bluuebunny/crossref_metadata_2025 huggingface dataset:
An all‐sky‐camera format for radar auroral studies
Authors: Fremouw E. J. , Fang D. J.
Published: February 2008

Installation of a phased‐array antenna on a UHF radar located at Homer, Alaska, makes possible a variety of data presentations for studying the radar aurora. In this paper we describe a data handling procedure that permits rather direct comparison of radar auroral developments with optical auroral displays. The procedure involves coordinate transformation of digitized radar data to produce a display resembling an all‐sky‐camera photograph from a selected location beneath the radar's field of view in the E layer. We present here five representative case studies of auroral developments as displayed in the radar all‐sky‐camera format and simultaneously recorded by means of optical all‐sky cameras located in central Alaska (Fort Yukon and Chatanika).
Techniques for the calculation of attenuation from precipitation for single station and path diversity satellite communication systems from digital radar data
Authors: Austin Lydia B. , Austin G. L.
Published: February 2008

Digital radar reflectivity data may be used to estimate the slant path attenuation which would have been obtained on a ground‐to‐satellite path using a frequency higher than that of the original radar. The crucial role of the small intense cells is illustrated and the necessity of maintaining the radar data at their highest spatial resolution is discussed. A technique to simulate path diversity systems is demonstrated for a squall line case and shows that diversity pair orientation perpendicular to the elongation of the precipitation line studied yields the best diversity performance.
Generalized cross‐correlation analysis of phased array admittance
Authors: Zaghloul Amir I. , MacPhie Robert H.
Published: February 2008

A new method is introduced to analyze phased array antennas of the aperture type, and is based on the Fourier transform relationship between the aperture electric field's cross‐correlation function and the angular cross‐spectral power density. The theory is first presented in the general form for planar arrays and then is applied to a linear array of infinitely long narrow slots covered by a dielectric slab. The array input admittance as well as the active reflection coefficient are deduced. It is shown that the point of unit reflection coefficient (blindness) in the scanning pattern, which occurs for ideal infinite periodic arrays, no longer exists for arrays with positioning errors. Instead, a near‐zero reflection point is preceded and succeeded by two reflection maxima. The cross‐correlation method helps also to clarify the nature of blindness for large finite periodic arrays; again, the blindness angle is one at which there is a near‐zero reflection coefficient with two high reflection coefficient regions on either side.
Correction [of numerical results in “ELF terrestrial radio wave field calculations with the zonal‐harmonics series”]
Authors: Lewis Richard L. , Ralph Johler J.
Published: February 2008

The presence of a numerical error in a previous publication is noted and the error source identified. However, the theoretical formulation is correct. Corrected numerical results are presented which favorably compare with results computed by other researchers. Also, theoretical results are produced using a predicted ionospheric profile of an upper atmosphere nuclear detonation. Finally, field attenuation for hypothetical two‐layer ionospheric profiles is plotted as a function of lower‐layer conductivity. It is seen that some hypothetical cases can exhibit high attenuation values in comparison to the normal‐day's attenuation value. Some new theoretical expressions for the zonal‐harmonics analytical formulation are exhibited, and the improvement expected in computational efficiency and in numerical precision by breakoff of the ground wave from the rest of the summation is discussed.
Two‐way communication with an earth penetrator
Authors: Caffey Thurlow W. H.
Published: February 2008

A telemetry link capable of communicating from a depth of 50 m to the surface is described. The buried package fits within a diameter of 100 mm and provides a bit error rate of less than 10−4 at a rate of 1000 bits per second while consuming 8 w. A control link capable of turning on and off the buried telemetry transmitter from the surface is also described together with results from typical tests in a three‐layer soil. The included propagation analysis is intended for use at frequencies below 100 kHz.
A comparison of field patterns for bare and insulated circular‐loop antennas
Authors: Smith Glenn S.
Published: February 2008

An apparatus designed to measure field patterns of circular‐loop antennas immersed in fresh water is described. Measured field patterns are presented to show the differences between bare and insulated loop antennas and to compare loops having different forms of insulation. The insulation is seen to alter the field pattern significantly when the loop dimensions are such that it is electrically large in the water but not in dielectric material forming the insulation. Some shaping of the field pattern can be accomplished by placing the wire loop asymmetrically in the insulation. The measured field patterns are in good agreement with theoretical patterns calculated using the Fourier series analyses for bare and insulated circular‐loop antennas.
Remote profiling of lake ice using an S‐band short‐pulse radar aboard an all‐terrain vehicle
Authors: Cooper Dale W. , Mueller Robert A. , Schertler Ronald J.
Published: February 2008

