bluuebunny/crossref_metadata_2025 huggingface dataset:
Frequency dependence of slant path rain attenuations at 15 and 35 GHz
Authors: Altshuler E. E. , Telford L. E.
Published: February 2008

The main objective of this paper is to examine the frequency dependence of slant path rain attenuation at 15 and 35 GHz in order to determine how well the attenuation at one frequency can be predicted from that at another; this has application in the design of earth‐to‐satellite communications. Also, some inferences on the drop size distribution of rain can be drawn from simultaneous attenuation measurements at two frequencies. The theory of rain attenuation is reviewed, and it is noted that the attenuation is a complex function of drop size, shape, orientation, index of refraction, and rain intensity along the path. Attenuation ratios are computed on the basis of both drop size and rain rate for frequencies at which there are measured data. Results obtained by other investigators are reviewed, and it is found that frequently, attenuation ratios that would not have been predicted on the basis of a surface rain model such as a Laws and Parsons model have been reported; indications are that attenuation is often produced from a widely dispersed distribution of large raindrops. During eight rainy days in 1975–1976, more than 10,000 simultaneous measurements of 15‐ and 35‐GHz attenuations were recorded in the Boston area. On the basis of these results it is concluded that it is not possible to represent the drop size distribution of rain along a slant path in the Boston area by a Laws and Parsons model, since the ratios of the 35‐GHz attenuations to the 15‐GHz attenuations are significantly below those that would have been predicted by that model. The ability to predict slant path rain attenuation at one frequency on the basis of that at another is shown to be a function of frequency separation, climatology, and the type of statistics which are desired.
Fields of a horizontal loop of arbitrary shape buried in a two‐layer earth
Authors: Wait James R. , Hill David A.
Published: February 2008

Expressions have been derived for the magnetic field in air produced by a buried horizontal loop of arbitrary shape. Numerical results are presented for both circular and rectangular loops. Rectangular loops produce an azimuthal magnetic field component which is not present in the case of a circular loop. The results have application to source location in mine rescue techniques. In such cases, frequencies in the audio range are employed, and the assumption of a uniform current in the source loop is well justified.
Polarization errors in a two‐channel system
Authors: McCormick G. C.
Published: February 2008

The two‐channel system includes a two‐terminal antenna with ancillary devices. A general treatment of polarization errors in such a system is given, including the transformation of error parameters and scattering coefficients with a change of polarization base. Calibration procedures are discussed and formulas developed for the calculation of polarization‐related quantities in the presence of errors. The effects of polarization errors in transmission and radar systems are outlined.
A direct profile inversion: Beyond the Born model
Authors: Raz S.
Published: February 2008

All inversion procedures based on the single scatter (Born) model proposed in recent years possess two outstanding drawbacks which appear to be inherent to this approach. The first drawback is the unavoidable need to make an a priori choice of the ‘background’ problem. It is the reconstruction of the perturbation about this background that is subsequently sought. A successful outcome of the inversion sequence depends crucially on this initial decision. Although useful clues relevant to the background selection may, at times, be available, they are not an integral part of the Born inversion sequence. A second unfortunate feature of the Born inversion is the existence of mechanisms that give rise to error accumulation with range and to ‘scaling’ errors. The inversion sequence proposed in this paper seems to overcome the above deficiencies and to provide more accurately reconstructed results. The present scheme proposes a definite and unique choice of the background, namely, a WKB reference. This z dependent reference, although more complicated than the constant background, ordinarily selected for the single scatter model, can still be handled. Since the WKB background ensures correct relative phase (time delay) relations, it also seems to overcome the ‘scaling’ and error accumulation problems, which can be backtracked to ‘phase’ errors in the background (incident and backscattered) wave.
Magnetic field strength below a horizontal magnetic dipole located at the earth or ocean surface
Authors: Layman Gene E.
Published: February 2008

A radiating loop antenna located at the earth or ocean surface produces a magnetic field within the conductive medium. The strength of this field is normally expressed by a set of integral equations for which there are no known solutions. The author develops approximations within the integrand that allow a closed form solution to be found for all points directly below the antenna. This accurate solution is valid for all combinations of frequencies and ranges at which practical communications between surface and submerged locations are possible.
Numerical inversion of Laplace transform and some applications to wave optics
Authors: Hosono Toshio
Published: February 2008

First, a new method for numerical inversion of the Laplace transform is proposed. The essential point of this method is to approximate the exponential function in the Bromwich integral by the function Eec(s, a) d= exp (a)/2 cosh (a – s). With this we can get an infinite series which gives a good approximation to the inverse transform. In practice, we accelerate the convergence of the series by the Euler transformation. Thus in ordinary cases, only twenty to thirty terms give satisfactory results, and even a $100 pocket calculator can solve practical problems which are not so easy by the usual method. Second, the wave propagation in dispersive media is studied by using the above method. This problem has been investigated analytically by many authors. The problem is so difficult that there has been no detailed solution available other than asymptotic expressions. Some detailed numerical results by our method are given for the transient phenomena in a waveguide and the medium discussed by Sommerfeld and Brillouin. Our numerical results show that Brillouin's results should not be taken quantitatively except the first forerunner whose approximate variation is predicted by Sommerfeld correctly.
The torus antenna over a conducting plane
Authors: Ledinegg E.
Published: February 2008

