bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Ions on Very‐Low‐Frequency Propagation During Polar‐Cap Absorption Events
Authors: Field E. C.
Published: February 2008

The propagation of electromagnetic waves in the VLF range in the earth‐ionosphere waveguide has been theoretically analyzed. The results of full‐wave calculations indicate that transpolar VLF waves suffer considerably more attenuation during a moderately strong polarcap absorption (PCA) event than during the undisturbed daytime. Computed height profiles of dissipation and field strengths show clearly that this increased attenuation is due mainly to ohmic losses associated with ion heating. Calculations based on a model of a relatively weak PCA event indicate no pronounced increase in attenuation at most VLF frequencies. For this model, ions are found not to be an important factor. The calculations do not include the possible effects of the Greenland ice cap. During a moderately strong PCA event, the height range over which long‐path VLF waves interact strongly with the ionosphere is substantially lower than in the undisturbed daytime. For all ionospheric models considered, the width of the height range of substantial wave‐ionosphere interaction at a given frequency was less than about 20 km. VLF probing experiments must therefore use several frequencies and incidence angles if a broader ionospheric height range is to be sampled effectively.
Dipole Antenna Radiation in a Compressible, Anisotropic Electron Plasma Overlying an Imperfectly Conducting Half‐Space—Lunar Applications: 1. Formulation of the Solution
Authors: Phillips R. J. , Ward S. H.
Published: February 2008

The problem of the electromagnetic response of infinitesimal electric and magnetic dipole sources in a compressible, anisotropic electron plasma overlying a lossy dielectric half‐space is solved by integral transform and matrix techniques to assess antenna radiation in the lunar environment. In part 1, the solutions are formulated in terms of Fourier‐Bessel integrals operating on matrix quantities. In particular, the field solutions are shown to linear combinations of classical plane‐wave modes in a compressible, anisotropic plasma. The introduction of a lossy dielectric half‐space yields uncoupled TE and TM modes propagating into the dielectric plus three reflected plasma modes. The modal reflection coefficients represent reflections coupled to all plasma modes.
Modes of Propagation in a Parallel‐Plate Waveguide with Lossless Reactive Surfaces
Authors: Arora R. K. , Vijayaraghavan S.
Published: February 2008

An analysis of the modes that can propagate in a parallel‐plate waveguide with lossless reactive guiding surfaces is presented. Three cases are considered: (1) where both surfaces are inductive, (2) where both surfaces are capacitive, and (3) where one of the surfaces is inductive and the other is capacitive. In general, we found two surface waves and an infinite number of waveguide modes. Although all the waveguide modes exhibit the cutoff phenomenon, the surface wave modes may either propagate down to zero frequency or may be critical. At certain ‘threshold’ frequencies, a transition is observed from one to the other type of mode.
Solar Microwave Scintillation
Authors: Badillo Victor L.
Published: February 2008

With the sun as a source, scintillations at four microwave frequencies were observed for 1 year. Scintillation was a daily occurrence at sunrise at elevation angles from 1.5° to 7°. This observation indicates the continued presence of point sources on the sun during the peak of the sunspot cycle. It also suggests that the peculiar terrain configuration along the propagation path is conducive to the production of irregularities in the troposphere. Scintillation data can provide information about the troposphere and about the spectrum of the slowly varying component of solar emission.
On Height‐Gain Studies Over a Long Mountain‐Obstacle Diffraction Path
Authors: Barsis A. P. , Hause L. G.
Published: February 2008

Height‐gain measurements conducted previously over a mountain‐obstacle diffraction path at 751 MHz are re‐evaluated in terms of the calculated lobe patterns.
A One‐bit VLBI Recording and Playback System Using Videotape Recorders
Authors: Michelini R. D.
Published: February 2008

A flexible, hybrid very long baseline interferometry (VLBI) instrumentation system, which uses videotape recorders for recording digitized data, has been developed for making routine observations for geodetic and geophysical measurements. The system records data on videotape in the field and later generates conventional digital magnetic tapes for programed correlation in a high‐speed, general‐purpose computer. By selection of an appropriate data rate, these tapes can be made compatible with the present National Radio Astronomy Observatory‐Arecibo Ionospheric Observatory (NRAO‐AIO) Mk 1 format. In addition, the major components have been designed and chosen so that they can be incorporated into the Mk 2 system now being developed at NRAO. This is a high‐density, wide‐bandwidth system that uses direct videotape correlation. Other more immediate advantages of using videotape recorders are: low initial cost, low cost per bit, long recording time, portability, and minimization of the field installation. This paper describes the entire instrumentation back end, including the video converter, recording system, and computer‐compatible reformatting units. Station timekeeping, which is integral with the recording format, is also discussed.
Very Long Baseline Interferometry of Decametric Radiation From Jupiter
Authors: Stannard Kent M. , Dulk George A. , Rayhrer Benno
Published: February 2008

