bluuebunny/crossref_metadata_2025 huggingface dataset:
Scattering by obstacles in an inhomogeneously filled waveguide
Authors: Batorsky D. V. , Felsen L. B.
Published: February 2008

This paper explores the application of a previously developed ray‐optical theory for scattering by discontinuities in weakly inhomogeneous parallel‐plane waveguides or ducts. Emphasis is placed on peculiarities that distinguish scattering calculations in inhomogeneous mediums from those in homogeneous mediums. Attention is given to the role of edge‐diffraction singularities in the computation of modal reflection and transmission coefficients, to the relation between ray‐optical and Kirchhoff diffraction solutions, to modifications of the ray method in regions of strong variation of refractive index, and to the sensitivity of ray‐optical results to the choice of certain generating functions employed in the theory. Numerical computations for guides with linear profiles, inverse‐square profiles, and related homogeneously filled circular‐waveguide configurations illustrate details of these considerations and permit comparisons with results obtained eslewhere.
Commission 6. Radio waves and transmission of information
Authors: Felsen L. B.
Published: February 2008

In the paper, ‘Active antenna arrays, 1,’ I. B. Bott (UK) described the various forms of phased arrays that could be made and highlighted problems associated with active arrays. Particular reference was made to the active modules, dealing with their construction and with the assembly of such modules to make a satisfactory antenna.

K. Fujimoto (Japan) in the paper, ‘Active antenna arrays, 2,’ discussed the properties of an active antenna with a transistor circuit incorporated, having a variable pattern. He also discussed a multiplicative array, and pointed out the potential advantages of negative‐impedance converters in active arrays.
The insulated dipole antenna in a relatively dense medium
Authors: Wu T. T. , King R. W. P. , Giri D. V.
Published: February 2008

The properties of an insulated dipole antenna are derived when the wavenumber of the surrounding infinite, homogeneous, and isotropic medium is large compared with that of the insulation. It is shown that even when the surrounding medium is a perfect dielectric, the distributions of current and charge along the antenna and its driving‐point admittance are substantially like those of a section of transmission line with a distributed radiation loss appearing as a part of the series impedance per unit length.
Excitation of a homogeneous conductive cylinder of finite length by a prescribed axial current distribution
Authors: Wait James R. , Hill David A.
Published: February 2008

The boundary value problem posed is a truncated cylindrical region excited by a specified distribution of electric current over a concentric cylindrical surface. The end conditions are that the total normal current density is zero. The solution is carried through for excitation by a symmetrically located axial current filament that is adjacent to the cylinder. Numerical results of the resultant magnetic field are given for the quasi‐static situation for a perfectly conducting cylinder. It is indicated that the results depend significantly on the length of the cylindrical target. Even for very long cylinders, there is no quantitative similarity with the corresponding two‐dimensional model of a cylinder of infinite length.
Some problems of the F region
Authors: Rishbeth H.
Published: February 2008

This paper outlines some of the currently outstanding problems of F region theory. It is suggested that a basic understanding of F region storm phenomena now exists, and an outline description of the main processes operating at middle and low latitudes during storms is given.
Simultaneous interferometer phase and water vapor measurements
Authors: Wesseling K. H. , Basart J. P. , Nance J. L.
Published: February 2008

Phase fluctuations on the three‐element, 11‐cm wavelength interferometer at the National Radio Astronomy Observatory (NRAO) were compared with the difference in the atmospheric water vapor content over the respective antennas along a line‐of‐sight path to a celestial radio source. At times the correlation coefficient for phase and precipitable water was as high as 0.8. At other times when the minute‐to‐minute correlation was low, there was still a direct relationship between the rms of the phase fluctuation and the rms of the water vapor fluctuation. This study was conducted as part of an experimental program undertaken by NRAO to predict the severity of the phase fluctuation in the very large array (VLA) telescope proposed for construction.
Model investigations of radio wave propagation in the lower ionosphere to determine electron densities from MF pulse sounding
Authors: Gruschwitz E.‐H.
Published: February 2008

In this paper full‐wave calculations are described to investigate the propagation of MF radio waves in the range from 255 to 950 kHz in the lower ionosphere. The method of investigation makes use of matrix multiplications with the ionosphere divided into homogeneous layers of 100‐m thickness. The model calculations provide conclusions from MF pulse sounding results on electron density and collision frequency profiles in the height interval from 50 to 100 km. The diurnal variation of electron density in the lower ionosphere is presented. Reflections observed from heights of about 75 and 87 km during the day are shown to be produced by steep gradients of electron density.
Control of radiation patterns of ion acoustic waves
Authors: Ohnuma T. , Tamura Y. , Fujita T. , Adachi S.
Published: February 2008

The radiation field patterns of an ion acoustic wave from a circular disk‐shaped antenna is controlled by applying a bias voltage to another mesh. The change of the radiation patterns is explained as a result of the in‐phase reflection of an ion acoustic wave at an electron‐rich sheath.
Refraction effects in turbulent media
Authors: Graf K. A. , Guthart H. , Douglas D. G.
Published: February 2008

