bluuebunny/crossref_metadata_2025 huggingface dataset:
Mathematical models for the reflection coefficients of dielectric half‐spaces
Authors: Evans Daniel D.
Published: February 2008

The reflection coefficients at normal incidence are found for a large class of one‐dimensionally inhomogeneous or stratified half‐spaces, which contain a homogeneous half‐space. The formulation of the problem involves a combination of the classical boundary value technique, and the nonclassical principle of invariant imbedding. Solutions are in closed form and expressible in terms of Bessel functions. All results are given in terms of the ratio of the distance between free space and the homogeneous half‐space to the wavelength in vacuo. One special case is that of an arbitrary number of layers lying on a homogeneous half‐space where the dielectric constant of each layer has a constant gradient. A number of other special cases, limiting cases, and generalizations are developed including one in which the thickness of the top layer obeys a probability distribution, and another formulation that is computationally efficient in which there is an extremely small change in the dielectric constant such as with atmospheric inversion layers.
Reflection at oblique incidence of an impulsive transverse magnetic plane wave from a cold, lossy, semi‐infinite plasma
Authors: Price Gary H.
Published: February 2008

Branch‐cut integrals are used to calculate the reflection of transient pulses from the surface of a cold, lossy, semi‐infinite plasma. For the case considered in detail, small to moderate losses and an impulse‐incident waveform with transverse magnetic polarization, the reflected waveform is oscillatory for small losses (collision rate much less than the plasma frequency) but decays monotonically for a collision rate of half the plasma frequency. The reversal of polarity of the initial half cycle of the reflected waveform observed as the incidence angle increases through 45° is interpreted as a Brewster‐angle phenomenon.
Review of auroral morphology, auroral dynamics, and modern observational techniques
Authors: Romick G. J.
Published: February 2008

Our present understanding of auroral morphology has been developed in a large part from a vast accumulation of all‐sky camera photographs taken at many stations around the world. In order to further our understanding of the concepts of the auroral oval and the auroral substorm and their relation to influences on our atmosphere, we now need to express these concepts in terms of the latitudinal distribution of the type and energy of the associated incident particles. In this review, data are presented on precipitating particles in the evening and midnight sectors in relationship to the electron trapping boundary motion within the substorm. The complex height distribution of ionization associated with particle precipitation shows some of the possible complexities in the interpretation of incoherent scatter radar data obtained in the auroral regions. Data obtained by modern satellite imagery can provide the auxiliary data needed to understand the particle effects in the polar regions. The rapid temporal and spatial changes in the aurora are seen in data from rapid scanning photometer systems and high sensitivity color television systems. The general review of these data attempts to show that local auroral dynamics and the phase and global extent of the auroral substorm imply drastic changes in the incident particle energies. These in turn produce variable atmospheric effects of direct concern to all incoherent scatter radar studies of the neutral and ion composition, temperature, and motion of the earth's atmosphere.
Electron densities within aurorae and other auroral E‐region characteristics
Authors: Baron M. J.
Published: February 2008

The L‐band incoherent scatter radar located at Chatanika, Alaska (L ≃ 5.6) has been used to measure the characteristics of the auroral E layer. In this paper, the term auroral E layer refers to nighttime ionization between altitudes of 90 to 150 km produced by particle precipitation. Electron density profiles have been measured using time resolutions as short as 0.2 sec and range resolutions of 5 to 10 km. For the shortest integration time, the statistical accuracy of the measurement is on the order of 10%. Results obtained to date show auroral ionization to align with the earth's magnetic field and to have lengths along the field of typically 20 to 30 km and thicknesses across the field of less than 5 km (both distances measured between the half‐peak‐density points). Within the auroral ionization, the maximum electron density at times approaches 2 × 106 el cm−3. The measured quantities have been analyzed to deduce (a) energy of the particle precipitation, (b) flux of particle precipitation, (c) production rates, and (d) effective recombination coefficients. For a few cases, estimates of the pitch‐angle distribution of the primary electrons have been made.
Quiet and disturbed electron density profiles in the auroral zone ionosphere
Authors: Bates Howard F. , Hunsucker Robert D.
Published: February 2008

Electron density profiles of the auroral zone ionosphere for quiet, aurorally disturbed, and magnetic storm conditions have been obtained by the Chatanika incoherent scatter radar (magnetic latitude 65.7°, L = 5.7). The magnetically disturbed F region is found to be reduced somewhat in maximum density and greatly modified in shape during daylight. Field‐aligned ion transport caused by neutral winds is suggested as the cause of this behavior. The maximum density in the disturbed, dark ionosphere usually occurs in the auroral E layer, a thick layer with typical densities of 2 to 5 × 1011e m−3 extending for several degrees of latitude. The auroral F layer has typical maximum densities of 0.5 to 2.0 × 1011e m−3 at 300 to 400 km altitude; upward transport and secondary ionization by soft auroral primaries are suggested as the cause of the auroral F layer. During quiet periods between May and September, the high latitude F1 layer exists as a well‐defined thick layer, sometimes with a distinct valley between it and the F2 layer. In addition to high D‐region absorption accompanying disturbances, the observed high variability of the E and F regions can explain much of the behavior of transauroral HF propagation that has been noted by past studies. This paper reviews recent incoherent scatter results with regard to their implications to high latitude HF propagation. In particular, the importance of Joule heating effects on the F‐region atmosphere are discussed in terms of their effect on the F layer. A few clear cases of spread‐F in the College ionograms have been found for times when the radar was observing near the ionosonde zenith. In all of the cases found, the maximum density of the layer corresponded to the inner edge of the spread trace; current scaling practice therefore appears to be correct.
Internal field pulse diffraction by an ice sphere
Authors: Stephens J. J. , Ray Peter S.
Published: February 2008