Ground reaction on an active or passive torus antenna whose plane is parallel to the ground, is treated by an iterative method. At first the unperturbed antenna current is impressed along the circle of centers of the torus; then the ground reaction field induced by this loop antenna is computed; this is then inserted into an integro‐differential equation for the current density which finally gives the antenna current as modified by the ground reaction.
A coordinate‐free approach to wave reflection from an anisotropic medium
Authors: Chen Hollis C.
Published: February 2008

The object of this paper is to present a coordinate‐free method in solving the problem of wave reflection from the surface of an anisotropic medium. Based on the direct manipulation of vectors, dyadics, and their invariants, the method eliminates the use of coordinate systems. It facilitates solutions and provides results in a greater generality. The paper contains the following results in coordinate‐free forms: (1) the dispersion equation, (2) the laws of reflection and refraction, (3) the Booker quartic equation, and (4) the transmission and reflection coefficient matrices.
Electromagnetic scattering from a buried cylindrical inhomogeneity inside a lossy earth
Authors: Mahmoud Samir F. , Ali Sami M. , Wait James R.
Published: February 2008

A solution is given for electromagnetic wave scattering from an infinitely long circular cylinder with a possibly radially stratified internal structure and which is buried in a lossy half space. The fields of the primary source are allowed to vary along the cylinder's axis. The scattered fields result from induced multipole line sources of electric and magnetic types located at the cylinder's axis. Explicit expressions are obtained for the source amplitudes up to the dipole terms that take into account the presence of the air‐earth interface. The dipole sources may contribute significantly to the scattered fields even when the cylinder's radius is small relative to the wavelength in the surrounding medium. Some specific results are given for a buried tunnel and a conducting cylinder surrounded by an air gap and for an incident plane wave from the air region.
Scattering cross sections for composite random surfaces: Full wave analysis
Authors: Bahar Ezekiel
Published: February 2008

The full wave approach to rough surface scattering is applied to composite models of rough surfaces. In this work the principal distinguishing feature of the individual rough surface is its correlation distance. Thus this model can be applied to scattering by rough seas as well as by hilly terrain. It is shown that the full wave approach accounts for both specular scatter and Bragg scattering. The scattering cross section for the composite surface, with two or more roughness scales, is shown to be a weighted sum of the scattering cross sections for the individual rough surface heights. Shadowing effects are accounted for explicitly in the analysis. The full wave solutions satisfy reciprocity, duality, and realizability relationships in electromagnetic theory.
Finite element analysis of discontinuity problems in a planar dielectric waveguide
Authors: Suzuki Michio , Koshiba Masanori
Published: February 2008

A method for the solution of discontinuity problems in a planar dielectric waveguide is described. The approach is a combination of the finite element method and the analytical method. The finite element approach is used for the interior region enclosing the waveguide discontinuities, while the analytical approach is utilized for the exterior region. The singularities of Green's functions can be excluded by overlapping these regions. In order to minimize the details, the symmetric transverse electric mode excitation of a symmetric slab waveguide is considered. The extension to the antisymmetric case, the transverse magnetic case, and the asymmetric slab waveguide presents no difficulty.
Numerical analysis of an embedded optical waveguide
Authors: Yasuura Kamenosuke , Miyamoto Tokuo
Published: February 2008

The analytical foundations of the mode‐matching method, based on the Rayleigh principle, are presented for the problem of an unbounded object. This method is applied to the numerical analysis of an embedded optical waveguide. The Rayleigh principle for an unbounded object is derived through the transition process from periodic structure to an open system. In the mode‐matching method, the approximate fields are represented by the superposition of plane waves with band‐limited spatial spectra. These fields are matched to the boundary conditions in the least squares sense. The uniform convergency of the sequence of the approximate fields is ensured by the Rayleigh principle. The dispersion relation and the field distribution are calculated, and the propagation characteristics of each guided mode are investigated.
Two‐dimensional finite‐element method calculation of propagation characteristics of axially nonsymmetrical optical fibers
Authors: Oyamada Kimiyuki , Okoshi Takanori
Published: February 2008