An airborne short‐pulse radar system to measure ice thickness was designed and operated during the 1973–74 and 1974–75 ice seasons. This system supported a joint effort among NASA, the US Coast Guard, and NOAA to develop an all‐weather Great Lakes Ice Information System which aids in extending the winter navigation season. This paper describes experimental studies into the accuracy and limitations of this short‐pulse radar system. A low‐power version of this system was built and operated from an all‐terrain vehicle on the Straits of Mackinac during March 1975. The vehicle allowed rapid surveying of large areas and eliminated the ambiguity in location between the radar system and the “ground truth” ice auger team which is unavoidable for the airborne versions of the system. These in situ measurements also permitted an assessment of the effects of snow cover, surface melt water, pressure ridging, and ice type upon the accuracy of the system. Over 25 sites were explored which had ice thicknesses in the range from 29 to 60 cm. The maximum radar overestimate was 9.8%, while the maximum underestimate was 6.6%. The average error of the 25 measurements was 0.1%.
Emissivity of half‐space random media
Authors: Tsang L. , Kong J. A.
Published: February 2008

Scattering of electromagnetic waves by a half‐space random medium with three‐dimensional correlation functions is studied with the Born approximation. The emissivity is calculated from a simple integral and is illustrated for various cases. The results are valid over a wavelength range smaller or larger than the correlation lengths.
Electromagnetic penetration through an aperture in an infinite, planar screen separating two half spaces of different electromagnetic properties
Authors: Butler Chalmers M. , Umashankar Korada R.
Published: February 2008

Integro‐differential equations are formulated for the general problem of electromagnetic diffraction by an aperture in a planar conducting screen of infinite extent separating two half spaces of different electromagnetic properties. With the aperture specialized to the case of an infinite slot, equations appropriate for TE and for TM illumination are deduced from those for the general aperture. These slot equations are solved numerically, and results are presented for several cases of interest.
Semidiurnal tide in the E region from incoherent scatter measurements at Arecibo
Authors: Wand R. H.
Published: February 2008

A five‐pulse technique was implemented for the 430 MHz incoherent scatter radar at Arecibo Observatory (18.3°N), to explore the detailed thermal structure of the E region from 105 to 130 km with an altitude resolution of 3 km. Five days of measurements in Sept–Oct 1970 showed long‐period temperature fluctuations having a downward phase progression. The temperature oscillations are interpreted as manifestations of a semidiurnal tide which is quite stable over a 12‐day period, together with a superimposed spectrum of shorter‐period gravity waves which are randomly phased from day to day. The semidiurnal tide increased to a maximum amplitude of 17% of the mean temperature near 115 km and decreased above this altitude as dissipative effects became important. The vertical wavelength, deduced from the altitude variation of semidiurnal tidal phase, showed a smooth increase from about 20 km at an altitude of 109 km to about 50 km at an altitude of 127 km. No ready interpretation of the observed tidal characteristics was possible in terms of present theories for the semidiurnal tide. Altitude profiles of mean daytime temperature and ion‐neutral collision frequency were also obtained from the measurements. The mean temperature gradient between 115 and 130 km was 15 K/km, which is somewhat larger than that given by current atmospheric models.
Coupled insulated antennas in a relatively dense medium: currents and admittances
Authors: King R. W. P. , Wu T. T. , Shen L. C.
Published: February 2008

The analysis of the insulated dipole in a relatively dense medium is extended to coupled, individually insulated elements arranged in a circular array. It is shown that the transmission‐line‐like distributions of current are preserved for each phase sequence but with different complex wave numbers that depend not only on the electrical properties of the insulating and ambient media but also on the coupling among the elements. Special attention is given the two‐element and three‐element arrays.
Electromagnetic scattering by two perpendicular wire grids over a conducting half‐space
Authors: Wait James R. , Hill David A.
Published: February 2008

A doubly infinite set of linear equations is derived for the currents excited on a rectangular wire mesh that is located over a conducting half space. The mesh consists of two parallel grids whose wires are perpendicular to each other. In the formulation, the spacing between the grids is arbitrary but the numerical method, involving direct matrix inversion of the truncated set, is only feasible if the intergrid spacing is nonzero. The numerical results show that the reflection properties of the grid are a strong function of the azimuthal direction of incidence. This characteristic is consistent with earlier results for unbonded meshes in free space. An important conclusion is that wire mesh ground systems used, for example, in high frequency antenna installations should employ unbonded (i.e., unsoldered) wire junctions.
Two‐frequency mutual coherence function and pulse propagation in a random medium: An analytic solution to the plane wave case
Authors: Sreenivasiah I. , Ishimaru Akira , Hong Shin Tsy
Published: February 2008

Pulse propagation in a random medium is determined by the two‐frequency mutual coherence function which satisfies a parabolic equation. In the past, approximate or numerical solutions of this equation have been reported. This paper presents an exact analytical solution for a plane wave case when the random medium is approximated by A(0) − A(ρ) ∝ ρ2. Analytic expressions for two‐frequency mutual coherence function, pulse shape, temporal and angular spectra are presented in universal forms, and should be applicable to a large number of practical problems.
The ionospheric sounder and its place in the history of radio science
Authors: Villard Oswald G.
Published: February 2008

