bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐Field Ion Collection by a Spherical Direct‐Current Probe
Authors: Balmain K. G.
Published: February 2008

An integral expression for the current‐voltage relationship of a spherical dc probe is derived assuming that the ambient gas pressure is high and that the probe potential is large and negative. The analysis applies to any gas in which the ion velocity is proportional to the applied electric field strength raised to an arbitrary power. A simplified current‐voltage relationship applicable to small probes is also derived.
Multimode and Dispersive Distortion in the Very‐Low‐Frequency Channel
Authors: Kelly Francis J.
Published: February 2008

The distortion of short, quasi‐monochromatic VLF pulses by dispersion and multimode propagation in the earth‐ionosphere waveguide is studied. The delays between received pulses on three waveguide modes are calculated with a β = 0.5 ionospheric electron‐density profile having an ionospheric height of 70 km (day) and 90 km (night). The fractional spreading of short pulses caused by dispersion on individual modes is also calculated. Delays of up to 0.7 msec between pulses arriving on different waveguide modes were obtained. The dispersive spreading on the important modes is only a few percent for a 2‐msec pulse.
A Modified Iteration Technique for Use in Computing Electron Density Profiles from Topside Ionograms
Authors: Lockwood G. E. K.
Published: February 2008

An iteration technique used in the computation of topside electron density profiles from topside ionograms of Jackson, 1969, fails to converge for some ionograms. An alternative method of iteration, which converges for all ionograms tested, is suggested.
Results of a Single‐Pulse Sounding Experiment
Authors: Watt T. M.
Published: February 2008

A prototype single‐pulse ionospheric sounding system has been devised at the Radio Physics Laboratory of Stanford Research Institute. The sounding system was installed and operated at a field site near Menlo Park, California, between July 1968 and January 1969. From a single transmitted RF pulse, it has been possible to obtain a vertical‐incidence ionogram over a frequency range exceeding 7 MHz. In addition, the very narrow (nominally 1 μsec) transmitted pulse of the system has permitted the detection and identification of E‐region echoes <600 meters thick, a determination not possible with conventional sounders.
Transient Properties of an Infinite Cylindrical Antenna
Authors: Latham R. W. , Lee K. S. H.
Published: February 2008

The field of a perfectly conducting, infinitely long, cylindrical antenna with a slice generator excited by a step‐function voltage wave form is computed at several positions in space. For field points remote from the source, analytical simplifications are possible, and the case where the antenna is loaded with uniform resistance can then be treated. A simple formula for determining the generator voltage wave form required to radiate a specified far‐field wave form is derived.
Impedance of Arbitrarily Oriented Cylindrical and Helical Antennas in Magnetoplasma
Authors: Weil Herschel
Published: February 2008

The derivation of an analytic formula for the impedance of cylindrical and helical antennas in cold magnetoplasma is outlined. The method used is a conventional one reducing to integration of a three‐dimensional integral involving the Fourier transforms of the current distribution and tensor Green's function. It is shown that the impedance decomposes into three parts corresponding, respectively, to the axial and circumferential components of current, and a mutual impedance depending on both current components. The explicit formulas are in the form of one‐dimensional integrals suitable for machine computation. The integrands are made up of many simple terms, and for brevity only the impedance terms referring to the axial current are written out explicitly.
A Numerical Method for Global Mapping of Plasma Frequency
Authors: Jones William B. , Stewart Frank G.
Published: February 2008

A method is given for producing world maps of plasma frequency that includes variation with height above the surface of the earth as well as variations with latitude, longitude, and local mean time. The maps, based on a numerical analysis of ionospheric data, are expressed in a functional form suitable for computer calculation of the value of plasma frequency and any of its partial derivatives at a given position and instant of time. The representation of vertical profiles of plasma frequency is based on a technique introduced by Lanczos for accelerating the convergence of trigonometric approximations. Diurnal and geographic variations are represented by methods previously developed for ionospheric mapping. An illustration is given using the monthly average value of plasma frequency for November 1966 from vertical profiles at 36 stations.
A Note on Correlation Distance of VHF Fading From Irregularities in the Equatorial Ionosphere
Authors: Golden Thomas S.
Published: February 2008

Tests using satellite signals at 136 MHz have been conducted at NASA STADAN (Satellite Tracking and Data Acquisition Network) in Santiago, Chile, and the spatial correlation coefficient for an equatorial ionospheric disturbance has been computed. Test data were obtained on telemetry antennas separated from east to west by 1168 feet. The polarization correlation of the signal (horizontal and vertical) at one antenna is shown to be high (0.68) The correlation for the 1168‐foot spacing is shown to be low (0.2). Other data from Minitrack interferometer measurements are also included.
The High‐Latitude F‐region Irregularity Structure During the October 30–November 4, 1968, Magnetic Storm
Authors: Aarons Jules
Published: February 2008