Very long baseline Michelson interferometry measurements were made on Io‐related radio emissions from the planet Jupiter at 34 MHz. The data include a single baseline observation made on December 1, 1968, between the Arecibo Ionospheric Observatory (AIO) and Boulder, Colorado (436,000 λ), and a three‐station observation made on April 27, 1969, between the University of Maryland Radio Observatory in California, the University of Texas Radio Astronomy Observatory (UTRAO) in Texas, and Boulder, Colorado (typically 100,000 λ). Frequency analysis of the cross‐correlated signals shows that there is a tendency toward lower observed fringe rates than had been calculated. If we interpret the results entirely in terms of source motion, the data imply a velocity near 200 km/sec eastward. We attribute the phase fluctuations in the cross‐correlated signals to interplanetary scintillation; however, source motion effects cannot be distinguished from scintillation. The implied rms phase variations at the scintillation screen are 0.7 radian at an elongation of 65° (December 1, 1967) and 0.3 radian at an elongation of 145° (April 27, 1969).
On the Renormalization Method in Random Wave Propagation
Authors: Varvatsis A. D. , Sancer M. I.
Published: February 2008

In this work it is shown that the diagrams that correspond to the first renormalization equation for the coherent field, in a statistically homogeneous and isotropic medium, are the dominant diagrams. To study the cumulative effect of the omitted diagrams, which increase in number with each power of the expansion parameter ∈, we sum the next largest omitted diagrams. This sum is proportional to the propagation path length times the usual first renormalization solution. The above analysis and a more compact one that utilizes the full Dyson equation both yield a validity criterion that is basically distance independent. The derivation of the validity criterion is primarily based on two observations that are not used by other authors. First we note and account for the fact that the solution of the first renormalition integral equation is always approximated. Secondly, we utilize the simple observation that phase accumulation and rate of decay are unimportant if the amplitude of the wave is already insignificant. We obtain the same criterion as other authors for kol ≫ 1, where ko is the free space wave number and l is the correlation length of the dielectric fluctuations; for kol ≪ 1 the criterion is new. Finally, a relatively simple method of solving the first renormalization integral equation for the correlation function of the field is presented for the case kol ≫ 1 and some justification for the validity of this equation is given.
Calculation of the Admittance, Isolation, and Radiation Pattern of Slots on an Infinite Cylinder Covered by an Inhomogeneous Lossy Plasma
Authors: Fante Ronald L.
Published: February 2008

We discuss here a computer program that has been developed for computation of the self and mutual admittances and of the radiation pattern of apertures on an infinite cylinder covered by an inhomogeneous lossy plasma. Numerical results are obtained and compared with equivalent results of apertures on a plasma‐covered ground plane.
An Alternative Integral Equation for Propagation Over Irregular Terrain, 2
Authors: Ott R. H.
Published: February 2008

An integral equation for cauculating the attenuation of radio waves propagating over irregular terrain is rederived. The integral equation is applied to three terrain profiles, and the solutions are compared with solutions obtained by using classical methods such as the residue series and diffraction theory.
Electromagnetic Wave Propagation in a Uniformly Accelerated Simple Medium
Authors: Mo Tse Chin
Published: February 2008

The theory of electromagnetic wave propagation in a uniformly accelerated simple medium is generalized to cover the case of arbitrary initial wave direction. The wave splits into two natural modes relative to the plane of acceleration and the wave vector. The case of high frequency and weak acceleration is solved in detail; to observers at rest with respect to the medium, a drag effect due to apparent gravity is demonstrated, and to inertial observers a drag effect due to medium acceleration is demonstrated. A preferred asymptotic cone of propagation determined by (μϵ – 1)½ is found in the accelerated frame. Various drag effects are physically interpreted.
Observations of F‐region Vertical Velocities at Millstone Hill 2. Evidence for Fluxes into and Out of the Protonosphere
Authors: Evans J. V.
Published: February 2008

The vertical flux of O+ in the F region has been obtained from incoherent scatter radar measurements at Millstone Hill. The paper reports an investigation of the altitude variation of the flux during two 24‐hour periods in March taken a year apart. We find that except for a brief period around sunrise the flux is always directed downwards at altitudes below 500 km and its magnitude seems governed simply by the competing processes of production, loss, and diffusion. On the quiet day above 535 km the flux is directed upward in the afternoon when the electron density is not changing with time. This upward flux reached a peak value of ∼108 ions cm−2 sec−1 near 700 km altitude and then decreased at higher altitudes. This decrease is attributed to charge exchange with hydrogen. During the night on this day there is evidence for a downward flux of 3 × 107 O+ ions cm−2 sec−1 from the protonosphere. Additional H+ ions may be diffusing through the 1000‐km level and contributing to the maintenance of the nighttime F layer, but they would not be detected in our observations. On the disturbed day there is no evidence of a flux of ionization into the protonosphere except at sunrise. We suggest that this change is brought about by a large reduction in the abundance of neutral hydrogen, resulting from increased escape either via the polar wind or from the heating of the atmosphere in the vicinity of the auroral zones. Thus, it is suggested that the abundance of neutral hydrogen at the base of the exosphere is reduced at high latitudes during magnetic storms.
Conversion of Electrostatic Plasma Waves into Electromagnetic Waves: Numerical Calculation of the Dispersion Relation for All Wavelengths
Authors: Oya Hiroshi
Published: February 2008

