bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffraction by a Flanged Parallel‐Plate Waveguide
Authors: Hongo K.
Published: February 2008

Radiation from a flanged parallel‐plate waveguide is studied analytically using the Weber‐Schafheitlin discontinuity integral when the waveguide is excited by TE‐mode waves, TM‐mode waves, or an electromagnetic line source. Electromagnetic fields are represented by the discontinuity integral in the exterior space, and in the waveguide region they are expanded by normal modes of the waveguide. Imposing the boundary conditions in the aperture gives a set of simultaneous equations for the expansion coefficients. Once the solutions of these equations are determined, quantities of interest, such as reflection coefficients, modal coefficients of higher‐order modes excited at the aperture, and radiation patterns, are readily obtained without knowing the field distribution in the aperture. Numerical calculations for the radiation patterns, reflection coefficients, and modal coefficients of higher order modes are carried out, and a part of the results is compared with the asymptotic solution by Lee [1970]. The effect of truncation in solving the equations numerically is also studied, and this method is found to exhibit rapid numerical convergence.
Height‐gain experimental data for groundwave propagation: 2, Heterogeneous paths
Authors: King R. J. , Cho S. H. , Jaggard D. L.
Published: February 2008

Analytical as well as experimental height‐gain studies for mixed‐path groundwave propagation are virtually nonexistent. Therefore, it was shown how the theoretical height‐gain for a homogeneous path relates to heterogeneous‐path experimental measurements versus height and distance. The results show that the magnitude of a groundwave field which crosses an abrupt boundary rapidly acquires the characteristic properties of the second medium, and the field over a heterogeneous surface attenuates at essentially the same rate as the field on the surface. The groundwave which has crossed an abrupt boundary can be predicted for small heights above the surface by simply multiplying the well‐established mixed‐path theory for antennas located on the surface by appropriate homogeneous‐path height‐gain factors corresponding to the local surface impedance, provided the field is predominantly a surface wave.
Attenuation and phase rotation of radio waves due to rain: Calculations at 19.3 and 34.8 GHz
Authors: Oguchi Tomohiro
Published: February 2008

Computations are made of the forward‐ and back‐scattering intensities of oblate spheroidal raindrops at 19.3 and 34.8 GHz, assuming plane waves at normal incidence to the drop axis. Two kinds of polarization are considered in the incident field: one is parallel to drop axis; the other is perpendicular. Numerical values of these basic scattering intensities are listed in tables. Forward‐scattering intensities are then used for determining the effective propagation constants of rain‐filled space. From these propagation constants, attenuations and phase rotations for parallel and perpendicular polarizations are computed for several rain rates. One significant conclusion is that the difference between phase rotations in the two polarizations at 19.3 GHz becomes very large as the rain rate increases, whereas that at 34.8 GHz is bounded in a very small range throughout all possible rain rates.
The UV nitric‐oxide experiment for Atmosphere Explorer
Authors: Earth Charles A. , Rusch David W. , Stewart A. Ian
Published: February 2008

The UV nitric‐oxide (UVNO) experiment on Atmosphere Explorer‐C and ‐D (AE‐C and AE‐D) is a two‐channel, fixed‐grating Ebert spectrometer which will measure the airglow in the (1, O) gamma band at 2150 Å. The observed intensity is produced by resonance fluorescence of sunlight by the NO molecules in the instrument's field of view, and the intensity profiles obtained will be inverted to yield altitude profiles of NO density. These density profiles will be obtained as functions of time and geographic location. The results will be used in investigations of the sources, sinks, and transport of NO and, in cooperation with other AE experiments, in investigations of thermospheric ion chemistry, the morphology of the turbopause, and auroral perturbations of the thermosphere.
A time‐domain integral‐equation solution for linear antennas and scatterers
Authors: Liu Tom K. , Mei Kenneth K.
Published: February 2008

The integral equation of Hallen's type is derived in the time domain. The solution of the integral equation is carried out numerically, and the electromagnetic behavior of linear antennas and scatterers under various excitations is presented. The integral equation may be used to obtain time‐domain responses of coupled parallel linear antennas, and scatterers with loads. Combining with the method of characteristics in solving transmission line problems, the integral‐equation formulation is applied to the cases in which antennas and scatterers are connected to transmission lines.
Bow shock and its interaction with interplanetary shocks
Authors: Dryer Murray
Published: February 2008