In an axially symmetrical single‐mode optical fiber, the polarization plane of the propagated HE11 mode is subject to unstable rotation due to slight changes in ambient conditions. Such an instability can be prevented by making the refractive index distribution in the fiber axially nonsymmetrical. This paper describes a two‐dimensional, vectorial‐wave finite‐element method calculation of the propagation characteristics of such axially nonsymmetrical fibers. It is an improved version of Yeh's program; the field outside the central core region is expanded by a series of modified Bessel functions. Some numerical examples are described.
Decimeter radio wave propagation in the turbulent plasma near the sun, using Venera 10 spacecraft
Authors: Kolosov M. A. , Yakovlev O. I. , Efimov A. I. , Rogal'sky V. I. , Razmanov V. M. , Shtrykov V. K.
Published: February 2008

The 1976 Venus superior solar conjunction resulted in the occultation of the spacecraft Venera 10 by the sun at solar minimum. At the conjunction time, decimeter radio waves passed through the solar corona. The broadening of the spectrum line, as well as amplitude and frequency fluctuations, was observed over extensive distances of the radio link from the sun. The fluctuation characteristics of the radio waves are used to determine solar wind parameters. The fluctuations of the electron concentration have been shown to decrease rapidly with the increasing distance from the sun, but in the region between 12 and 20 solar radii (Rs) the irregularities have increased values. The shape of the spatial spectrum is closely described by the power function ΦN(q) ∝ q−p, but the spectral index may have different values in different parts of the spectrum. The spectral index of the small‐scale part of the spectrum decreases with the decreasing distance from the sun, and at radial distances shorter than 12 Rs its value is close to 3.0 ± 0.2. The inner scale of turbulence of the near‐sun plasma is of the order of several kilometers at distances between 6 and 10 Rs. Typical values of the velocity of motion of the inhomogeneities are 30–40 km/s at radial distances from 2 to 6 Rs, while at distances greater than 18 Rs the velocity exceeds 400 km/s.
Effects of lateral ionospheric gradients on ELF propagation
Authors: Field E. C. , Joiner R. G.
Published: February 2008

This paper analyzes the propagation of the transverse electromagnetic (TEM) ELF mode when the earth‐ionosphere waveguide is not stratified. It treats a localized disturbance by recasting the wave equation as a two‐dimensional integral equation. Numerical solutions show that such a disturbance behaves like a cylindrical lens filling a narrow aperture. Lateral diffraction, focusing, and reflection can cause the TEM mode to exhibit a standing wave pattern before the disturbance, and a transverse pattern of maxima and minima beyond it. Such phenomena can contribute to the spatial fluctuations occasionally observed in ELF transmissions. The focusing and diffraction diminish when the transverse dimension of the disturbance approaches the width of the first Fresnel zone—typically, several megameters. The analysis models exceedingly widespread inhomogeneities, such as a disturbed polar cap or the day/night hemispheres, as semi‐infinite regions having diffuse boundaries. It then derives full‐wave analytic expressions for the lateral reflection and transmission coefficients of the TEM mode. Reflection can be important in two situations: first, when a great‐circle propagation path is nearly tangential to the boundary of the disturbed polar cap and second, when the TEM mode is obliquely incident on the day/night terminator, in which case a phenomenon analogous to internal reflection can occur.
A review of theories of coherent radio wave propagation through precipitation media of randomly oriented scatterers, and the role of multiple scattering
Authors: Olsen R. L.
Published: February 2008

In most practical problems involving radio wave transmission through precipitation, the average, or coherent, field is one of the most important quantities. Although the classical formulation describing coherent propagation effects such as attenuation has existed for many years, it is only recently that this formulation has been extended to adequately include polarization effects. In the last 10 years, a number of theories that take into account the polarization effects caused by the random orientations of the precipitation scatterers have been developed. The similarities and differences between these theories, however, and the role of multiple scattering, are not yet well understood. This paper reviews recent work on the subject. Emphasis is placed on a clarification of (1) the similarities and differences of the various generalizations to the classical theory and (2) the role of multiple scattering in both the classical theory and these generalizations and their approximations. Some improvements to existing theories are also presented.
Physical modeling of em wave propagation over the earth
Authors: King R. J.
Published: February 2008

To obtain experimental data for correlation with the theoretical results obtained from mathematical ground wave propagation models, it is often expedient to conduct experiments on laboratory models using microwaves. Besides the obvious convenience and reduced cost, practical difficulties encountered in full‐scale experiments are avoided (e.g., weather and other uncontrolled parameters such as path nonhomogeneities, earth curvature, buildings, right‐of‐ways, etc). There is no need to use exact similitude scaling; the media and geometries are generally chosen to test the limits of validity of the theory. The designs of several such models in the frequency range of 4–5 GHz are discussed, and typical experimental results are compared with the corresponding theory. Specific examples are propagation in the earth‐ionosphere waveguide and propagation over planar and curved surfaces (including stratified media, for example, layered earth and sea ice), mixed paths (including media having abrupt discontinuities such as land‐sea boundaries and gradual nonuniformities such as sloping beaches), uniaxially anisotropic media, and media having an index of refraction near unity (e.g., heavy vegetation). When using such models, instrumentation systems and field probing techniques are key factors in their success. These are also discussed.
Ionospheric absorption of the extraordinary wave
Authors: Olatunji E. O.
Published: February 2008