The dispersion curves have been computed for a wide range of wavelengths from electromagnetic waves to electrostatic waves in a magnetoactive warm plasma with a Maxwellian velocity distribution function. The computation was carried out mainly for the perpendicular propagation mode. The upper hybrid resonance is the connection point of the electrostatic waves and the electromagnetic waves. The electrostatic waves not associated with the upper hybrid resonance are subjected to electron cyclotron damping when the wavelength becomes long. Oblique propagation is allowed for the electrostatic waves in a frequency range from the plasma frequency to the upper hybrid resonance frequency in the long‐wavelength region where Landau damping can be neglected and where the electrostatic mode smoothly connects to the electromagnetic X‐mode. In a slightly inhomogeneous plasma, the Bernstein‐mode electrostatic wave can escape by being converted into the O‐mode electromagnetic wave; two reflections take place during this escape process. The frequency range of the escape coincides with the Cerenkov radiation of the electromagnetic waves, but these two mechanisms indicate clear contrast in its origin. The electromagnetic Cerenkov radiation is produced interacting with the high‐energy plasma beam with velocity range l00υth < υ < l000υth (for the nonrelativisitic plasma), where υth is the electron thermal velocity, whereas the origin of the electrostatic waves is in the interaction with the low‐energy plasma beam.
Correction of Satellite Tracking Data for an Arbitrary Tropospheric Profile
Authors: Marini John W.
Published: February 2008

A procedure is given for deriving elevation‐error and range‐error correction equations in a form suitable for use in the rapid processing of satellite tracking data. The refractivity of the troposphere is assumed to have spherical symmetry, but may have any given profile that does not depart greatly from standard. When the procedure was tested for numerical accuracy by application to an exponential profile, the corrections calculated agreed with those obtained by ray tracing to 0.3% or better over a range of surface refractivity from 200 to 450 and a range of radiowave arrival angles from horizontal to vertical.
Propagation in an Evaporation Duct: Results in Some Simple Analytic Models
Authors: Joseph R. I. , Smith G. D.
Published: February 2008

The purpose of the present paper is to provide insight into the fundamental mechanisms involved in the trapping of energy which is propagated in an evaporation duct. The emphasis is upon the solution of the problem for simple meteorological models with the intent of not obscuring the important principles with involved mathematics or exhaustive computer studies. Simple exponential‐type profiles are assumed, and the wave equation is solved for these profiles by the well‐established methods of mode theory. The results allow for inclusion of a large number of modes but are restricted to trapped modes. The results indicated that, for cases in which multiple modes are trapped, considerable signal fades occur at two‐ to three‐mile intervals for centimeter wavelengths and such fades are strongly dependent upon receiver or transmitter heights. Further, it was found that the duct height is not a critical parameter unless it is comparable with mode heights.
Multiple‐Pulse Incoherent‐Scatter Correlation Function Measurements
Authors: Farley D. T.
Published: February 2008

For monostatic radar measurements of the correlation function in the lower ionosphere, suitably spaced short pulses must be transmitted in order to obtain adequate height resolution. The efficiency of the measurement is greatly increased if several (five or more) pulses, rather than the usual pair, are transmitted with a particular irregular spacing. With this procedure many delays (10 or more) can be studied simultaneously. The increase in number of lags more than compensates for the increase in clutter. Various such multipulse schemes are described and their merits compared. The rather formidable amount of data processing associated with these procedures often cannot be done with a general purpose computer but can easily be handled by special purpose digital devices.
Time‐ and Frequency‐Domain Characterizations of Multipath Propagation at 910 MHz in a Suburban Mobile‐Radio Environment
Authors: Cox D. C.
Published: February 2008

Time‐ and frequency‐domain statistics are presented for multipath propagation in a suburban mobile‐radio environment for vehicle‐travel distances on the order of 30 m. These statistics were obtained by measuring the quadrature components of the bandpass impulse response for the medium as a measuring vehicle was driven along the streets. For suburban residentialand commercial areas on relatively flat terrain, the delay spread is generally less than 1/4 μsec, and the correlation bandwidth at .9 correlation is greater than 250 kHz. Some extreme areas exhibit multiple‐propagation paths with significant amplitudes at excess delays of 5 to 7 μsec, (delay spreads of 2 μsec) and associated correlation bandwidths as low as 40 kHz.
Calculated pattern of a vertical antenna with a finite radial‐wire ground system
Authors: Hill David A. , Wait James R.
Published: February 2008

The appropriate form for the surface impedance of a radial‐wire ground screen is utilized to obtain quantitative effects of the important parameters (number of radials, length of radials, wire radius, and ground constants) on the low‐angle radiation of a vertical antenna. An approximate correction term is derived to account for currents reflected from the edge of the screen. The effect is small for large screens, but it may be important for smaller screens.
The retarding‐potential analyzer on Atmosphere Explorer
Authors: Hanson W. B. , Zuccaro D. R. , Lippincott C. R. , Sanatani S.
Published: February 2008

