bluuebunny/crossref_metadata_2025 huggingface dataset:
Worldwide Behavior of Average VHF‐UHF Scintillation
Authors: Fremouw E. J. , Bates H. F.
Published: February 2008

A description of the latitudinal, diurnal, seasonal, and solar‐cycle variations of F‐layer‐produced scintillations, based on a comprehensive review of the literature, is given. Three distinct latitudinal regimes are discussed in regard to scintillation behavior and the quantitative utility of observations reported in the literature. A semiquantitative empirical model is suggested to describe the strength of scintillation‐producing irregularities of F‐layer electron density. Recent work suggests that more quantitative modeling might now be fruitful, but gaps in fully quantitative data exist. The prime needs are for observations at very high latitudes and for calibration of scintillation indices used at very low latitudes.
A Comparison of Selective Summation Techniques for the Coherent Green's Function in Random Media
Authors: Collin R. E.
Published: February 2008

A comparison is given of Keller's method, renormalization techniques, and approximations commonly employed in obtaining approximate solutions to the exact Dyson equation for the coherent field. It is shown that the Dyson equation, Keller's method, and the renormalization theory all lead to identical results. It is also shown that the Dyson equation is the most convenient since it is inherently free of unconnected (factorizable) diagrams.
Operational Comparison of Meteorological Measurements and Missile‐Tracking Radio Interferometer Noise
Authors: Vickers William W. , Dyer Rosemary M.
Published: February 2008

Undesirable noise in the radio‐interferometer tracking system (General Electric Mod III) at Cape Kennedy during the Mercury‐Atlas and Ranger‐Atlas orbit series is alleged to have resulted from stochastic refractive ray bending and associated multipath conditions. Surface‐to‐16,000‐foot meteorological data for eight to nineteen shots were examined, using various functions of water vapor‐related parameters and temperature as noise predictors. Spearman rank correlations, significant at the 1% level, were found between all the water vapor‐related measurements tried and a measure of tracking noise. A threshold level of 370 N‐units surface value was found (corresponding to about 19 gm‐m−3 of water vapor), beyond which tracking problems are likely to develop. Results of earlier investigators are confirmed, and the present investigation strongly implies that the source of the noise problem indeed lies in the lowest layers of the atmosphere. Limited attempts to correlate noise with atmospheric inhomogeneities were unsuccessful.
Forward and Backscatter of RF Waves by Spherical Overdense Clouds for Several Electron Density Distributions
Authors: Klein Milton M.
Published: February 2008

A determination, in geometric optics approximation, of the forward and backscatter characteristics of spherical overdense clouds having (1) a Gaussian decrease with distance from the center, (2) a sech2, or exponential, decay, and (3) an inverse‐square decrease, showed that the backscatter cross section for the inverse‐square distribution is always larger than for the other two distributions. As the center‐point density increases, the backscatter cross section obtained with the Gaussian sphere most rapidly takes on the characteristics of a conducting sphere, that of the sech2 distribution lags slightly behind, but that of the inverse‐square sphere never gets close to the result for a conducting sphere. In forward scatter, the inverse‐square distribution shows the largest cross section and a fairly rapid increase with center‐point density, the sech2 distribution has an essentially constant cross section, and the Gaussian, which has the lowest forward scatter cross section, shows a slight decrease with center‐point density.
Impulse Reflection with Arbitrary Angle of Incidence and Polarization From Isotropic Plasma Slabs
Authors: Chabries D. M. , Bolle D. M.
Published: February 2008

The nature of the reflected signal is considered for an electromagnetic impulse impinging on a semi‐infinite plasma and a finite plasma slab terminated by a perfectly conducting surface at arbitrary angles of incidence and for both polarizations. The inverse Fourier transform technique is used and leads to a statement for the reflected signal in terms of Bessel functions of the first kind. The results are shown graphically for both the TE and TM case for all angles of incidence between normal and π/2.
Interferometric Direction Finding on an FM/CW Ionosonde
Authors: Sherrill W. M. , Green T. C. , Martin P. E.
Published: February 2008

DF interferometry on an FM/CW sounder has been successfully performed using a three‐element crossed baseline array and twin channel receiver modified for linear FM synthesis. Measured baseline phase differences obtained from a sum‐and‐difference CRT phase display were used to compute incident azimuth and elevation. Phase ambiguities were resolved by prior knowledge of the sounder location. Measurements in San Antonio, Texas, on cooperative FM/CW targets in Pueblo and Boulder, Colorado, showed essentially constant azimuth within ±2°, commensurate with ionospheric lateral deviation effects. Corresponding elevation data showed increasing elevation angle with frequency indicative of increasing ray penetration. The azimuth/elevation measurements were made without benefit of IF spectral analysis for time‐delay‐mode resolution. Consequently, measurements were successful over those frequency ranges at which the sounder signal dominated interfering stations. This limitation would be eliminated by the use of cross‐spectrum analysis at the receiver output.
Sporadic‐E and Wind‐Profile Interrelation Over Hawaii
Authors: Smith Lawrence B. , Wright J. W.
Published: February 2008