A normalized Poynting vector impulse response approximation evaluated computationally at selected points within and near an ice sphere is used to show that the actual physical processes in diffraction of plane waves are consistent with high frequency analogs proposed previously. Failure of the low frequency pulse components to satisfy Snell's law of refraction leads to differences in a detailed description of scattering by an ice sphere.
Oblique resonances excited in the near field of a satellite‐borne electric dipole antenna
Authors: Koons H. C. , Pridmore‐Brown D. C. , McPherson D. A.
Published: February 2008

Near‐field patterns of a short electric dipole antenna were measured in the magnetospheric plasma by an instrument aboard the polar orbiting satellite OV1‐20S. The most common antenna pattern observed at the fixed operating frequency, 300 kHz, was a dominantly biconic pattern with major axis parallel to the geomagnetic field. The measured cone angles are in reasonable agreement with those predicted by warm plasma theory.

There was no discernible systematic asymmetry in these angles such as could be attributed to field‐aligned currents in the plasma or to the motion of the satellite through it.
The impulse response of a cold stratified plasma in the presence of collisions and a vertical magnetic field by a multiple‐scattering technique
Authors: Gray K. G. , Bowhill S. A.
Published: February 2008

The multiple‐scattering technique is extended to include the effects of simple collisions and a vertical magnetic field on the impulse response of a stratified cold plasma. In this case as in the free‐electron case it is possible to formulate a multiple‐scattering integral for the nth scattered field in terms of the (n – 1)th scattered field. The total response is the sum over all orders of scatter. By an appropriate convolution process it is possible to find the nth scattered field in the presence of collisions and a magnetic field from the corresponding scatter for the free‐electron case. This method is used to find the response of an infinite region of exponentially increasing electron density and a half space of uniform electron density in the presence of collisions and a magnetic field.
Stimulated amplification of ULF waves by magnetospheric injections of plasma clouds and particle beams
Authors: Liemohn Harold B.
Published: February 2008

Our understanding of wave particle interactions in the magnetosphere has progressed to the point where it may be possible to stimulate wave amplification at ULF (about 0.1 to 10 Hz) by disturbing the cyclotron resonance conditions through catalytic injections of plasma clouds or particle beams. Modification of the interaction can be achieved by the introduction of localized clouds of plasma that reduce the phase velocity of the waves and cause enhanced amplification by lowering the resonance velocity. Alternatively, direct injection of hot energetic particle beams can also appreciably alter the local amplification characteristics. Different methods for injecting clouds of lithium plasma and proton beams have been modeled quantitatively to assess their relative merits. Amplifications of many tens of decibels appear to be feasible with lithium clouds of only 1 to 2 kg of material. With present technology the beam diameter from a conventional particle gun on board a satellite or rocket is too small for an effective interaction, but appreciable amplification is indicated. Such a prospect has great significance. First, it offers a direct test of the fundamental physical processes that are believed to control the state of the magnetosphere. Second, controlled injections might be used to stimulate artificial amplification of ULF emissions on command and allow them to be used as a wide‐area communication system.
Estimating reverse path loss from oblique ionospheric sounder signals
Authors: Clapp G. A. , Fay W. J. , Hansen P. M. , Hoff L. E. , Johnson G. B.
Published: February 2008

Tests are performed over a 4300‐km path to determine the accuracy of reverse path loss estimates using the step‐frequency sounder of the Navy Tactical Sounder System. The objective is to develop computational techniques for real‐time estimates of communication channel performance. Experimental results are presented which indicate the statistical performance of several path loss estimation techniques. It is concluded that, for Navy applications, reverse path loss can be predicted to within 6 db for 90% of the time.
A Monte Carlo technique for finding the impulse response of stratified cold plasma
Authors: Gray K. G. , Bowhill S. A.
Published: February 2008