Characteristics of x wave absorption are investigated by using the phase integral method. For various noon models of the mid‐latitude ionosphere, empirical relations are derived to represent the dependence on wave frequency, dip angle, and gyrofrequency, and to take account of seasonal changes. A quantitative relationship between x wave and o wave absorption is established.
Observations of tropospheric phase scintillations at 5 GHz on vertical paths
Authors: Armstrong J. W. , Sramek R. A.
Published: February 2008

We report here observations of tropospheric phase fluctuations at 5 GHz on the near‐vertical paths relevant to a number of astronomical and geophysical measurements. Using the Very Large Array near Socorro, New Mexico, the spatial structure function of phase was measured in the scale size range 1–35 km. The 23 data sets reported here were taken over a 2.5‐year interval. During 15 observing sessions there is a clear detection of tropospheric phase fluctuation, while only upper limits can be constructed on the remaining 8 days. The measured structure functions vary as (baseline)x, with the average value of x being 1.4. Where comparisons with other microwave observations (e.g., water vapor radiometry) are possible, there is reasonably good agreement in both the level and shape of the power spectrum of these tropospheric phase fluctuations. Some implications of these observations for precision Doppler tracking of spacecraft and geodesy/radio interferometry observations are discussed. Although the level of these tropospheric scintillations is highly time variable, very low frequency gavitational radiation searches using Doppler tracking of distant spacecraft will have, if uncalibrated, tropospheric propagation noise at a typical level Δƒ/ƒ∼ 5 × 10−15 for 1000‐s integration times.
ELF magnetic fields in electrosteel and welding industries
Authors: Lovsund P. , Oberg P. A. , Nilsson S. E. G.
Published: February 2008

All the measurements were performed in the working positions at the machines. Field flux densities in the range 0–10 mT at mostly 50 Hz were found in both types of industries. Near induction heaters, both the magnetic flux density and the frequency may be very high (up to 10 kHz). Knowledge of industrial field characteristics such as frequency, flux density, and distribution will facilitate laboratory research aimed at determining possible biological effects of magnetic fields. These results indicate that biological effects of the magnetic fields probably occur (magnetophosphenes), although these phenomena are difficult to recognize in industrial localities with high background illumination.
Effects of continuous and pulsed chronic microwave exposure on rabbits
Authors: Chou Chung‐Kwang , Guy Arthur W. , McDougall John A. , Han Lock‐Fong
Published: February 2008

Eighteen young adult New Zealand rabbits (nine males, nine females) were equally divided into three groups. One group was exposed to CW 2450‐MHz fields at an incident power density of 1.5 mW/cm2 for 2 hours daily for 3 months. Another group was exposed to pulsed fields with pulses of 10 μ s duration occurring 100 times per second. The third group was sham exposed. Each rabbit was placed in a Plexiglas cage and exposed in a miniature plane wave exposure chamber. An S band horn was mounted 1 m above the animal. Thermographic data showed a peak specific absorption rate of 1.64 W/kg in the head and 2.1 W/kg in the back. Body weights were measured every other day. Electroencephalogram and evoked potentials were recorded weekly via implanted carbon‐loaded Teflon electrodes. Blood samples were taken monthly for hematological, chemical, and morphological studies. Eyes were examined for cataract formation. Before the animals were sacrificed, apomorphine‐induced behavioral excitation and hyperthermia were studied. Finally, pathological examinations on many tissues and organs were performed. Statistically, there were no significant differences in measured parameters observed between the exposed and sham animals.
A pole‐zero modeling approach to linear array synthesis: 1. The unconstrained solution
Authors: Miller Edmund K. , Goodman Dennis M.
Published: February 2008

Prony's method, a procedure for estimating the parameters of a sum of exponentials, is applied here to linear array pattern synthesis. Unlike most approaches to this problem, Prony's method provides source locations as well as source strengths, so that the synthesized distributions generally involve nonuniformly spaced sources. In this paper, the procedure is developed, its numerical characteristics are discussed, and its application is illustrated for several different radiation patterns. Because the unconstrained procedure discussed here can lead to a requirement for directive sources, paper 2 will treat a version of Prony's method constrained to produce isotropic sources.
Modeling of atmospheric radio noise near thunderstorms
Authors: Nakai Taketoshi
Published: February 2008