It is suggested that Breit and Tuve's 1925 application of pulses to ionospheric sounding, which led to the most widely used form of radar, also gave rise to a scientific instrument whose utility, flexibility, and general suitability for intended applications place it on a par with such familiar and standard devices as the telescope or spectrograph. By way of background, there is included a discussion of the circumstances attendant upon the first measurement of ionospheric layer height, which took place in 1912.
Poynting vector behavior in lossy media and near a half space
Authors: Lytle R. J. , Lager D. L. , Miller E. K.
Published: February 2008

Although the real part of the complex Poynting vector,
cannot be strictly interpreted to indicate power flow, its previous use for this purpose has produced no logical inconsistencies. Results of
for sources in lossy media, for plane waves interacting with a lossy half‐space, and for Hertzian sources located near a lossy ground have been generated. The power flow results for these problems provide unexpected but physically consistent results.
A technique for simultaneous measurement of attenuation and bistatic scatter due to rainfall at millimeter waves
Authors: Mink J. W.
Published: February 2008

A shuttle‐pulse technique for simultaneous measurement of the attenuation and bistatic scatter of millimeter waves is described. Measurements were obtained using a propagation path through rain of only a few meters; therefore, the rainfall statistics can be considered constant within the sample volume. Absorption data resulting from this experiment show a disagreement with theory similar to that previously reported. A “total bistatic scatter coefficient” for rain is defined, and the technique of using a shuttle pulse for its measurement is discussed.
Wave propagation in an inhomogeneous multi‐mode medium
Authors: Askne J. , Lisak M.
Published: February 2008

Starting from a description of mode propagation in a homogeneous medium, coupling between different modes at an interface is derived based on a general formulation of the boundary conditions for a medium without spatial dispersion. The results are then applied to a layered medium which yields a simple way to derive the first‐order coupled differential equations for a multi‐mode, inhomogeneous medium in the case of vertical incidence. By this method the results are easily interpreted. As an application the magnetoionic medium is studied.
Effects of horizontal refractivity gradients on the accuracy of laser ranging to satellites
Authors: Gardner C. S.
Published: February 2008

Numerous formulas have been developed to partially correct laser ranging data for the effects of atmospheric refraction. These formulas all assume the atmospheric refractivity profile is spherically symmetric. The effects of horizontal refractivity gradients are investigated by ray tracing through spherically symmetric and three‐dimensional refractivity profiles. The profiles are constructed from radiosonde data. The results indicate that the horizontal gradients introduce an rms error of approximately 3 cm when the satellite is near 10° elevation. The error decreases to a few millimeters near zenith.
Antenna radiation patterns in the whistler wave regime measured in a large laboratory plasma
Authors: Stenzel R. L.
Published: February 2008

The radiation pattern of electric dipole and magnetic loop antennas is determined experimentally in the parameter regime 0.1 ≲ ω/ωc ≲ 1, 1 ≲ ωp/ωc ≲ 30 (ωp, ωc = electron plasma, cyclotron frequency, respectively). The measurements are performed in a uniform, dense magneto‐plasma (density 1010 < ne < 1012 cm−3, temperature 0.2 < kTe < 3 eV, magnetic field B0 ≲ 100 G) of very large dimensions (50 cm diameter, 300 cm length) where boundary effects are negligible even for many far‐field patterns. When the antenna dimensions are small compared to the parallel whistler wavelength (k¶ Lant≪ 1) the radiation pattern is characterized by resonance cones. For finite sized antennas (k¶ Lant≳ π) no cones are observed, but a dipole‐like pattern with a field‐aligned narrow lobe. Amplitude and phase distribution in the near zone and far zone are investigated. The antenna orientation with respect to the static magnetic field is varied. At large amplitudes (Brf/B0 ≃ 1%) the radiation pressure modifies the plasma density and the wave self‐focuses. In this regime nondiverging filaments of radiation are seen.
On the time and amplitude properties of electric fields near sources of lightning in the VLF, LF, and HF bands
Authors: Nakai Taketoshi
Published: February 2008

Observations of electric fields near sources of lightning, followed by analysis of the observed data statistically with an electronic computer, were made at the Imaichi Observatory in Japan during the summers of 1969, 1970, and 1971. The electric fields were measured simultaneously with four narrow‐band receivers having the following central frequencies (and 3 dB bandwidths): 3 kHz (460 Hz), 50 kHz (480 Hz), 90 kHz (850 Hz), and 5 MHz (1 kHz). Particular emphasis was placed on analyzing the field data for which the ground discharges can be assumed to have outnumbered the cloud discharges. The characteristics of the electric fields near the sources in the VLF, LF, and HF bands are described in terms of (1) the envelope‐level occurrence‐time‐interval distribution (OTID), and (2) the envelope‐level crossing‐rate distribution (CRD). The median curves of OTID and CRD are given for each of the four measurement frequencies. Relationships between the OTID and CRD from the same data sample are derived in an averaged form. The procedure used for describing the characteristics of the electric field make it possible to model the electric field near the source for each frequency by taking into account both the amplitude and the time characteristics. The behavior of the CRD in the VLF to HF range is observed over the same time interval during general variations in the lightning discharge conditions.
Brillouin optical‐fiber ring oscillator design
Authors: Johnson D. C. , Hill K. O. , Kawasaki B. S.
Published: February 2008