A study of multi‐station scintillation observations of the 137‐MHz transmissions from ATS‐3 during the magnetic storm of October 30 to November 4, 1968, was made to separate the diurnal pattern of high‐latitude irregularities from storm‐time effects. The night maximum was maintained during magnetic storms, but the pattern was modulated by storm‐time effects. Daytime scintillation indices were increased at specific times during the magnetic storm; a universal time correlation was observed for stations in Europe and in North America. Peak scintillation activity shifted from before midnight (under quiet magnetic conditions) to the 0130 to 0430 time period. A sharp boundary of less than 2° was noted between scintillating and non‐scintillating regions. 40‐MHz transmissions from Explorer 22 during one period of the storm verified that the irregularity structure extended from 48° to 50° GN to auroral latitudes. Using records of 54‐MHz transmissions from Transit 4A taken between 1962 and 1965, as well as the ATS‐3 data, it was found that during magnetic storms the lower edge of the scintillation boundary, which bounds the irregularity structure, moves below its quiet positions to lower latitudes, particularly in the midnight‐to‐dawn time period. It was found that the observations were more adequately ordered by invariant latitudes than geomagnetic (dipole) latitudes used in scintillation papers. Latitude variations in position of the boundary are compared with the trough. It is found that the irregularity‐boundary changes as a function of K index and as a function of local time. Latitude variations in the position of the boundary are compared with the trough. Akasofu's concept of nearly open field lines in the plasmapause during magnetic storms might account for the increased scintillation indices as well as for the lower position of the scintillation boundary during magnetic storms.
Calculations for an Equatorial F2‐region Solar Eclipse
Authors: Sterling D. L. , Hanson W. B
Published: February 2008

The effects of a total solar eclipse on the equatorial F2 layer are studied by obtaining transient solutions of the time‐dependent continuity equation. Electron concentrations for solar minimum conditions are calculated for two meridians that intersect the eclipse path, each at a different latitude. Inter‐hemispherical coupling of ionization during an eclipse does not appreciably affect the electron concentrations. After maximum solar obscuration, an upward moving ionospheric layer develops below the F2 peak (on ionograms it appears as a cusp between f0F1 and f0F2 and is known as the eclipse F1.5 layer), and it is explained in this paper in terms of electrodynamic drift. The assumed vertical component of drift is upward and approximately 14 m/sec at noon. The latitudinal extent of the eclipse F1.5 layer is approximately ±10° magnetic latitude. Qualitatively there is good agreement between the calculations and equatorial ionospheric observations. The technique used by ionospheric observers for deducing the daytime electron production rate q and the linear loss coefficient β from eclipse data is applied to the calculated profiles to judge its efficiency in recovering these parameters. At 300 km, q is approximately 100 cm−3 sec−1 and β is approximately 1×10−4 sec−1. If a drift of 14 m/sec is ignored, the calculated value of β at 300 km altitude is too large by approximately a factor of 3.
Solutions to a Class of Half‐Plane Diffraction Problems
Authors: Tan H. S. , Cheng David K.
Published: February 2008

Sommerfeld diffraction functions are used to develop a general method of solution for a class of two‐dimensional half‐plane diffraction problems for which the boundary conditions contain first‐ and second‐order derivatives. The diffraction functions are themselves wave functions and satisfy both the radiation and the edge conditions. In comparison with the Wiener‐Hopf technique frequently used for such problems, this method is considerably simpler and easier to apply. Problems involving multimode surface reactances and half‐plane scatterers imbedded in anisotropic plasma and ferrite media are solved as examples.
Atmospheric Effects in Very Long Baseline Interferometry
Authors: Mathur N. C. , Grossi M. D. , Pearlman M. R.
Published: February 2008

High‐accuracy measurements made by using very long baseline interferometry require corrections for the effects of the atmosphere. A ray‐tracing analysis shows that the phase path through the troposphere differs from the free‐space value by about 3 meters at the zenith. The ionospheric effect predominates at frequencies below 1 GHz. The net atmospheric correction in the experiment can be several tens of meters. To calculate the corrections, atmospheric probing is necessary at the same time and in the same direction as the observation of the radio source. Ionospheric probing methods do not have the desired accuracy, but the ionospheric effect can be taken out by observing at two frequencies. Although tropospheric probing is possible by radiometric measurements, the laser back‐scattering approach appears to be more promising.
Pulse Distortion in Resonant and Nonresonant Gases
Authors: Vogler L. E.
Published: February 2008

The effect of resonant and nonresonant gases on the propagation of an arbitrarily modulated pulse is investigated. A general expression is derived for the transient response of the signal; the result is valid even for carrier frequencies near the resonant frequency. For propagation through a nonresonant medium, the expression is exact. The application to tropospheric pulse propagation is briefly discussed, and the effects on a rectangular pulse are shown.
Spherical Wave Theory for MF, LF, and VLF Propagation
Authors: Johler J. Ralph
Published: February 2008