Measurements on laminar and turbulent flames indicate that refraction effects can be calculated in a turbulent flame if the refractive index is assumed to depend on the mean electron density. Refraction effects are important when incoherent scattering cross sections of turbulent wakes are calculated at small aspect angles. Incoherent cross sections were measured at aspect angles of 20° and 40°, for backscatter and bistatic scatter. The measured cross sections deviated from a square‐law dependence on electron density in a way that was not well accounted for by a refraction calculation. Both cross‐section data and spectral data agreed better with a “modified” refraction calculation in which some energy was said to scatter from the “shadow zone” predicted by refraction.
Electron acceleration by parametrically excited Langmuir waves
Authors: Fejer J. A. , Graham K. N.
Published: February 2008

Simple physical arguments are used to estimate the downward‐going energetic electron flux due to parametrically excited Langmuir waves in ionospheric modification experiments. The acceleration mechanism is a single velocity reversal as seen in the frame of the Langmuir wave. The flux is sufficient to produce the observed ionospheric airglow if focusing‐type instabilities are invoked to produce moderate local enhancements of the pump field.
The effects of atmospheric turbulence on the propagation of pulsed laser beams
Authors: Gardner C. S. , Plonus M. A.
Published: February 2008

The effects of turbulence on the propagation of pulsed laser beams are examined. Using the Rytov theory, general expressions for the pulse fluctuations are derived in terms of arbitrary beam geometries and pulse shapes. Physical interpretations of the pulse distortion and the effects of the beam geometry on the pulse statistics are discussed.
Analysis of discrete oblique ionogram traces in sweep‐frequency sky‐wave high resolution backscatter
Authors: Rao N. Narayana
Published: February 2008

A method is presented for the analysis of discrete oblique ionogram traces observed in high resolution sweep‐frequency sky‐wave backscatter technique to obtain quasiparabolic ionospheric layer parameters. The method employs three data points on the oblique ionogram with one of the data points being the point of coincidence of the oblique ionogram trace with the leading edge of the backscatter. The method is applied to the analysis of an experimental oblique ionogram trace and the validity of the results is examined.
Ionospheric scintillation by a random phase screen: Spectral approach
Authors: Rufenach Clifford L.
Published: February 2008

The theory developed by Briggs and Parkin, given in terms of an anisotropic gaussian correlation function, is extended to a spectral description specified as a continuous function of spatial wavenumber with an intrinsic outer scale as would be expected from a turbulent medium. Two spectral forms were selected for comparison: (1) a power‐law variation in wavenumber with a constant three‐dimensional index equal to 4, and (2) gaussian spectral variation. The results are applied to the F‐region ionosphere with an outer‐scale wavenumber: (1) κ0 = 2 km−1 approximately equal to the Fresnel wavenumber, and (2) κ0 = 0.2 km−1. The power‐law form with a small outer‐scale wavenumber is consistent with recent F‐region in‐situ measurements, whereas the gaussian form is mathematically convenient and, hence, mostly used in the previous developments before the recent in‐situ measurements. Some comparison with microwave scintillation in equatorial areas is made.
Electromagnetic wave scattering from a turbulent plasma
Authors: Martens Charles P. , Jen Norman C.
Published: February 2008

The Doppler spectrum of electromagnetic radiation scattered by a turbulent plasma is calculated for the case in which the incident wave is a high frequency microwave or a laser beam and is not of sufficient intensity to heat the plasma. The differential scattering cross section is expressed in terms of the power spectrum of the current density fluctuations, and the wave equation and the equations of continuity and momentum for the electrons are analyzed by means of the repeated cascade theory of turbulence. The equation governing the current density spectrum in the universal equilibrium range consists of three terms: a term representing the excitation of the spectrum near the wave number of the incident wave, a term which transfers energy across the spectrum at a rate controlled by an eddy viscosity, and a molecular dissipation term. Solutions for the spectrum are obtained in the inertial and dissipation subranges which reduce to Kolmogorov and Heisenberg type spectra, respectively, in the limits of zero scattering or for wave numbers far from the wave number of the incident wave. Near the frequency ω0 of the incident wave, the differential cross sections, or equivalently Doppler spectra, for scattering at frequency ω vary exponentially as − Δω−5/3 in the inertial subrange and as −Δω3 in the dissipation subrange, where Δω = ω ‐ ω0. The characteristic frequencies controlling the Doppler half widths depend upon the scattering angle, the intensity of the incident wave, and the root‐mean‐square electron density fluctuation.
Concluding remarks, session 2: Structure, ionization sources
Authors: Davies Kenneth
Published: February 2008

There are three major topics which arose in Session 2 on which I would like to comment, namely, maintenance of the night ionosphere, particle ionization, and modelling.