A theoretical model is developed to describe the CW operation of a Brillouin optical‐fiber ring oscillator. Expressions describing both the oscillation threshold and the Brillouin output power are derived as a function of the design parameters and the conditions to maximize the output power are then determined. For the ring resonator configuration considered it is shown that the maximum external conversion efficiency that can be achieved is 25%. Also, a comparison of the results of the theoretical model with experimental data indicates that the operation of the device is affected by the fiber birefringence.
Silicon, monolithic optical integrated circuits for laser system applications
Authors: James K. A. , August R. R. , Coker J. E.
Published: February 2008

Monolithic optical integrated circuits comprised of input coupler, waveguide, frequency selective element, and integrated detector for 1.06 μm laser applications are discussed. In particular, the analyses, fabrication, and design‐optimization of these circuits as well as experimental results for them are presented.
A model of radar scattering from a turbulent cylindrical plasma
Authors: Bisbing Paul E.
Published: February 2008

A theory of scattering from a weakly fluctuating random medium is formulated in terms of the effect of the background medium on the propagation of the incident and scattered waves. The nonrandom background medium is treated by a rigorous representation for electromagnetic waves interacting with a cylindrically symmetric, radially nonuniform plasma. The resulting boundary value problem is solved numerically using a 50‐layered approximation of the radial distribution. The scattering from the turbulent fluctuations, including depolarization effects, is calculated using existing theories that approximate the plasma by a weakly fluctuating refractive index except that the propagation in the background medium determines the local effective wavenumber and the weight factor for local turbulence scattering. This model is in good agreement with published data on microwave scattering from laboratory plasma where the microwaves do not interact with collisionless overdense regions in the plasma because of refractive effects.
ATS‐6 ascending: Near horizon measurements over water at 30 GHz
Authors: Vogel W. J. , Straiton A. W. , Fannin B. M.
Published: February 2008

The return of the ATS‐6 satellite to a western longitude during the fall of 1976 presented a unique opportunity to perform low‐angle‐of‐elevation measurements at 30 GHz. For this purpose a receiver using a 1.5 m antenna was set up at Port Aransas, Texas, resulting in a propagation path entirely over water. The 30 GHz beacon was monitored daily for at least one hour from 8 September to 21 September 1976. During the time the elevation angle changed from 1.5° to 17.3°, the mean attenuation decreased from 20 to 2 dB and the standard deviation from over 6 dB to less than .2 dB. The deep fades at angles below 4° show significantly sharper nulls than peaks on a log scale. Spectra of the log amplitude fluctuations vary as the (−8/3) power of the spectral frequency in the limit. A flattening is noticeable at the low frequencies. A precipitation event at 8.5° elevation produced a 16 dB fade and significantly increased the variance.
Ionospheric scintillation calculations based on in situ irregularity spectra
Authors: Costa Emanoel , Kelley M. C.
Published: February 2008

Recent results from rocket, satellite, and radar experiments have greatly increased our understanding of equatorial spread‐F and its effects upon communication systems. In situ measurements have shown that the typical irregularity spectrum is a power law with a one‐dimensional index of −2. Previous applications of scintillation theory to such irregularities have utilized an anisotropic power law, in an effort to model elongation of irregularities along the magnetic field, and have found approximate solutions for the scintillation index S4, the rms phase deviation, and the characteristic scale size of the scintillation spectrum. We present here rigorous closed‐form solutions for these quantities which are valid to the extent that weak scattering thin screen theory allows. In addition we introduce a second “hybrid” form for irregularity spectra which is gaussian along the magnetic field and a power law in the perpendicular plane. The index is chosen in such a way that a one‐dimensional spectrum obtained on a spacecraft whose velocity
makes a reasonable angle to the magnetic field and varies as k−2. Such a spectrum is introduced since it seems likely that at least at long wavelengths equatorial spread‐F is an interchange instability and that the density variation along
is that of the zero‐order density variation. One‐dimensional spectra for small angles between
and
would hence be steeper than k−2 at intermediate k values, a result consistent with some in situ measurements. If particle precipitation is responsible for high latitude irregularities at long wavelengths, the hybrid spectrum might also be more appropriate for their characterization. At longer k, waves with small but finite kz such as drift waves might be important and hence the anisotropic power law more appropriate. Using both spectral forms, curves are presented for S4 and the characteristic scale as a function of x = 2 k20/k2ƒ, where k0 is the outer scale wave number of the irregularity spectrum and kƒ the Fresnel wave number. The frequency dependence of S4 based on the power law spectrum is also plotted in the regime where the theory is applicable.
A model of F2 peak electron densities in the main trough region of the ionosphere
Authors: Halcrow Barry W. , Nisbet John S.
Published: February 2008