If (n) is the set of positive integers, spherical waves like ζn(1, 2)(kr)Pn(cos θ) in r, θ, ϕ spherical coordinates are used to develop a new approach to terrestrial radio wave field calculations. The spherical wave functions of integer order are used as building blocks for the solution of Maxwell's equations and boundary conditions. Instead of a direct summation of the zonal harmonics or n series, a double summation of a modified zonal harmonics series and the geometric series is used to obtain rapid convergence of the former. The most important disadvantage of an n‐series summation is the construction of the solution at the ground interface, which generally causes the n series to converge slowly. This difficulty is overcome by the geometric series approach that permits removal of the ground wave from the n series. The ground wave is then calculated by using classical methods. The remaining ionospheric waves are then calculated with the integer‐order spherical wave functions. The formulation presented is applicable to VLF, LF, and MF; anisotropic reflection coefficients based on electron and ion density profiles of the ionosphere are introduced into the analysis. Results obtained with a computer simulation of the formulas using integer‐order spherical wave functions have been found to be in close agreement with another computer simulation of formulas using complex‐order spherical wave functions at VLF. An interesting standing wave as a function of distance along the ionosphere and the ground has been found by using the integer‐order techniques.
Metallic and Dielectric Antennas in a Conducting Environment
Authors: Franceschetti Giorgio , Bucci Ovidio M. , Latmiral Gaetano
Published: February 2008

The input resistance and the effective height are computed, with reference to several antennas in conductive environment in the limiting static case. For a gap type excitation, it is found that the above parameters are logarithmic functions of the gap thickness. Experiments performed on models confirming theoretical deductions are also reported. The possibility of extending static results to the dynamic case is also discussed, as well as the performance of the antennas in the more realistic semi‐infinite (and possibly layered) conducting environment.
The Lunar Tide in ƒbEs
Authors: Tarpley J. D. , Matsushita S.
Published: February 2008

Hourly measurements of the blanketing frequency of sporadic E(ƒbEs) made during the years 1958 through 1965 have been analyzed for lunar daily variations. The data, which came from ten stations, were analyzed by the Chapman‐Miller method. Both seasonal and yearly average lunar variations were obtained. The lunar semidiurnal oscillations in ƒbEs ranged from 0.01 to 0.04 MHz, with maximums occurring from 7 to 9 hours lunar time. The amplitude of the lunar tide in ƒbEs is an order of magnitude less than the lunar variations of ƒ0Es. Since ƒbEs is close to the plasma frequency of Es, the oscillation in ƒbEs represents a lunar variation in the electron density of Es layers, whereas the significance of the lunar variation of ƒ0Es is not clear. The phases of the lunar tides in ƒbEs, ƒ0Es, and h′Es are found to be nearly the same. Two sources of lunar influence on Es electron density are considered (1) wind shears in the lunar tide acting to augment or decrease the wind shears responsible for E8, and (2) interaction of E8 with electrostatic fields associated with the lunar current system.
Nonlinear Collisionless Plasma Waves and Intensity of the Electric Field of the Ionospheric Irregularities
Authors: Prasad B. , Sen Hari K. , Bakshi P. , Kalman G.
Published: February 2008

An exact longitudinal wave solution of nonlinear equations for a cold and collisionless one‐fluid magneto plasma has been obtained. The wave is found to be anharmonic (non‐sinusoidal) in form and its amplitude involves an arbitrary parameter. By means of a pseudo‐potential well, the domain of nonlinear oscillations is defined and the maximum amplitude up to which a nonlinear wave can grow is determined. Intensity of the equatorial sporadic‐E irregularities is computed and the coherent energy density is found to be of the order of 10−9 erg/cm3.
Analysis of Magnetic Storms with DR Indices for Equatorial Ring‐Current Field
Authors: Kamide Yohsuke , Fukushima Naoshi
Published: February 2008

The asymmetry of the equatorial ring‐current and its progressive change during magnetic storms are studied by introducing the new DR indices, which contain the following four parameters: 1, intensity of symmetric ring‐current, 2, intensity of partial ring‐current, 3, local time of the center of the partial ring‐current, and 4, longitudinal width of the partial ring‐current.
Efficiency of Radiometers Using Digital Integration
Authors: Ohlson J. E.
Published: February 2008

The performance of total‐power and balanced Dicke‐type radiometers using digital integration is considered. The square‐law device output is considered to be smoothed by an RC filter and then sampled. Degradation due to finite sampling rate and quantization noise is derived.
A Reciprocity Theorem for Magnetoionic Modes
Authors: Altman C. , Postan A.
Published: February 2008

An arbitrary plane slab is considered within a magneto plasma whose parameters vary in a direction perpendicular to the (horizontal) plane of stratification, the plane of the slab faces. 2 × 2 reflection and transmission coefficient matrices are defined for the slab in terms of up‐going waves incident from below, Ru and Tu, and in terms of downgoing waves incident from above, RD and TD. The matrix elements compare amplitudes of the wave fields of the characteristic magnetoionic modes, so normalized that in regions of negligible absorption the squares of the amplitudes are proportional to the mean Poynting vector. The theorem that is proved states that the matrix Tu is the transpose of the matrix TD and that the matrices Ru and RD are symmetric. Some applications are discussed.
Second‐Order Effects in the Faraday Rotation of Satellite Signals
Authors: Titheridge J. E. , Heron M. L.
Published: February 2008