Principal qualitative and semiquantitative expectations of the wind‐shear theory of sporadic‐E are stated, with special emphasis on the significance of observed time variations in deciding whether the theory is operative and whether the vertical‐shear mechanism is dominant. Nine wind profiles and twenty‐two sporadic‐E observations made in Hawaii are examined in the light of these expectations and are judged to behave consistently with the wind‐shear theory.
Influence of the Tidal Wind System on the Frequency of Sporadic‐E Occurrence
Authors: Harris R. D. , Taur R.
Published: February 2008

Sporadic‐E (ES) data from Japan were presented to show the temporal variations in sporadic‐E blanketing frequency (ƒbES), virtual height (h′ES), and frequency of occurrence. Tidal winds were substituted into the wind‐shear theory of ES to calculate electron density profiles and determine the influence of the tidal winds in the asymmetry of the ES occurrence variation. Results showed that the tidal wind model used was not strong enough to significantly influence the formation of molecular ion ES layers, but that the winds did have the proper orientation to accumulate and layer metallic ions in the late afternoon. The role of metallic ions in afternoon ES will have to be established.
Enhanced Microwave Absorption in the Lower Atmosphere of Venus
Authors: Richter Kurt R.
Published: February 2008

The enhanced microwave attenuation in the altitude range between 35 and 52 km is explained by the assumption of an atmospheric layer consisting of water vapor and water droplets. The mass density distributions were calculated from the attenuation coefficient, and refractivity was measured during the Mariner 5 occultation experiment; temperature and pressure were measured by the Venera probes. These independent measurements lead to a reasonable altitude distribution of the water droplets and the water vapor content. The results show good agreement with assumptions which have to be made to explain the brightness temperature of the planet Venus.
Analytic Ray Solutions for High‐Frequency Radio‐Wave Propagation Through Plane Stratified Ionosphere Models
Authors: Price Gary H.
Published: February 2008

The transmission of high‐frequency radio waves through the ionosphere is examined for a plane‐stratified, isotropic ionospheric model and an impulsive point source. Explicit solutions for the path relations and the signal amplitude for the homogeneous‐slab model illustrate the breakdown of straight‐line approximations to the ray path. Implicit solutions for the path relations that are useful for iterative evaluation are also found for more general ionospheric profiles.
The Empirical Connection of Riometer Absorption to Solar Protons During PCA Events
Authors: Potemra T. A.
Published: February 2008

Linear relationships between daytime 30 MHz polar‐cap absorption and the square root of integral and differential proton fluxes have been studied experimentally, using satellite and riometer measurements, and theoretically, by means of power‐law model proton spectrums together with D‐region ionization models developed previously by the author. Relationships of riometer absorption, A, to the 2π omnidirectional integral proton fluxes greater than the threshold energy E0 were found to be least sensitive to varying model proton spectrums for E0 = 7 Mev. In this case the following formula was computed: A = 0.083[J(>7 Mev)]½ db, where the flux units are cm−2sec−1. Using data collected from the 2π omnidirectional integral proton detectors on the polar‐orbiting satellite 1963 38C with E0 = 2.2, 8.4, and 25 Mev on 93 passes and polar cap 30 MHz riometer data during three markedly different events, the best linear correlation was found to be A = 0.084[J(>8.4 Mev)]½ db with a root‐mean‐square deviation of 0.38 db. Daytime 30 MHz absorption during PCA's is affected most by 15 Mev protons, which produce their greatest ionization at a 65 km altitude in the D region.
Computation of Dispersion Curves for a Hot Magnetoplasma with Application to the Upper‐Hybrid and Cyclotron Frequencies
Authors: Muldrew D. B. , Estabrooks M. F.
Published: February 2008

Rapid calculations of the dispersion relation can be made for a hot, Maxwellian electron magnetoplasma, with collisions and for any angle β between the wave normal and static magnetic field without using the low‐temperature or the quasi‐static approximations. The dispersion equations of Lewis and Keller [1962] are discussed and interpreted for the purpose of computer programming; these equations are valid for a Vlasov‐Maxwellian plasma and contain a particle‐preserving collision term. Examples of dispersion curves for homogeneous plane waves show: (1) protrusions from some refractive‐index surfaces and (2) the usual multiplicity of solutions for a Maxwellian plasma when the real and imaginary components of the refractive index are of similar magnitude. For a wave frequency 1.11 times the plasma frequency and about 1.78 times the gyrofrequency, a minimum is found in the collisionless damping at β = 0° and a maximum is found at about β = 14°. Three alternatives for the gyroresonance observations on topside ionograms can be found from a study of the dispersion curves near the gyrofrequency: (1) an energy transfer between the highly damped whistler mode and electrons in the vicinity of the sounder, (2) the field resulting from the multiplicity of solutions mentioned above, and (3) an evanescent field.
Radar‐Derived Statistics on Slant‐Path Attenuation at 10 GHz
Authors: Rogers R. R.
Published: February 2008

Attenuation due to rain at 10 GHz over the radar line of sight has been measured automatically during the past three summer seasons. Data from five months were analyzed to give statistics on the frequency of occurrence, the extent in azimuth, the duration, and the dependence on elevation angle of 5‐ and 10‐db attenuation events. Results show that the frequency of occurrence diminishes rapidly as the elevation increases from horizontal to 10°, and is essentially constant from there on to 20°. 5 db is exceeded 10 hours per year at 3° elevation, 4 hours per year at 10°, and 3.5 hours per year at 20°. At all elevations 10 db is exceeded about one‐fifth as frequently as 5 db.