Harbingers of significant magnetospheric motions consist of the interactions of interplanetary discontinuities with the standing bow shock. The most common discontinuity is the tangential discontinuity. Less frequent in occurrence, but of major significance to subsequent magnetospheric dynamics, is the flare‐generated interplanetary shock wave and its initiation of bow shock and magnetopause motion toward Earth. Early studies utilized the ordinary gas‐dynamic analogy of the well‐known Riemann splitting of an initial discontinuity (i.e., bow shock) into a reflected shock (the moving bow shock) and the transmitted shock (the inward‐moving interplanetary shock). It was shown that order‐of‐magnitude pressure increases at the subsolar point of the magnetopause are readily found for typical shock‐on‐shock studies. Phenomenological studies also demonstrated, in agreement with observations, that the magnetopause motion could be predicted on the basis of quasi‐static variation of the solar wind dynamic pressure. Recent hydromagnetic studies (for the simplified case of perpendicular shocks) have extended the theory to predict bow shock and magnetopause velocities which appear to be observed by spacecraft. Such one‐dimensional studies provide upper limits for all average plasma parameters within the region of the Sun‐Earth axis. The general case of the time‐dependent interaction in three dimensions has, as yet, not been done. Nevertheless, the general configurational and plasma details are, in principle, amenable to examination with the use of multiple spacecraft measurements during the interaction and the ensuing dynamic motions on a time scale of tens of min to the several hr required for the magnetopause to move to smaller geocentric distances. The physical processes of various energy transfers from kinetic to thermal and magnetic as predicted by the hydromagnetic theory could then be assessed by study of the plasma average velocity, direction of flow, magnetic field, temperature, and density.

The magnetosheath plasma properties following such interactions could, on a more speculative note, provide new boundary conditions (associated with appropriate magnetosheath and magnetosphere magnetic field polarities) which could, in turn, initiate and drive the reconnection process within the magnetopause.
Experimental study of the reconnection process
Authors: Baum P. J. , Bratenahl A. , White R. Stephen
Published: February 2008

We briefly review the results of a laboratory field‐line reconnection experiment. In doing so the flux transfer rate is defined and contrasted with magnetic Mach numbers as measures of the reconnection rate. We examine the origin of the reconnection electric field to determine some of the requirements of nonsteady versus steady reconnection. The dependence of various measures of the reconnection rate on electrical conductivity is discussed as well as some experimental features which may relate to previous theory. Finally, we present some approximate scaling between laboratory events and the geomagnetic substorm. We reach three major conclusions: (a) The flux transfer rate as a measure of the reconnection rate is different from a magnetic Mach number. (b) The early reconnection process is quasi‐steady state or “Petschek‐like” and we associate this phase with magnetic energy storage. A later rapid flux transfer event is more energetic and is associated with storm events. The flux transfer event is triggered by a change in resistivity. (c) The laboratory event scales reasonably well to the duration and energy of a substorm.
IMF sector structure effects on the quiet geomagnetic field
Authors: Matsushita S. , Tarpley J. D. , Campbell W. H.
Published: February 2008

A correlation of the interplanetary magnetic field sector structures including the east‐west component with the polar geomagnetic field variations has recently been suggested by several scientists. To clarify the details of the correlation and to facilitate discussion of the physical mechanism involved in the interaction, 2.5‐min digitized geomagnetic data from 40 stations located from the northern polar cap through the southern subauroral zone are examined during quiet days in 1965. The Sqp equivalent overhead current systems are investigated with respect to seasonal changes and variations corresponding to toward‐ and away‐sector structures by the technique of spherical harmonic expansions of the data. In addition to obvious seasonal variations of the Sqp, a clear shift of the average Sqp pattern toward the afternoon (early morning) side of the polar cap for the toward‐sector (away‐sector) structure is obtained. Furthermore, small but remarkable sector effects on the quiet geomagnetic field in middle and low latitudes are discovered. The results of this work contribute to the discussion of sector structure effects on magnetic field merging at the magnetopause and convective patterns in the magnetosphere.
Substorms in space: The correlation between ground and satellite observations of the magnetic field
Authors: McPherron R. L. , Russell C. T. , Kivelson M. G. , Coleman P. J.
Published: February 2008

Satellite studies of magnetospheric substorms are necessarily statistical since there are few properly instrumented satellites in space at any one time. To carry out these studies, one selects an ensemble of similar substorms, determines an origin for substorm time, and performs an ensemble average to eliminate noise. Similarity between different substorms can be determined from contour maps of midlatitude magnetic perturbations as a function of longitude and universal time. The origin of substorm time can also be determined from midlatitude perturbations and is usually taken as the beginning of the positive bay near midnight. Use of these techniques has led to a phenomenological model of magnetospheric substorms that includes a growth phase. The controversy over the existence of the growth phase is at least partially a consequence of differing definitions of the origin of substorm time. Use of auroral zone magnetograms often gives an earlier onset than midlatitude magnetograms. However, midlatitude onsets do appear to order satellite data systematically. In this paper we illustrate the discrepancy between these two onset times and show how midlatitude onsets order satellite data in agreement with the growth phase model. Three events of increasing complexity are considered. Each has been previously reported in the literature and later criticized. We speculate that a polar magnetic substorm begins when a pair of X‐ and O‐type neutral lines form on closed field lines within the plasma sheet. Subsequently, the midlatitude positive bay begins when magnetic merging first encounters open field lines in the lobe of the tail.
Daytime three‐dimensional drifts at Millstone Hill Observatory
Authors: Carpenter L. A. , Kirchhoff V. W. J. H.
Published: February 2008

