bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term effects of 2.45‐GHz radiation on the ultrastructure of the cerebral cortex and on hematologic profiles of rats
Authors: Switzer Walter G. , Mitchell Daniel S.
Published: February 2008

A multimode microwave (MW) exposure chamber was employed to investigate the effects of multiple exposures to low‐intensity CW radiation on the ultrastructure of the cerebral cortex of female Sprague‐Dawley rats. In order to maximize the opportunity to observe long‐term structural changes, a 6‐week recovery period was interposed between the last of 110 daily MW‐exposure sessions and the preparation of tissue samples for subsequent electron microscopic examination. Relative to sham‐irradiated control subjects, exposure to 2.45‐GHz radiation at an averaged specific absorption rate (SAR) of 2.3 mW/g produced a statistically significant increase in the occurrence of myelin figures in cortical dendrites of irradiated animals. No other remarkable structural changes were observed. Hematologic analyses revealed a significant elevation in the RBC counts of irradiated rats; differential WBC counts produced evidence of several marginally significant irregularities. Periodic samples of rectal temperature obtained during the course of irradiation revealed no indication of whole‐body heating.
The forward scattering of microwave solar radiation from a water surface
Authors: Wentz F. J.
Published: February 2008

The forward scattering of microwave solar radiation from a smooth and from a rough water surface is computed. The smooth surface is assumed specular, and the rough surface is represented by a two‐scale surface, for which two small‐scale perturbation parameters, 0.10 and 0.25, are considered. The contribution of the scattered sunlight to the antenna temperature is found using the scalar approximation, and the results are compared with radiometer measurements of the Cape Cod Canal. The overall agreement is good, but in some cases the smooth‐surface measurements are higher than the computations. This discrepancy possibly indicates an absolute calibration error or a slight misalignment of the antennas' boresights. The computations for the two perturbation parameters bracket the rough‐surface measurements except when the sun's mirror image is far removed from the boresight direction. The small disagreement in this case may be due to a peaked large‐scale slope distribution.
The transparency characteristics of Es types
Authors: Kolawole L. B.
Published: February 2008

The transparency characteristics of different Es types are examined using the blanketing power, ƒbEs/ƒ0 Es. This parameter is used to study the structural, seasonal, and solar‐cycle variations of the different forms of sporadic‐E observed over the northern hemisphere. The results of the study are compared with those of studies by previous workers who utilized different methods, and substantial agreement is observed. While clear evidence of solar‐cycle variations was observed in the Es layers at upper temperate and auroral zones, the Es layers at low‐latitude and lower temperate regions showed no evidence of solar‐cycle variations.
Temperate zone sporadic‐E maps (ƒ0Es > 7 MHz)
Authors: Smith Ernest K.
Published: February 2008

This paper offers three maps of ƒ0Es > 7 MHz for temperate zones of the world. The maps were prepared for CCIR Interim Working Party 6/8 (“VHF Propagation by Sporadic‐E”) and are intended for use in connection with a companion paper in this issue by Miya, Shimizu, and Kojima.
Analytic partial derivatives for least‐squares fitting incoherent scatter data
Authors: Swartz Wesley E.
Published: February 2008

Partial derivatives are given for efficient least‐squares fitting electron temperature, ion temperature, composition, or collision frequency to incoherent scatter spectra and autocorrelation functions without the need for massive off‐line storage requirements for function tables. The Debye length term is included explicitly in all appropriate functions so that no corrections need be made after the fitting sequence. One complete fit iteration (including the generation of the theoretical function and its derivatives, and including the construction and inversion of the matrix equation in the nonlinear least‐squares code) can be performed on an IBM 370 computer in 8 to 15 msec, depending on the number of data points required and the number of parameters being fit. Fitting most incoherent scatter data in parallel with data acquisition should now be feasible using these functions and the fast floating point hardware currently available.
STARE: A new radar auroral backscatter experiment in northern Scandinavia
Authors: Greenwald R. A. , Weiss W. , Nielsen E. , Thomson N. R.
Published: February 2008