The azimuth extents of attenuating rain regions vary from 1°, the narrowest extent measurable, to values exceeding 60°. At low elevations the distributions of azimuth extent are strongly peaked at the narrow end. With increasing elevation the distributions flatten. The average azimuth extent of a 5‐db region increases approximately linearly from 10° at an elevation of 3° to 33° at an elevation of 20°. For all elevations the average 10‐db extents are about half the 5‐db extents. The average duration of a 5‐db event decreases from about 30 min at near‐horizontal paths to less than 10 min at an elevation of 20°. For all elevations the average duration of a 10‐db event is about two‐thirds that of the 5‐db event. These results indicate the characteristics of rain attenuation to be expected over satellite‐to‐ground communication links for the Montreal area.
Complex Permittivity of the Antarctic Ice Sheet in the VLF Band
Authors: Peden I. C. , Webber G. E. , Chandler A. S.
Published: February 2008

The lower wall of the Antarctic earth‐ionosphere waveguide is composed of rock covered by an ice sheet, the depth of which can be an appreciable fraction of a wavelength at very low frequencies. The complex permittivity of the ice cap is therefore an important parameter in connection with the prediction of propagation velocities and attenuation in the guide over long paths on the Antarctic continent. This paper describes an experiment conducted near Byrd Station during November, 1971, in which the properties of the surface magnetic field between 5 and 20 kHz were measured in the immediate vicinity of a buried 34‐km dipole antenna just under the surface of the snow. The related analytical problem and data reduction process are described briefly to clarify the means for converting the data into bulk average values of the complex permittivity parameter of the ice over the frequency range of interest. The resulting dielectric and loss parameters are new and have not been determined before in connection with the Antarctic ice sheet.
Letters: Attenuation of Electromagnetic Waves in the Earth‐Crust Waveguide From ELF to VLF
Authors: Wait James R. , Spies Kenneth P.
Published: February 2008

Using an idealized model, the attenuation rate of the lowest order mode is calculated for a range of deep crustal conductivities. It is shown that attenuation rates may be as low as 1 db/100 km at 1 Hz for a waveguide conductivity less than 10−6 mhos m−1
An Investigation of the Ionospheric D Region at Sunrise: 2, Estimation of Some Photodetachment Rates
Authors: Turco R. P. , Sechrist C. F.
Published: February 2008

The photodetachment rates of several negative ions believed to be present in the D region are estimated for sunrise conditions. The photodetachment cross sections of O− and O2− which have been measured in the visible and infrared wavelength ranges are used. Since the photodetachment cross sections of NO2− and NO3− are not yet known, the behavior of their rates could only be estimated. Infrared band absorption by H2O and CO2 is included in the calculations. For atoms and molecules with large electron affinities the ozone ultraviolet absorption is important. The effects of photodetachment on D‐region behavior are discussed and found to be relatively unimportant.
LETTERS, Incoherent Scatter Observations at Arecibo Using Compressed Pulses
Authors: Ioannidis G. , Farley D. T.
Published: February 2008

Pulse‐compression techniques are now being used successfully in incoherent observations at Arecibo. In most observations a 13‐bit Barker code and 6‐μsec baud length are used, giving a compression ratio of 13 to 1 with very low range sidelobes and an altitude resolution of 0.9 km. A few of the first measurements with this technique are presented here and include observations of (a) the E region and sporadic E layers, (b) the D‐region ledge near 80 km, and (c) narrow enhanced echoes associated with HF heating of the ionosphere.
Transient Responses: Resonance Spikes of Topside Sounders: Summary Report
Authors: Petit M.
Published: February 2008

In summarizing the discussions, the following statements appeared well established:

At the plasma frequency, ƒN. The waves responsible for resonance signals are electrostatic in character. Their propagation vector k is directed nearly parallel to the magnetic field. These waves with frequency slightly greater than the plasma frequency do not exist in cold plasma theory, while in kinetic theory they appear inside the resonance cone.
VLF Emissions: Summary Report
Authors: Kimura I.
Published: February 2008

In addition to a review on whistler mode propagation and VLF emissions, the introductory talk by M. J. Rycroft (University of Southampton, England) covered several recent topics, three of which were mostly discussed: (a) recent results of a ray tracing to be compared with Walter and Angerami's [1969] and Scarabucci's [1970] computations, (b) effect of thermal anisotropy on the real part of the refractive index, hence on raytracing, especially in plasmas with β = 1, (c) simultaneous rocket observation of electron flux (energies higher than 45 kev) and whistler‐mode noise intensity.