A model of atmospheric radio noise produced by a near thunderstorm is presented to give a physical interpretation to the properties of the fields in terms of the peak amplitude distributions of received impulses at the input of a narrow‐band receiver. In connection with the model, propagation over a short distance from any discharge inside the thunderstorm and the statistics of varying peak currents of return strokes and K changes are examined, and two different expressions, one expressing a lognormal distribution only for return strokes and the other a combination of two different lognormal distributions for the coexistence of return strokes and K changes, are presented, both of which are available in calculating the respective part of the peak amplitude distribution. The emphasis is on the variation in the shape of the distribution with the distance to the thunderstorm. Comparisons have been made between calculated distributions and evvelope crossing rate distributions (CRD's) at the output of the receiver. Comparisons have been found to be good for a frequency of 3 kHz in the high‐amplitude range of measured CRD's, which is nearly equal to the corresponding peak amplitude distribution at the input of the receiver. Further application of the model is shown to be appropriate to higher frequencies, 50 kHz and 90 kHz, on the basis of the observed behavior of CRD's.
Potentialities of electric and magnetic wave tilt measurements
Authors: Singh Ramesh P.
Published: February 2008

A comparative study of TM and TE mode wave tilt magnitude and phase variations in the extended frequency range have been carried out for some electrical parameters of the earth's surface as a half‐space model. The TM and TE mode wave tilts show complementary behavior in the extended frequency range. The problem of excitation and propagation of TE mode wave has been discussed. It is shown that the measurement of Wm and We in the extended frequency range would reveal the surface and subsurface features.
The influence of electric fields on radar measurements of winds in the upper mesosphere
Authors: Reid George C.
Published: February 2008

The mesosphere‐stratosphere‐troposphere radar technique deduces wind speeds and directions from the Doppler velocities of small‐scale irregularities in the refractive index. In the upper mesosphere, where the refractive‐index irregularities are due to corresponding irregularities in plasma density, the velocities may depart significantly from the wind vectors, especially at auroral‐zone latitudes, where electric fields can be large. The magnitude of the effect is estimated for spherical irregularities in the height region from 60 to 120 km. In the case of horizontal drifts, the departure of the plasma velocity from that of the neutral wind is small in comparison to typical horizontal wind velocities at heights below 90 km except under highly disturbed conditions. The average vertical component of the neutral wind, however, is small, and attempts to measure it in the upper mesosphere can be seriously affected by electric fields mapped down from the auroral‐zone magnetosphere, and even by the dynamo action of local horizontal winds.
Initial Studies of Small‐Scale F Region Irregularities at Very High Latitudes
Authors: Greenwald R. A. , Baker K. B. , Villain J. P.
Published: February 2008

In this paper we describe a recently developed HF radar system designed to study F region irregularities at high latitudes. The radar utilizes a 7‐pulse multipulse sequence enabling it to determine 17‐lag autocorrelation functions of E and F region irregularities. These autocorrelation functions and the associated Doppler spectra are not subject to the range‐frequency ambiguity that occurs with other spectral techniques. The radar has been operated from the Cleary field site near Fairbanks, Alaska, for a short period in February 1982. The primary field of view of these measurements was poleward of Inuvik in northwestern Canada. Initial results from these measurements indicate a great deal of spatial and temporal variability in the irregularity Doppler characteristics; however, the overall pattern is generally consistent with the nominal pattern of very high latitude convection. Some anomalies existed, including evidence of an appreciable component of dawn‐dusk drift near the most poleward latitudes of observation in the dawn local time sector.
Determination of current induced on a conducting strip embedded in a dielectric slab
Authors: Michalski Krzysztof A. , Butler Chalmers M.
Published: February 2008

Integral equations for the current density on a TM‐ and a TE‐excited conducting strip embedded in a dielectric slab are derived and solved numerically. The Sommerfeld‐type integrals incorporated in the kernels of the integral equations are evaluated numerically along various specified paths in the complex spectral plane, and a path switching criterion is used to maximize the efficiency of the integration. Results are presented for current induced on strips in lossy and lossless slabs for both plane wave and line current excitations. The effects of varying slab thickness, strip width, displacement of the strip from the slab center, and the loss tangent of the slab material on the current distribution are demonstrated.
Ionogram analysis: Least squares fitting of a Chapman‐layer peak
Authors: Titheridge J. E.
Published: February 2008

A formulation is described which uses plasma frequency F as a function of real height h near a layer peak. This allows profile data from lower heights, and scaled critical frequencies from both magnetoionic components, to be combined in a single least squares solution. The scaled critical frequencies do not define the final value, but provide additional input to the least squares calculation. Results give directly the rms fitting errors for the critical frequency, the peak height and the scale height. Calculations begin with an assumed model value for the scale height near the peak. With good data the final result is independent of this model. As the amount and consistency of the data decreases, the solution automatically gives more weight to the initial (model) scale height. This greatly reduces the normal tendency for peak extrapolations to become erratic or absurd as the quality of the data decreases. With very poor data the model scale height is imposed directly. The critical frequency is still obtained from a least squares solution, using the known scale height plus some physical checks to ensure a reasonable range of extrapolation. Thus optimum results are obtained with good data, and acceptable peak profiles are obtained from all useful ionograms.
Ionospheric effects on C3I satellite communications systems in Greenland
Authors: Johnson Allen , Taagholt Jorgen
Published: February 2008