An empirical model of the peak electron densities in the region of the northerly main trough in the ionospheric F region is presented. The model was derived from measurements made by the satellites Alouette I and II and is in the form of a multiplicative modification factor to the CCIR peak electron density model. The model is a computer program which, when provided with the location, universal time, day number, sunspot number, and Kp index, provides the modification factor, the CCIR model prediction of NmF2, and the new prediction including the effect of the trough. The model is expected to be of considerable use for propagation calculations in the affected region.
Symmetry and selection rules for wave‐wave interactions
Authors: Harker K. J.
Published: February 2008

Selection rules for nonlinear three‐wave interactions are derived on the basis of the symmetry of the background medium and the waves themselves. The process described bypasses the formal derivation of the coupling coefficient itself. The primary concern is with the effect of the polarization of the waves on the selection rules. Although consideration is limited to three‐wave interactions, the method is easily generalized to more waves. Results are derived for these examples: three waves with parallel propagation vectors in an unmagnetized medium, and three waves propagating parallel, and then perpendicular, to a static magnetic field.
Nonlinear wave‐wave interactions without resonance conditions
Authors: Verheest Frank
Published: February 2008

Third‐order nonlinear wave‐wave interactions are possible without any resonance conditions which link frequencies and wave‐vectors of the interacting waves. Usually, but not always, interactions without resonances result in a mere frequency shift. Some models, however, involve changes in the amplitudes as well. This is illustrated on several examples of the self‐modulation of one wave, firstly in general terms, then for a model equation in a dissipative medium, and finally for an electrostatic wave in a medium with various nonlinear conductivities. Depending upon the medium, three cases are possible: either the wave amplitude does not change, or the wave dissipates its energy into the medium, or the medium feeds an explosive instability.
The effect of microwave radiation (2450 MHz) on the morphology and chromosomes of lymphocytes
Authors: Huang A. T. , Engle M. E. , Elder J. A. , Kinn J. B. , Ward T. R.
Published: February 2008

Effects of microwave radiation have been examined on blood lymphocytes from Chinese hamsters that were irradiated 15 minutes each day during five consecutive days by 2450‐MHz (CW) energy at power densities from zero to 45 mW/cm2. Measurements of absorbed energy were accomplished by twin‐well calorimetry. One hour after sham or microwave radiation, blood was obtained by orbital hemorrhage and was cultured for one day if unstimulated or for three days if stimulated with phytohemagglutinin (PHA) to induce mitosis. Cultures were terminated with a brief colchicine treatment to arrest cells in metaphase; lymphocytes were then processed for morphological and cytogenetic analyses. Microwave radiation caused a transient, reversible and dose‐dependent (albeit curvilinearly related) change in rate of blastic transformation of unstimulated lymphocytes. Rate of transformation was maximum at a power density of 30 mW/cm2, which is associated with a post‐radiation body temperature of 39.3 °C. However, frequency of mitoses from PHA stimulation was reduced in irradiated samples. Both the enhancement of transformation and the inhibition of mitosis were evident at 5 mW/cm2. Autoradiography of cells labelled with 3H‐thymidine showed no evidence of radiation‐related DNA repair. Cytogenetic analysis demonstrated no difference in chromosomal aberrations in irradiated and control samples.
Transient electromagnetic response from nonparallel stratified models of the earth's crust: 1, Scattered radiation field
Authors: Bahar E. , Fitzwater M.
Published: February 2008

A full wave approach is used as the basis for determining the transient electromagnetic field response from nonparallel stratified models of the earth's crust. The full wave analysis which satisfies the reciprocity relationships in electromagnetic theory accounts for the scattered radiation fields (considered in Part 1) as well as the scattered surface waves (considered in Part 2). These investigations are relevant to electromagnetic probing in geophysics (active remote sensing) and to problems of communications and navigation using pulsed radio signals. Thus, in this work analytical expressions are derived for the propagation delays and distortions due to nonuniform ground effects. Both analytical and Fast Fourier Transform techniques are used to obtain the solutions.
Transient electromagnetic response from nonparallel stratified models of the earth's crust: 2, the scattered surface wave
Authors: Bahar E. , Fitzwater M.
Published: February 2008

In this part of the paper the excitation of the scattered surface waves is considered in detail. Since these solutions satisfy the reciprocity relationships in electromagnetic theory, they can also be applied directly to derive the scattered radiation fields due to incident surface waves. A detailed examination of the modal equation is presented and the complex wave parameters for the surface waves (guided modes) of the structure are plotted as functions of frequency and overburden depth. Since the scattered radiation fields vanish very near the earth's surface, the scattered surface waves constitute the dominant part of the total scattered fields near the earth's surface. This work may also be applied to problems of coupling into and out of dielectric waveguides.
An application of a variational principle for scattering by random rough surfaces
Authors: Gray Ernest P. , Hart Robert W. , Farrell Richard A.
Published: February 2008

This paper constitutes a first step in the application of a recently developed variational principle to the study of scattering from random rough surfaces. The variational principle has been applied here to assess and extend the range of validity of the perturbation approximation for the scattering of a horizontally polarized electromagnetic wave by a random configuration of non‐overlapping parallel hemicylindrical bosses of equal radii protruding from a conducting plane. The results for this model of a rough surface suggest that, besides extending the range of validity of the perturbation approximation, the variational approach also provides an improved first‐order correction at the long‐wavelength limit in the expansion of the reflection coefficient in powers of the scatterer concentration.
Space‐variant transfer functions for the characterization of inhomogeneous scattering media
Authors: Checcacci P. F. , Scheggi A. M.
Published: February 2008