The rest of this session was mainly devoted to generation mechanisms of VLF emissions; a few other topics such as an electrostatic instability in the magnetosphere were also included.
Excitation: Summary Report
Authors: Rawer K.
Published: February 2008

Three short papers were read after the review paper by T. W. Johnston.

P. E. Vandenplas (Ecole Royale Militaire, Brussels, Belgium) gave a survey concerning resonances observed in laboratory plasma capacitors. For such a capacitor with plate distance l and plates covered with rarified sheaths, cold plasma theory gives the main resonance of an infinite plane capacitor as a serial one at a frequency ƒN (1 − a/l)1/2, where a is the thickness of the (homogeneous) plasma sheath between the plates. In warm plasma theory apart from a correction term of the order λDe2/a2(λDe is electron Debye‐length) this resonance splits up into a narrow series of successive resonances, the distance of which is controlled by the same parameter. Furthermore, since the ‘warm’ dispersion equation is of fourth order now, other eigenvalues lead to new resonances of another type, which have been found in the laboratory also.
Measurement of Best Time‐Delay Resolution Obtainable Along East‐West and North‐South Ionospheric Paths
Authors: Lynch J. T. , Fenwick R. B. , Villard O. G.
Published: February 2008

A high‐resolution, frequency‐modulated, continuous‐wave (FMCW), oblique‐incidence sounder was used to measure the minimum equivalent pulse widths that could be transmitted over two different oblique paths. One path, 1880 km long, was substantially an east‐west path from Lubbock, Texas, to Stanford, California. The second path, 1300 km long, from Bozeman, Montana, to Stanford had characteristics representative of north‐south propagation. The data from each path indicated that for 50% of the daylight hours, pulse widths as small as 3 to 5 μsec could be transmitted without significant ionospheric broadening if the minimum dispersion frequency was used.
Reflection and Transmission of Electromagnetic Waves by a Moving Inhomogeneous Medium
Authors: Tanaka K. , Hazama K.
Published: February 2008

This paper describes the rigorous solution of the problem of reflection and transmission of a plane E wave incident from a homogeneous medium upon a lossless inhomogeneous medium moving uniformly parallel both to the interface and to the plane of incidence by using Maxwell's equations and the constitutive relations for a moving medium. The inhomogeneous medium is assumed to have a linear transition profile of specific permittivity. To describe the influence of the moving inhomogeneous medium in detail, some numerical illustrations of the reflection coefficient and the reflection point of geometrical optics in the inhomogeneous medium are shown. It is found that the reflection point is shifted and the dependence of the reflection coefficient on the width of the inhomogeneous medium is modified in an interesting manner by the motion of the medium.
Effects of Pseudosonic and Electroacoustic Waves on the Radiation of a Plasma‐Coated Spherical Antenna
Authors: Maxam Garth , Chen Kun‐Mu
Published: February 2008

A spherical antenna covered by a layer of lossy, hot plasma is considered. The radiated electromagnetic wave and the pseudosonic and electroacoustic waves excited in the plasma layer are determined. The effects due to the pseudosonic and electroacoustic waves on the radiated power, the input conductance, and the input susceptance of the antenna are obtained. Resonance phenomena due to the pseudosonic and electroacoustic waves and the enhancement in radiated power due to the electromagnetic and pseudosonic waves are discussed.
Radar Measurement of Ionosphere Motion in the Presence of Current‐Induced Spectral Asymmetries
Authors: Rino Charles L.
Published: February 2008

The technique of measuring ionosphere motion from the shift in the incoherent‐scatter ion line has been known for some time. The underlying assumption in the adaptations of the technique applied so far is that there are no detectable current‐induced asymmetries in the spectrum. In the auroral zone this assumption can be violated during magnetospheric storms. To cope with this possibility we use an estimate of the first moment of the spectrum together with a matched‐filter‐like estimate.

The first moment is the sum of the first moment of the unshifted spectrum plus the Doppler shift. The matched‐filter estimate, while not unaffected by asymmetries, tends to give an estimate closer to the Doppler shift. Hence, a difference between the two estimates is an indication of a current flowing in the range gate where the spectrum is measured. We assume that no other sources of asymmetry are present, although a large temperature gradient would have a similar effect. In principle the difference can be calibrated to give the magnitude of the current. This step is not yet completed owing to uncertainties in the composition of the ionosphere at low altitudes and a loss of frequency resolution due to the finite pulse length. The detectability of the currents by our method, however, is not affected by poor frequency resolution.

Preliminary results from the Chatanika Auroral‐Zone Incoherent‐Scatter Radar are presented which show large velocities correlated in detail with simultaneous magnetometer data. Also an indication of a current flow has been observed in premidnight data taken on a very active night. An azimuth scan showed the sense of the current to be predominantly westward.
Some Aspects of the Day‐to‐Day Variability of the Equatorial Anomaly: American and Japanese Sectors
Authors: Rush C. M. , Miller D.
Published: February 2008

The day‐to‐day variability observed in the structure of the equatorial anomaly during a period of high solar activity is investigated. Using hourly values of ƒ0F2 observed at a number of ionosonde locations in the American and Japanese longitude sectors during 1958, the structure of the equatorial F2 region has been obtained on an hourly basis for an entire year. It is observed that the equatorial anomaly shows considerable day‐to‐day fluctuations in both its structure and its diurnal development.