A simple derivation of the second‐order Faraday rotation relation is given that shows the contribution of the different effects. A rapid ray tracing program is used to evaluate the errors in first‐ and second‐order relations, and these are plotted under a variety of conditions. A modified form of the second‐order relation is suggested to reduce the errors. Magnetoionic path splitting does not affect the Faraday rotation to the third order. The only significant errors are those caused by the high‐frequency approximation and by refraction. The first of these is almost independent of zenith angle. The second is zero for magnetically east‐west propagation, when accurate results can be obtained to very large zenith angles. The ratio of the Faraday fading rates on 20 and 40 MHz, near the center of the transit, can be used to determine the critical frequency of the ionosphere to within 1 MHz.
The Response of the Magnetosphere to Sunspots as Indicated by Geomagnetic Storminess Levels
Authors: Chernosky Edwin J.
Published: February 2008

The rather well defined level of geomagnetic activity that occurs with developing sunspots has been examined by using 38 years of daily geomagnetic Ap activity indices and sunspot number Rz. It is found that the Ap values between about 70 and 160 are characteristically associated with sunspots that develop rapidly and reach a peak in number about three days before the occurrence of these levels of Ap. The daily Kp sums from about 45 to 55 were found earlier to be similarly associated with Rz. This relationship predominates at this Ap level during the years in which the average annual Rz is above 50 or more. In quieter solar years some of this range of Ap values tend to be part of a broad recurrence tendency for Rz that peaks about a week before this level of geomagnetic activity is attained; this pattern is a characteristic of a lower level of geomagnetic disturbance. The rapidly developing spots with their high association to solar flares apparently contribute to the magnetospheric energy budget through enhanced electromagnetic radiation. The broad recurrence tendency of lesser disturbance that peaks six to eight days earlier would probably be predominantly due to the Chapman‐Ferraro compression of the magnetosphere by corpuscular emission from the solar ‘M regions’ of Bartels.
Fields Excited by an Arbitrarily Oriented Dipole in a Cylindrically Inhomogeneous Plasma
Authors: Woo Richard , Ishimaru Akira
Published: February 2008

In this paper we derive the closed‐form solution of the three‐dimensional fields excited by an arbitrarily oriented dipole in a cylindrically inhomogeneous isotropic plasma. Geometrical optics is used to represent the fields. The eikonal equation is solved to give the wave fronts from which the rays are obtained. A closed‐form representation is obtained for the differential cross‐section of a three‐dimensional tube of rays thus yielding the amplitude of the wave. Closed‐form expressions are also obtained for the normal vector, binormal vector, and torsion along the rays so that polarization is readily determined. For the special case where the antenna is located on axis, the radiation patterns depend only on the on‐axis and peak electron densities. The solutions show good agreement with solutions obtained for a cylindrically stratified plasma in an earlier study.
Kinetic Approach to Self Modulation of an Amplitude Modulated Wave in Magnetoplasmas
Authors: Sodha M. S. , Sawhney R. L.
Published: February 2008

A rigorous theory for the self modulation of an amplitude modulated electromagnetic wave propagating along the direction of the magnetic field has been developed; the effects of self interaction and mutual interaction for both extraordinary and ordinary modes of propagation have been considered simultaneously. It is shown that the ordinary mode of propagation becomes demodulated and that the extraordinary mode shows strong over‐modulation during its propagation through the medium, when the carrier frequency equals the electron gyrofrequency.
Observations Suggesting Particle Precipitation at Latitudes Below 40°N
Authors: Doherty Robert H.
Published: February 2008

Low‐frequency pulse transmissions are received over reciprocal paths after being reflected once from the ionospheric D region. The daytime reflection height is near 70 km and the nighttime height is near 90 km. Over an 1830‐km path between Nantucket, Massachusetts, and Jupiter Inlet, Florida, with a midpoint at 34°15′N, 75°28′W geographic (or 45°40′N, 352°20′E geomagnetic coordinates), rapid simultaneous phase and amplitude fluctuations are frequently observed at night. Statistically these events occur more frequently near the equinox (seasonally) and near dawn (diurnally). They seem to occur more frequently on the path indicated above than on higher latitude paths at quite different geomagnetic longitudes; the events have not appeared at all on paths at geomagnetic latitudes below 30°N. A possible explanation for the more frequent occurrence on the Nantucket‐Jupiter path is the fact that the midpoint lies slightly west of the magnetic conjugate to the South Atlantic anomaly. Detailed correlation of both phase and amplitude at both ends of reciprocal propagation paths tends to rule out gradients, offpath reflections, or instrumentation as causes of these events. Investigations of several different propagation paths suggest that these effects may be quite localized but that paths with similar geomagnetic latitudes can be similarly affected even when they are separated by more than 100° in geomagnetic longitude. LF ionospheric propagation is very sensitive to relatively small changes in electron densities in the D region. The events described above become less pronounced as the path length increases; this pattern suggests that they are quite localized and that the integrating effect of longer paths tends to mask the effects. Particle fluxes capable of producing electrons in the 10‐ to 100‐electron cm−3 sec−1 range near 80 km at night would be expected to produce variations such as those measured. These LF phase measurements over oblique paths may prove to be an excellent method for detecting leakage or dumping of charged particles from the radiation belts into the lower ionosphere.
ELF Propagation in an Inhomogeneous Waveguide
Authors: Galejs Janis
Published: February 2008