A set of transfer functions is outlined which turn out to be suitable for characterizing space‐variant propagation media. The purpose of the paper is to show the possibility of using such functions for predicting the performance of a given antenna looking through an inhomogeneous medium as well as for indicating the type of measurements necessary to characterize the medium.
Modal theory of long horizontal wire structures above the earth: 1, Excitation
Authors: Kuester Edward F. , Chang David C. , Olsen Robert G.
Published: February 2008

The current excited on a horizontal thin‐wire structure above the surface of a finitely conducting earth is derived, and is shown to be the sum of discrete modal contributions as well as a number of continuous spectrum (radiation) components for any source of finite extent. The wire structure need only be characterizable approximately by an axial surface impedance, and so particular cases previously treated in the literature can be recovered. In particular, an expression for the current excited by a transverse aperture of finite extent is given, and using orthogonality properties between different parts of the mode spectrum, it is concluded that any of the discrete modes can, in principle, be excited with arbitrarily high efficiency by an appropriately chosen aperture field of finite extent.
Land‐to‐seafloor electromagnetic transmissions in the 0.1 to 15 Hz band
Authors: Bostick F. X. , Cox C. S. , Field E. C.
Published: February 2008

During the summer of 1976, an electromagnetic propagation experiment was performed on the Olympic Peninsula in northwest Washington. A grounded horizontal electric dipole transmitter, with a peak moment of 1.6 × 105 A m, was used to generate square‐wave signals having periods from 10 to 1 sec. Strong signals were received on a 100 m long electrode pair emplaced on the seafloor at a depth of 312 m and at a range of 22 km from the transmitter. The fundamental was received with a 20 to 30 dB signal‐to‐noise ratio (snr), and many harmonics—14 in one case—were also clearly detected. Calculations based on the assumption that the above‐ground near‐fields penetrate downward through the ocean to the receiver give results that agree well with measurements at 22 km and 312 m, namely, theory and experiment agree to within a factor of two for all periods transmitted and harmonics detected. Even if a relatively strong signal had reached the ocean through the suboceanic crust, it would have been masked by this over‐down mode. Measurements were also made on the seafloor at ranges from 110 to 135 km and a depth of 2500 m, using receiving antennas 540 to 1000 m in length. At these sites, the ocean screened out the over‐down mode, and any signal detected would have had to propagate through the crust. Although the equipment was working well, no signals were detected. This negative result indicates that the effective conductivity of the suboceanic path was at least 10−3 mhos/m. However, unknown factors such as the possible existence of a subduction zone on the suboceanic path might well have caused the nondetection.
A pulse‐spectrum technique for remote sensing of stratified media
Authors: Tsien D. S. , Chen Y. M.
Published: February 2008

The applicability of the new iterative numerical algorithm of the pulse‐spectrum technique (PST) to remote sensing of the electric permittivity of a stratified medium is demonstrated. Numerical simulations are carried out to test the feasibility and to study the general characteristics of this numerical algorithm without the real measurement data. These numerical results are compared with those obtained by the spectral domain method (SDM) favorably. The effects of the initial guess and the contaminating instrument noise on the accuracy and the efficiency of numerical computation are investigated. Furthermore, it is shown by numerical simulations that this particular numerical algorithm can be applied to SDM as well as to PST.
Surface wave propagation on a rectangular bonded wire mesh located over the ground
Authors: Hill David A. , Wait James R.
Published: February 2008

A mode equation is derived for surface wave propagation along a rectangular bonded wire mesh over a lossy half space. The mode equation is solved numerically for the complex propagation constant of the surface wave. For a sufficiently small mesh size, the attenuation rate of this surface wave is considerably less than that of the Zenneck surface wave for an isolated half space or homogeneous ground.
Plane wave scattering in inhomogeneous turbulence
Authors: Gardner C. S. , Lam P. C.
Published: February 2008

The parabolic equation method is used to study wave propagation in inhomogeneous random media. Differential equations for the average field and second‐order mutual coherence function are derived. The equations are similar in form to those obtained for homogeneous media but are considerably more difficult to solve. Approximate solutions for plane wave propagation are obtained and their region of validity determined. Numerical examples of a localized turbulent ball are presented to illustrate some of the features of the average field and mutual coherence function. The results show a high dependence on the transverse extent of the medium and are significantly different from the corresponding results for homogeneous media.
Numerical calculation of the scattered field from a periodic deformed cylinder using the smoothing process on the mode‐matching method
Authors: Ikuno H. , Yasuura K.
Published: February 2008