Vertical drift measurements in the topside F region at midlatitudes have confirmed the importance of dynamical processes, but it has been difficult isolating those processes due to E × B drifts from those due to neutral winds. To remove this ambiguity three‐dimensional drift measurements were made at Millstone Hill Observatory with the steerable L‐band radar in conjunction with the vertical UHF antenna. The geometry of the experiment is discussed and daytime drifts are presented. Unusual lifting of the F‐layer peak was observed on two occasions. A reversal in the deduced meridional neutral wind is observed in one case and an enhanced eastward electric field in the other.
Simultaneous riometer and incoherent scatter radar observations of the auroral D region
Authors: Hunsucker Robert D.
Published: February 2008

The purpose of this paper is to present some incoherent scatter radar observations of high latitude D‐region ionization profiles during auroral disturbances and during the great magnetic storm of August 1972. Simultaneous 30‐MHz riometer and magnetometer data from the College, Alaska area and IMP‐5 and ‐6 satellite data are utilized to interpret the ionization profiles.
Electromagnetic scattering by random dielectric constant fluctuations in a bounded medium
Authors: Stogryn A.
Published: February 2008

The electromagnetic scattering properties of a medium bounded by a plane surface and whose (scalar) dielectric constant is the sum of a nonrandom part assumed to vary only with depth and a small random part are investigated by means of an approximate, first‐order perturbation method. It is shown that the equivalent dielectric constant to be used in calculating the average reflected power in the specular direction is a function of depth even in the case where the nonrandom part of the dielectric constant is independent of depth. Further, the equivalent dielectric constant is shown to be a tensor. Nonspecular scattering is also considered.
Analytical investigation of waveforms radiated by a resistively loaded linear antenna excited by a Gaussian pulse
Authors: Sengupta Dipak L. , Liu Yu‐Ping
Published: February 2008

The waveforms radiated by linear antennas loaded nonuniformly and continuously with resistance are investigated analytically. The antennas considered are symmetrical and excited at the centers by slice generators having a Gaussian pulse type of time dependence. Closed form expressions are developed for the far‐field waveforms produced by such antennas in any direction. The analytical results are compared with those obtained by direct numerical means.
Coherence and intensity fluctuations of light in the turbulent atmosphere
Authors: Gurvich A. S. , Tatarski V. I.
Published: February 2008

This paper deals with a review of theoretical and experimental work performed in the USSR on strong fluctuations of the intensity of light.
Coherence equations governing propagation through random media
Authors: Beran Mark J.
Published: February 2008

In this paper we consider the equations governing the second‐ and fourth‐order coherence functions in random media. We first treat radiation propagating in a homogeneous and isotropic random medium in the limit of small wavelengths. We summarize the solutions that are available and report on some recent unpublished work. We next show how these equations may be generalized to include a nonhomogeneous background and the effects of anisotropy under acoustic conditions. The utility of the equations for considering free‐space propagation is also discussed.
Scintillations due to a concentrated layer with a power‐law turbulence spectrum
Authors: Rumsey V. H.
Published: February 2008

The spatial spectrum of intensity fluctuations due to a concentrated layer of turbulence is derived from the parabolic wave equation. The spectrum of refractive index fluctuations is taken to be an unmodified power law of arbitrary strength, with exponent α, 2 < α < 6. For 2 < α < 4 it is shown that the intensity spectra for a plane wave can be expressed in terms of a single parameter U, which is the Born approximation to m2, the normalized variance of intensity fluctuation. For U ≪ 1 the Born approximation applies. The high frequency approximation to the intensity spectrum is the angular spectrum that would result from twice the strength of turbulence. It applies above the spatial frequency κf or 2π κf/U, whichever is smaller, where κf is the frequency at the first null of the Born approximation. For U > 30, it represents essentially all of the intensity fluctuations and shows that m saturates at unity for a plane wave as U → ∞. Simple formulas for m when the source has finite angular extent show that m decreases with increasing turbulence as Uα−2 for U ≫ 1. These results are confirmed by exact calculations for the case α = 3 and by extensive observations of interplanetary scintillations.
Effect of small ionospheric irregularities on radio wave absorption
Authors: Chen H. C. , Fejer J. A.
Published: February 2008

The ionospheric absorption of a radio wave caused by small‐scale irregularities with a gaussian autocorrelation function is calculated for various values of the linear scale height, the radio frequency, the scale size of the irregularities, and the mean‐square fractional electron density fluctuations. The absorption is due to scattering of the radio wave into plasma oscillations by the irregularities. It is concluded that the absorption due to such irregularities with a mean‐square fractional electron density deviation greater than about 10−6 exceeds the normal collisional height‐integrated absorption. Absorption of this type could play a significant part in heating experiments or in an ionosphere containing naturally occurring irregularities.
Numerical modelling of a metallic ion sporadic‐E layer
Authors: MacLeod Malcolm A. , Keneshea Thomas J. , Narcisi Rocco S.
Published: February 2008