The laterally inhomogeneous anisotropic ionosphere is represented by a changing ionospheric surface impedance. The fields across such discontinuities can be estimated by computing the propagation characteristics on the various segments as in a homogeneous environment and by applying the resulting propagation parameters to the appropriate segments of the path. For fields observed across a day‐to‐night boundary, the resulting error is of the order of one percent. The effects of more localized ionospheric perturbations depend on their azimuthal and transverse extent. In the lower ELF range, areas with transverse dimensions of one to two thousand kilometers affect the propagation path across the perturbation to about the same extent as a propagation path tangential to the periphery of the perturbed region.
Differential Phase Shift of Partially Reflected Radio Waves
Authors: Connolly D. J.
Published: February 2008

The addition of phase difference measurements to differential absorption experiments is shown to be both feasible and desirable. The phase information can provide a more sensitive measurement of electron density above about 75 km. The differential phase shift is only weakly dependent on collision frequency in this range, and so an accurate collision frequency profile is not a prerequisite. The differential phase shift and differential absorption measurements taken together can provide both electron density and collision frequency data from about 70 to 90 km.
Measurement of Total Electron Content with a Geostationary Satellite During the Solar Eclipse of March 7, 1970
Authors: Rangaswamy S. , Schmid P. E.
Published: February 2008

This note deals with the measurement of the total electron content of the ionosphere at the Goddard Space Flight Center, looking towards the geostationary satellite ATS 3 during the solar eclipse of March 7, 1970. Obscuration at this site was nearly total. Faraday rotation was measured with a stationary circularly polarized antenna and a dual‐channel phase‐lock receiver tuned to 137.350 MHz. By comparing the electrical phase of the two opposite circularly polarized components, a continuous chart recording was made of Faraday rotation versus local time. A depletion of about 25% in electron content was observed from first contact to the time of minimum electron content. The time variations of the electron content during the eclipse are briefly examined in the light of current theories of ionospheric processes.
Conditions for Orthogonality Between the Geomagnetic Field and an HF Sky‐Wave Ray
Authors: Kelso John M.
Published: February 2008

At HF or higher frequencies, in computing the polarization conditions along a radio ray traveling in the ionosphere, it is often sufficient to express the results in terms of the Faraday rotation of the plane of polarization, obtained as an integral (along the path) of the phase difference between the ordinary and extraordinary components. The computation simplifies when the quasilongitudinal (QL) approximation of magneto‐ionic theory can be applied. The QL approximation is invalid at any point where the ray becomes transverse to the geomagnetic field, and in some regions around that point. In 1963 George A. Dulk showed that neglect of this effect may lead to major errors. In considering an oblique path with sky‐wave reflection, it is easy to be misled into thinking that a transverse condition is unlikely except on east‐west paths, particularly in equatorial regions. On the contrary, transverse conditions are likely to occur under a wide range of conditions at all latitudes and for all propagation directions. This presentation describes conditions of ray geometry and magnetic latitude, which result in transversality at some point along the path. The method for defining the conditions is shown to be applicable even when the ray is permitted to follow a twisted path in three dimensions, and the geomagnetic field is defined under very general assumptions. The basic results are also directly applicable to problems concerned with the reflection of HF signals by field‐aligned ionization.
High‐Frequency Backscattering From a Perfectly Conducting Sphere Coated With a Radially Inhomogeneous Dielectric
Authors: Alexopoulos Nicolaos G.
Published: February 2008

In this paper, the backscattered electric field is derived when a plane electromagnetic wave is incident upon a perfectly conducting sphere coated with a radially inhomogeneous dielectric. The Mie series is obtained and then subjected to an asymptotic analysis that is valid for very short wave‐lengths. In particular, the first two terms for the reflected portion of the electric field are derived and the formulation for the creeping wave contribution is presented. Also, a numerical computation of the monostatic cross section is performed for various thicknesses of the coating by considering the reflected portion of the backscattered electric field. It is shown that this particular type of inhomogeneous sheath reduces considerably the monostatic cross section of the perfectly conducting sphere as its thickness increases.
Anticipated Super‐Refraction Over India, Based on the Climatology of the Vertical Structure of Radio Refractivity
Authors: Chatterjee K.
Published: February 2008

From the monthly average values of radiorefractivity near the ground surface and at the 850‐mb level (approximately 5000 ft above sea level), values of refractive index gradient have been computed between ground surface and 5000 ft above sea level for the 12 Indian radiosonde stations. These values of N gradients have been examined to estimate super‐refraction of radio waves in the lower troposphere over India. Maps showing isopleths of refractive index gradient over the country during different seasons are also presented.
Theoretical and Experimental Determination of the Near‐Field Correction for Backscatter Gain at the Arecibo Observatory
Authors: Steinfeld A. H. , Brice N. M. , Conrad J. C. , LaLonde L. M.
Published: February 2008