The anomaly is generally best developed in the evening hours, and day‐to‐day changes in the time of best development are typically on the order of 2 to 4 hr. It is observed that the time when the anomaly attains its maximum development is not the same on both sides of the magnetic equator, although this time is closer to coincidence during the equinoctial months than during the solstices. Also during the equinoctial months, the anomaly crests tend to be more symmetric about the equator than during the solstices. The relative magnitudes of the crests display a noticeable changeover with time during the northern solstice in both longitude sectors. The crest on the winter side of the magnetic equator is larger during the day, and the summer crest is larger at night. The exact time that this changeover occurs varies on the order of 5 to 7 hr on a day‐to‐day basis. During the southern solstice this crest changeover is observed only in the Japanese sector.
Estimation of the Cumulative Amplitude Probability Distribution Function of Ionospheric Scintillations
Authors: Whitney H. E. , Aarons J. , Allen R. S. , Seemann D. R.
Published: February 2008

The fading characteristics of ionospheric amplitude scintillations can be described by a cumulative amplitude probability distribution function (cdf). The cdf expresses the probability (percentage of time) that the signal amplitude will equal or exceed a given amplitude. Distributions of amplitude variations are made with the use of ionospheric scintillations observed on beacon signals from synchronous satellites transmitting at 136 MHz. The resulting distributions are divided into six groups corresponding to ranges of the scintillation index, the predominant measure in scintillation studies. The model distributions are then combined with the occurrence of scintillations in various index ranges to produce cumulative amplitude probability distributions. These have been done for long‐term observations made at Hamilton, Massachusetts, Narssarssuaq, Greenland, and Huancayo, Peru. The results allow engineers to determine margins necessary for communication and navigation systems. Individual 15‐min distributions have been compared to the theoretical distributions obtained by Nakagami [1960] in his m‐distribution method of characterizing amplitude scintillation and were found to be in good agreement. The m parameter is shown to be a measure of the frequency dependence of scintillations and can be used to determine a spectral index for interpolating the amplitude distributions to other frequencies of interest.
Remote Probing of Inhomogeneous Media Using Parameter Optimization Techniques
Authors: Mostafavi M. , Mittra R.
Published: February 2008

This paper discusses the problem of remote probing and diagnostics of an inhomogeneous medium of which the properties vary only along a single dimension. The medium is described in terms of a set of unknowns that are determined via parameter optimization techniques such that the response of the trial medium agrees closely with that of the actual medium.
Path diversity for mm‐wave earth‐to‐satellite links
Authors: Wulfsberg Karl N.
Published: February 2008

The major obstacle in utilizing recently allocated frequency bands in the mm‐wave spectrum for earth‐satellite communications is rain attenuation. Since heavy rain is generally quite localized it has been proposed that the required reliability could be achieved through path diversity, which requires two or more earth receiving terminals. This paper describes a year‐long diversity experiment in the Boston area involving two sun trackers separated by 7 mi and operating at 35 GHz.
A modified Monte Carlo model for the ionospheric heating rates
Authors: Mayr H. G. , Fontheim E. G. , Robertson S. C.
Published: February 2008

Following Cicerone and Bowhill [1970a, b, 1971] a Monte Carlo method is adopted as a basis for the derivation of the photoelectron‐heat input into the ionospheric plasma. Considering that the size of the source elements must be small compared with the range over which photoelectrons dissipate their energy, a great number of Monte Carlo runs are required normally for the computation of the heating rates. This approach is modified in an attempt to minimize the computation time. The heat‐input distributions are computed for arbitrarily small source elements that are spaced apart at distances corresponding to the photoelectron dissipation range. By means of a nonlinear interpolation procedure their individual heating‐rate distributions are utilized to produce synthetic ones that fill the gaps between the Monte Carlo generated distributions. By varying these gaps and the corresponding number of Monte Carlo runs the accuracy of the results is tested to verify the validity of this procedure. It is concluded that this model can reduce the computation time by as much as an order of magnitude, thus improving the feasibility of including Monte Carlo calculations in self‐consistent ionosphere models.
Error analysis for the Mariner‐6 and ‐7 occultation experiments
Authors: Stewart Richard W. , Hogan Joseph S.
Published: February 2008

The Mariner‐6 and ‐7 occultation experiments provide sets of Doppler residuals from which physical properties of the Martian atmosphere, such as the ionospheric electron‐density distribution and the lower‐atmosphere temperature profile, may be derived. The Doppler residuals contain both systematic and random errors. The former are removed during the data reduction, and the latter are analyzed to yield error limits on the derived physical properties of the atmosphere.
Computer simulation of HF frequency‐selective fading and performance of the mode‐averaging diversity combiner
Authors: Kawachika N. M. , Villard O. G.
Published: February 2008