The smoothing process on the mode‐matching method is applied to scattering problems for a periodic deformed cylinder with perfect conductivity. If the body is unaltered on rotation through an angle 2π/ν(ν = 2, 3, 4, …) about some axis, the polyphase wavefunction allows us to deal with the problems only in a sector region with the angle 2π/ν. Consideration of the symmetry of the scatterer reduces the dimension of the linear equations to one part of ν in comparison with the formulation without consideration. The smoothing process together with the improved point‐matching method can be regarded as the computer‐aided algorithm; the algorithm is simple and the accuracy of the solutions can be evaluated explicitly. The numerical results show that the speed of convergence of the solutions by the smoothing process is faster than that of the conventional mode‐matching method, and that for a moderately large truncation size the smoothing process highly improves the accuracy of the solutions. The radar cross section for a non‐convex body is calculated.
Spectra of fluctuations in refractivity, temperature, humidity, and the temperature‐humidity cospectrum in the inertial and dissipation ranges
Authors: Hill R. J.
Published: February 2008

Recent theoretical and experimental advances have produced a model of the power spectrum of quantities mixed by turbulence. This model is applicable for arbitrary diffusivity and is thereby capable of predicting the high wavenumber shape of the spectra of refractivity, temperature, humidity, and the temperature‐humidity cospectrum. Equations for the mean refractivity and the refractivity variance are formed from temperature, pressure, and humidity fluctuations; the accuracy of neglecting the higher‐order terms in the fluctuations is determined. In order to apply the model power spectrum for temperature and humidity fluctuations in the atmosphere, it is first determined under what conditions temperature and humidity satisfy a simple continuity equation that balances temporal changes, advection, and diffusion. Experiments have shown that the temperature spectrum in air has a “bump” at high wave numbers. This feature is understood in terms of the theoretical model, and the bump is predicted to appear in the refractivity and humidity spectra and in the temperature‐humidity cospectrum as well as in the temperature spectrum. The bump in the humidity spectrum is smaller than that in the temperature‐humidity cospectrum, which is in turn smaller than the bump in the temperature spectrum; this effect is caused by the fact that the diffusivity of water vapor in air is slightly greater than that of heat in air. The shape of the refractivity spectrum depends on the relative contributions of the temperature spectrum, humidity spectrum, and temperature‐humidity cospectrum. The refractivity spectrum can have an enhanced bump if the contribution of the temperature‐humidity cospectrum is negative and nearly cancels the contributions of the temperature and humidity spectra. The impact of these developments on radio wave propagation is discussed.
Antenna radiation pattern of cyclotron harmonic waves in a hot magnetoplasma
Authors: Lembège B.
Published: February 2008

The near and far field radiation pattern of a very short antenna is studied in the plasma regime. ωc < ω < 2ωc, ωp ≫ ωc (where ωp and ωc are the electron plasma and cyclotron frequencies, respectively). The experiment is performed in a large laboratory magnetoplasma. Cyclotron harmonic waves are detected in all directions, not only those corresponding to the purely perpendicular direction of detection as was observed previously. This new result is theoretically explained and studied in detail. Constant phase curves deduced from the dispersion relation for a hot Maxwellian electron magnetoplasma are considered. They are found to be described by the low damped part of the polar dispersion curves. The different shapes of the wave surfaces (convex and concave with respect to the excitation source) are in good agreement with experimental results. The effects of plasma and magnetic field inhomogeneities on the dispersion relation are discussed. Experimental isoamplitude curves are presented in the whole space around the transmitter. The theoretical dispersion curves show that the energy of the cyclotron harmonic waves tend to propagate principally outside a cone whose apex is the transmitter and whose axis is parallel to the direction of the magnetic field. The theoretical opening angle of this cone is given by the direction of the group velocity at the inflexion point of the polar dispersion curve where the Landau damping increases suddenly. This theoretical result is in reasonable agreement with the spatial distribution of energy observed experimentally. From this study it is shown that the simple dispersion relation for perpendicular propagation can be used to predict qualitatively the distribution of cyclotron harmonic waves in all directions for dense magnetoplasma conditions.
Relativistic effects on time scales and signal transmission
Authors: Bertotti Bruno
Published: February 2008

The current view of space‐time chronometry is reviewed in its different elements, clock transport and the ‘twin paradox,’ the effect of a gravitational field, and the Doppler effect. In this view a class of privileged, local inertial frames is assumed, and all good clocks measure proper time, the only observable one needs. Relativistic effects on clock synchronization and frequency comparison are described, and the essential role of the geoid is stressed. The available experimental precision makes these effects an essential ingredient of current and future work in this field. The role of distant matter in determining inertia and local dynamics (‘Mach's principle’) is not adequately described in this view. The cosmic background radiation provides a precise definition and a measurement of the local standard of rest with respect to the universe, which might have a privileged character among all the inertial frames. Different kinds of violations of the conventional view based upon this conjecture are discussed in terms of free dimensionless parameters. Finally, we review the upper bounds to the discrepancies from the relativistic values as deduced from several experiments.
A fresh look at the radar reflectivity of clouds
Authors: Gossard E. E.
Published: February 2008