For the past 25 years the effects of the polar ionosphere on satellite communications has been under evaluation in Greenland. As a result of the testing, models have been developed which quantify the effects of solar flux, magnetic index, time of day, season, elevation angle, and frequency on ionospheric scintillation fading. For the past 10 years, operational type of satellite communications testing has been conducted in Greenland to evaluate the feasibility of replacing the traditional HF radio links with satellite communications links. This paper reviews the effects of polar ionospheric scintillation fading, describes the operational testing, and identifies plans for operational use of satellite communications in Greenland.
Characteristics and sources of ionization in the continuous aurora
Authors: Robinson R. M. , Vondrak R. R.
Published: February 2008

The continuous aurora is defined as E region ionization that is steady in time and uniformly distributed over a large portion of the auroral oval. We have examined the characteristics and sources of ionization in the continuous aurora using data from the Chatanika incoherent scatter radar and several polar orbiting satellites. The altitude profile of ionization in the continuous aurora usually has an E region maximum of 0.5 to 5×105 cm−3 at altitudes between 110 km and 140 km. The profile is very similar to that expected from precipitating electrons with a Maxwellian energy distribution of 0.5–4 keV characteristic energy and an energy flux of 0.2 to 16 erg/cm2 s. We have used simultaneous electron flux data from the DMSP satellites to assess the extent to which precipitating electrons are responsible for the continuous aurora. We show two cases in which the simultaneous incoherent scatter radar data revealed substantial ionization equatorward of the region of electron precipitation. We attribute this ionization to precipitating protons. The presence of significant ionization produced by proton precipitation is confirmed by a third data set in which measurements of precipitating proton fluxes made by the NOAA 6 satellite over the diffuse aurora near Chatanika indicated a proton energy flux of about 0.5 ergs/cm2 s. The energy flux carried by precipitating electrons was more than an order of magnitude less. Ionization produced by proton precipitation can have an altitude distribution very similar to electron aurora. In addition, the proton aurora has the same latitudinal profile as the electron aurora, so that distinction between the two cannot be made on the basis of electron density measurements alone.
A theoretical model of artificial spread F echoes
Authors: Kuo S. P. , Lee M. C. , Kuo Steven C.
Published: February 2008

Four invariants of the ray trajectory are found for a ray propagating in a horizontally stratified ionosphere under the density perturbation of HF wave‐induced field‐aligned irregularities. The reflection height of the ray can then be determined with the aid of those invariants. The results show that the reflection height of the ray varies drastically (namely, strong spread F echoes) in the presence of irregularities that polarize in the magnetic meridian plane. By contrast, the reflection height is not affected (namely, no spread F echoes) by those irregularities that polarize in the direction perpendicular to the meridian plane. Spread F is quite insensitive to the magnetic dip angle θ0 in the region from 20° to 70°. The dependence of spread F on the scale length of the irregularity has also been examined for the case θ0 = 50°. It is found that spread F is not caused by irregularity with scale length less than about 100 m.
Multiple scattering of electromagnetic waves from two infinitely conducting prolate spheroids which are centered in a plane perpendicular to their axes of revolution
Authors: Dalmas Jeannine , Deleuil Roger
Published: February 2008

In this new work on multiple scattering of electromagnetic waves from two infinitely conducting prolate spheroids, we study the configuration corresponding to two scatterers centered in a plane perpendicular to their parallel axes of revolution. As in a previous paper we have pointed out the influence of a shape factor on the multiple scattering cross section (MSCS). This shape factor is independent of the state of polarization of the incident plane wave. The multiple scattering cross section is calculated at oblique incidence with two identical prolate spheroids described by c = 5 and ξ = 1.1547 and located according to two particular configurations. As an illustration, some MSCS patterns are presented here. They are drawn in several azimuthal planes and in the equatorial (or broadside) plane. We note the existence of lobes located along the polar axis in particular azimuthal planes. In the equatorial plane the lobes are differently located according to the position of the centers of spheroids in this plane. It must be noted that the number of lobes increases when the distance between the centers of the spheroids also increases.
Three‐dimensional saturation spectrum of the parametric decay instability
Authors: Das A. C. , Fejer J. A. , Martinic N. J.
Published: February 2008

The three‐dimensional saturation spectrum of the parametric decay instability is obtained numerically, taking the true polarization of the pump field into account. In previous works the pump electric field was taken to be parallel to the inclined geomagnetic field, although that condition is only satisfied generally by an ordinary (pump) wave if its frequency ω is equal to the plasma frequency ωp or if its propagation vector is perpendicular to the magnetic field. The spectrum obtained numerically for ω0 = 1.04 ωp deviates strongly from axial symmetry about the geomagnetic field, especially for the large angle of inclination existing at Tromsø. The results obtained will therefore be important for the interpretation of the saturation spectrum observed with the aid of the EISCAT 933‐MHz UHF radar (which detects Langmuir waves for which ω0 ∼ 1.04 ωp) during ionospheric modification experiments near Tromsø.
On the detection of acoustic‐gravity waves generated by typhoon by use of real time HF Doppler frequency shift sounding system
Authors: Huang Yinn‐Nien , Cheng Kang , Chen Sen‐Wen
Published: February 2008