1. THE NIGHT IONOSPHERE

The maximum densities of the E and intermediate layers decay at night to values of the order of 3×103 cm−3. Taking a low value of α ≈ 10−8 cm3 sec−1, then Ne = 4.96×104 cm−3 at sunset and the electrons would completely disappear within an hour after production ceases. Not only does the E‐layer ionization persist but evidence (Geller et al.) indicates that after midnight, the ion production in the upper E region increases markedly. Incidentally, ionospheric total content data show that the content of the F region can also increase around midnight. Hence, a source of plasma is required.
Incoherent scattering of microwaves from the ocean
Authors: Spetner L. M.
Published: February 2008

The conventional wisdom that the incoherent portion of the forward‐scattered signal off a rough surface approaches a constant asymptote as the roughness parameter (RP) grows large is reexamined and shown to be incorrect. Essential use is made of the fact that the incoherent‐scattered component has been observed to come mainly from the specular direction. With this approximation, a remarkably close fit to the data is achieved when one further assumes that the surface is illuminated by a very narrow beam. Asymptotic expressions show that the rms of the incoherent portion of the signal first rises linearly with RP, and then eventually falls off as the inverse square root of the RP. This general shape is independent of the form of the surface autocorrelation function.
Effective wave tilt and surface impedance over a laterally inhomogeneous two‐layer Earth
Authors: Hughes W. J. , Wait J. R.
Published: February 2008

Using a perturbation method, we consider the effect of a simple two‐dimensional model on the electromagnetic fields at the surface of the Earth for a postulated downcoming plane wave. We examine the calculated change in the surface impedance and wave tilt due to lateral inhomogeneities. It is found that the magnetic wave tilt (Hz/Hx) is most seriously affected by such anomalies. This may have important consequences on electromagnetic probing of nonuniform portions of the Earth's crust.
Electromagnetic scattering by a half plane with two face impedances
Authors: Bucci Ovidio M. , Franceschetti Giorgio
Published: February 2008

The solution for the problem of electromagnetic scattering by a half plane with two different face impedances is presented for both normal and oblique incidence. Illustrative examples are discussed and a chart relative to the existence of surface wave contributions is presented.
A physical explanation of electromagnetic surface wave formulas
Authors: Lytle R. J. , Miller E. K. , Lager D. L.
Published: February 2008

The behavior of electromagnetic surface waves generated by both elevated and buried sources is explained with physical reasoning and described with mathematical formulas. All combinations of source and receiver orientations are considered. Applications of generalized surface wave formulas for mixed‐path and spatially varying terrains are discussed. The generalized surface wave formulas for elevated and buried sources are validated with Sommerfeld integrals and are applicable over a wider range than previous approximate surface wave formulas.
Borehole measurements of conductivity and dielectric constant in the 300 kHz to 25 MHz frequency range
Authors: Grubb R. N. , Orswell P. L. , Taylor J. H.
Published: February 2008

Two borehole instrumentation systems for the measurement of complex propagation constant in the frequency range from 300 kHz to 25 MHz are described. The first system measures the ratio of the signals coupled to two identical receivers in separate boreholes at different ranges from an isolated transmitter in a third borehole. The second system operates in a single borehole by measuring the mutual impedance between two magnetic dipoles aligned parallel to the borehole. This second system has an automatic digital data acquisition system based on a programmable calculator which reduces the data to conductivity and dielectric constant versus frequency. Examples of data on conductivity and permittivity of actual boreholes in various geologic materials are given.
Radiation and propagation of a surface‐wave mode on a curved open waveguide of arbitrary cross section
Authors: Chang David C. , Kuester Edward F.
Published: February 2008

A general scheme for calculating the change (both the real part and the imaginary part) of the propagation constant of a surface‐wave mode on a general open waveguide structure is presented. By carefully keeping track of lower‐order terms in the analysis, it is shown how approximations commonly made in other analyses can result in quite significant errors in the determination of the radiation loss. The resulting formulas require knowledge only of the fields and propagation constant of the corresponding straight waveguide mode, and the value of the radius of curvature of the waveguide axis. As a simple example, the curvature loss of a Goubau line is calculated.
Scientific highlights of the XVIIIth General Assembly of URSI
Authors: Johnson Francis S.
Published: February 2008

The XVIIIth General Assembly of URSI was held in Lima, Peru, 8–19 August 1975. Four symposia were held in conjunction with the Assembly: (a) radio waves and ionosphere, (b) nonstationary signal analysis, (c) telecommunications noise and interference environment, and (d) the teaching of electromagnetics and telecommunications science. The organization of these symposia contributed a great deal to the success of the Assembly. The chairmen of the US Commissions were asked to submit brief reports on the scientific highlights in the sessions of interest to their commissions, or to designate others to do so on their behalf. This document is a compilation of those responses, made up of summaries provided by George Birnbaum, Commission I; Alfred H. LaGrone, Commission II; J. M. Kelso, Commission III; D. L. Carpenter, R. W. Fredricks, and C. Russell, Commission IV; Alan Barrett, Commission V; A. A. Ksienski, Commission VI; R. J. Collins, Commission VII; and George Hagn, Commission VIII.
On the expansion of cylindrical vector waves in terms of spherical vector waves
Authors: Pogorzelski R. J. , Lun E.
Published: February 2008