A ray‐tracing technique for simulating the performance of the mode‐averaging diversity combiner (MADC) [Villard et al., 1972] is described, which extends the methods developed by Croft [1969] to the analysis of frequency‐selective fading. It is shown that the computer procedure satisfactorily predicts observations made during a test representative of conditions encountered in practice. Using the parameters of this test, the method is applied to the original MADC configuration to investigate the dependence of performance on antenna spacing and ionospheric profile. Two MADC schemes which incorporate alternative methods of forming the running average are described. Their performance is also evaluated for the above parameters and shown to be roughly equal to that of the original. It is concluded that for the given parameters at least, a choice between the three alternative configurations can be made on the basis of convenience.
Synthesis of three‐dimensional ionograms
Authors: Rao N. Narayana
Published: February 2008

A previously reported method of exact calculation of ray‐path parameters for a spherically symmetric ionosphere with its center of curvature displaced from the center of the earth is extended to permit the synthesis of three‐dimensional ionograms, i.e., group path, azimuthal angle of arrival, and elevation angle of arrival versus frequency, for a specified set of transmitter and receiver locations. An example of a synthesized three‐dimensional ionogram is presented.
Mutual electromagnetic coupling of coaxial loops in a borehole
Authors: Fuller James A. , Wait James R.
Published: February 2008

The exact integral solution is obtained for the fields of a small circular loop that is coaxially located in a cylindrical borehole in homogeneous rock. The result is employed to calculate the mutual impedance between two coaxial loops within the borehole. It is found that, under most conditions, mutual impedance does not depend on the presence of the borehole, and thus the configuration is well suited for electromagnetic probing of the host rock.
Commission 3. On the ionosphere
Authors: Schmerling E. R.
Published: February 2008

This session was chiefly concerned with the chemical and dynamical factors that are now known to control the distribution of electrons in the D region. The current status of knowledge of the electron‐density profile in the D region was reviewed by G. C. Reid (USA), with emphasis on the diurnal and seasonal variations and on the rapid changes that occur during sunrise. With regard to the overall electron ‘budget’ of the region, it was pointed out that important discrepancies between theory and observation still remain and that we are not yet certain whether these result from imperfect knowledge of production rates or of loss mechanisms, or from a combination of both.

L. Thomas (UK) reviewed the current status of knowledge of the ion chemistry of the D region. A central feature of this is the formation of heavy, water‐cluster, positive ions, and although a satisfactory mechanism for producing these ions from O2+ has been known for some time, we still do not know the mechanism involved in the case of NO+, the dominant primary ion species. With regard to negative ions, the need for definitive measurements of composition was emphasized, because the existing measurements show major disagreements. Laboratory measurements of photodetachment cross sections are also urgently needed, particularly for such species as NO3−, CO4−, and their hydrates, since model calculations indicate that these should be the dominant species in the D region.
Increase of error in range correction with elapsed time, evaluated by ray tracing through radiosonde‐generated atmospheric models
Authors: Levine Daniel , Cromack John C. , Bjorn Theodore
Published: February 2008

Previous studies of range and angular errors caused by variation of atmospheric refractivity with altitude generally have used functional expressions, averaged data, or data from a small number of radiosonde ascents. In this investigation a large data base was employed consisting of radiosonde measurements made at intervals of about 2 hr for a period of 1 week. In the analysis it was assumed that the refractivity varied only as a function of altitude and that there was no ducting. Curves showing the deterioration of range correction with time for selected terminal points were developed by tracing rays at a succession of elevation angles. Thus, for a ground range of 416.7 km and an aircraft at 15.24 km, the standard deviation of the ground‐to‐plane radio distance 4 hr after a radiosonde ascent is .9 m, increasing to 1.3 m after 8 hr, and 1.6 m after 12 hr.
An iterative mathematical technique for deriving electron‐density profiles from multifrequency riometer data
Authors: Lavergnat J. , Berthelier J. J.
Published: February 2008

The determination of the D‐region electron‐density profile may be obtained by the solution of an integral equation when the absorption at several frequencies is known. A new method based upon an iterative process is derived and is found to be more reliable than the previous methods.
Small antennas in a dispersive environment
Authors: Franceschetti Giorgio
Published: February 2008

The input admittance or impedance and the effective height of small metal antennas, with a finite gap, located in a dispersive environment, is obtained in an analytical form by properly renormalizing a modal series. The equivalent network of the antenna turns out to be composed of physically realizable elements, thus allowing the computation of the transient response by using Laplace transform techniques. The extension to the case of an inhomogeneous or a uniaxial anisotropic environment is also suggested.
On the optimum radiometer
Authors: Ohlson John E.
Published: February 2008

The optimum signal processing to follow a given radiometer front‐end is derived when it is desired to estimate, with smallest rms error, the temperature of a radio source. We find, for the important special case of small sources, that the optimum radiometer is implemented by the use of a compensating filter followed by square‐law detection and integration. We consider two examples of receiver front‐end gain characteristics, the Lorentzian and Gaussian shapes. Improvement over conventional radiometer performance is shown to be possible.
Interpretation of energetic heavy ion fluxes observed during the magnetic storm of 17 December 1971
Authors: Cladis John B.
Published: February 2008