A one‐dimensional time‐dependent model of the ionosphere has been developed and applied to the study of a metallic ion sporadic‐E layer observed in the Aladdin 1 experiment carried out at Eglin AFB, Florida, 20 November 1970. The model develops the molecular ion background ionosphere using a dynamic photochemical calculation from noon to a time near model sunset. A representative metallic ion altitude profile is then introduced, the divergence terms included in the continuity equations, and the integration carried forward. Introducing an ad hoc constant electric field of 2 mv m−1 directed to the south, the model metallic ion sporadic‐E layer forms at the proper altitude and reaches the measured peak density in about a half hour. Changing the initial metallic ion profile changes the time to reach peak density and the degree of asymmetry of the layer, but the layer altitude is determined asymptotically by the location of the convergent node of the vertical ion velocity profile. The background ionospheric density calculated with the model agrees within experimental error with the experimental profile. The calculations support the hypothesis that midlatitude sporadic‐E layers are caused by neutral‐wind‐induced compression of metallic ions resulting from meteoric ablation in the lower E region.
Incoherent scatter multiple‐pulse measurements at Arecibo
Authors: Zamlutti Carlos Jose , Farley D. T.
Published: February 2008

The important points governing the design of a multiple‐pulse measurement of the incoherent scatter autocorrelation function in the E region are discussed. Since the requirements for good signal‐to‐noise ratio and good resolution are contradictory, compromises must be made. These considerations dictated the choice of two multiple‐pulse schemes which are now being used at the National Astronomy and Ionosphere Center in Arecibo, Puerto Rico. These schemes, one involving five pulses and one involving seven, are described and a few typical examples of the results obtained are presented. The data show that it is now practical during the day, or at night in reasonably strong sporadic‐E layers, to make accurate measurements of the complex autocorrelation function in the E region with an altitude resolution of the order of 1 to 3 km in a time of less than 10 min. The number of heights which can be studied simultaneously is limited only by computer capabilities. In the measurements reported here ten altitudes were sampled.
Frequency and spatial correlation functions in a fading communication channel through the ionosphere
Authors: Liu C. H. , Yeh K. C.
Published: February 2008

Equations for the two‐frequency two‐position mutual coherence functions are derived under the usual parabolic and Markov approximations. These equations are then solved numerically. It is shown that the mutual coherence functions occur naturally in the study of pulse distortion through a random communication channel and in the investigation of signal correlations. Contour plots of correlation functions show the possibility of having equal values at two frequency separations for a given spatial separation. This behavior is explainable in terms of overlapping Fresnel zones.
The Yosemite experiments: HF propagation through rock
Authors: Lytle R. Jeffrey , Lager Darrel L.
Published: February 2008

A variety of continuous wave, swept frequency, and pulse transmission experiments were conducted in and around the Wawona Tunnel at Yosemite National Park. The experiments were performed to obtain data on the HF electrical properties of large volumes of rock. The experiments involved the propagation of electromagnetic waves through more than 300 m (1000 ft) of granite. In situ bulk conductivities of 2–5 × 10−4 mho/m and relative dielectric constants of 5–7 were measured in the 3–50 Hz band. Experimental errors in these values are estimated to be less than ±9% and ±10%, respectively.
The submarine‐towed ELF loop antenna
Authors: Burrows M. L.
Published: February 2008

To obtain omnidirectional reception, a solenoidal loop antenna can be built into the same cable as that used for the ELF electrode‐pair antenna. The loop's noise voltage is higher in level and is more complex than that of the electrode‐pair antenna. Measurements of towed cable vibration, of towed antenna noise, and of the physical and electrical properties of antenna cable samples have been made to clarify the noise production process. The results have included (i) the development of a quantitative theory for each significant noise type, (ii) the identification of a number of noise suppression techniques, (iii) the realization of a low noise level, in agreement with theoretical predictions, when an antenna incorporating some of these techniques was tested at sea, and (iv) the construction of various laboratory facilities for testing candidate antenna designs, the most notable being an antenna‐towing simulator in the form of a shielded water‐flow tunnel.
Input impedance of a short dipole antenna in a warm anisotropic plasma, 2, Experiment
Authors: Nakatani D. T. , Kuehl H. H.
Published: February 2008

The measured input impedance of a short, cylindrical dipole immersed in a pulsed, RF discharge, anisotropic, argon plasma is presented. The experimental results show that the input impedance undergoes a pronounced change when the antenna frequency passes through the harmonics of the electron cyclotron frequency, which is in agreement with the predictions of kinetic theory. In general, the correlations between experimental and theoretical results are judged as fair to very good over a wide range of plasma parameters. Effects of the plasma sheath are found to be important and a sheath correction term based on a simple sheath model is included for correlating experimental and theoretical results. Using a curve‐fitting technique, a sheath thickness of 3λDwas determined. Impedance measurements at dipole frequencies above the harmonics showed anomalous results which are explained by kinetic theory.
Optimization of one‐state and two‐state matching systems for phased arrays
Authors: Zaghloul Amir I. , MacPhie Robert H.
Published: February 2008