A Monte Carlo technique is described for finding the response of a horizontally stratified cold plasma to a plane impulsive wave at vertical incidence. The effects of electron collisions with neutral particles and a vertical magnetic field are included in the analysis. The technique is arrived at by replacing a continuous scattering process (by continuous we mean the electrons are uniformly distributed through any horizontal plane in the plasma ( with a sequence of scatters. All orders of scatter are computed from this sequence of scatters, and the Monte Carlo approximation to the exact solution is the sum over these orders of scatter. The method is applicable for any electron density function N(z), collision frequency, or cyclotron frequency. The Monte Carlo solution presented here is valid only for small and intermediate values of time; the solution diverges for large values of time. The Monte Carlo method is applied to the uniform half‐space problem since there are exact and approximate analytical solutions to compare with the Monte Carlo results.
A transformation property of the mapping between points on a ray path
Authors: Gelman Harry
Published: February 2008

In some applications of ray tracing, it is useful to know the behavior of certain ray‐related quantities under a transformation of the variable of path parameterization. One such quantity is the Jacobian of the mapping between small regions surrounding two points on a ray path. A narrow bundle of rays emanating from a point source in an inhomogeneous, anisotropic propagation environment is considered. The mapping between a small region surrounding a reference point on an interior ray of the bundle, and the corresponding region surrounding an observation point on the same ray, is investigated. The Jacobian of the mapping is studied as a function of an arbitrary path parameter, and a new relation expressing the behavior of the Jacobian under a transformation of the parameter is derived.
A summary of vertical incidence radio observations of ionospheric modification
Authors: Utlaut W. F. , Violette E. J.
Published: February 2008

Within the past four years, experiments with high power, high frequency radio waves have proved the feasibility of temporarily altering the ionosphere's properties. Many different radio and photometric effects have been observed as a result of the ionospheric modification. This paper provides a survey of some of the effects observed with vertical incidence radio techniques when the US Department of Commerce's Platteville facility, near Boulder, Colorado, is used to illuminate the overhead ionosphere with an equivalent isotropically radiated power of the order of 100 Mw. A variety of different and repeatable phenomena are observed to occur in the F region. A few always occur; for others, apparently, certain ionospheric conditions must exist. E‐region effects observed by these techniques are small, but substantial effects are noted in the D region.
HF phased array observations of heater‐induced spread‐F
Authors: Allen E. M. , Thome G. D. , Rao P. B.
Published: February 2008

A large circular HF phased array radar has been used to study the angular spectrum of spread‐F returns from an ionosphere modified by the intense radio waves from the high power Platteville transmitter. The results obtained are presented to show the dependence of angular spectrum on range delay, Doppler shift, operating frequency, and on the power of the heater transmitter. The phenomenon of wideband attenuation observed with the o‐mode diagnostic wave is examined for its dependence on the angle of arrival of the received signal. The angular spectrum of the spread‐F returns exhibits a systematic behavior. It is found that the angle of arrival migrates from north to south and the Doppler changes from positive to negative as the range delay examined is changed from the leading edge of the return to the trailing edge. The height dependence of the angular spectrum shows that the volume containing the spread‐F irregularities is aligned along the earth's magnetic field. The dependence on the heater power is such that the angular extent of the returns is reduced by a factor of 3 when the heater power is reduced to −9 db of its maximum value of 1.8 Mw. The attenuation suffered by the diagnostic o‐mode upon heater turn‐on changes with the angle of arrival to reach a maximum with the signal returns arriving from the south. It is shown by means of ray‐tracing simulation that the observed interdependence of angle of arrival, Doppler shift, and range delay is consistent with a model of field‐aligned ducts for the heater‐induced spread‐F irregularities. The model, when applied to the conditions at Arecibo and the results compared to that for Platteville, reveals that the range delay spread is about the same and the angular spread is approximately in the same ratio as the heater beamwidths at the two places.
Geometric considerations in the design of communications circuits using field‐aligned ionospheric scatter
Authors: Stathacopoulos A. D. , Barry G. H.
Published: February 2008

The aspect sensitivity of man‐made, field‐aligned ionospheric irregularities implies that the geometry of VHF communications circuits using these scatterers must be carefully designed. The design problem is sufficiently complex that it is best approached with the aid of a computerized model. Examples are presented showing the results of path modeling for man‐made clouds located in Colorado and in Italy. The effects of variations in cloud height and communications circuit frequency are evident from these examples. It is concluded that geometric restrictions are sufficiently strong as to limit the application of the technique to certain specialized point‐to‐point or point‐to‐zone uses.
Microwave scattering and the straining of wind‐generated waves
Authors: Keller W. C. , Wright J. W.
Published: February 2008

The modulation in backscattered power from wind‐generated waves due to the presence of a 0.575‐Hz plunger‐generated wave has been measured in a wave tank as a function of air friction velocity and plunger wave amplitude. The measurements were made at 9.375 GHz, a depression angle of 45° and vertical polarization. The straining of the wind waves is treated by a first‐order perturbation of the Boltzmann transport equation and the scattering is calculated from a simple application of composite surface scattering theory utilizing first‐order Bragg scattering. The theory predicts a characteristic relaxation behavior for the wind‐speed dependence of the components of the modulation amplitude in phase and out of phase with the horizontal component of orbital velocity of the plunger wave. This relaxation behavior is closely followed by the observed modulation amplitudes for air friction velocities less than about 40 cm sec−1, i.e., winds less than about 7 m sec−1.
Backscattering of wideband signals from turbulent slabs
Authors: Valley George C.
Published: February 2008