A development of a direct vision type high‐frequency Doppler frequency sounder and a setup of HF Doppler frequency sounding array at the northern part of Taiwan Island were presented. By use of all typhoons that occurred in 1982 and 1983, the detectability of the typhoon‐generated acoustic‐gravity waves by use of this HF Doppler frequency sounding array was presented. The results show that the acoustic‐gravity waves generated by a typhoon can be detected by this sounding array; however, the detectability is only 2 out of 12.
Absolute intensities of low‐latitude whistlers as deduced from the direction‐finding measurement
Authors: Hayakawa M. , Ohta K. , Okada T. , Tanaka Y.
Published: February 2008

The direction finding measurement has enabled us to estimate the absolute intensity of whistlers at low latitudes. Based on the long‐term automatic measurement since December 1981 at Yamaoka (geomagnetic latitude 25°N), nine events are selected for daytime (1500–1900 LT) whistlers and four events for nighttime (0300–0900 LT) whistlers. It is found that the daytime whistlers are more intense than nighttime ones, such that the absolute intensity of the maximum occurrence is 100–125 μV/m and the peak value is 225–250 μV/m during daytime, while the corresponding peak value at night is 150–175 μV/m, about a few decibels weaker than the daytime peak value. Finally, we attempt to interpret this day‐night asymmetry of the absolute intensity.
Comparison of mesospheric wind spectra with a gravity wave model
Authors: Smith Steve A. , Fritts David C. , VanZandt Thomas E.
Published: February 2008

We present radial wave number spectra of wind fluctuations obtained from heights near the mesopause by the Poker Flat, Alaska, mesosphere‐stratosphere‐troposphere (MST) radar running in a high spatial resolution mode (300 m). The spectra are of radial wind fluctuations along one vertical and two oblique (15° zenith angle) beams measured at heights of 82–88 km during summer. The oblique wave number spectra have amplitudes that are within a factor of 3 of each other and appear to follow power laws with exponents in the −2 to −2.8 range. In order to infer what portion of the spectral amplitude can be attributed to gravity waves, the ratio of oblique to vertical amplitudes is compared with the ratio predicted by the gravity wave model of VanZandt. The observations are found to be consistent with the model, suggesting that gravity waves are the dominant motion in the high‐latitude summer mesosphere.
A simple rain attenuation model for earth‐space radio links operating at 10–35 GHz
Authors: Stutzman W. L. , Yon K. M.
Published: February 2008

The simple attenuation model has been improved from an earlier version and now includes the effect of wave polarization. The model is for the prediction of rain attenuation statistics on earth‐space communication links operating in the 10–35 GHz band. Simple calculations produce attenuation values as a function of average rain rate. These together with rain rate statistics (either measured or predicted) can be used to predict annual rain attenuation statistics. In this paper model predictions are compared to measured data from a data base of 62 experiments performed in the U.S., Europe, and Japan. Comparisons are also made to predictions from other models.
On the physical contents of some integral equations for inverse scattering from inhomogeneous objects
Authors: Wolf Emil , Porter Robert P.
Published: February 2008

The physical contents of some integral equations that have been frequently used in recent years in connection with solutions of inverse source problems and of inverse scattering problems are discussed. It is shown that the integral equations can only provide information about a filtered structure of a source or a weak scatterer. The filtering is found to remove all the Fourier components of the source distribution or of the scattering potential that represent details smaller than about a wavelength of the radiated or of the scattered field. The nature of the associated filtered field is also studied, and a comparison of the integral equation method with an older reconstruction method is made.
Simultaneous reconstruction of permittivity and conductivity profiles in a radially inhomogeneous slab
Authors: Habashy T. M. , Chew W. C. , Chow E. Y.
Published: February 2008

This paper considers the simultaneous reconstruction of permittivity and conductivity profiles in a cylindrically stratified geometry. It is assumed that both the permittivity and conductivity may only vary in the radial direction, and that the unknown region, to be probed, is an annulus of known thickness. An iterative method for the simultaneous inversion of the radial permittivity and conductivity profiles inside this annulus is presented. This method employs a distorted‐Born approximation at each iteration step. The inherent nonuniqueness of the problem is circumvented by imposing additional constraints that limit the set of feasible solutions. Numerical simulations show that good results can be obtained for smoothly varying profiles even when a limited number of measurements at a single frequency are used.
The amplitude spectra of lightning radiation fields in the interval from 1 to 20 MHz
Authors: Weidman C. D. , Krider E. P.
Published: February 2008