A planar retarding‐potential analyzer will be included in each of the Atmosphere Explorer (AE) payloads. The primary functions of the instrument are to supply ion‐temperature and ion‐concentration data, which it will do at least once every 40 km of flight path in the region of interest with an expected accuracy of better than 2%. In addition, the instrument will determine ion‐drift velocities and energy spectra of both the thermal and suprathermal electrons. During eclipse, negative‐ion concentrations greater than 0.3 cm−3 can be detected, though the normal positive‐ion sensitivity is approximately 1.5 ions cm−3. Changes in the ion concentration along the flight path greater than 0.1% can be monitored with a spatial resolution of less than 40 m.
Current distribution on an infinite tubular antenna immersed in a cold collisional magnetoplasma
Authors: Bhat Bharathi
Published: February 2008

Based upon a boundary‐value formulation, a new approximate expression is derived for the total axial current on an infinite antenna immersed in an unbounded, cold, collisional magnetoplasma with a dc magnetic field oriented parallel to the antenna. Numerical results are presented for the current distributions over plasma parameters corresponding to each of the eight regions of the Clemmow‐Mullaly‐Allis diagram and for different values of the collision frequency. These results show that the propagation constant of the current wave on the antenna is very nearly equal to k0(K⊥)½
General remarks concerning theories dealing with scattering and diffraction in random media
Authors: Bremmer H.
Published: February 2008

The theories to be considered in this review deal mostly with the effect of random media on the propagation of electromagnetic or other waves traversing them. The purpose aimed at thus consists of finding connections between the statistical properties of these waves and the given statistical properties of the medium itself. The characteristics of this medium are to be fixed by one or more wave equations or by equivalent dispersion relations. The waves may be investigated as such, considering the wave function Ψ(r, t) of one or more associated scalar or vector components, or, more generally, the theory may refer to related quantities, e.g., the squared modulus |Ψ|2 which fixes an energy density or, as in quantum mechanics, a probability density.
Electron density profiles in the lower ionosphere deduced from long path VLF wave propagation
Authors: Rinnert K.
Published: February 2008

Based on waveguide mode theory and a simple model to calculate the ionospheric reflection coefficient, electron density profiles are deduced from VLF data. A simplified day/night transition model is described. It is appropriate for explaining the mode conversion during sunset and sunrise and leads to conclusions concerning the change of the electron density profile within the transition region.
The log‐periodic array at the Clark Lake Radio Observatory
Authors: Erickson W. C. , Kuiper T. B. H.
Published: February 2008

A log‐periodic array, three km in length, is operating at Clark Lake Radio Observatory. It makes one‐dimensional sweeps of the solar brightness distribution in the frequency range 20 to 65 MHz once per sec. The phasing of the array and the receiving system are described, as well as how the dynamic spectra are analyzed for the positions of solar radio sources. Simultaneous measurements at many frequencies enable the observer to remove the effects of ionospheric refraction and to obtain fundamental positions to an accuracy of about one arc min at decametric wavelengths. Fundamental positions are given for Cassiopeia A.
Spectral composition of geomagnetic field variations in the period range of 5 min to 2 hr as observed at the earth's surface
Authors: Campbell W. H.
Published: February 2008

From geomagnetic records of sixteen observatories distributed about the earth, a spectral analysis of the geomagnetic field was prepared for each day of 1965, a year of relatively quiet solar‐terrestrial activity. Field amplitudes were found to increase almost linearly with periods in the 5 min to 2 hr range of study. The northward and eastward components of field are about equal at all latitudes with slightly larger vaues of H in the auroral and equatorial electrojet region. The vertical component of field is less than the others at all but the auroral zones. Seasonal changes in the amplitude appear at all locations but are more pronounced in the polar cap. Summer solstitial field strengths are about twice those of the winter period. On most quiet days of a month the amplitudes vary from about 0.5 to 0.1 times that of the monthly average levels. On most active days of the month the fields are between 4 to 10 times the size of the average monthly level amplitudes. The greatest variations in these levels occur at the equatorial and auroral zones. The lowest field values occur between 10° and 35° geomagnetic latitude with a minimum near 20° to 25°. Maximum values of the field are found at 65° to 75° geomagnetic latitude. Allowing for induced currents within the earth and for the global area of the distribution, about 91% of the magnetic energy is found between 60° and 80° geomagnetic latitude, about 4% in the higher latitude polar cap, and only 1% between the equator and 15°.
Radar ionospheric refraction corrections by a digital ionosonde
Authors: Paul A. K.
Published: February 2008

Ionospheric refraction is one of the factors limiting the accuracy of radar systems tracking objects in or beyond the ionosphere. In advanced systems it may be desirable to perform accurate corrections for these effects in real time, and because of the extreme variability of the ionosphere, this presupposes real time, local ionospheric measurements, e.g., by a modern digital ionosonde. The ionosonde could then be required to monitor the state of the ionosphere, compare it with model conditions, and forecast the radar refraction environment in real time. One component in this problem is the calculation of the radar refraction effects, given the ionospheric electron density profile, the apparent radar range, and look angle. Assuming that the electron density depends on height only, this paper describes such a procedure suitable for use within the Dynasonde or a similar digital ionosonde interfaced to an active radar system.
Design considerations for the Upper Atmosphere Observatory incoherent scatter radar
Authors: Evans J. V. , Moorcroft D. R.
Published: February 2008

A new large incoherent scatter radar system has been proposed as the principal element in a binational center for studies of the upper atmosphere. The radar has been designed to yield a sensitivity comparable to the best now available and yet provide a latitude coverage of the F region of ±13°.

