scintillating signals
Authors: Rino C. L. , Owen J.
Published: February 2008

In this paper, we have reprocessed a set of previously published intensity coherence time data to correct for wave front curvature. The spherical wave correction decreases the coherence time for a simple plane wave. Under conditions of strong scatter, theory predicts a simple power law relationship between the intensity coherence time and the phase turbulent strength. In the theory the power law index is simply related to the phase spectral index, which is usually assumed to be constant. Previously, this theory had been applied to test the consistency of the results. Evidence has recently come to light, however, that both the phase and in situ spectral indices vary systematically with changing perturbation strength. By accommodating this variation as well as the wave front curvature correction, we were able to greatly improve the theoretical fit to the intensity coherence time data.
Echo duration and diffusion coefficient measurements using meteor wind radar
Authors: Devara P. C. S. , Iqhbal Ahmed Mohammed , Rao M. Srirama
Published: February 2008

The Meteor Wind Radar at Waltair (17°43′N, 83°18′E), India, was operated during June–July 1979 to study the echo durations and diffusion coefficients of underdense meteor trails. These measurements have also been used to evaluate the elevation angles of the specular reflection points. The most probable echo duration and elevation angle for the present system are found to be 60 ms and 23°, respectively. The values of measured diffusion coefficients (log10 D) are found to vary between 4.6 and 5.5 cm2 s−1. The diurnal variation of the diffusion coefficient showed a broad maximum during morning hours and a broad minimum during evening hours. The results are compared with the measurements at other stations.
Use of a key point in the F layer for N(h) analysis of ionograms
Authors: Gulyaeva T. L.
Published: February 2008

This paper describes a single‐component method of correcting for underlying and valley ionization in N(h) analysis of ionograms. The h′min(ƒL) point is suggested for use in calculating the F layer real heights when only one magnetoionic component is available in an ionogram. Formulae are presented which relate the real height at the frequency ƒL to the corresponding virtual height via the peak parameters of the E layer.
Ray theory of diffraction by a half‐sheet parallel to a flat earth
Authors: Sunahara Yonehiko , Sekiguchi Toshio
Published: February 2008

In this paper, the diffraction by a half‐sheet parallel to a flat earth for H‐ and E‐polarized plane waves are discussed. The half‐sheet is assumed to be perfectly conducting, and the flat earth is an imperfectly conducting dielectric with the complex refractive index n. This problem is solved by using the angular spectrum proposed by Clemmow, which may be also solved by using the Wiener‐Hopf technique. When kd is large, the diffraction fields can be approximated by the geometrical rays even for small r except in the neighborhood of θ = π/2 and 3π/2. Here, r and θ are polar coordinates of the observation point, with the origin as the edge, and d is the distance between the half‐sheet and the flat earth. The far field can be approximated by the simple geometrical rays in all regions (0 < θ < π). The interaction between the edge and the flat earth can be evaluated even for small kd. Exact values by the numerical integration show that these approximate solutions can give very good accuracy even for small r except in the neighborhood of θ = π/2 and 3π/2. These results will give a fundamental concept to the understanding of the diffraction by a finite conducting plane over a flat earth.
Fiber optics research and development in the 1980's
Authors: Kao C.
Published: February 2008

Research and development trends in the 1980's are established from the projected market demands of optical fiber systems and the technology progress needed to enable these system products to be realized.
Rules of refractive index and a potential well model of the optical waveguides
Authors: Tien P. K.
Published: February 2008

This is the text of an invited paper presented at the North American Radio Science Meeting of the International Union of Radio Science held in the University of Leval in Quebec, June 2–6, 1980. In integrated optics, it has been possible to explain various complex wave phenomena by two simple rules of refractive index which, however, have never been rigorously proved. The purpose of this paper is to examine these rules critically and to define them more precisely based on a Potential well model of the optical waveguides, which we will discuss in detail.
Narrow stripe lasers for optical fiber systems
Authors: Lindström C. , Tihanyi P.
Published: February 2008

A novel development of the proton isolated narrow stripe GaAs/GaAlAs DH‐structure laser is presented. These lasers show excellent linearity, high power output and good coupling possibilities for optical fibers. They have a predicted lifetime above 106 hours at room temperature. The fabrication and characteristics of these lasers are presented.
Asymptotic analysis of planar and cylindrical inhomogeneous waveguides
Authors: Arnold J. M.
Published: February 2008