During the summer of 1968, two‐beam, incoherent‐scatter radar measurements were made at Arecibo. The two beams were formed by two separate feeds for the Arecibo reflector, one a line feed which illuminated essentially all of the reflector, and the other a horn feed which effectively illuminated about 500 feet of the reflector. A by‐product of this experiment was the calibration of the near‐field correction to the backscatter gain of the line‐feed system. This was obtained by comparing the power received as a function of range in the two radar systems. The measured loss of gain in the near field for the line feed was about 1.5 db at a height of 100 km.
Radiation From Layered Structures of Variable Thickness
Authors: Bahar E.
Published: February 2008

Explicit expressions are derived for the fields radiated by layered structures of linearly and sinusoidally varying thickness. Both plane‐wave and concentrated‐source excitations are considered. The solutions are based on a full‐wave analysis which uses the exact boundary conditions. It is shown that the solutions are, in general, consistent with the reciprocity relationships.
Antarctic Ice Cap Attenuation Rates of VLF Signals Determined From Short and Long Great Circle Paths
Authors: Crary J. H. , Crombie D. D.
Published: February 2008

Recordings of the relative phase and amplitude of the signal from GBR, Rugby, U.K., have been made for several years at Byrd Station, Antarctica. Diurnal variations and the behavior of the signal received on a loop and a vertical antenna are consistent with the hypothesis that the dominant signal arrives at Byrd over the short great circle path when it is in maximum darkness and over the long great circle path when it is in maximum darkness. This is to be expected for a path of this length (short path, 16,248 km; long path, 23,759 km) because the attenuation of VLF signals is very much less for dark than for sunlit conditions. The short and long paths from GBR to Byrd contain portions of the Antarctic ice cap about 1250 and 725 km long, respectively. Using reasonable assumptions about the attenuation over the non‐ice‐cap portions of the path, calculations were made of the excess attenuation introduced by the ice cap on the two paths when the ice cap is completely dark or illuminated, assuming that the inconsistencies in the signal level over the two paths were due to the additional attenuation over the ice cap. The results indicate that the excess attenuation rate over the sunlit ice cap is between 17 and 31 db/1000 km, which corresponds to a range of conductivities between 0.01 and 0.05 mmho/m for 16 kHz. The nighttime data indicated an attenuation rate of 17 to 22 db/1000 km, which is outside the range of calculated attenuation rate versus conductivity.
Scattering of HF Radio Waves by a Spherical Electron Cloud
Authors: Klein Milton M.
Published: February 2008

Numerical and analytic solutions in the ray‐optics region have been obtained for the scattering of HF radio waves by a spherical electron cloud with a Gaussian distribution of electron density in the radial direction. The results show that a highly overdense or hard cloud has a wide range of backscatter angles for which the cross section is almost constant with a value close to that of an equivalent conducting sphere (critical radius size). A slightly overdense or soft sphere has a much narrower range of almost constant cross section whose value is proportional to the fourth power of the critical radius and considerably below that of an equivalent conducting sphere. In the region of forward scatter, all spheres have essentially the same cross section, independent of hardness. For underdense spheres, the cross section is generally the same as that characteristic of forward scattering except in the region of maximum deflection where the cross section increases very sharply. It is found that when an underdense sphere becomes critical, the maximum deflection is 90°, whereas an overdense sphere retains its maximum deflection of 180° at the critical density. For overdense spheres, the analytic results are in good agreement with those obtained numerically; but for underdense spheres, they are not in good agreement at the higher electron densities.
Ionospheric Winds and Viscous Dissipation
Authors: Rosenberg N. W. , Zimmerman S. P.
Published: February 2008

Analysis of frequency distribution of vertical shear of horizontal winds is reported for 2000 samples obtained between 90 and 136 km. The distribution is independent of altitude when shears are normalized by dividing by limiting shears of .075 sec−1 below 110 km, decreasing to .035 sec−1 at 128 km. Associated vertical wavelengths are also altitude independent when normalized, with shortest wavelengths increasing from 3 km at 90 km to 10 km at 136 km. The Richardson number, as a criterion of turbulence, shows that 7% of space/time samples below 110 km will permit turbulence to initiate, while no samples above 115 km will permit onset of turbulence. Viscosities (computed by Hines equation relating viscosity and limiting wavelength) are 30‐fold greater than molecular at 90 km, approaching molecular above 115 km. The rate of deposition through viscous shear is 2000–4000 erg g−1 sec−1, but 10% of the samples have a five‐fold higher rate, which will significantly affect temperature profiles. The shears found are capable of increasing molecular ion and electron density to about 4×103 cm−3 from background ionization levels below 103 cm−3, and to 2×104 cm−3 from backgrounds of 104 cm−3. They cannot significantly enhance 105 cm−3 backgrounds.
The Position of Electron Density Maxima with Vertical Ionization Movements
Authors: Whitehead J. D.
Published: February 2008

A common test of the wind‐shear theory of sporadic E is to compare wind profiles with corresponding electron density profiles. The relationship between the two measurements is not always obvious. The presence of electric fields and vertical movement of the wind profile has been suggested to account for this. However, it is shown that the position of electron density maxima relative to the horizontal winds must lie in certain height ranges irrespective of electric fields or wind profile movements, provided these are steady. If the winds were suddenly to change, it would take time for the electron density profile to change. The time constants involved are estimated. Thus it should be possible to say whether the experimental results are consistent with the idea that the elecron density profile is produced by the wind profile.
The Impedance Characteristic of a Spherical Probe in an Isotropic Plasma
Authors: Tarstrup J. , Heikkila W. J.
Published: February 2008