The radar shall comprise a 100‐m diameter parabolic reflector antenna that can be tilted in the magnetic meridian plane by ±85° from the zenith. This antenna will be coupled to a UHF pulse transmitter with a peak power of 10 Mw, and will serve for both transmitting and receiving. Two auxiliary fully steerable antennas will be located northeast and northwest of the main antenna and will also receive the signals. This will enable the velocity of the ion drift to be studied, permitting measurements of neutral winds, electric fields, and fluxes of ions into or from the magnetosphere. The auxiliary antennas will form 10 coplanar pencil beams, so that these drift measurements may be made at 10 heights simultaneously.

The paper describes how the above concept was developed and the work of selecting a site for the radar. By locating the main station near L = 4, and the auxiliary stations about 550 km distant, it will be possible to measure the electric fields in the F region over the range 3 ≤ L ≤ 8 to an accuracy of ±2 mv m−1. Thus, the radar should be able to map the electric fields produced by substorms at auroral and subauroral latitudes. In addition, the properties of the ionosphere and many parameters of the atmosphere will be determined over the altitude range 100 to 1000 km.
Comparisons of techniques for measurement of D‐region electron densities
Authors: Sechrist C. F.
Published: February 2008

This paper reviews the ground‐based and rocket techniques that are presently being used to determine electron density profiles in the ionospheric D region. Ground‐based techniques include VLF, LF, and MF sounding, differential absorption and differential phase using partial reflections, wave interaction, and incoherent scatter. Rocket techniques include differential absorption and Faraday rotation in association with high‐resolution dc probes calibrated by means of the radio measurements. The characteristics of the aforementioned techniques are presented, including time and height resolution, accuracy estimates, preferred height ranges, and problems encountered. Electron density profiles obtained with these techniques are presented for comparable solar zenith angles and undisturbed solar and geophysical conditions, and variances are described.
Mesospheric positive ion concentrations, mobilities, and loss rates obtained from rocket‐borne Gerdien condenser measurements
Authors: Conley T. D.
Published: February 2008

The theory and operation of a Gerdien condenser in a collision‐controlled regime is reviewed. Its operation under supersonic flow conditions is then presented and the results of calibration of the instrument in a wind tunnel are discussed. The theory of mobility is reviewed and the importance of a mean‐free‐path or mean‐free‐time model between ion‐neutral collisions is discussed. Experimental positive ion mobility data are presented and compared with the data of Rose and Widdel [1972] and the extrapolated values of small ion laboratory results. The assumption of chemically frozen flow is then considered concerning the equilibrium distribution of the water cluster ions and their temperature‐dependent decomposition rates. It is shown for flow at Mach 3 that when the shock is detached the dominant cluster ions are not frozen. However, when the shock is swallowed the H+(H2O)3 ion is frozen at all altitudes above 40 km and the H+(H2O)4 ion is frozen above 65 km. The predicted mobility of the dominant positive ions, i.e., H+(H2O)3 and H+(H2O)4, based on a mobility dispersion curve for nitrogen, is compared with experimental data. Positive ion density data are presented for four rocket flights during a PCA and one flight during an auroral absorption event. Finally, positive ion loss rates are shown based on the positive ion measurements and proton flux data obtained from rockets and satellites.
Cross‐correlation formulation of the complex power from planar apertures
Authors: Zaghloul Amir I. , MacPhie Robert H.
Published: February 2008

A novel formulation of the complex power radiated from planar antenna apertures is presented in terms of the cross‐correlation functions of the aperture fields. The analysis makes use of the Fourier transform relationship between the cross‐correlation function and the cross spectral power density. We start with the well‐known Poynting vector integration which involves plane wave intrinsic impedances and which can be given in five different forms according to the choice of the field representation. Through simple mathematical manipulations we arrive at the cross‐correlation form which is applicable not only to simple apertures but also to nonperiodic as well as periodic arrays either with or without dielectric sheets. This formulation is specially useful in analyzing aperture problems having a statistical nature where the conventional Poynting vector approach is not directly applicable.
Around‐the‐world propagation
Authors: Rumi G. C.
Published: February 2008

Data on around‐the‐world (RTW) propagation obtained at Ithaca, N.Y., between the years 1965 and 1968 are described and discussed using a ray optics approach. The role of the oblique ionospheric shells that are known to exist near the 75° dip of the northern geomagnetic field in producing RTW echoes is emphasized. The possibility of utilizing RTW waves for ionospheric sounding is pointed out.
Radio probing of the troposphere
Authors: Little C. Gordon
Published: February 2008