There is now considerable evidence that long‐wavelength radars measure backscatter from clouds better than would be predicted from the classical incoherent Rayleigh scatter theory. This could be explained by substantial coherence (in the Bragg sense) in the scattering process. Such scattering could arise from cloud‐enhanced fluctuations in the dielectric constant of the gaseous medium or from significant spatial correlation in the drop‐size/drop‐number density distribution within clouds. Recent cloud modeling and computer simulation suggest that important sources of variance in both the liquid water concentration and the dielectric fluctuations exist in the thermodynamic cloud processes through their irreversible coupling with the cloud dynamics (Clark and Hall, 1979). In this paper these variances are compared with estimates of the conventional dynamical variance resulting from clear‐air turbulence and also with that due to spatial correlation in the droplet distribution. It is concluded that gaseous water vapor fluctuations are about 30 times as important as fluctuations in cloud liquid water if the power (variance) in both spatial spectra are the same. It is found that the variance in water vapor resulting from thermodynamic processes in the cloud is at least comparable with typical water vapor variances generated dynamically in the clear atmosphere. Temperature‐humidity covariance resulting from thermodynamic processes in clouds can be negative and may thus lead to significantly enhanced radar reflectivity.
Some peculiarities of auditory sensations evoked by pulsed microwave fields
Authors: Tyazhelov V. V. , Tigranian R. E. , Khizhniak E. O. , Akoev I. G.
Published: February 2008

Rectangularly pulsed, 800‐MHz microwaves were coupled via waveguide from a 500‐W source to the parietal area of the head of normal human observers (Os). Pulse widths from 5 to 150 μS and pulse‐repetition rates (PRRs) from 50 to 20,000 pulses per second (pps) were employed. Sine‐wave audio‐frequency (AF) signals could be presented alternately to or concurrently with microwave pulses (RF signal) under conditions in which O could adjust the amplitude, frequency and phase of the AF signal. By matching timbre and loudness of the perceived RF and AF signals during a succession of psychophysical measures—some while O's head was being immersed in water—the Os yielded the following results: (1) Both loudness and perceptual thresholds of the RF signal were biphasic functions of pulse width and of PRR; (2) When pulse widths increased toward 100 μs, some subjects perceived a different sound that was lower in pitch and was referred externally to the head; (3) By appropriate phasing of AF and RF signals after matching for pitch and timbre, loudness of the RF signal could be reduced below the threshold of perception; and (4) Extent of immersion of the head in water was correlated with reduced loudness of the RF signal. Some of the data are interpreted as posing explanatory difficulties for an exclusively ther‐moelastic mechanism of RF hearing.
Localized embedding of labelled microspheres by microwave heating in tissues of hypothermie dogs
Authors: Popovic V. , Popovic Pava
Published: February 2008

In this study a hind leg of dogs was profoundly cooled while the gracilis muscle of the same leg was kept normothermic or slightly hyperthermic (37 to 39°C) by microwave heating (differential hypothermia). The circulation (measured by trapping of Technetium Tc99 labelled carbonized microspheres in capillaries) through the warmed muscle tissues was five to 12 times greater than that through the cold muscles of the same leg. When differential hypothermia was used to induce selective embedding of (Y90) Yttrium‐loaded microspheres in the warm gracilus muscle of the cooled leg, pronounced damage (or even complete destruction) of normothermic muscle tissue was observed while leaving undamaged all other muscle tissue that was protected by cooling. It is suggested that differential hypothermia might be a useful tool for preferential embedding of biologically important Pharmaceuticals or for preferential embedding of medical radio‐nuclides whenever a superselective catheterization of tumors or of other tissues is not possible.
On the relevance of Fuchsian differential equations for the propagation of waves in layered plasmas
Authors: Sluijter Frans W. , van Duin Cornelis A.
Published: February 2008

The theory of propagation of electromagnetic waves in layered plasmas with Epstein type density gradients is investigated. Depending on polarization, the presence of a nonzero magnetic field and the angle of incidence with respect to the gradient, the number of regular singular points is determined, and thus the type of relevant Fuchsian equation is indicated.
The morphology of high‐latitude VHF scintillation near 70°W
Authors: Basu Sunanda , Aarons Jules
Published: February 2008

The long‐term VHF scintillation data from ATS 3 obtained at three stations situated in the North Atlantic sector at auroral and subauroral locations during the period 1968–1974 are used to determine the morphology of high‐latitude scintillations near the 70°W longitude sector. The variation of the average level of scintillation at each observatory is studied as a function of time of day, season, and magnetic activity in a manner suitable for incorporation into statistical models of scintillation occurrence. The most prominent feature of the data is a seasonal dependence of scintillations with a 2:1 variation from northern summer to winter under quiet magnetic conditions. This also causes a large variation in the latitudinal gradient of scintillations from 2 dB per degree in summer to 1 dB per degree in winter for latitudes >60° invariant. The observed seasonal control of scintillations is related to the variation of the tilt angle of the earth's magnetic dipole and consequent modulation of the particle precipitation in the North Atlantic sector of the auroral oval.