The problem of determining the eigenvalues of an inhomogeneous waveguide, subject to boundary conditions at an interface with an exterior homogeneous medium (cladding) is considered. A recently developed asymptotic method is summarised. Previous work dealt with planar waveguides; here we incorporate the extensions necessary to accommodate cylindrical waveguides, as encountered in optical fibres. The method uses a nonlinear transformation between variables to reduce a given differential equation to canonical form; this transformation has more tractable asymptotic properties than the original differential equation.
Modal interference of laser light emitted from an optical fiber
Authors: Imai Masaaki
Published: February 2008

Average intensity and average contrast distributions of the far‐field interference patterns of laser light emitted from end faces of optical fibers are theoretically studied with the consideration that mode conversion takes place in the optical waveguide. The optical fiber considered here is a multimode graded‐index fiber having random fluctuations of the refractive index in the core as well as in the cladding. The index fluctuations are assumed to obey a normal probability distribution so that the fourth moment of the radiation field can be obtained in terms of the second moment. Using the properties for the index fluctuations, average contrast, defined as a normalized deviation of the speckle intensity, is calculated within the second‐order approximation of perturbation. The results show that the average contrast decays with lateral distance in the far‐field plane, and its decreasing tendency is rather sharp in the off axis when the fluctuation scale of the refractive index becomes small.
Radiation and reception characteristics of an oblate spheroidal antenna for electron plasma waves 2. Experiment
Authors: Ohnuki Shigeo , Adachi Saburo , Ohnuma Toshiro
Published: February 2008

The radiation and reception characteristics of circular plate (disk) and mesh antennas for an electron plasma wave are investigated experimentally to verify the theoretical prediction given in the preceding paper. As a result, it is shown that the measured directional radiation and reception patterns, when the circular plate antenna is appropriately biased by a dc potential, agree fairly well with the theoretically predicted ones. It is also indicated that the measured radiation patterns and the radiated wave potential of the circular mesh agree with the theoretically predicted ones better than those for the circular plate.
Cross polarization during clear‐air conditions on terrestrial links: A review
Authors: Olsen R. L.
Published: February 2008

This paper reviews experimental and theoretical research on cross polarization that occurs during clear‐air conditions on terrestrial microwave links. After consideration of the various clear‐air mechanisms that have been suggested, the conclusion is drawn that multipath mechanisms interacting with the cross‐polarized patterns of the antennas are the most important. Theoretical models that explain these mechanisms and semi‐empirical models that characterize the cross‐polarized signal statistics are then discussed. Particular attention is given to the semi‐empirical models since they can be used most readily for statistical predictions in design applications. Some new insight into the similarities and differences between models developed in France, Japan, and the United States is provided. Finally, application of the semi‐empirical models in the design of digital systems is briefly considered, and the relative importance of cross polarization during clear‐air and precipitation conditions is discussed.
Prediction of attenuation due to rainfall on terrestrial links
Authors: Fedi Francesco
Published: February 2008

In this review, attention is confined to rain attenuation and to its influence on the availability of terrestrial radiocommunication systems operating at frequencies above 10 GHz. The availability objectives recently established by the Comité Consultatif International des Radiocommunications for digital systems, the information necessary, and a calculation procedure applicable for system design are examined. Various methods for predicting attenuation due to rain are compared and reviewed. Present trends for the use of frequencies above 10 GHz in terrestrial systems are illustrated, and areas in which further study is needed are indicated.
Sea state frequency features observed by ground wave HF Doppler radar
Authors: Forget P. , Broche P. , De Maistre J. C. , Fontanel A.
Published: February 2008

This paper investigates the relationship between the frequency features of the directional spectrum of ocean waves (cutoff frequency and peak frequency of wind waves, frequency of quasi‐monochromatic swell) and the properties of the spectrum of the sea echo obtained by HF Doppler radar. A theoretical analysis is performed to check the validity of a simple result that states that at upper HF, a long‐wave spectral feature at frequency F0 affects the radar echo at frequencies ±ƒB ± F0 on either side of the Bragg lines at ±ƒB corresponding to resonant backscattering of radio waves with a given wavelength by half‐wavelength ocean waves. An experiment using both radar and standard in situ measurements for several weeks at different times of the year shows that this relationship can be used to formulate a method for estimating the frequency features of the sea with suitable accuracy.
Nonreciprocal phenomena of polarization conversion and anomalous beam shift in multilayered structures containing a film waveguide sandwiched by electrooptic and magnetooptic media
Authors: Kitajima Hiroe , Hano Kazunori , Suematsu Yasuharu
Published: February 2008