The traditional first Born approximation cross section for scattering of electromagnetic radiation by turbulent irregularities is generalized to include the effect of an arbitrarily modulated signal incident on the irregularities and the effect of cutting off the volume of the irregularities in the direction of propagation with an arbitrary function. This generalized cross section is proportional to a double convolution integral over the frequency spectrum of the incident signal, the spectrum of the turbulent irregularities, and the square of the Fourier transform of the function which cuts off the irregularities. Analytic and numerical results are given for the ratio of this generalized cross section to the traditional cross section for gaussian and rectangular slabs and for gaussian and rectangular pulses combined with several different turbulence spectra. The results show how the generalized cross section mixes Fresnel reflections with turbulent reflections and wideband scattering with scattering at twice the carrier frequency.
The travelling bifurcation of the equatorial F2 layer
Authors: Huang Chun‐ming
Published: February 2008

That the F2 layer is bifurcated into two sublayers and that this structure travels poleward has been revealed by previous computations published by the author. Examination of vertical sounding data shows that such a travelling bifurcation occurs mainly near noon in the seasons other than June solstitial months during years of high solar activity. It is found that the formation of bifurcation is principally due to the combined effect of the upward drift, which changes from increasing to decreasing at 1000 LT, and the slow diffusion. The effects of other parameters on the bifurcation and ionospheric characteristics and the cause of the bifurcation which occurs at sunrise are also studied. The continuity equation of electron density is then solved with appropriate values of ionospheric parameters suggested from the above study. The computed f0F2 at the equator during daytime is a very good reproduction of the observed one, and does not show any bifurcation as usually observed. The causes of agreement or disagreement between the computed and the observed values of critical frequency and height of layer peak are discussed.
The effects of the August 1972 magnetic storms on ionospheric scintillations
Authors: Aarons Jules , Martin Eileen
Published: February 2008

A “worst case” of scintillation activity is presented by the analysis of data of a period of severe magnetic activity, August 3–10, 1972. The effect of the dense ionospheric irregularities produced by these storms on scintillation at high latitudes is viewed as a function of local time and the invariant latitude of the propagation path, as well as magnetic activity. Storm period data taken at high, middle, and equatorial latitudes are analyzed and compared with the seasonal means. In the high‐latitude irregularity region, dramatic increases of scintillation index at 254 MHz were noted. Cumulative amplitude probability distribution functions are given for the high‐latitude data with the aim of giving to systems designers signal statistical data for “worst case” conditions. Middle‐latitude stations show little reaction to the magnetic activity. At equatorial latitudes during July and August, the longitude of the observatory determines the reaction. Accra (Ghana) data show a slight decrease in scintillations during the August storms. At Huancayo (Peru) scintillations increase in the postmidnight period.
Developments in the theory of radio propagation, 1900–1950
Authors: Booker Henry G.
Published: February 2008

Developments in the theory of radio propagation in the first half of the twentieth century are briefly traced from early work on diffraction around the curved surface of the Earth to the discovery of the magnetosphere with the aid of whistlers. Attention is drawn to the possibility that Marconi may have been initially inspired by the concept of the Atlantic Ocean as a giant cost‐free telephone wire linking the European and American continents.
Theoretical study of gyroresonances with application to rocket experiments
Authors: Bitoun J. , Fleury L. , Higel B.
Published: February 2008

The waveforms and envelopes of resonance signals observed in the ionosphere at 2, 3, 4, and 5fH by rocket experiment are compared with the analytical results provided by a spatial ray‐tracing procedure which takes the gradient of Earth's magnetic field into account. An approximate calculation yields the algebraic expression of the wave damping from whence the decrease of the received signals is deduced versus time as well as their frequency variations.
Summary of the Wisconsin Test Facility effective earth conductivity measurements
Authors: Bannister Peter R.
Published: February 2008

The effective conductivity of the geoelectrically complex Wisconsin Test Facility area has been measured by a number of different methods during the past few years. These methods include the H/I induction method, the wave impedance measurement technique (employing lightning discharges as the source), and two direct current methods (the four‐terminal‐array in‐line dipole and Schlumberger techniques). The principal results obtained from these measurements were: (1) The pattern of the EW antenna is skewed clockwise, while the pattern of the NS antenna is skewed counterclockwise. (2) The effective conductivity under the EW antenna is greater than that under the NS antenna. (3) The minimum distance for determining the effective earth conductivity by the H/I method is seven effective earth skin depths. (4) The method of measuring each half‐antenna in order to predict the effective conductivity of the whole antenna is correct within a factor of 1.22.
A consideration of the effects of ground reflections on Faraday rotation and related measurements on satellite radio transmissions
Authors: Jones J. , Webster A. R.
Published: February 2008