An experimental investigation of the impedance characteristic of a spherical plasma probe has been carried out for a quantitative assessment of theoretical work, and of hydrodynamic or fluid theory in particular. A stable, low temperature (T ∼ 500°K) plasma was produced in nitrogen by a cold cathode discharge, with a plasma frequency of the order of 15 MHz and with an electron collision frequency in the range of 106 to 107 sec−1. The probe consisted of two hemispheres, one serving as a guard to eliminate the effects of the connecting leads; this geometry provided an almost purely radial electric field over the test hemisphere. Probe diameters ranged from 7 to 20 mm (10 to 30 Debye lengths). Hydrodynamic probe theory was tested against the experimental results for the specific cases corresponding to the probe at floating potential and at space potential. Good agreement was obtained for both the real and imaginary parts. The real part of the impedance shows a peak near the plasma frequency, a small shift being explicable in terms of realistic sheath profiles. Electron density can thus be deduced rather accurately, and electron temperature approximately, on the basis of hydrodynamic theory. Accurate values of the electron‐neutral collision frequency were also obtained for plasmas where the collision frequency was larger than 0.4 times the radian plasma frequency. At lower pressures the presence of collisionless or Landau damping was clearly established, and the more accurate kinetic theory is necessary to explain the experimental results.
Letters: Visible Light Flux Affecting the D Layer
Authors: Gassmann G. J. , Wagner R. A.
Published: February 2008

An earlier experimental result of potential importance to D‐region chemistry and based on the effect of the earth's albedo is being reexamined and reconfirmed by presenting more detailed technical information on the airborne techniques employed. The interpretation of the observations, which consisted of radio soundings, suggests that the energy flux of visible light, distinct from the UV and X‐ray range, has a profound effect on the electron density of the D layer.
A Technique for Describing the Antarctic D Region at VLF Based on Waveguide Dispersion Measurements
Authors: Webber G. E. , Peden I. C.
Published: February 2008

Average ionospheric reflection heights are deduced for a trans‐Antarctic propagation path between Byrd Station and Scott Base. A technique is described for making relative phase measurements on VLF transmissions at several phase‐locked frequencies. Results are interpreted using waveguide mode theory which accommodates a horizontal dipole source and the effect of an anisotropic polar ionosphere. Reflection heights are presented for illustration during a period of solar activity in March 1969 and a quiet period in September of the same year; correlations are made with other indicators of ionospheric activity.
On Steepest Descent Evaluation of an Integral Describing Transient Wave Propagation in Anisotropic Plasmas
Authors: Chen Kenneth C. , Yen Jui Lin
Published: February 2008

In this paper, some properties of the steepest descent path of the integral describing transient plane wave propagation in anisotropic cold plasmas are determined. The relationship of the steepest descent method to the possible arrival of evanescent waves is illustrated by a numerical example. Also, it is shown through error estimates that the result obtained by the steepest descent method is valid for finite z and large t.
Synthesis of Jicamarca Data During the Great Storm of March 8, 1970
Authors: Woodman Ronald F. , Sterling D. L. , Hanson W. B.
Published: February 2008

Continuous measurements of electron temperature and electron concentration were made at Jicamarca from 0700 to 0830 LT and from 1130 to 2000 LT during the great magnetic storm of March 8, 1970, when the F2 peak rose as high as 800 km. Continuous measurements of the vertical component of E×B drift were made from 1130 to 1730 LT. A synthesis of the observed electron concentrations was made using a model that solved the time‐dependent electron‐ion continuity equation for O+ and the molecular ions; the latter chemistry was included to improve the solutions at lower heights. It was found, using the observed values of vertical drift, that most of the observed features of the F2‐region ionosphere were synthesized by the model. An interpretation of the synthesis that emphasizes the importance of horizontal diffusion at the equator is given. Observations are presented for March 7, 8, and 9, 1970, including the Huancayo magnetograms, which display a close correlation with the drift measurements.
The Behavior of Antennas in Plasma as a Function of the Frequency of Excitation: Summary Report
Authors: Bachynski M. P.
Published: February 2008

A feature of the session on the behavior of antennas in a plasma as a function of frequency of excitation was the variety of antenna configurations which was being investigated by various research groups.

The emphasis by the Groupe de Recherches Ionosphériques du Centre National d'Etudes de Télécommunications (France) was on quadrupole probes. L. R. O. Storey and J.‐M. Chasseriaux reported on theoretical studies of plasma probes based on the mutual electrical coupling between pairs of dipole antennas. Two types of antennas were analysed, Hertzian dipoles which are short compared with the Debye‐length and double‐sphere dipoles which are long compared with the Debye‐length. In both cases the complete probe is formed by two such antennas separated by a distance much larger than a Debye‐length. The mode of operation of these quadrupole probes can be either active (by driving a current in one dipole and measuring the open circuit potential difference induced on the other) or passive (by measuring the cross‐spectrum of the fluctuating potential differences induced on the two dipoles by the plasma microfield). The quadrupole probes can be applied to the measurement of plasma resonant frequencies, collision frequencies, and the velocity of motion with respect to the probes.
Laboratory Plasmas: Summary Report
Authors: Watanabe Tomiya
Published: February 2008

Three papers were presented in this session, two on plasma resonances and one about Bernstein‐mode electrostatic waves.