In this paper, nonreciprocal polarization conversion and anomalous beam shift phenomena of the output waves have been studied with respect to the direction of the input waves which are Gaussian beams impinging obliquely against the boundary in the dielectric multilayered structures containing a film waveguide sandwiched by electrooptic and magnetooptic media. For example, the efficient conversion characteristics for the input beams with various spot sizes have been presented, with respect to the polarization conversion. In the case of anomalous beam shift for the forward input direction, the magnitude of the shift for an incidence of a TM wave is nearly twice that of the reverse input direction. However, when the incidence in the structure is a TE wave, the magnitude of the beam shift is almost zero.
Conversion of radiation modes to trapped modes due to lateral inhomogeneity of a simple elevated layer
Authors: Pappert R. A.
Published: February 2008

It often happens that tropospheric ducts produced by elevated layers have a modal system in the microwave range consisting of many virtually lossless modes. These weakly attenuated modes have their energy localized about the layer and are insignificantly excited by sources far removed from the layer where the modal height gains are characteristically evanescent. Despite such an unfavorable geometry for direct excitation of these essentially loss‐free modes, they may be indirectly excited within the line of sight region by mode conversion processes associated with lateral inhomogeneity of the layer. In this paper an approximate theory is developed for the mode conversion produced within the line of sight region by large‐scale lateral inhomogeneity of an idealized, vertically homogeneous layer. The theory is applied to a 3‐GHz case study with the following results: (1) lateral inhomogeneity associated with layers of low elevation is more effective for converting to lossless modes than is lateral inhomogeneity associated with layers of high elevation; and (2) lateral inhomogeneity near the horizon is more effective than lateral inhomogeneity near the transmitter for converting to lossless modes.
Analysis of mode conversion phenomena in a non‐uniform parallel plate wave guide (Summary)
Authors: Henrot Denis M. , Wait James R.
Published: February 2008

A coupled mode analysis of a parallel plate wave guide with non‐uniform impedance boundaries is presented. Closed form solutions for the first order estimates of the modal amplitude coefficients are obtained assuming small variations. An analytical comparison with an exact mode‐matching solution in the case of a stepwise change of the lower wall impedance is given and verified numerically. As an extension of the method, a wave guide with perfectly conducting but rough walls is analyzed. The possibility of selective mode coupling is pointed out.

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Validity of a selective summation technique in analysis of wave propagation through random media
Authors: Tateiba Mitsuo
Published: February 2008

The so‐called moment equation for a successively forward scattered wave was derived under a definite condition. The condition shows that the applicability of the equation is much more extensive. When a selective summation technique is applied to the derivation of the moment equation, another condition besides the above is necessary for the existence of the equation. The extra condition is due to the selective summation of scattered waves and shows the validity of the technique for the nth moment of forward scattered waves. For example, if the waves propagate along the z axis, a necessary condition for the technique to be valid for the first, second, and fourth moments is k2l2B(0, 0) ≪ 1 where k is the wave number in free space and l and B(r, z) are the correlation length and the correlation function of fluctuation of the medium, respectively. For all the higher moments the technique is applicable only to the case of B(r, z) = Br,(r)δ(z) where δ(z) is the Dirac delta function.
Resonant energy absorption in the ion sheath of a plate antenna
Authors: Weenink M. P. H.
Published: February 2008

In this paper we consider an antenna consisting of an infinite plane metallic plate divided into two half planes by an infinitely narrow slit across which an alternating electric field of frequency ω is applied. The antenna is immersed in a cold nonmagnetized plasma. Between the homogeneous plasma and the antenna surface an ion sheath is assumed to be present. The fields are calculated for a given density profile of the electrons by a small signal theory. The electromagnetic energy radiated from the slit is determined for frequencies below the plasma frequency. It is shown that the radiated energy is completely absorbed in the sheath. The radiation admittance is calculated as a function of frequency, the sheath thickness, and the plasma density.
Remote sensing of atmospheric waves in O2 and H2O microwave emissions
Authors: El‐Raey M.
Published: February 2008