Although the interactions of lightning with aircraft and many other structures are critically dependent on the amplitudes of the electromagnetic fields in the 1 to 20 MHz frequency interval, there are relatively few measurements of these spectra in the lightning literature. In this paper, we present amplitude spectra of the fast‐rising, initial portion of fields that are produced by return strokes, leader steps, and cloud pulses. These data have been derived from ground‐based measurements of dE/dt signatures that were recorded in the time‐domain on a triggered oscilloscope. The spectral amplitudes of first return strokes match previously published data at 1 MHz and decrease with increasing frequency as 1/ƒ between 1 and about 6 MHz and as 1/ƒ2 between 6 and 20 MHz. The spectral amplitudes of leader steps just before return strokes and the fast portion of cloud pulses that triggered the recording system tend to lie 5 to 10 dB below the amplitudes of first return strokes over the entire frequency interval.
A semi‐empirical low‐latitude ionospheric model
Authors: Anderson David N. , Mendillo Michael , Herniter Bruce
Published: February 2008

Since current empirical models specifying low‐latitude electron density profiles severely underestimate the daytime plasma density scale‐height and total electron content (TEC) values, a semi‐empirical low‐latitude ionospheric model (SLIM) has been developed which is not only computationally fast, but also more realistic. Electron density profiles (180–1800 km) are theoretically calculated as a function of latitude (every 2° between 24°N and 24°S dip latitude) and local time (every half hour, over 24 hours LT) by solving the time‐dependent plasma continuity equation. Using simple exponential functions, sets of coefficients are then generated which reproduce these individual profiles. The coefficients themselves are easily stored, quickly retrieved and form the basis for a fast, portable, semi‐empirical computer code. This paper describes briefly the input parameters used to theoretically calculate the profiles and the procedures used to generate the coefficients. The SLIM profiles are compared with the Chiu and Bent empirical models for equinox, solar maximum conditions, while calculated 6300 Å airglow intensities and TEC values are compared with available observations. The SLIM profiles, their coefficients, TEC and 6300 Å airglow intensities are available in tabular and computer formats.
Atmospheric emission variation measurements at 3, 0.9, and 0.33 cm wavelength
Authors: Smoot G. F. , Levin S. M. , Kogut A. , De Amici G. , Witebsky C.
Published: February 2008

We have measured the fluctuation power spectrum and correlation of fluctuations of atmospheric emission at wavelengths of 3, 0.9, and 0.33 cm. The fluctuations measured at different wavelengths are well correlated with each other and can be described with a simple parameterization. Our results are in agreement with other measurements of phase and absorption variation and with the hypothesis that atmospheric water fluctuations dominate other effects. Our measurements are in good agreement with the predictions of the Kolmogorov turbulence model, which can be used to predict the temporal and spatial spectra of atmospheric scintillation and emission variation.
Three‐dimensional ray tracing of electrostatic cyclotron harmonic waves and Z mode electromagnetic waves in the magnetosphere
Authors: Hashimoto K. , Yamaashi K. , Kimura I.
Published: February 2008

Three dimensional ray tracing is made for electrostatic electron cyclotron harmonic waves and Z mode electromagnetic waves in the earth magnetosphere, using the hot plasma dispersion relation. For a large wave number region, the so‐called electrostatic approximation for the dispersion relation can be used to trace the ray paths. The necessary initial conditions for an electrostatic electron cyclotron harmonic mode wave to be continuously converted to a Z mode electromagnetic mode wave can be investigated by the electrostatic approximation. Only the waves generated in the very vicinity of the geomagnetic equatorial plane can propagate over a long distance. The waves can be converted to Z mode if the initial wave normal direction lies near the geomagnetic meridian plane. The algorithm of ray tracing using the full hot plasma dispersion relation is also developed. A complete traverse of the wave starting from the electrostatic electron cyclotron harmonic mode to the Z mode can only be confirmed by the ray tracing based on the full hot plasma dispersion relation. A possibility of conversion from the electrostatic mode finally to a free space electromagnetic mode can also be investigated by this ray tracing. These results are not contradictory with the conversion mechanism for the generation of escaping continuum radiation in the earth magnetosphere.
A numerical method for solving edge‐type scattering problems
Authors: Okuno Y.
Published: February 2008

A numerical method for solving the two‐dimensional edge‐type scattering problems is presented. The method is basically the mode‐matching method with a smoothing procedure which has been known as a numerical technique for the problems with smooth scatterers. It is made clear that the method with the smoothing procedure can be applied also to the edge‐type problems when it is accompanied by an appropriate transformation of the coordinate variables along the contour of the scatterer. Mathematical theory of the method with the variable transformation is stated, and the algorithm for numerical computation is derived. The problem of a rectangular cylinder is analyzed to show the effectiveness of the present method.