The effect of ground reflections on Faraday rotation and angle‐of‐arrival measurements using satellite radio transmissions is considered. It is shown that, in experiments where such techniques are used to monitor small ionospheric perturbations, errors in the measured polarization angle can be significant and may lead to spurious results. Methods of reducing these errors are suggested.
A mode‐expansion theory for the EM fields from a circular loop antenna
Authors: Chang Hsi‐Tien
Published: February 2008

The electric and magnetic fields from a circular loop antenna are decomposed into various field modes which depend only on the coordinate system being used. These modes can be calculated in advance even if the source and loading function of the antenna are unknown. The excitation factor for each mode, which is related to the current distribution on the antenna, is the only variable that must be determined from time to time as the loading impedance and the source function of the antenna are changed. It is found that the mode‐expansion technique is quite convenient for field computation at many locations where only a few modes will be sufficient to represent the field distribution.
Theory of laser beam intensity profile distortions in turbulent media
Authors: Taylor Leonard S.
Published: February 2008

Analytical expressions are obtained for the mean‐square nth moments of beam intensity profile, for the mean‐square perturbation of the spatial spectrum, and for the variance of intensity integrated over an aperture for finite beams propagating in turbulent media. The theory is based on the assumption of the existence of a phase autocorrelation which is a function of the transverse difference coordinates and is illustrated using the approximation of linear optics and the Rytov approximation. The theory can be applied to determine the capabilities of optical beam systems in the presence of turbulence.
Microscopic Lagrangian description of warm plasmas: 1. Linear wave propagation
Authors: Kim H. , Crawford F. W.
Published: February 2008

This three‐part paper describes linear and nonlinear plasma wave phenomena in an infinite, homogeneous, collisionless, warm magnetoplasma by means of a microscopic Lagrangian. Part 1 derives the dispersion relation for all modes of linear wave propagation. To do so, the charged particle position vectors and the fields are first expanded in terms of sinusoidal perturbations from equilibrium. The contribution to the microscopic Lagrangian, expanded to second order in the perturbations, is then averaged over space and time to remove rapidly varying terms. The Euler‐Lagrange equations, obtained from variations of the Lagrangian with respect to the amplitudes of the perturbation parameters, are the first‐order Maxwell equations and the perturbed particle trajectory. Variation with respect to the phase gives the equation of conservation of action. The Lagrangian is specialized to waves propagating nearly parallel, and exactly perpendicular, to the static magnetic field, and familiar wave dispersion relations are obtained. In Part 2, the nonlinear coupling of these waves is studied. In Part 3, both wave‐wave and wave‐particle interactions are taken into account.
Microscopic Lagrangian description of warm plasmas: 2. Nonlinear wave interactions
Authors: Kim H. , Crawford F. W.
Published: February 2008

The averaged‐Lagrangian method is applied to wave‐wave interactions in an infinite, homogeneous, collisionless, warm magnetoplasma. The amplitudes of the waves are assumed to vary slowly in time and space, due to coupling between them. Euler‐Lagrange equations are obtained from the contributions to the averaged microscopic Lagrangian second and third order in perturbation, by variation with respect to the wave amplitudes. These are the coupled‐mode equations. The phase variation yields the action transfer equation. As applications of the method, coupled‐mode equations are derived in explicit forms for all possible interactions among waves propagating nearly parallel, and among those propagating exactly perpendicular, to the static magnetic field. Some of the coupling coefficients are new. Where comparisons with previous iterative analyses are possible, the advantages of the method are discussed.
A method for exposing cell cultures to electromagnetic fields under controlled conditions of temperature and field strength
Authors: Guy Arthur W.
Published: February 2008

A system was developed for exposing a sample of cells in a culture medium for short periods to broadband electromagnetic energy under controlled conditions of field and temperature. The system can produce a reasonably uniform electric field of strengths to 100 V/cm in a 5‐ml sample; the system has a continuously controllable input power to 600 W and a frequency range from dc to 100 MHz and beyond. Control of the sample's temperature over a wide range is achieved through a high‐rate, circulating‐liquid heat exchanger. The cooling capacity is sufficient to maintain one of a wide range of steady‐state temperatures during exposure of the sample to a CW field of strength in excess of 20 V/cm. Accurate monitoring of the sample's temperature at frequencies below 100 MHz is achieved during exposures through on‐line measurement of feedline impedance. Nonperturbing thermal measurement of sample can be made at all frequencies by a Teflon‐insulated sensor of special design.
New artifact‐free electrodes for recording of biological potentials in strong electromagnetic fields
Authors: Tyazhelov V. V. , Tigranian R. E. , Khizhniak E. P.
Published: February 2008

Conventional metal electrodes as used to record electrophysiological events are likely to introduce artifactual stimulation and spurious signals when the preparation to which they are attached or in which they are implanted is exposed to electromagnetic (EM) fields of high frequency. To combat these artifacts, electrodes of high linear resistance (> 100 kΩ/m) were devised for use in chronic and in acute experiments. The electrodes minimize diffractive problems and control for artifactual stimulation by eliminating spurious currents at the junction between the electrode tip and the biological preparation. Contamination of amplifier‐recording circuits by demodulation artifact is prevented by proper filtration.
Behavioral and thermal effects of microwave radiation at resonant and nonresonant wavelengths
Authors: D'Andrea J. A. , Gandhi O. P. , Lords J. L.
Published: February 2008