Radio wave interactions with the atmosphere and its constituents have been used to derive information on many aspects of the troposphere. Passively (i.e., in the radiometric mode), they have been used to measure temperature profiles and the water vapor and liquid water contents of the atmosphere, and to identify tornadic storms. In the active mode, three‐dimensional fields of precipitation and velocity have been measured. These have permitted studies of horizontal and vertical velocities, vorticity, convergence, turbulence spectra, turbulent kinetic energy dissipation rates, and fluxes of momentum and kinetic energy, as well as studies of such atmospheric phenomena as thermal plumes, convective cells, internal gravity waves, breaking waves, and convective and orographic storms.
An automated mapping technique for representing the hourly behavior of the ionosphere
Authors: Rush C. M. , Edwards W. R.
Published: February 2008

A technique to generate global maps of ionospheric parameters on an hourly scale is presented. The technique is based on the updating of predicted monthly median maps of ionospheric parameters with hourly observations. The updating procedure is accomplished by computing the differences between the predicted medians and the hourly values of ionospheric parameters that are observed at specific locations on the globe. These differences are extended to areas where data are not available by employing weighting factors that are derived from correlation coefficients determined from past observations. By applying the present technique to observations of the critical frequency of the F2 region, maps representing the daily‐hourly structure of the F2 region can be obtained that have accuracies commensurate with the observations used to update the median maps.
Thermal microwave emission from a random inhomogeneous layer over a homogeneous medium using the method of invariant imbedding
Authors: Tsang L. , Kong J. A.
Published: February 2008

The radiative transfer approach is used to study the thermal microwave emission from an inhomogeneous slab of random medium bounded by different dielectrics on both sides. The random medium can have nonuniform absorption, scattering and temperature profiles. With the method of invariant imbedding, the boundary value problem of the radiative transfer equations is cast into an initial value problem starting at zero slab thickness. The invariant imbedding equations so obtained are in the form of first‐order ordinary differential equations and incorporate the boundary conditions. Random fluctuations of a structure both laminar and with three‐dimensional variations are considered and illustrated. The frequency, angular, and polarization dependences of brightness temperatures are discussed.
Coupling between a dipole antenna and an infinite cable over an ideal ground plane
Authors: Hill David A. , Wait James R.
Published: February 2008

A formulation is given for the fields radiated by an electric or magnetic dipole of arbitrary orientation in the presence of a cable suspended above a flat and perfectly conducting ground. The cable can be a solid conductor, a leaky coaxial cable, a CATV cable, or a surface‐wave transmission line. Illustrative numerical results for both the far‐field radiation pattern and excitation of the modal currents on the cable are given for the case of a vertical electric dipole source. Among other things, we find that the resultant radiation or far fields are not markedly influenced by the presence of the cable unless the dipole source is very near the cable. However, there is a significant cross‐polarized component produced by the presence of cable that could have important consequences in producing bearing errors in low frequency beacon navigation systems.
The role of radio science in investigating electromagnetic biological hazards
Authors: Johnson Curtis C.
Published: February 2008

After the rapid development of microwave power generating devices during World War II for military purposes, many practical uses of microwave power were identified. One of the early applications in medicine was the use of microwave heating, or “diathermy,” to warm tissues for therapeutic benefits [Moor, 1965; Schwan, 1965]. It is still believed that increased localized tissue temperature promotes blood flow and healing, relieves pain, and there is some biochemical basis for this presumption. A more recent medical application of microwave power has been to generate local tissue hyperthermia, or temperature elevation, as a possible cancer therapy. It has long been reported in the literature that temperature elevation retards cancer growth. Recent studies have indicated that heat may preferentially kill cancer cells in comparison with normal cells, and it has also been demonstrated that local hyperthermia can make radiation therapy and chemotherapy more effective [Proceedings, 1975].
Diathermy versus the microwaves and other radio‐frequency radiations: A rose by another name is a cabbage
Authors: Justesen Don R.
Published: February 2008

There are symptoms of schizophrenia in the body scientific with respect to the mixed but fervent attitudes of its constituents toward the potential perils of exposure to microwaves and other radio‐frequency radiations. The Rose: exposure of human beings to fields of high power density is common, therapeutic, and viewed with sanguinity in some sectors. The Cabbage: in other sectors the suspicion that even weak fields are present raises the pejorative finger of anguish and alarm. The paradox is explored in terms of historical, geographical, personal, impersonal, and nominal manifestations. Subsequent discussion of both simple and complex thermal effects of radio‐frequency radiation is followed by several conclusions. Among them are: (1) Focal or general thermal insult from simple heating of tissues can in principal result from exposure to fields as low as or even lower in density than l mW/cm2, although the practical likelihood of damage at this density is remote. (2) Consensual resolution as to the existence and nature of weak‐field hazards, thermal and nonthermal, will only be reached when dosimetry—the measurement of absorbed energy—is adopted as a rule of procedure in the laboratory. (3) The assumption of hazardous nonthermal effects at low densities of radiation, which are suspected by some but are as yet unsubstantiated by anyone, is a fabrication from the whole‐cloth of fear. This fear, which feeds on the absence of verified or verifiable evidence, is hampering basic studies and may thereby restrict medical development and application of radio‐frequency radiations.
Ion sheath effects on RF plasma probes—Experimental results in laboratory plasmas
Authors: Kist R.
Published: February 2008