For a specific scanning range of a phased array antenna we define the optimum array as that which has either the minimum maximum reflection coefficient or the minimum mean square reflection coefficient. For every scanning range there are matching angles, one for each criterion, at which the pattern is optimum. This is studied for infinite slot arrays both with and without interelement positioning errors. A two‐state matching system is also introduced in which the array is perfectly matched at two angles within the scanning range. The results for the optimization problem for the two‐state matching are also given to show howpositioning errors and this matching systemcan result in a large scanning range over which the reflection coefficient is very small.
Two‐frequency mutual coherence function, coherence bandwidth, and coherence time of millimeter and optical waves in rain, fog, and turbulence
Authors: Hong S. T. , Ishimaru Akira
Published: February 2008

Propagation characteristics of pulse waves in rain, fog, and turbulence are determined by a two‐frequency mutual coherence function. Parabolic differential equations applicable to strong fluctuation cases are derived for the two‐frequency mutual coherence function for randomly distributed scatterers and turbulence. These equations are solved for the plane wave case using the eigenfunction‐eigenvalue method. Numerical calculations are given for millimeter waves (100 GHz) and optical waves (0.6943 and 10.6 μm) in rain, fog, and turbulence over the distance of 5 km. The coherence bandwidths are found to be in the range of MHz for millimeter waves (100 GHz) in heavy rain (25 mm/hr) and for optical waves in fog, and considerable distortion of pulse shape may result in these situations. For other cases, the effect on pulse shape distortion may be negligibly small.
Depolarization over a link due to rain: Measurements of the parameters
Authors: McCormick G. C. , Hendry A. , Allan L. E.
Published: February 2008

Observations of depolarization caused by rain at 16.5 GHz taken over a short link during parts of four seasons, 1972–1975, at Ottawa, Canada, are presented. They include determinations of the mean canting angle and the real and imaginary parts of the differential propagation constant.
Probability distribution of irradiance fluctuations of beam waves in a weakly turbulent atmosphere
Authors: Furuhama Yoji
Published: February 2008

The integral expression for theNth‐order moment of irradiance fluctuations of a finite beam wave traversing a weakly turbulent atmosphere is derived by the parabolic‐equation method. The expression for theNth‐order moment, evaluated for the weak scintillation limit, is the same form as theNth‐order moment of the log‐normal distribution. This expression provides a necessary condition for the log normality of the irradiance fluctuation of beam wave. For the plane‐ and spherical‐wave limits, the result is valid at all distances ρ¯ from the axis of the beam less than the propagation distanceszand the distribution function depends upon ρ¯. The values of the variance coincide with the results of the usual first‐order perturbation theory, and log‐normality also holds.
Effects of 200 km propagation on Florida lightning return stroke electric fields
Authors: Uman M. A. , Swanberg C. E. , Tiller J. A. , Lin Y. T. , Krider E. P.
Published: February 2008

The electric fields produced by lightning return strokes near Kennedy Space Center, Florida, have been measured simultaneously at distances of about 5 to 25 km and about 200 km. Detailed records of the first 12 μs of waveforms from four strokes are presented, as well as data on the initial field risetimes for 58 first and 92 subsequent strokes. The mean field risetime measured between the 10 to 90% points was about 1 μs at the close station and about 2 μs at the distant one.
Scattering properties of Pruppacher‐and‐Pitter form raindrops and cross polarization due to rain: Calculations at 11, 13, 19.3, and 34.8 GHz
Authors: Oguchi Tomohiro
Published: February 2008

Forward‐scattering amplitudes of raindrops are computed at 11, 13, 19.3, and 34.8 GHz for a real raindrop shape given by Pruppacher and Pitter, assuming plane waves at normal incidence to the drop axis. Horizontal and vertical polarizations are considered in the incident field. These forward‐scattering amplitudes are then used to estimate cross polarization by rain. Cross‐polarization factors are calculated for two kinds of raindrop canting angle distributions: gaussian distributions and a photographically measured distribution. The results show that the scatter of the drop canting angles reduces the cross polarization considerably as compared with that for equioriented raindrops.
Refractive index variance and its height distribution in different air masses
Authors: Gossard Earl E.
Published: February 2008

With the advent of radars capable of detecting backscatter from turbulent inhomogeneities in the clear air, there is renewed interest in the refractive character of the atmosphere. The radio refractive index structure constant and its spatial and temporal distribution are of particular importance. The general refractive properties of air masses are discussed in this paper. Based on certain assumptions, the distribution of optical and radio refractive index structure constants are then calculated and the results are compared with the limited observational data available.
Scattering from arbitrarily‐shaped lossy dielectric bodies of revolution
Authors: Wu Te‐Kao , Tsai Leonard L.
Published: February 2008