An interpretation is given for the high fluxes of 0+ ions with energies to 12 kev observed during the magnetic storm of 17 December 1971. It is suggested that the ions were accelerated initially by the absorption, near the altitude of the 0+ resonance (ω = Ω0+), of ion cyclotron waves amplified at a slightly lower altitude by ring current protons moving downward along magnetic field lines. The energized ions then moved toward higher altitudes along the field lines where they diffused in pitch angle and energy due to resonant interactions with ion cyclotron turbulence. The gradient of the geomagnetic field plays an important role in the amplification of the ion cyclotron waves at low altitudes. It is shown that ring current protons may lose considerable energy while resonating with ion cyclotron waves propagating upward. Conversely, ions may gain substantial energy while resonating with waves propagating downward. The observations of the 0+ ions are correlated with simultaneous measurements of the ring current protons, and it is argued that the observed energy loss of the protons near the plasmapause may be due to off‐equatorial resonant interactions between the protons and ion cyclotron waves.
Spin modulation of high‐latitude hiss measured by an electric dipole
Authors: James H. G.
Published: February 2008

Natural radio noise received by the ISIS satellites in the polar and auroral regions often exhibits spin modulation. For noise in the whistler‐mode frequency domain observed on seven high‐latitude passes, the data indicate that temporal‐spatial variations in the level of the noise source are not important on a time scale of one spin period, and thus the dependence of the signal on the attitude of the receiving dipole antenna can be studied. Relative variations in level during one half of a spin period have been synthesized by simply convolving the attitude dependence of the antenna impedance with a spatial distribution of electric vectors. The resonance cone angle, corresponding to the infinity in the refractive index, has been predicted to an accuracy of 3°, while the theoretical amplitude and shape of the modulation agree well with what is observed. It is found that longitudinal electric waves yield better agreement than transverse electromagnetic waves. In some cases, preferred horizontal propagation directions can be roughly identified. The computations confirm the relevance of established theory for the antenna impedance and the ion sheath.
Electromagnetic radiation from a slot antenna surrounded by a moving magnetoplasma sheath
Authors: Kojima T. , Higashi T.
Published: February 2008

Radiation from a slot antenna surrounded by a plasma sheath moving parallel to an external magnetostatic field is considered. It is shown that the radiation pattern is inclined in the direction of the sheath motion as the velocity is increased except for the case where the condition of upper hybrid resonance is satisfied in the rest frame of the plasma. When such a relativistic upper hybrid resonance caused by the sheath motion arises for certain values of normalized plasma and cyclotron frequencies and the velocity parameter, a deep null and a rapid oscillation appear in the radiation pattern, and as a result the shape of the pattern is extremely deformed.
Transient response of stratified media: Multiple‐scattering integral and differential equation for an impulsive incident plane wave
Authors: Gray K. G. , Bowhill S. A.
Published: February 2008

This paper deals with the response of a stratified cold plasma to an infinite plane impulsive electromagnetic wave incident vertically on the ionization. The impulse response is found by utilizing a multiple‐scattering technique, by summing a large number of scalar functions described as first scatter, second scatter, etc. A multiple‐scattering integral is derived for finding the nth scattered field in terms of the (n‐1)th scattered field. Also, a partial differential equation for the impulse response is derived using the multiple‐scattering technique. Its solution is found for an impulsive wave incident on a half‐space of uniform electron density, and on an infinite region whose electron density increases exponentially with height.
Transient response of stratified media: Response to an arbitrary incident plane wave
Authors: Gray K. G. , Bowhill S. A.
Published: February 2008

This paper deals with the response of a stratified cold plasma to an infinite plane electromagnetic wave incident vertically on the ionization. The transient response is found by utilizing a multiple‐scattering technique, by summing a large number of scalar functions described as first scatter, second scatter, etc. A generalized formula is used for finding the nth scattered field in terms of the (n‐1)th scattered field. Specifically two cases are considered: the generalized response of a half‐space of uniform electron density to any incident wave expressible in a Maclaurin series, and the response of an infinite region whose electron density increases exponentially with height to an incident step‐modulated sine wave.
The UK incoherent scatter radar
Authors: Williams P. J. S. , Taylor G. N.
Published: February 2008

The UK incoherent scatter system operates in two modes. The monostatic pulsed system has been in operation since 1968, and a summary of the results obtained in this mode is given. The full multistatic CW system has been operating since September 1972 and among the preliminary results are measurements of the total vector of velocity drift.
Magnetic activity variations of the nighttime E region at Arecibo
Authors: Rowe John F.
Published: February 2008