Behavioral and thermal effects of radiating an animal with differing wavelengths of microwave energy at the same power density were investigated in the first of two studies. Five Long‐Evans rats were trained to perform a lever‐pressing task and were rewarded with food on a variable interval schedule of reinforcement. Rats were individually exposed in random order to 400‐, 500‐, 600‐, and 700‐MHz CW radiation at a power density of 20 mW/cm2 with the long axis of the rat's body parallel to the vector of the electric field. Radiation at all wavelengths produced rises of body temperature and stoppage of lever pressing. The averaged rise in body temperature was greatest and work stoppage was most rapid during exposures at 600 MHz. In the second study, six rats were exposed in random order to 600‐MHz CW radiation at power densities of 5, 7.5, 10, and 20 mW/cm2 while performing the same behavioral task. Exposures at 10 and 20 mW/cm2 resulted in work stoppage, while exposures at 5 and 7.5 mW/cm2 did not. In addition, three of the rats were subsequently exposed while responding to 600‐MHz pulsed radiation (1000 pps, 3‐ or 30‐μs pulse durations at a peak power density of 170 mW/cm2 (averaged 0.51 and 5.1 mWcm2). No work stoppage occurred to pulsed radiation. Taken in sum, the data show that the mature Long‐Evans rat is resonant at a frequency near 600 MHz while work stoppage during short‐term exposures to 600‐MHz radiation occurs at a power density between 7.5 and 10 mW/cm2.
Remote sensing of buried resistive inhomogeneities by electromagnetic transmission measurements between the ground surface and a borehole—Theory and experiment
Authors: Cauterman M. , Degauque P. , Demoulin B. , Gabillard R.
Published: February 2008

A theoretical solution for the electromagnetic response of a three‐dimensional inhomogeneity in a conductive half space has been developed for horizontal electric dipole excitation. We assume that the transmitting frequency is sufficiently low that we may use the quasi‐static approximation. The solution for the subsurface electric field is obtained in the form of an integral equation system which is reduced to a matrix equation and solved numerically. This theoretical model is applied to determine the feasibility of remote sensing of underground quarries by transmission measurements between the ground surface and a borehole. The first experimental results are also given and they show that it is possible to find a cavity (of about 100 m3) situated at a depth of 15 m and at a distance of 5 m from the drillhole.
Electrodynamics of long metallic tethers in the ionospheric plasma
Authors: Dobrowolny M.
Published: February 2008

A study is presented of the electrodynamic interactions of long metallic tethers (lengths up to 100 km) with the ionospheric plasma. The study, which is of interest in view of possible future experiments using long tethers in space, includes the derivation of current and potential distribution along the tether, taking also the effects of internal resistance into account. Electrostatic and electrodynamic drag forces are computed and compared with aerodynamic drag.
Wave propagation experiments at medium frequencies between two ionospheric satellites, 2, Whistler‐mode pulses
Authors: James H. G.
Published: February 2008

Intersatellite whistler‐mode propagation experiments at 0.48 MHz have been performed between the two ISIS spacecraft during rendezvous. Transmitted pulses of 100 μsec length are temporally dispersed by 100 times and more. The shape of the received pulse envelope depends on the orientation of the dipole antennas with respect to the ambient magnetic field. The distortion is greatest when both transmitting and receiving antennas are perpendicular to the field and least when they are parallel. Received pulse amplitudes and shapes have been compared with existing theory. For propagation well inside the resonance cone, received pulse amplitudes are within about two orders of magnitude of theoretical prediction. Near the resonance cone where large amounts of energy appear to be radiated, primary and secondary pulses are observed which are evidence of the antenna resonances of the finite‐length dipole. Because the occurrence of highly elongated whistler‐mode pulses and irregularities in the ambient electron density are correlated, it is deduced that irregularities are efficient scatterers of whistler‐mode waves.
Results of an experiment to detect field‐normal plasma‐line scattering in the auroral ionosphere
Authors: Minkoff J. , Laviola M. , Tsunoda R. , Presnell R.
Published: February 2008

Field‐normal plasma‐line scattering at radio frequencies has been observed during ionospheric heating experiments. An experiment to search for this scattering mode in the auroral ionosphere was carried out. The results are found to be negative by many orders of magnitude. This underlines the importance of the coherency of the heating wave for production of the scattering effects observed during the heating experiments.
Skew incidence on a right‐angled impedance wedge
Authors: Senior T. B. A.
Published: February 2008