An expansion of the nonsingular solutions of the vector wave equation in cylindrical coordinates in terms of the nonsingular solutions of the vector wave equation in spherical coordinates is presented. As an example application of the expansion, the scattering of a particularly simple gaussian beam of electromagnetic radiation by a spherical obstacle is discussed. Both perfectly conducting and dielectric spheres are treated.
The effects of phase‐front distributions on echosonde antenna radiation patterns
Authors: Adekola S. Adeniyi , Davis Dean T.
Published: February 2008

The effects of phase‐front distributions on the radiation patterns of an echosonde (acoustic echo‐sounding) antenna are studied. A radiation integral is used to compute an equivalent excitation at the transmitting antenna aperture at a height H above the illuminating aperture of smaller radius. A two‐dimensional Fourier transform utilizing the Kirchhoff‐Fresnel diffraction formula is used to obtain the far‐field expressions. The results reported for linear, square‐law, cubic, and periodic phase‐front distributions, indicate that (while details of the antenna pattern depend upon the specific phase distribution used) all distributions tended to raise the sidelobes and broaden the mainlobe for stronger phase modulations. In some cases, the stronger phase modulations actually reduced the central portion of the mainlobe, producing a hollow conical beam. Some computed beam patterns at a carrier frequency of 2 kHz and with different phase modulation coefficients were compared with two recent sets of experimentally measured patterns. The agreement overall is good with any variations probably being due to the fact that the actual phase distributions on the antennas were not exactly known and also due to the lateral drifts that might be experienced by the tethered weather balloon supporting the microphone probe (used for some of the pattern measurements) as a result of wind breezes.
Transmission line theory of antenna impedance in a magnetoplasma
Authors: Adachi S. , Ishizone T. , Mushiake Y.
Published: February 2008

Transmission line theory for the impedances of wire antennas immersed in a cold magnetoplasma is proposed. The theory is applicable to antennas which are not necessarily small in terms of a wavelength measured along the antenna wire. The transmission line theory for the impedance of a very thin cylindrical dipole antenna leads to the Balmain quasi‐static theory when the antenna length reduces to zero. New impedance resonances which would be observed for antennas of finite length in a magnetoplasma in the frequency region below and near the electron cyclotron frequency are predicted by the present theory.
The effect of ionospheric scintillation on VHF/UHF satellite communications
Authors: Whitney Herbert E. , Basu Santimay
Published: February 2008

Periods of intense ionospheric scintillations were analyzed in order to provide information for the design and evaluation of the performance of satellite communication links. Scintillation data were available for the auroral and equatorial regions. The amplitude fluctuations are described by cumulative amplitude distributions and show good agreement with the Nakagami m‐distribution. A Rayleigh distribution appears to describe the ‘worst’ case scintillations in the 225–400 MHz band. The rate of scintillations is described by level crossing techniques, power spectra, and correlation functions. The effectiveness of diversity techniques is indicated. The spectral index was measured as approximately f−0.2 indicating that intense scintillations can become almost frequency‐independent in the strong scattering limit.
A model for sea backscatter intermittency at extreme grazing angles
Authors: Wetzel Lewis B.
Published: February 2008

The behavior of microwave sea backscatter at extreme grazing angles (0°–1°) tends to be spiky and irregular, with ill‐defined statistics. Intuition suggests that at these extreme angles, most of the surface is in shadow, and only an occasional peak is visible to the radar. In order to sharpen this intuition, the conventional shadowing function is taken to define a scattering threshold whose height above the mean surface is a function of grazing angle and average surface slope. Using the spatial analogue of the familiar idea of “surges” and “fades” of a thresholded random process, the surface is found to be pockmarked by scattering islands of relatively constant size, but whose density (spacing−2) is a sensitive function of grazing angle and sea state. This model leads to the definition of a “backscatter intermittency index,” which describes the number of localized scattering regions within a given surface area as a function of wind speed and grazing angle, and to a modified shadowing function for grazing angles less than 1°.
Antenna properties of probes used in ion‐acoustic wave experiments
Authors: Christensen Thomas , Hershkowitz Noah , Scheller Alfred , Lonngren K. E.
Published: February 2008

This paper describes a series of experiments designed to examine the antenna characteristics of probes which are used as detectors in ion‐acoustic wave experiments. Reception patterns are measured which are in qualitative agreement with theoretical predictions. The near‐field antenna pattern of the wave‐launching grid is found to be important.
Nonlinear steady state structures for inhomogeneous plasma
Authors: Trotignon J. G. , Feix M. R.
Published: February 2008