Using 13‐bit Barker‐coded pulses, high resolution (0.9 km) incoherent scatter measurements of nighttime E‐ and F‐region electron densities have been conducted at Arecibo. Electron density profile sequences are presented for four nights characterized by a wide range of magnetic activity. The data show a deep valley in electron density above 120 km during quiet periods which fills in with plasma to levels of 104 cm−3 during a magnetic storm (Kp ≃ 8). An intermediate layer frequently appears near 125 km, independently of magnetic activity. In view of the observations, the connection between nighttime valley content and magnetic activity is discussed.
Combined airglow and incoherent scatter observations as a technique for studying neutral atmospheric variations
Authors: Cogger L. L. , Wickwar V. B. , Carlson H. C.
Published: February 2008

Night airglow 6300 Å intensities and electron density altitude profiles observed at Arecibo have been combined with dissociative recombination theory to obtain information about the nighttime variation of F‐region N2 and O2 densities. The application of this technique is illustrated using data from two nights in March 1971. The gross nighttime variation shows reasonable similarity to the Jacchia [1970] model, and also follows the time variation of the measured exospheric temperature. However, on both nights there is evidence of a postmidnight enhancement of the O2/N2 density ratio associated with a rapid decrease in the height of the F layer.
Global temperature distributions from OGO‐6 6300 Å airglow measurements
Authors: Blamont J. E. , Luton J. M. , Nisbet J. S.
Published: February 2008

The OGO‐6 6300 Å airglow temperature measurements have been used to develop models of the global temperature distributions under solstice and equinox conditions for the altitude region from 240 to 300 km and for times ranging from dawn in this altitude region to shortly after sunset. The distributions are compared with models derived from satellite orbital decay and incoherent scatter sounding. The seasonal variation of the temperature as a function of latitude is shown to be very different from that derived from static diffusion models with constant boundary conditions.
Tidal waves within the thermosphere
Authors: Volland H. , Mayr H. G.
Published: February 2008

The eigenfunctions of the atmosphere (the Hough functions within the lower atmosphere below about 100 km) change their structure and their propagation characteristics within the thermosphere due to dissipation effects such as heat conduction, viscosity, and ion drag. Wave dissipation can be parameterized to a first‐order approximation by a complex frequency, the imaginary term of which simulates an effective ion drag force. It is shown how the equivalent depth, the attenuation, and the vertical wavelength of the predominant symmetric diurnal tidal modes change with height as functions of effective ion drag. The boundary conditions of tidal waves are discussed, and asymptotic solutions for the wave parameters like pressure, density, temperature, and wind generated by a heat input proportional to the mean pressure are given. Finally, diffusion effects upon the minor constituents within the thermosphere are described.
A comparison between meteoric radar and incoherent scatter measurements in the lower thermosphere
Authors: Bernard R.
Published: February 2008

The main characteristics of the atmospheric tides observed at St. Santin and Garchy are examined and compared. It is found that the semidiurnal tide is very variable in the meteoric range (80 to 100 km) and more regular above. Some direct comparisons, corresponding to simultaneous measurements, show the same features and exhibit a good agreement in the region where the two types of measurements overlap.
Impedance of a short antenna in a warm magnetoplasma
Authors: Meyer P. , Vernet N.
Published: February 2008

The impedance of a short dipole antenna has been computed using the quasistatic approximation, a triangular current distribution, and the full adiabatic hydrodynamic description of the plasma. Some typical results are presented which show that for parameters typical of the ionosphere the temperature affects mainly the radiation resistance.
An antenna system using a plasma column having a central conductor and excited by a waveguide
Authors: Ram Dhani , Verma J. S.
Published: February 2008

The radiation pattern of an open‐ended circular cylindrical waveguide (excited in the circular symmetric TE01 or TM01 modes) in a plasma column having a central conductor is studied. The field distribution at the open‐end cross section of the waveguide is assumed to be equivalent to the vector sum of current rings of various radii ranging from the outer radius of the central conductor to the inner radius of the circular waveguide at the open end. The radiation pattern is obtained as a vector sum of field components due to individual rings of current. This type of configuration gives rise to an enhanced radiation peak near and before the critical angle. The amplitude and sharpness of the radiation peak depends upon the dimensions of the plasma column, central conductor and the waveguide. The direction of the radiation peak can be changed by changing the plasma density. These results suggest development of an electronically scannable plasma antenna system.
Transient radiation from a resistive, tubular antenna
Authors: Marin Lennart
Published: February 2008

The time dependence is calculated of the radiated field from a resistively loaded, tubular antenna excited by a step‐function voltage across a circumferential delta gap. The resistive loading along the antenna is taken to be uniform and independent of frequency. Analytical expressions for the early‐time and late‐time behavior of the far field are derived. For intermediate time intervals the field is evaluated numerically. It is found that the late‐time behavior of the radiation field is inversely proportional to time squared, whereas in the case of zero resistance it varies in inverse proportion to the logarithm of time.
Microwave radiometer measurements of the Cape Cod Canal
Authors: Swift C. T.
Published: February 2008

Microwave radiometer measurements were conducted from a railroad bridge which spans the Cape Cod Canal in Massachusetts. Data were collected as a function of viewing angle and polarization at frequencies of 1.4, 4.0, and 7.5 GHz. The results compare differences in the microwave emmissivity of a smooth vs. rough water surface. Results are also given which show the effects of roughness on the bistatic scattering of sunlight.