A surface integral equation (SIE) technique is developed to analyze the scattering properties of arbitrarily‐shaped lossy dielectric bodies of revolution. Two coupled vector integral equations formulated via Maxwell's equations, Green's theorem, and the boundary conditions are used. The unknown surface currents (both electric and magnetic) are calculated by, first, Fourier decomposition, and then, the moment method, Galerkin's procedure. The far scattered field and radar cross section (RCS) are then readily determined from the reciprocity theorem and the measurement matrix concept. For a dielectric sphere good agreement is obtained between the SIE and exact solutions. Solutions of a thick dielectric cylinder are next used to demonstrate the arbitrary geometry capability of the SIE method. This method is suitable for homogeneous dielectric bodies and only the axially incident plane wave is considered here. The method also applies for a wide range of dielectric parameters (with ∈rfrom 1.44 to 80 and conductivity σ from 0 to 103mho/m).
A general perturbation solution for reflection from two‐dimensional periodic surfaces
Authors: Rosich Rayner K. , Wait James R.
Published: February 2008

Reflection of a vertically polarized electromagnetic plane wave from a periodic rough surface is considered. The surface is characterized locally by a boundary impedance. By using a perturbation analysis, a general expression is obtained for the amplitudes of the scattered waves which is valid for all spectral and all perturbation orders. It is shown that the results obtained here are consistent with earlier analyses of Rice, Wait, and Barrick. In addition, the general expression permits one to discern some important properties of the amplitudes for a purely sinusoidal surface. Among other things, we show that all odd perturbation orders are zero for the specular mode.
The effect of repeated microwave exposure on neonatal rats
Authors: Guillet Ronnie , Michaelson Sol M.
Published: February 2008

Thirty‐six neonatal rats were exposed daily at a power density of zero or 40 mW/cm2 to 2450‐MHz CW radiation for five minutes from day one through day six of postpartum life. On day seven, control and experimental rats either were euthanized, were exposed to sham or microwave radiation for a seventh time, or were injected with ACTH. The two treated groups of pups were euthanized 20 minutes after the final exposure or injection. Trunk blood and adrenal glands were saved. No difference was found in concentration of plasma corticosterone between exposed rats and controls. Basal plasma concentration of corticosterone was less than 2 μg% in both groups. Following either microwave exposure or injection of ACTH on day seven, levels of plasma corticosterone remained low (< 3 μg%) both in radiated and in control animals but were significantly higher in the former (2.08 μg% ±0.85 SD) as compared with the latter (0.72 μg% ±0.60 SD). A statistically significant increase in the wet mass of adrenal glands was noted in animals that were exposed to microwaves during the first six postnatal days. The cause and the biological significance of this enlargement are unknown. Because the first two to three weeks of postnatal life are critical in the development of the rat, the effects of exposure to microwave radiation during this period may be readily manifested at this time or at a later stage in life.
Microwave hearing: The response of single auditory neurons in the cat to pulsed microwave radiation
Authors: Lebovitz Robert M. , Seaman Ronald L.
Published: February 2008

Inferences regarding the mechanism of “microwave hearing” heretofore have been based upon theoretical studies, reports of human observers, animal behavioral experiments, and the recording of auditory field potentials. To gain more insight into the phenomenon we have examined the effect of pulsed microwave radiation (MWR) at 915 MHz on single auditory neurons in the cat. The responses to pulsed acoustic stimuli (“clicks”) and to pulsed MWR were compared by means of post‐stimulus time histograms. Although the response to MWR was dependent upon parameters of the pulse of incident MWR, it was independent of the averaged rate of energy absorption. Threshold effects were observed at an energy dose as low as 4 μJ/g per pulse. Auditory units with characteristic frequencies (CFs) below 1.2 kHz appeared to be more responsive to pulsed MWR than were units with higher CFs. Many neurons demonstrated a response to pulsed MWR that was similar to the response to acoustic clicks, which may provide a means by which to define the acoustic equivalent of MWR. Our results support the view that microwave hearing is mediated, at least in part, by an electromechanical interaction that is initiated distal to the cochlea.
Studies of the 0.5–14 μm optical extinction due to atmospheric aerosols
Authors: Hågård A. , Nilsson B. , Ottersten H. , Steinvall O.
Published: February 2008

The aerosol extinction is a source of uncertainty in predictions of the atmospheric attenuation of infrared radiation. We model the dependence of aerosol extinction in the atmospheric boundary layer on meteorological variables such as visibility, humidity, and air mass type by accounting for their influence on a bimodal particle size distribution consisting of two log‐normal distributions, and calculating the extinction from Mie theory. The model is fitted to results from simultaneous measurements near the ground with a multiwavelength transmissometer and meteorological sensors, including a nephelometer and a rain gauge. The transmissometer measures the atmospheric extinction along a 500‐m horizontal path in 15 bands in the 0.5–14 μm wavelength interval. A complete sequence of transmissometer data and meteorological values is collected automatically every 10‐min period. Preliminary results show the anticipated increase of the aerosol extinction with increasing relative humidity and with decreasing wavelength to be in general consistency with the model. Whether the observed variations in wavelength dependence of the aerosol extinction can be interpreted in terms of weather influence in accordance with the model cannot be established until a larger data base has been obtained.
Solar wind velocity estimation from multi‐station IPS
Authors: Coles W. A. , Kaufman J. J.
Published: February 2008