M. P. Bachynski and B. W. Gibbs (RCA Laboratories, Montreal, Canada) gave the results of their experiment which concerns electrostatic resonances excited in a layer of isotropic plasma by means of plane transverse electromagnetic waves incident from free space. The angle of incidence was small, i.e., θ = 0° ∼ 12°. Incident waves are polarized, circularly and linearly, and have a fixed frequency, 9.2 GHz. The incident power density was of the order of 0.1 mw cm−2. The thickness of the plasma slab was 1.56 free‐space wave lengths. Two electric dipoles were used as receiving antennas, one totally immersed in the plasma and the other placed outside the plasma. The immersed dipole was oriented normal to the plasma‐slab boundary and consequently nearly longitudinal to the incident wave. Strong electric fields were observed in the regions under conditions in which the frequency of the incident wave equaled the plasma frequency, and the electric vector of the incident field was in the plane of incidence. These strong fields seem to be longitudinal electrostatic fields, since only weak electric fields of longitudinal direction were observed if the incident electric field was perpendicular to the plane of incidence.
The Effect of the Subsurface on the Depolarization of Rough‐Surface Backscatter
Authors: Rouse John W.
Published: February 2008

Most theoretical treatments of single‐surface scatter indicate negligible depolarized scatter into the plane of incidence. However, experimental measurements show that this scatter component is present. Several investigators have attempted to develop an explanation for the contradiction by attributing the depolarization to multiple scatter on the surface, but there is also evidence that the depolarization arises from volume scatter beneath the surface. In the Reneau et al. [1967, p. 463] measurements of laser scatter from inhomogeneous dielectrics they found, “… strong evidence that the depolarization process occurs primarily within the volume.” In similar studies Leader [1970, p. 11] also found, “The depolarized component is many orders of magnitude less than the polarized component when there is little contribution from the volume of the sample.” This paper presents a development for backscatter from rough surfaces, based on the single‐surface Kirchhoff method as employed by Fung [1967], which incorporates components due to volume scatter from the subsurface. The resulting expression contains a depolarized backscatter component due exclusively to the volume scatter. Calculation of polarized and depolarized backscatter and depolarization ratios are shown for several values of dielectric constants and volume reflection coefficients.
Velocity‐Dependent Multiple Scattering by Two Thin Cylinders
Authors: Censor Dan
Published: February 2008

A relativistically exact formulation is presented for multiple scattering of electromagnetic waves by arbitrary, uniformly moving objects. The formulation is based both on spectral representations which are easily transformed from one frame of reference into another and on a successive scattering scheme which iteratively satisfies the boundary conditions on the surface of the obstacles. Explicit expressions and computational results are given for scattering by two thin dielectric cylinders.
Radiation From an Open‐Ended Waveguide With Extended Dielectric Loading
Authors: Fong T. T.
Published: February 2008

The relative contributions of leaky, surface, and space waves are studied for an open‐ended dielectric‐loaded waveguide structure using Wiener‐Hopf technique with the key step in factorizing the kernel being carried out numerically. The relative field contributions are evaluated by both ordinary saddle‐point and modified saddle‐point integration methods, and the accuracy of each method in different spatial regions is examined.
Wider Aperture Sine‐Cosine Direction Finders
Authors: Travers Douglas N. , Green Terry C.
Published: February 2008

Higher‐order sine‐cosine azimuth patterns for Adcock direction finding are investigated to determine spacing errors, reradiation errors, and pickup factor. The higher modes achieve wider apertures and reduced wave interference error; they exhibit comparable pickup factors but require an increase in the minimum number of antennas and different sensing methods. The 1.220λ spacing limit is appropriate only to the dipole mode, the corresponding limit for the quadrupole mode being 1.684λ and correspondingly greater for the higher modes. Reduced spacing error for the minimum number of antennas occurs at increasingly wider apertures which also tend to more closely approach the theoretical limits with increasing mode. The higher modes exhibit reduced response in the vicinity of the zenith. The resolution of the additional bearing ambiguities involves the use of one or more lower‐order patterns. Predicted sense performance as a function of reradiated field amplitude is computed for a combination of quadrupole and dipole modes.
Radiation by arbitrary sources in anisotropic stratified media
Authors: Daniele V. G. , Zich R. S.
Published: February 2008

The radiation of an arbitrary source in a stratified system including anisotropic slabs is considered. Starting from an abstract‐operator formulation given by Bresler and Marcuvitz [1956, 1957], the transverse field is evaluated by using a Fourier‐integral representation. The Green's function is expressed through the evaluation of the source‐free solutions. The scattered field and the plane‐wave response are examined. An example is given concerning the field radiated in the presence of an anisotropic ferrite slab. The far field is evaluated through a saddle‐point integration.