We study the nonlinear steady state structures created in a one‐dimensional collisionless electron plasma by a transparent grid raised to a given potential. Moreover, natural structures, i.e., in the absence of a grid and consequently of any external charge, can also be obtained. For the electrons (here ions are supposed motionless and uniform), the structure must involve a hole in the trapped electron density distribution and is consequently attractive. A relationship between the depth of the potential and its possible length is obtained. These studies are preliminary to the problems of stability and waves propagating in strongly inhomogeneous plasma structures.
Drug‐induced ectothermia in small mammals: The quest for a biological microwave dosimeter
Authors: Putthoff D. L. , Justesen D. R. , Ward L. B. , Levinson D. M.
Published: February 2008

In a passive state, the pelted mammal is well insulated against loss of thermal energy. Further, the rapidity with which the circulatory system equilibrates thermal energy would render the living animal a useful whole‐body calorimeter but for the complicating factors of physiological and behavioral thermoregulation. Moderate thermal loading of the intact mammal by, say, microwave radiation, will bring a host of responses into play by which an excess of energy is actively dissipated. If, however, a reversible chemical lesion could be introduced that rendered the mammal ectothermic–cold blooded–then one could use pre‐ and post‐radiation temperatures of the living animal to make fairly accurate estimates of quantities of absorbed energy. An ectothermic preparation would be useful in dosimetric studies in the free field where an empirical fit between measures of incident and absorbed energy is the objective with the freely behaving animal. We report studies of two compounds, sodium salicylate and cortisone acetate, and their effects upon body temperatures of rats, guinea pigs, and rabbits of both sexes and of pigmented and albino strains. While the salicylate produced a reliable hypothermal response in the albino rat, it was less effective in the pigmented rat, and was virtually ineffective in the guinea pig and rabbit. Cortisone appeared to produce a more uniform hypothermal response; studies of rats revealed that increments of colonic temperature after short periods of highly thermalizing microwave radiation yield estimates of energy dosing that are accurate within 15%.
Incoherent scattering of radio waves by whistler mode oscillations in the ionosphere
Authors: Behnke R. A. , Hagen J. B.
Published: February 2008

The received power spectrum in incoherent scatter can contain two sharp resonances removed from the center frequency. The first is due to ordinary electrostatic plasma oscillations and is known as the plasma line. The second depends on the presence of a magnetic field and corresponds to the high‐frequency end of the whistler mode in magnetoionic theory. Here we report an experimental detection of this second resonance.
Collaboration between URSI and CCIR in the study of tropospheric radio wave propagation problems
Authors: Saxton J. A.
Published: February 2008

At the last General Assembly of URSI in Lima, 1975, the terms of reference of the Union were modified in accordance with the wish to give greater emphasis to studies related to the advancement of telecommunications science. One way of achieving this aim is through a greater interaction than that which has previously existed between URSI and the technical activities of the International Telecommunication Union (ITU), though the previous collaboration has by no means been negligible.

The ITU was founded in 1865 and is now a Specialized Agency of the United Nations organization: it has 148 member countries. These countries generally agree to conform to the Regulations of the International Telecommunication Convention in the way they operate their telecommunications services. in the radio field there is a set of Radio Regulations to cover the manner in which radio systems and services shall be operated, the use of frequencies for different services and a whole range of technical criteria which should be observed. These Radio Regulations are formulated, and revised as necessary, at a series of World Administrative Radio Conferences (WARCs) of the ITU attended by the responsible Administrations of the member countries of the ITU.
Transient electromagnetic response from irregular models of the earth's surface
Authors: Bahar E.
Published: February 2008

The principal motivations for conducting this work are to determine the distortions and delays an electromagnetic pulse undergoes when it propagates across an irregular model of the earth's surface, and to determine whether the electromagnetic signatures due to transient excitations can reveal the electrical and geometrical characteristics of the earth's surface. Thus, in this work, the phase anomalies and the propagation delays and distortions due to irregular ground effects are examined in detail.
Scattering of electromagnetic waves by a perfectly conducting half plane below a stratified overburden
Authors: Olsson Olle
Published: February 2008

By expanding the electromagnetic field into plane wave eigenfunctions, an integral equation is obtained which describes the coupling between an overburden, consisting of an arbitrary number of plane layers and an arbitrary object beneath a stratified half space. As an example of the technique, a perfectly conducting half plane inclined to the strata in a substratum is discussed. In this case the kernel of the integral equation may be expressed in terms of elementary functions. Numerical results are discussed for a plane wave incident on the ground.
An analysis of a resonant loop as an electromagnetic sensor of coal seam thickness
Authors: Chang D. C. , Wait J. R.
Published: February 2008