Three‐station and four‐station observations at 74 MHz are used to study the spatial structure and temporal rearrangement of the intensity pattern of interplanetary scintillations (IPS) in weak scattering. Velocity estimators from three models, two of which include rearrangement, are applied to the data and evaluated. It is shown that for certain radio sources the spatial anisotropy of the pattern is determined by elongated source structure. An upper bound on the average pattern axial ratio for an isotropic ecliptic source is 1.3 for data of mid‐1972. An upper bound on the average random velocity for the same period is 40% of the bulk velocity. We discuss a simple velocity estimator that is independent of the spatial anisotropy and has a low sensitivity to the random velocity.
Small‐scale irregularities of electron density in the F region from ƒN resonances observed by a rocket‐borne relaxation sounding experiment
Authors: Higel B.
Published: February 2008

The plasma resonance phenomena observed near the plasma frequency ƒN through active experiments of relaxation sounding have been experimentally investigated within the range 100‐500 km in the ionosphere by means of the three rocket launches of the EIDI payloads (Experiment on the Impedance of a Dipole in the Ionosphere). The design of the EIDI relaxation sounders has been improved with respect to that of previous topside sounding experiments (Alouette and ISIS programs) in that it records both the envelope and the waveform of the resonance signals in a large dynamic range. This allows the study of spectral features of the plasma resonance phenomena. The data of EIDI 3 are first used to point out the accuracy and the reliability of relaxation sounding experiments for the measurement of the ionospheric electron density; the electron density profile obtained is typical of a midlatitude, winter, nighttime ionosphere. Secondly, the spectral features of the ƒN resonance signals are investigated. Their comparison with those predicted by the theory of oblique echoes for the ƒN resonances leads to a disagreement, although the waves received are shown to be the electrostatic slow ones used in this theory. However, a correlation processing between the Fourier spectra of the ƒN resonance signals observed in sequence allows us to point out the existence of small‐scale irregularities of the electron density. This result is inconsistent with the theoretical hypothesis of a linear density variation versus altitude. By taking these irregularities into account, the features of the resonance signals can then be qualitatively explained. The properties deduced from the data regarding the size and the amplitude of the density irregularities are in agreement with those obtained under comparable ionospheric conditions through another kind of experiment for measuring the irregularities (Retarding Potential Analyzer on the OGO 6 satellite). Moreover, the unexplained phenomena of beat frequency oscillations observed on the Alouette and ISIS ƒN resonance data are tentatively interpreted in a similar way through the existence of sinusoidal irregularities of the electron density. Finally, it is pointed out that the relaxation sounding experiment on‐board the GEOS satellite has been designed to provide an effective measurement of the electron density irregularities in the magnetosphere.
Measurements at 13.9 GHz of the radar backscattering cross section of the North Sea covered with an artificial surface film
Authors: Hühnerfuss Heinrich , Alpers Werner , Jones W. Linwood
Published: February 2008

The reduction of the Ku‐band (13.9 GHz) normalized radar cross section (NRCS) by an artificial monomolecular surface film (oleyl alcohol) on the sea surface was measured in the North Sea during the 1975 Joint North Sea Wave Project, JONSWAP 75 experiment. The aim of the surface film experiment was to simulate natural surface films which often occur on the ocean surface and are produced by plankton or fish. NRCS measurements were obtained from an aircraft at incidence angles of 41° and 47° at vertical and horizontal polarizations. For winds between 3.5 and 4.4 m/sec the maximum measured reduction was 7.3 ± 3.5 dB relative to the mean. In‐situ measurements showed that the oleyl alcohol film reduced the surface tension from 74 to 43 dyne/cm. Similar reductions in surface tension have also been measured on the ocean due to natural surface films of biological origin. It is noted that variations of the NRCS due to natural surface film effects may significantly limit the techniques used currently to infer surface wind vector over biologically active ocean regions.
Characterization and measurement of time and frequency stability
Authors: Lesage P. , Audoin C.
Published: February 2008

The roles which spectral density of fractional frequency fluctuations, two‐sample variance, and power spectra play in different parts of the electromagnetic spectrum are introduced. Their relationship is discussed. Data acquisition in the frequency and the time domain is considered, and examples are given throughout the spectrum. Recently proposed methods for the characterization of a single high‐quality frequency source are briefly described. Possible difficulties and limitations in the interpretation of measurement results are specified, mostly in the presence of a dead time between measurements. The link between past developments in the field, such as two‐sample variance and spectral analysis from time domain measurement, and recently introduced structure functions is emphasized.
Microwave to visible frequency synthesis
Authors: Jimenez Juan J.
Published: February 2008