Atmospheric microwave emissions from oxygen near 58.0, 54.0, and 51.0 GHz and water vapor at 22.235 GHz are monitored simultaneously at a time interval of 10 s. Power spectral analysis of radiometer output indicated frequent occurrence of enhanced emissions at periods between 3 and 13 min. These are attributed to local buoyancy Brunt‐Väisälä oscillations in the earth's atmosphere. Inversion of integrated brightness temperatures makes it possible to remote sense temperature profiles and natural waves simultaneously. It is suggested that spectral analysis of microwave and/or infrared emissions, as monitored by a geostationary satellite‐borne radiometer, may reveal important characteristics and relationships between temperature profiles and natural oscillations in the earth's atmosphere over a wide height range.
Backward and forward scattering of microwaves by ice particles: A review
Authors: Mon J. P.
Published: February 2008

Approximate and exact mathematical techniques for the calculation of the scattering properties of a single ice particle are first reviewed. Then, for dealing with practical applications such as radar meteorology or radio wave transmission along earth‐space links, the problem of the scattering by an assembly of particles is examined. This problem involves the knowledge of the particle size distribution and of the orienting mechanisms which can affect the ice crystals in the clouds. Although the T matrix formalism has been successfully used in a greater range of scattering problems than the other techniques, the Rayleigh approximation may be used with confidence for calculating the cross‐polarization properties of radio waves at frequencies up to at least 25 GHz. Alignment of ice particles is not expected to occur in high‐altitude cirrus clouds while alignment is observed in strong thunderstorms. Thus different models are to be used in order to predict the cross polarization along earth‐space links.
Propagation of centimeter/millimeter waves along a slant path through precipitation
Authors: Fang D. J. , Chen C. H.
Published: February 2008

Meteorological uncertainties severely limit the usefulness of models of existing microwave propagation in the presence of precipitation. Major uncertainties, including raindrop shape, drop size distribution, and the penetrating distance of precipitation are discussed in this paper in terms of their impact on satellite communications systems. On the basis of more than 30 measurements of raindrop sizes under different meteorological conditions, a new set of distributions is proposed for slant‐path transmission in lieu of the conventional Laws and Parsons distribution. Basic propagation parameters, i.e., specific attenuation and specific phase shift, are evaluated, and comparisons with existing models are made. The results provide a yardstick for establishing a dynamic model meaningful for advanced systems.
A theory and model for wave propagation through foliage
Authors: Brown Gary S. , Curry William J.
Published: February 2008

A theory is presented and a model is developed to predict the effects of foliage on a line‐of‐sight propagating field. In view of the sparse concentration of foliage, the Foldy‐Twersky theory for wave propagation through discrete random media is used to obtain the complex propagation constant for the coherent field. On the basis of the measurements of Stutzman et al. (1979), the dominant foliage components are taken to be Rayleigh‐like in their scattering and absorbing characteristics. The effective fractional volume of foliage comprising the Rayleigh components is constructed as a function of frequency using forest stand table data. Trunks and branches are modeled as Rayleigh cylinders; leaves are ignored because of their small total volume. The model fails above the frequency for which the effective fractional volume goes to zero. The model provides reasonably good agreement with propagation measurements and is capable of explaining some of the observed polarization effects.
Surface impedance concepts of electromagnetic wave propagation in layered isotropic and anisotropic media
Authors: Papousek W. , Schnizer B.
Published: February 2008

Integral representations for the electromagnetic field generated by an electric or magnetic dipole line source located within the atmosphere of the two‐layer configuration atmosphere‐ionosphere rendered anisotropic by a uniform static (terrestrial) magnetic field are evaluated by the method of steepest descent to give analytical expressions for the far field along the interface of the two media. These expressions are used to calculate the surface impedance tensor for the lower boundary of the ionosphere. The surface impedance tensor permits one to replace the continuity conditions by approximate boundary conditions along the interface. Results obtained for an arbitrary direction of the static magnetic field (arbitrary geomagnetic latitude) are specialized to polar and equatorial zones. For these cases, dependence of attenuation and phase velocity of the first few modes of the earth‐ionosphere waveguide on ionospheric height and on electric properties of the ground (which enter a scalar surface impedance for the ground plane) is shown. TM modes are much more sensitive to electrical properties of the adjoining media than TE modes. Attenuation is lower for propagation from west to east than in the reverse direction. Icy ground causes severe attenuation of TM but not of TE modes. Various other applications of the surface impedance model are reviewed.
Wave tilt calculations in the layered troposphere above a slightly rough sea
Authors: Chrissoulidis D. P. , Kriezis E. E.
Published: February 2008