We consider the use of a resonant loop as a probe for the determination of roof thickness in a coal mine operation. The roof structure typically consists of a thin slab of uncut coal of the order of 10 cm in thickness, situated in front of a thicker layer of slate of relatively higher conductivity and permittivity. We model the structure by a two‐layer half space, with the first layer consisting of a slightly lossy dielectric material (coal) and the second layer of infinite extent. To determine thickness of the bottom layer, i.e., the so‐called roof, we propose that a horizontal loop be placed near the coal interface and the self‐impedance of this loop be measured over a range of frequencies. The effectiveness of such a probing scheme is then determined, to a large extent, by our analytical ability to interpret such data in terms of the layer thickness. For a loop which is operating near its first resonance (where the cosinusoidal current is predominant), the measured change in the resonance characteristics provides additional information from which the layer parameters can be extracted. Such a remote sensor is relatively simple and presents no particular alignment problems.
Simple expressions for horizontal electric dipole quasi‐static range subsurface‐to‐subsurface and subsurface‐to‐air propagation
Authors: Bannister Peter R. , Dube Rene L.
Published: February 2008

Simple engineering expressions for the quasi‐static fields produced by a subsurface horizontal‐electric‐dipole (HED) antenna have been derived by employing finitely conducting earth‐image theory techniques. Both subsurface‐to‐subsurface and subsurface‐to‐air propagation cases are considered. It is shown that the resulting subsurface‐to‐air propagation field‐strength expressions are the result of simple modifications to the previously derived quasi‐static range air‐to‐air propagation equations of one of the authors.
The accuracy of water vapor and cloud liquid determination by dual‐frequency ground‐based microwave radiometry
Authors: Westwater Ed R.
Published: February 2008

A dual frequency ground‐based radiometer operating in the 1 to 1.4 cm wavelength range can provide continuous measurements of integrated water vapor and cloud liquid water. Using climatological data, the accuracy of the vapor and liquid determinations is estimated as a function of cloud amount. Limiting factors in the water determination are uncertainties in water vapor absorption coefficients and, during cloudy conditions, uncertainties in cloud temperature. For integrated water vapor content greater than 10 mm, the accuracy of the vapor determination is better than 15% for a wide range of cloudy conditions.
Coordinated measurements of ELF transmission anomalies and the precipitation of energetic particles into the ionosphere
Authors: Imhof W. L. , Reagan J. B. , Gaines E. E. , Larsen T. R. , Davis J. R. , Moler W.
Published: February 2008

Stimulated by previous findings of a positive qualitative correlation between anomalous ELF signal levels and the occurrence of significant fluxes of precipitating energetic particles, coordinated exercises were conducted between satellite measurements of the precipitating particles and ELF transmissions between the US Navy Wisconsin Test Facility and receiving stations in Maryland, Greenland, Norway, and Italy. Significant fluxes of precipitating electrons were often measured with the Lockheed pay load on the polar‐orbiting satellite 1972–076B. In March‐April 1976 the received signal strengths were found generally to increase during periods when the geomagnetic K indices were higher and when the fluxes of precipitating electrons >160 keV were greater on the average. During other coordinated exercises in March‐April 1975 the general correlations were less evident. Based on the fluxes, energy spectra, and pitch‐angle distributions of the particles, ion‐pair production profiles have been calculated and electron density profiles subsequently obtained with application of known effective electron loss rates. From the coordinated data, correlative studies between signal strengths and electron density profiles have been performed with use of an ELF waveguide mode computer program developed at the Naval Ocean Systems Center. The propagation path to each station of interest is segmented into different regions with an averaging perpendicular to the direction of propagation of the waveguide parameters. With the inclusion of data from several stations, the transmission signal strengths could be studied simultaneously under a variety of ionospheric conditions. The waveguide computer program calculations indicated that energetic electron precipitation events may cause a signal enhancement or degradation, depending upon where the disturbance is occurring along the path. The consistent occurrence during electron precipitation events of signal strength anomalies in either direction is supported by the coordinated satellite/ELF station measurements.
Techniques for the study of TID's with multi‐station rapid‐run ionosondes
Authors: Morgan M. G. , Calderón C. H. J. , Ballard K. A.
Published: February 2008

Individual daytime traveling ionospheric disturbances (TID's) in the F‐layer are studied using three ionosondes mutually approximately 150 km apart in northern New Hampshire and Vermont. The ionosondes were operated continuously for long periods of time, making ionograms every two minutes. Methods of scanning the continuous data for TID's, and of analyzing them, are described. Iso‐height contours are emphasized as superior to iso‐ionic contours for analysis. It is found that the direction toward which a TID travels is essentially independent of height within the disturbance and that the directions of travel cluster about the south‐southeast. Other parameters are found to be height‐dependent and will be the subject of future papers.
Electromagnetic response of an anisotropic conducting cylinder to an external source
Authors: Wait James R.
Published: February 2008

A novel analytical solution is obtained for the boundary value problem of a circular cylinder of infinite length that is excited by a prescribed external field. The cylinder is anisotropic in the sense that the complex conductivity and magnetic permeability are diagonal uniaxial tensors with generally unequal elements. The solution involves Bessel functions of nonintegral order. Known special cases are recovered.
Impedance of a short antenna in a warm magnetoplasma: Experiment and comparison with theory
Authors: Meyer‐Vernet N.
Published: February 2008