A problem which is relevant to propagation in a rectangular waveguide with imperfectly conducting walls is a plane wave at skew incidence on a right‐angled wedge whose surfaces have nonzero impedances either scalar or tensor. The solution is obtained as a power series in the impedance η through terms O(η2). Its properties are discussed and it is shown that unless an impedance compatibility relation is satisfied the solution contains an edge wave whose amplitude is proportional to η2 and whose form is similar to the wave emanating from the edge of a ‘black’ half plane.
Radiative transfer theory for active remote sensing of half‐space random media
Authors: Tsang L. , Kong J. A.
Published: February 2008

In active remote sensing of low‐loss and scattering‐dominant areas, the effect of volume scattering can be modelled as a half‐space random medium with lateral and vertical fluctuations. Correlation functions are assumed to be gaussian laterally and exponential vertically. The radiative transfer theory is developed in this paper to calculate backscattering cross sections. An iteration process is used. When calculated to first order in albedo, the result gives the single‐scattering effects and confirms previous work. Calculated to second order, we find that the backscattered power exhibits depolarization effects. This important consequence is studied numerically by illustrating the backscattering cross sections as a function of incidence angles and frequencies.
Theory of short‐scale field‐aligned density striations due to ionospheric heating
Authors: Lee Min‐Chang , Fejer J. A.
Published: February 2008

The theoretical saturation spectrum of parametrically excited Langmuir waves in a locally uniform ionosphere is shown by the present claculations to produce, by ohmic dissipation, short‐scale field‐aligned density striations. The spectrum of the calculated striations is not inconsistent with observations of field‐aligned scatter of VHF and UHF waves in ionospheric modification experiments if local increases of the pump field due to focusing are invoked.
ATS‐6 satellite radio beacon measurements at Ootacamund, India
Authors: Davies K. , Donnelly R. F. , Grubb R. N. , Rama Rao P. V. S. , Rastogi R. G. , Deshpande M. R. , Chandra H. , Vats H. O. , Sethia G.
Published: February 2008

ATS‐6 radio beacon measurements of modulation phase and Faraday rotation made at Ootacamund, India, in 1975–1976 are discussed with emphasis on the measurement and analysis errors. The modulation‐phase measurements are insensitive to the geomagnetic field and provide an accurate determination of the total columnar electron content. Comparison of modulation‐phase measurements at different frequencies shows a minor sensitivity to the ATS‐6 pitch angle. For the low geomagnetic latitude and nearly transverse propagation conditions of Ootacamund, the use of a fixed conversion coefficient gives an unreliable Faraday content. However, the Faraday rotation measurements may be used to determine the shape factor F, which provides information about the electron density altitude profile. Corrections to the measured Faraday rotation for the ATS‐6 pitch and yaw are important, particularly at night when the rotation on 140 MHz can be of the order of 10° to 20°. Thus the reduction of data to plasmaspheric electron content is not recommended. Sample data are presented showing that, in the daytime, total content is about twice that in middle latitudes. The shape factor shows a low predawn minimum indicating the nearly complete erosion of the F2 layer peak.
Absorption around the electron cyclotron frequency in a thermal plasma of finite density
Authors: Bornatici M. , Engelmann F.
Published: February 2008

Cyclotron absorption around the electron cyclotron frequency in a weakly relativistic plasma of finite density in thermal equilibrium is considered for both perpendicular and quasi‐perpendicular propagation. A comprehensive analysis which includes thermal effects together with finite density corrections is given and the resulting scaling of the absorption of the extraordinary and the ordinary modes is examined. The line profiles are discussed and the optical thicknesses of a typical tokamak plasma are evaluated.
Surface wave diffraction by a truncated dielectric slab recessed in a perfectly conducting surface
Authors: Pathak P. H. , Kouyoumjian R. G.
Published: February 2008

The diffraction of a TM0 surface wave by a terminated dielectric slab which is flush mounted in a perfectly conducting surface is studied. The incident surface wave gives rise to waves reflected and diffracted by the termination; these reflected and diffracted fields may be expressed in terms of the geometrical theory of diffraction by introducing surface wave reflection and diffraction coefficients which are associated with the termination. In this investigation the surface wave reflection and diffraction coefficients have been deduced from a formally exact solution to this canonical problem. The solution is obtained via a combination of the generalized scattering matrix technique and the Wiener‐Hopf procedure. Expressions for the reflection and diffraction coefficients contain integrals which can be evaluated numerically.
The effects of space and time resolution on the quality of sea echo Doppler spectra measured with HF sky wave radar
Authors: Georges T. M. , Maresca J. W.
Published: February 2008