The tilt of an EM wave propagating above the sea in a direction parallel to its mean surface is theoretically calculated in an attempt to investigate the possibility to use the wave tilt probing method for the approximate determination of the sea state. A layered tropospheric slab having a typical index profile is considered above the slightly rough sea; the effective surface impedance of the sea is calculated according to a known model for a number of characterisitc wind speeds in the band 10–50 MHz. These models are combined for the calculation of the wave tilt for both horizontally and vertically polarized electromagnetic waves at various altitudes in the troposphere. Results show that the effect of the roughness of the sea surface on the wave tilt in the lower troposphere is not negligible and can also be measured at certain frequencies by using ordinary airborne wave tilt measurement methods.
Excitation of the earth‐ionosphere waveguide by an ELF source in the ionosphere
Authors: Tripathi V. K. , Chang C. L. , Papadopoulos K.
Published: February 2008

It is shown that for polar regions, where the conductivity is predominantly reactive, the wave functions for the transverse electromagnetic mode of the earth‐ionosphere waveguide are Hankel functions of the first kind with real argument; therefore they extend up to large heights over the polar ionosphere. A Green's function for the excitation of the waveguide by extended current or field sources in the ionosphere is obtained for an exponential ionosphere. The potential of ELF waveguide excitation by wireless antennas is discussed.
Measurements of satellite beacon attenuation at 11.7, 19.04, and 28.56 GHz and radiometric site diversity at 13.6 GHz
Authors: Vogel W. J.
Published: February 2008

The results from about 2 years of space and frequency diversity measurements of attenuation, obtained in Austin, Texas, are presented. The data from 11.7, 13.6, 19.04, and 28.56 GHz were analyzed with regard to fade probability, seasonal and diurnal variations, time duration between fades, frequency scaling, and, at 13.6 GHz, site diversity. With reasonably typical weather, fades were found to be most likely to occur during summer afternoons. The diversity gain was about 80% of the attenuation value, and the frequency scaling, based on the statistical results, closely follows a dependence given by (ƒ/ƒ0)2.
Numerical analysis of nonreciprocity for spatial coherence and spot dancing in random media
Authors: Tateiba Mitsuo
Published: February 2008

Nonreciprocity for spatial coherence and spot dancing in an inhomogeneous random medium is numerically analyzed by using a multiple scattering theory which provides that the local correlation length of the medium is much greater than the wavelength in free space. In striking contrast to the variance of spot dancing, the degree of spatial coherence of a spherical wave, written as Cs, largely depends on the medium close to the receiver. Therefore, it easily happens that Cs for the case where spot dancing occurs strongly becomes higher than that for the case where it occurs slightly when the transmitter and the receiver are replaced with each other. The effects of the local strength and the local correlation length of the medium on Cs are also made clear.
Physically motivated approximations in some inverse scattering problems
Authors: Bolomey J. C. , Lesselier D. , Pichot C. , Tabbara W.
Published: February 2008

In this paper we review some approximate methods in inverse scattering problems. The approximations are physically motivated and allow more physical insight than in rigorous approaches. The methods are described along with their advantages and limitations, and when possible, general indications on approximate methods are mentioned.
Theoretical determination of the effects of multiple scattering by hydrometeors in monopulse systems at millimeter wavelengths
Authors: Capsoni Carlo , Mauri Mario , Paraboni Aldo
Published: February 2008

The incoherent radiation incident on a receiving antenna after having been scattered by raindrops can cause some problems in the case of a monopulse system whose directive pattern presents a deep null toward the coherent incoming wave. This null is then filled with incoherent radiation, therefore giving rise to a degradation of the performances of the measuring equipment. In this paper this degradation is theoretically assessed assuming a simplified geometry (a rain cell embedded in stratified rain); the drops are assumed to be of spherical shape, and typical system configurations for the earth station are considered.
Spatial investigations of mode conversion between an electrostatic cyclotron harmonic wave and an electromagnetic ordinary wave
Authors: Ohnuma T. , Watanabe T. , Sanuki H.
Published: February 2008