A description of the EIDI III experiment is given. The impedance of a short electric dipole was measured in the ionosphere in conditions where, at variance with the preceding EIDI experiments, the plasma anisotropy was non‐negligible (operating frequencies ∼1.6 and 2.7 MHz, ƒo F2 ∼ 3 MHz, ƒH ∼ 1 MHz). The simultaneous in‐situ measurement of the relevant parameters, as well as the numerous cross‐checks and experimental configurations (antenna length, dc bias, orientation, etc.), ensured a reliable comparison with theory. For the theoretical calculations, the plasma is described by the hydrodynamic equations with tensor pressure, and a vacuum sheath (the dimensions of which are calculated by using the measured plasma parameters) surrounds the antenna. The agreement is good in the part of the trajectory where the excitation frequency is above the plasma frequency; otherwise, the measured resistance is much higher than the calculated one. It is shown that the use of a more rigorous description (kinetic theory) of the homogeneous plasma cannot remove this discrepancy and it is suggested that taking into account the inhomogeneous plasma in the sheath may greatly increase the losses and explain the measured resistance, as occurred in an isotropic plasma (EIDI I experiment).
Diffraction from discrete and homogeneously structured ionospheric irregularities
Authors: Heron M. L.
Published: February 2008

Diffraction patterns produced by isolated irregularities have a maximum fading depth at radio frequencies near 0.6 ƒT where ƒT, the transition frequency, is a property of the electron density irregularity and marks the boundary between geometric and physical optics. A nearly homogeneous assembly of irregularities can produce scintillation which is speciously random. For such an assembly a peak in scintillation depth is also produced just below the mean fT. At radio frequencies below
the scintillation is fast and frequency independent; above ƒ¯T the amplitude pattern is directly related to the ionospheric structure.
Use of refractive scattering to explain SHF scintillations
Authors: Crain Cullen M. , Booker Henry G. , Ferguson Jerry A.
Published: February 2008

Ionization structure perpendicular to the line of sight can cause total internal reflection at glancing incidence, leading to refractive scattering that can dominate diffractive scattering. The long‐wave cutoff in the spectrum of amplitude fluctuations then occurs, not at the Fresnel scale but at a larger scale that increases as the percentage fluctuation of ionization density increases. The additional amplitude fluctuation arising from the band of scales extending from the usual diffractive cutoff scale up to the refractive cutoff scale is capable of explaining strong SHF scintillation. It also lowers the estimates of the fluctuation of ionization density needed to explain strong VHF scintillation. The concept of refractive scattering is also likely to be applicable to SHF‐EHF scintillation phenomena in the troposphere.
Radio occultation of the Venusian atmosphere and bistatic radiolocation of the surface of Venus using the Venera‐9 and Venera‐10 satellites
Authors: Kolosov M. A. , Yakovlev O. I. , Efimov A. I. , Pavelyev A. G. , Matyugov S. S.
Published: February 2008

Experimental results for the radio occultation of the Venusian atmosphere using the Venera‐9 and Venera‐10 satellites are discussed. The time dependences of the field strength and frequency during immersion of the vehicles behind the planet and during their emersion from behind it are given. The dependences of the refraction index, density, pressure, temperature, and electron number density on the altitude above the planet's surface have been obtained. The results of bistatic radiolocation of the Venus surface with the aid of the Venera‐10 satellite are also presented. An analysis is made of the energy spectrum and variations of the Doppler frequency of a radio signal reflected from the planet's surface. The distribution of the relative heights and of rms slopes of irregularities for two areas of the Venusian surface has been found.
Precise real‐time signal dissemination over the TV broadcasting satellite
Authors: Kovačević B. Ž. , Dimitrijević B. R. , Arsić M. Z. , Kovačević N. S.
Published: February 2008

The problem of dissemination of precise time signals over the TV broadcasting satellite is analyzed. The method described is designed to combine the existing system of time and standard frequency (T/ F) signal dissemination over the TV network and the broadcasting possibilities of the satellite, thus forming a new T/F distribution system which could retain the existing format of the T/F signals. Hence the user could utilize the same equipment for both systems. The high precision of the T/F signal dissemination over the ground TV system is retained in the new system, which uses the TV satellite for broader coverage, by possible methods designed to greatly reduce propagation time variations. The method is based on the Time and TV Synchro system previously developed at Studio Belgrade in Yugoslavia.
Scattering by resistive strips
Authors: Senior Thomas B. A.
Published: February 2008

For resistive strips of large electrical width kw illuminated by E‐ or H‐polarized plane waves the geometrical theory of diffraction is used to obtain expressions for the far zone scattered field through second‐order terms, valid for directions of incidence and observation away from grazing. The results are then cast as products of functions analogous to those appearing in the known (uniform) expansions for perfectly conducting strips. Each function involves the current on the corresponding half plane, and by invoking this connection, far field expressions are produced which are uniform in angle. In particular, for E polarization the backscattered field at edge‐on incidence is shown to consist of two terms, each of which is expressible in terms of the half‐plane current, and for all resistivities the resulting values of the field are in excellent agreement with those found by numerical solution of the integral equation, even for kw as small as unity.
Techniques for the determination of the polarization properties of precipitation
Authors: McCormick G. C. , Hendry A.
Published: February 2008