The helium‐neon methane‐stabilized laser frequency at 88 THz (3.39 μm) and higher frequencies (148 and 197 THz, frequencies of the Xe (2.03 μm) and Ne (1.52 μm) lasers) have been measured by comparison with the cesium frequency standard using a microwave to visible frequency synthesis chain. This paper will report on the techniques of laser frequency measurements, the nonlinear devices used for these measurements, and the different methods for laser frequency synthesis with emphasis on microwave and laser generators. The extension of laser frequency measurements to the visible will also be discussed.
Microwave time and frequency standards
Authors: Hellwig Helmut
Published: February 2008

Today's time and frequency standards which are in active use ranging from the definition of the second to spacecraft applications are all based on atomic resonances in the microwave region controlling high‐performance quartz crystal oscillators. The present status of these standards will be presented focusing in particular on cesium, hydrogen, and rubidium devices, as well as on new quartz crystal standards. A coherent picture of their physical principles and limitations is given based on the common attempt to reduce perturbations and Doppler effects. The sharpness of the resonance line is linked to the flicker noise stability limit of the various standards, and some speculation is made on where and how much further improvements may occur. It is demonstrated how new design concepts and new physical methods most likely will significantly improve the accuracy, stability, and practical usefulness of time and frequency standards.
Practical implications of relativity for a global coordinate time scale
Authors: Ashby Neil , Allan David W.
Published: February 2008

Frontiers of technology now need synchronization between remote clocks to an accuracy of about a nanosecond. Rate changes arising from the velocity and gravitational potential of a transported clock used for synchronization of a network must be accounted for. In addition, one cannot assume that the earth is an inertial frame, i.e., not spinning. If classical Einstein synchronization is used, where from the midpoint between clocks at A and at B, one simultaneously sends light pulses to A and B to synchronize them, two problems arise. First, the synchronization process will not be transitive; i.e., if A is synchronized with B and B with C, then A will not necessarily be synchronized with C. Second, starting at a point on the equator and transporting a portable clock eastward (westward), while establishing a synchronized time grid on the way, will result in a discontinuity upon returning to the original point of about −200 ns (+200 ns); minus (−) means that the portable clock will be late. This paper will discuss the construction of a coordinate clock network on the earth's surface which does not have these problems; i.e., synchronization is transitive, and there is no discontinuity. This may be done by adjusting clocks to read coordinate time on an underlying nonrotating local inertial frame. The theoretical and practical implications of setting up such a coordinate clock network using either electromagnetic signals (e.g., laser, Loran‐C) or portable clocks will be discussed. It will be shown how this network may be applied in making UTC or any other global scale more useful for state‐of‐the‐art navigation and communication systems.
Real‐time data acquisition and interpretation capabilities of the Dynasonde: 1. Data acquisition and real‐time display
Authors: Wright J. W. , Pitteway M. L. V.
Published: February 2008

Dynasonde software for data acquisition in three modes is described. The ‘I’ mode corresponds to an ionogram format but includes complete echo polarization and angle‐of‐arrival information. K mode provides time series and high time resolution at freely selected sounding frequencies. B mode combines features of the other two modes. All share a real‐time noise rejection method which is described statistically. The system includes a digitally driven CRT (cathode ray tube) display and a variety of display formats for real time or deferred examination of data; in particular, dynamic time‐lapse displays of ionospheric activity can be maintained by the Dynasonde.
Real‐time data acquisition and interpretation capabilities of the Dynasonde: 2. Determination of magnetoionic mode and echolocation using a small spaced receiving array
Authors: Wright J. W. , Pitteway M. L. V.
Published: February 2008

Phase measurements by the Dynasonde are obtained for each echo from four spaced receiving antennas in a square array. The antennas are oriented along the array diagonals, and the phase values thus contain contributions identified with echo polarization and arrival angle. A unified procedure for separating these contributions is described. Ionograms with discriminated ordinary and extraordinary polarizations are displayed. ‘Skymap’ and ‘Gonionogram’ formats are also illustrated.
On the ionospheric parameters which govern high‐latitude ELF propagation in the earth‐ionosphere waveguide
Authors: Greifinger Carl , Greifinger Phyllis
Published: February 2008

An approximate wave solution is obtained for the propagating ELF mode at high latitudes in the earth‐ionosphere waveguide. A simple approximate expression for the complex propagation constant emerges from the solution. The propagation constant depends on four parameters, two altitudes and a scale height associated with each altitude. The lower altitude is the height at which the conduction current parallel to the magnetic field becomes equal to the displacement current. The associated scale height is the local scale height of the parallel conductivity. Under daytime ionospheric conditions, the upper altitude is the height at which the local wave number becomes equal to the reciprocal of the local scale height of the refractive index. The associated scale height is the local scale height of the refractive index. Under the simplest nighttime conditions, the second set of parameters is replaced by the altitude of the E‐region bottom and the local wave number just inside the E region. The relative phase velocity depends, in first approximation, only on the ratio of the two altitudes. The attenuation rate depends on the other two parameters as well. The two principal attenuation mechanisms are Joule heating by longitudinal currents in the vicinity of the lower altitude and energy leakage of the whistler component of the ELF wave at the upper altitude.