In an inhomogeneous magnetized plasma, mode conversions of an electrostatic cyclotron harmonic wave into an electromagnetic ordinary wave and vice versa are spatially investigated by a study of the ray trajectories and the wave fronts. Electrostatic cyclotron harmonic waves are found to be spatially trapped between the upper hybrid frequency layers.
Population exposure to VHF and UHF broadcast radiation in the United States
Authors: Tell Richard A. , Mantiply Edwin D.
Published: February 2008

The U.S. Environmental Protection Agency has been collecting broadcast signal field intensity data for over 2 years to estimate population exposure to this form of nonionizing radiation. Measurement data have been obtained at 373 locations distributed throughout 12 large cities and collectively represent approximately 11,000 measurements of VHF and UHF signal field intensities. The VHF and UHF broadcast service is the main source of ambient radio frequency exposure in the United States. A computer algorithm has been developed which uses these measurement data to estimate the broadcast exposure at some 39,000 census enumeration districts within the metropolitan boundaries of these 12 cities. The results of the computations provide information on the fraction of the population that is potentially exposed to various intensities of radio frequency radiation. Special emphasis has been placed on determining the uncertainty inherent to the exposure estimation procedure, and details are provided on these techniques. A median exposure level (half of the population is exposed to greater than the median level) of 0.005‐μ W/cm2 time‐averaged power density has been determined for the population of the 12 cities studied, the cumulative population of which represents 18% of the total United States population. The data also suggest that approximately 1% of the population studied, or about 380,000, is potentially exposed to levels greater than 1 μ W/cm2, the suggested safety guide for the population in the USSR. Alternative techniques of using the measurement data to estimate population exposure are examined, and future extensions of this work are discussed.
A microwave method for estimating absolute value of average lung water
Authors: Iskander M. F. , Durney C. H. , Bragg D. G. , Ovard B. H.
Published: February 2008

A procedure using microwave transmission to estimate the absolute value of lung water content is described. The method involves obtaining a transverse cross‐sectional image of a human subject using a computerized axial tomographic X ray scanner, with the microwave applicators in position. The electromagnetic field problem, including the size and shape of the internal organs, is then solved numerically using the method of moments. Since the mismatch between the microwave applicators and the patient's skin is found to be highly insensitive to the changes in the underlying lung parenchyma, the transmission coefficient can then be directly related to the average amount of total water content in the lung. Results for human and animal cross sections are presented.
Statistical radiometry
Authors: Carter William H.
Published: February 2008

This paper reviews developments in recent research on the connections between classical radiometry and the modern theory of partial coherence. This research addresses some important questions such as, why does the classical theory appear to give correct results for electromagnetic radiation from thermal sources, and how can the theory be modified to apply to radiation from nonthermal sources? The following specific facts are explained. The far field radiation pattern from a localized source distribution generally depends on the coherence properties of the source and not simply on its emittance. Classical radiometry applies to thermal radiation not because this radiation is incoherent but rather because it is partially coherent in a particular manner. Also, some quantities defined in classical radiometry have physical meaning for an electromagnetic field, and some do not.
The dependence of rain attenuation statistics on meteorological parameters
Authors: Torlaschi Enrico , Zawadzki Isztar
Published: February 2008

Radar records were analyzed and divided into categories of the available parcel convective energy. Statistics of rain attenuation at 11.2 and 18.7 GHz were calculated for each category. Good stratification of the probability of rain attenuation as a function of the parcel energy is obtained. It appears, therefore, that the forecast of the thermodynamic mesoscale variables makes the forecast of rain attenuation possible.
Effects of propagation on the rise times and the initial peaks of radiation fields from return strokes
Authors: Cooray Vernon , Lundquist Stig
Published: February 2008

The theoretical solution to the problem of radiation from a pulsed vertical dipole over a flat homogeneous earth is employed to study the changes in rise times and the attenuation of the initial peaks of the radiation fields from lightning constructed according to the most recent experimental data on lightning return stroke radiation fields. Expected changes in rise times and the attenuation of the initial peaks for different values of distances and conductivities are presented. It is shown that for a given initial rise time there is a spread in distant rise times due to the variability of the shapes of the radiation fields. The expected spread in distant rise times for different values of distances and conductivities is calculated. The results show the importance of taking into account the propagation effects in any attempt to estimate return stroke current parameters such as rise time, rate of rise, and peak current from radiation fields which propagated over land. The predictions are compared with the available experimental data, and a good agreement is found between them.