Experimental techniques related to the use of a polarization diversity radar and a short transmission link are discussed. The equipment, operated at 16.5 GHz, located at Ottawa, Ontario, is for the observation of rain and other hydrometeors. Components related to the radar's polarization capability include the antenna and polarizer, a dual‐channel receiving system with power and correlation detection, and a 12‐gate video processor. There is a discussion of calibrations, errors, and extraneous effects.
Microwave‐induced hyperthermia and the visually evoked electrocortical response of the guinea pig
Authors: Bruce‐Wolfe Virginia , Justesen Don R.
Published: February 2008

Five experimentally naive female guinea pigs, all young adults, were observed during a succession of 11 experiments for visually evoked electrocortical responses (VERs). In each experiment, VERs were recorded within minutes after an animal had received a hyperthermalizing dose of microwave radiation in a 2450‐MHz field. Latency of the N1 component of the VER, an inverse index of conduction velocity of primary visual fibers, was recorded via an electroencephalograph on a signal‐averaging computer. Cortical and rectal temperatures were observed and recorded during measurement of VERs. The mean latency from onset of photic stimulation to the N1 peak diminished from 42.8 to 37.7 ms at respective cortical temperatures of 37.0 and 40.5°C, which represents a mean increase of conduction velocity of 3.4 percent per incremented Celsius degree. While cortical and rectal temperatures were highly correlated, the former were invariably lower by nearly 2°C, although they diverged slightly at higher elevations. Above a cortical temperature of 41.5°C, evidence of reversible and irreversible thermal toxicity was observed.
A numerical study of satellite reception of VLF signals using wave guide concepts
Authors: Pappert Richard A. , Moler W. F. , Ferguson J. A.
Published: February 2008

Full wave methods and wave guide concepts are used to calculate the nighttime 17.8‐kHz radio fields along the 40°W parallel of longitude at 500‐km altitude. The fields are generated by the ground‐based transmitter at Cutler, Maine. The results are compared with data obtained by the Ogo 4 satellite and with results of Souza and Scarabucci, which were calculated using other methods. Wave guide leakage accounts for general features of measurements made in the northern geomagnetic hemisphere. Measurements made in the southern geomagnetic hemisphere suggest that those fields can be estimated by assuming lossless whistler mode propagation of wave guide leakage fields at the geomagnetic conjugate.
Radar cross sections of conducting bodies over a lossy half space
Authors: Sarkar Tapan K. , Harrington Roger F.
Published: February 2008

A general analysis for obtaining both bistatic and monostatic radar cross sections of conducting bodies over an imperfectly conducting medium is presented. The resulting formulas are in matrix notation. Representative computations are made for the cases of a vertical half‐wave dipole and a horizontal half‐wave dipole situated over a half space of various constitutive parameters.
Coupled mode analysis for a nonuniform tropospheric wave guide
Authors: Wait James R.
Published: February 2008

We employ a two‐dimensional cylindrical model to analyze the normal modes in a laterally nonuniform tropospheric duct. The utilization of the impedance boundary condition at the earth's surface permits us to use a complete field representation in terms of discrete modes only. These modes are chosen to be locally orthogonal so that a tapered‐type nonuniformity can be handled with a systematic accounting of the mode conversion. Explicit formulas are given for the coupling coefficients. It is shown that the general coupled mode analysis reduces to the appropriate form when dealing with an abrupt but small lateral change of the refractive index structure. This step model had been treated previously using a nonrigorous mode matching procedure that neglected reflected waves at the outset.
Some physical insights into beam propagation in strong turbulence
Authors: Fante Ronald L.
Published: February 2008

In this paper we examine some of the physical implications of using the extended Huygens‐Fresnel principle to calculate laser beam properties in strong turbulence. We shall demonstrate the roles played by the log‐amplitude and phase fluctuations and will show that quadratic phase structure functions lead to results incompatible with experimental data. We shall also prove that the Huygens‐Fresnel principle automatically predicts a normalized irradiance variance of unity and Gaussian field statistics in strong turbulence provided that certain conditions on the turbulence strength and spectrum are satisfied.
Depolarization of electromagnetic waves scattered from an inhomogeneous half space bounded by a rough surface
Authors: Blanchard Andrew J. , Rouse John W.
Published: February 2008

This paper presents a development for backscatter from rough surfaces and inhomogeneous media that is valid for microwave frequencies. Calculations of polarized and depolarized backscatter are presented for several values of dielectric constants and volume reflection coefficients of direct interest in active microwave remote sensing of soil moisture content. This paper confirms the finding that depolarized backscatter measurements are much less dependent on incident angle than like polarized backscatter measurements. However, most depolarized measurements reported in the literature exhibit excessive dependence on incident angle. This is an artifact of the measurement technique and not of the depolarization phenomenon.