Measurements using the SRI Wide‐Aperture Research Facility (WARF) HF sky wave radar show that the radar's azimuthal beam width and integration time play important roles in determining the quality of sky wave (ionospherically propagated) sea echo Doppler spectra. Using as a quality index the equivalent width of a portion of the Doppler spectrum in the vicinity of the stronger Bragg line, we find a reduction of ionospheric multipath spectral contamination as beamwidth and integration time decrease. For nominal (3 dB) beam widths of 1/2°, 2°, and 4° and 256‐s averaging, the mean equivalent widths of 104 spectra were 0.090, 0.099, and 0. 105 Hz, respectively. Experiments using 51‐s integration time gave average widths of 0.061, 0.075, and 0.079 Hz for the same three beam widths. The additional contamination observed with the larger beamwidths and the longer averaging time is often sufficient to preclude the extraction of ocean wave height from the second‐order spectral structure. A geometrical optics, rough‐surface model of the ionospheric reflection process explains this beamwidth dependence by relating the number and width of multipath spectral lines to the size, shape, and number of ‘reflective glints’ in the ionospheric area illuminated by the radar. The lateral dimension of this area increases with antenna beamwidth. The model also predicts a greater dependence of contamination on beamwidth as the integration time is reduced. We use ionospheric measurements made with CW Doppler sounders to estimate the statistical parameters of the rough surface model and the amount of contamination the model predicts for finite beamwidth and integration time. Our main conclusion is that the best way to avoid spectral contamination caused by short‐term ionospheric motions is to involve the smallest possible spatial and temporal samples of the ionosphere in the radar measurement. Specifically, a successful sea state radar should have a 3‐dB beamwidth of less than 2° and preferably as small as 1/2° and should use coherent integration times shorter than about 100s.
The relativistic Doppler shift in satellite tracking
Authors: Harkins Michael D.
Published: February 2008

The recently launched (June 23, 1977) Navigation Technology Satellite 2 carries aboard it two high‐precision cesium beam atomic standards. The frequencies of these standards were preset to agree with similar ground‐based oscillators to within a few parts in 1012. An analysis of about 4 days of low‐noise Doppler tracking revealed a frequency bias between the orbiting clocks and the ground‐based clocks at the tracking sites. This observed bias was 4.47 parts in 1010, which is consistent with a predicted frequency bias arising from the special relativity time dilation effect coupled with a frequency blue shift predicted by general relativity.
Ramp time synchronization
Authors: Hietzke W.
Published: February 2008

A new method of intercontinental clock synchronization has been developed and proposed for possible use by NASA' s Deep Space Network (DSN), using a two‐way/three‐way radio link with a spacecraft. Analysis of preliminary data indicates that the real‐time method has an uncertainty of 0.6 μs, and it is very likely that further work will decrease the uncertainty. Also, the method is compatible with a variety of non‐real‐time analysis techniques, which may reduce the uncertainty down to the tens of nanosecond range.
Precise time recovery from transit satellites
Authors: Cashion R. E. , Hunt G. A. , Lavanceau J. D.
Published: February 2008

An instrument using time signals from the Navy Navigation Satellite System (Transit) to derive precise time referenced to the U.S. Naval Observatory (USNO) master clock is described. The two sources of system time error, receiver detection error and spacecraft timekeeping error, are analyzed. Performance data from production equipment tested at USNO are given. A cooperative program between USNO and the control agency to improve the spacecraft timekeeping is outlined. Phase One of this program is underway, and projected results are analyzed. System accuracy is forecast to be 3–5 μs rms when this program is completed.
Computer simulation and analysis of the Fejer gyrowave interaction experiment
Authors: Nath Narinder , Setty C. S. G. K.
Published: February 2008

The gyrowave interaction experiment yields the impressed modulation as a function of time delay (meeting height) between the wanted and the disturbing radio frequency pulses. This is referred to as the Fejer curve. In this paper we compute the Fejer curves for the geomagnetic conditions of Delhi, using an exponential model of the D region ionization, temperature dependent energy relaxation factor G, a model collision frequency v of the Sen‐Wyller magnetoionic theory, and the standard wave interaction theory. The Fejer curves are then inverted to recover the electron density profile, thus completing the close circuit computation. In the process of inversion of the Fejer curve the D region is assumed to be isothermal, and the effect of this assumption is investigated. It is found that it is possible to recover the original electron density profile if the mean D region temperature is adopted.
Transequatorial VHF propagation through equatorial plasma bubbles
Authors: Heron M. L. , McNamara L. F.
Published: February 2008

The support by the nighttime equatorial ionosphere of radio wave propagation at frequencies exceeding 50 MHz is explained in terms of guiding along field‐aligned tubes of depleted ionization resulting from the postsunset creation of equatorial plasma bubbles. By using the observed and theoretical properties of these bubbles, and considering in a numerical fashion a large ensemble of model bubbles, it is possible to reproduce many of the observed characteristics of transequatorial propagation at VHF.
A uniform GTD solution for the diffraction by strips illuminated at grazing incidence
Authors: Tiberio R. , Kouyoumjian R. G.
Published: February 2008

An asymptotic solution for the electromagnetic diffraction by a perfectly conducting strip illuminated at grazing incidence is obtained by an extension of the uniform GTD. Uniform expressions for the scattered field are given for plane, cylindrical, and spherical wave illuminations. Outside the transition regions these essentially reduce to results obtained by an ordinary application of the uniform GTD augmented by slope diffraction. In the case of plane wave illumination a very simple closed form expression is provided for the scattered far field. Numerical results are presented and compared with those calculated from a moment method solution.