In this paper, laboratory work dealing with the frequency characteristic of the plasma impedance of spherical and cylindrical electrode systems is reported. The influence of the ion sheath on various features of the impedance characteristic is considered as the main point of interest throughout this work. Those features are the series and parallel resonance as well as additional resonances due to the excitation of electroacoustic and cyclotron harmonic waves. The dependence of the series and parallel resonances on dc biasing leads to a method of determining the ion sheath capacity Ci for a cylindrical electrode system. These Ci values agree fairly well with those obtained from a theoretical model for the density and potential distribution in the sheath of a cylindrical sensor aligned with a supersonic plasma flow. The amplitude of resonances due to excitation of longitudinal plasma waves (electroacoustic and cyclotron harmonic) reduces or even vanishes for sufficiently negative dc bias. Positive bias first leads to an increased amplitude up to a certain dc bias value above which, however, the amplitude decreases again due to electron absorption at the sensor surface. It is verified experimentally that large RF amplitudes exist across both the ion sheath and the plasma body in the regime of the series resonance, leading to a strong rectification effect. In this regime cyclotron harmonic waves are effectively excited, even if a strong negative dc bias voltage is applied.
Measurement of microwave radiation absorbed by biological systems: 2. Analysis by Dewar‐flask calorimetry
Authors: Blackman Carl F. , Black John A.
Published: February 2008

Free‐field power density has long been used as an index of energy dosing in studies of biological effects of microwave radiation. However, this method of quantifying dose can lead to considerable error if it is used as an index of the rate of energy actually being absorbed by a specimen, because the relative absorption cross sections of different specimens may vary greatly. The integral of absorbed energy is a more meaningful measure of exposure; it can be accomplished by using such sophisticated equipment as twin‐well calorimeters, or by using the cruder system of saline‐filled phantoms This paper describes a calorimetric system for the measurement of absorbed energy in laboratory animals and in in vitro samples that can be assembled from such common laboratory equipment as Dewar flasks, magnetic stirrers, foamed polystyrene, and an accurate temperature measuring device. Measurements of absorbed energy by this system for a standard tissue‐culture flask are compared to values obtained by electrical measurements, by direct temperature measurements, and by heating and cooling curves. Also, application of the system to measurements of dose in experimental animals is demonstrated.
A comparative heating‐pattern study of direct‐contact applicators in microwave diathermy
Authors: Kantor Gideon , Cetas Thomas C.
Published: February 2008

Heating patterns, induced in planar and limb phantoms of simulated fat and muscle tissue by large and by small, direct‐contact microwave diathermy applicators operating at 2.45 GHz, were studied. Teflon slab‐loaded rectangular waveguides, circularly polarized horns, and other large radiators were investigated as well as the only two low‐power direct‐contact emitters presently in noninvasive clinical use. The integrity of temperature measurements by a thermographic camera was established and probe thermometry was used to compare polyethelene with a silk screen as the midplane phantom film. The width and depth of penetration of microwave heating were determined to evaluate energy deposition inside simulated muscle tissue. The results of temperature profiles show that a Teflon slab‐loaded rectangular waveguide and a circularly polarized horn provide uniform heating in the center of the phantom's midplane and that the focusing effects of limb phantoms enhance depth of penetration. Measurements of the electric field demonstrated that direct‐contact applicators can be designed to maintain leakage levels below 5 mW/cm2 per 100 watts of forward power for large applicators, and below 5 mW/cm2 per 10 watts of forward power for small applicators at a distance of 5 cm. Leakage of a circular aperture horn can be minimized with an output flange choke.
Spectral analysis of high‐frequency diffraction of an arbitrary incident field by a half plane—Comparison with four asymptotic techniques
Authors: Rahmat‐Samii Y. , Mittra R.
Published: February 2008

The knowledge of high‐frequency diffraction of an arbitrary wave incident on an edge is important in many applications, such as antennas mounted on aircraft and reflector antennas illuminated by complex feeds. In this paper the problem of a half plane illuminated by a nonplanar wave is investigated using the concept of the plane wave spectral representation. For large wave number k, a new higher‐order asymptotic solution for the total field up to and including terms of order k−5/2 relative to the incident field is derived. The behavior of the solution for the observation points which coincide with shadow boundary directions of a multipole line source is discussed in detail. Furthermore, numerical solution of the field integral representation is constructed for the observation angles in the transition regions. The results are compared with those of the Geometrical Theory of Diffraction (GTD), the Uniform Asymptotic Theory (UAT), the Uniform Theory of Diffraction (UTD) and the Modified Slope Diffraction (MSD).
Surface currents and charges on crossed electrically thick cylinders in a normally incident, plane‐wave field
Authors: King R. W. P. , Blejer D. J. , Burton R. W.
Published: February 2008

An experimental study is described of the surface currents and charges induced on crossed electrically thick conducting tubes (ka = 1) on a ground plane by an incident plane wave. Two locations of the cross along the vertical cylinder and three lengths of the horizontal member are investigated and graphical representations of the distributions of current and charge displayed. The measured currents and charges are compared with the corresponding theoretical and measured quantities on each cylinder when isolated and significant correlations are established.
Calculation of clear air EHF refractivity
Authors: Liebe Hans J. , Gimmestad Gary G.
Published: February 2008

A practical calculation procedure is presented for the complex refractivity N of air in the EHF (30 to 300 GHz) region. The absorption line spectra of the major constituents O2 and H2O and of the trace gases O3 and CO are expressed in a coefficient scheme relating N directly to frequency, dry air and water vapor pressure, temperature, and trace gas number density. The spectroscopic parameters for the O2 lines incorporate new experimental results obtained from our laboratory studies. The formulation allows radio engineers to make straightforward computations of transfer, shielding, and emission properties for modeled radio paths based upon the physical parameters of the atmosphere.
Large‐amplitude ULF electromagnetic fields from BART
Authors: Fraser‐Smith A. C. , Coates D. B.
Published: February 2008

Starting in 1972, persistent large‐amplitude magnetic signals were observed in recordings of ultra‐low‐frequency (ULF, frequencies less than 5 Hz) geomagnetic field fluctuations made on the Stanford campus. The energy of these ULF signals is concentrated predominantly at frequencies below about 0.3 Hz and their amplitude, which has increased greatly since 1972, is at least ten times greater than the normal natural background level of geomagnetic activity, i.e., it is comparable to the level observed during great geomagnetic storms. ULF magnetic field measurements at additional locations away from the Stanford campus have enabled us to identify the San Francisco Bay Area Rapid Transit (BART) system as the source of these large‐amplitude magnetic fields, which appear to be produced throughout the entire Bay area and vicinity (area ≈100 km2). Primary power for the BART trains is provided by a 1000 V dc third rail (total length ≈270 km) and a single loaded 10‐car train can draw as much as 7 Mw during acceleration. Large fluctuating currents (5 to 10 kA) therefore flow in the third rail and associated conductors, with the result that the entire BART system constitutes a large ULF “antenna.” Similar systems planned or already in operation in other parts of the US (e.g., the Washington, DC, Metro) will probably also produce similar large‐amplitude ULF electromagnetic fields.
A numerical study of the Kirchhoff approximation in horizontally polarized backscattering from a random surface
Authors: Chan H. L. , Fung A. K.
Published: February 2008

The backscattering characteristics of a computer‐generated known one‐dimensional random surface are studied by computing first the exact surface current distribution over the illuminated area (using four or more points per wavelength) by the moment methods and then calculating the backscattered field by the gaussian quadrature technique. These computations are repeated 40 to 65 times (depending on the incident frequency) over different surface segments to obtain enough scattered field samples to estimate the average scattered power. If the surface current distribution over the surface segment is estimated by the Kirchhoff approximation, the above calculations may be repeated to obtain the average scattered power under the Kirchhoff approximation. By comparing these two average scattered powers at different frequencies, it was found that (1) the two averaged powers can agree to within 2 dB over a range of frequencies in the incident angular range 0° ≤ θ ≤ 40°; (2) within the range of agreement specified in (1), the average backscattered power need not be proportional to the slope distribution of the random surface; and (3) further study is needed to establish the range of validity of the Kirchhoff approximation. Comparisons were also made between existing approximations to the Kirchhoff integral representing the average backscattered power and the numerically computed backscattered power under the Kirchhoff approximation. It was found that the choice of approximations depends upon the incident frequency and the shape of the surface correlation function.
Pulse propagation, scattering, and diffusion in scatterers and turbulence
Authors: Ishimaru Akira
Published: February 2008

The scale sizes of atmospheric turbulence are usually so large compared with a wavelength that the angular broadening is small and the forward‐scatter theory is applicable. For waves in scatterers such as clouds and fog, the particle sizes are comparable to a wavelength and diffusion phenomena become dominant at relatively short optical distances. This paper presents formulations and solutions for angular broadening, coherence bandwidth and pulse broadening of a spherical wave in forward‐scatter as well as diffusion regions.
The generation of time scales
Authors: Becker G. , Hübner U.
Published: February 2008

First the concepts of time and of time scales are discussed. Then the paper deals with the definition of time scales and with the relevant resolutions and recommendations of international organizations. After a discussion of frequency and time standards, at present of importance with respect to time scale production, clock models describing the clock behavior are treated. This is followed by a review of problems of time comparisons and a description of time service equipment and methods. Then averaging and extrapolation problems are discussed. The present qualities of the international atomic time and of atomic time scales produced by time‐keeping institutes are finally reviewed.