As part of the ground‐based program for the International Magnetospheric Study (IMS), a new two‐station VHF radar auroral experiment, STARE, has been constructed in northern Scandinavia. Each of these stations can provide good spatial and temporal resolution measurements of the intensity and Doppler velocity of radar auroral irregularities within a 300,000 km2 scattering region. Approximately 230,000 km2 of these scattering regions are common to both radars and within this area it is possible to compare the backscattered signals observed by the two radars and to combine the Doppler data to derive the mean irregularity drift velocity. The drift velocity can ultimately be related to the ionospheric electric field. In this paper we describe the operation of these radars and the method by which the data are processed. We also describe the assumptions used in the drift velocity analysis and present some initial measurements supporting their validity. Finally, we present several examples of the STARE data during two periods of counterstreaming currents in the late evening auroral oval. The irregularity drift patterns are consistent with the expected electron drift patterns for these periods and, from these patterns, one can determine the two‐dimensional structure of the ionospheric electric field.
A new method of array evaluation applied to very long baseline interferometry
Authors: Seielstad G. A. , Swenson G. W. , Webber J. C.
Published: February 2008

A technique is presented for evaluating aperture synthesis arrays of radio telescopes. Results can be either quantitative or graphical. A numerical quality index specifies the weighted average uniformity with which an aperture can be synthesized. Application to very long baseline interferometry is illustrated by analysis of arrays of existing antennas in the United States with and without a new telescope in the Midwest (prairie states). The optimum location for a new telescope is within 87.0°–89.2° west longitude and 38.3°–39.5° north latitude.
Calorimetric measurements of microwave energy absorption by mice after simultaneous exposure of 18 animals
Authors: Allen Stewart J. , Hurt William D.
Published: February 2008

A multiple‐cell calorimetric system was constructed, and the experimental procedure for its use was developed. An associated data‐readout system is small, relatively inexpensive, and provides automated thermistor calibration, precise temperature measurements, and a printout of whole‐body SARs. One system was used to determine the SAR of each of 18 mice that were simultaneously exposed to 2.6‐GHz radiation.
Discussion: The blood‐brain barrier, cerebral circulation, and mathematical modeling
Authors: Justesen D. R.
Published: February 2008

There is little doubt that intense biological stress, whether thermal, mechanical, or chemical in origin, can increase the permeability of the blood‐brain barrier. There is increasing doubt that microwave fields that result in trivial elevations of brain temperature are affecting the tight junctions of the barrier. One cannot discount the data—Allan Frey and Kenneth Oscar and their respective colleagues did observe some kind of neurocirculatory response in their studies—but it appears now that altered cerebral circulation, not a loosening of junctions, was responsible for their findings. While one cannot dismiss the possibility of augmented transport (passive or active) that is unrelated to the mechanics of the tight junction, one can argue that suitable biological assays will have to be deployed before final answers are achieved.
An asymptotic formulation for SAR images of the dynamical ocean surface
Authors: Valenzuela G. R.
Published: February 2008

An analytical framework to aid in the interpretation and prediction of synthetic aperture radar (SAR) images of the ocean is developed. Using stationary phase integration, explicit results are derived for high‐resolution images including the cross‐section modulation on the ocean and the weighting by the curvature of the phase distortion introduced by the wave motion into the backscattered fields. The general formulation demonstrates that SAR images of the ocean are a ‘map’ of the stationary points on the surface as interpreted by SAR. The general formulation is applied to predict the SAR image of a simple two‐scale ocean model using Bragg scattering. This work suggests that image formation of the ocean is due to the amplitude process for light winds (large modulations) and by the phase distortion process for high wind speeds (small modulations). Numerical results are obtained for the stationary points of our simple ocean model, and for the first time an actual SAR image of the ocean is predicted. Inherent in this formulation also is the wave number distortion of the dominant wave of the ocean if its phase speed is not negligible compared to the radar platform velocity.
A review of radar observations of turbulence in the lower stratosphere
Authors: Crane Robert K.
Published: February 2008

The use of high‐power radars for the observation of air motions and the occurrence of turbulence in the vicinity of the tropopause is reviewed. A model is presented for the interpretation of radar observations from the thin turbulent layers which occur in the stable regions of the upper troposphere and lower stratosphere. Radar observations are shown to be potentially important for the study of the transport processes that operate between the troposphere and the stratosphere.
A review of radar studies of the middle atmosphere
Authors: Harper R. M. , Gordon W. E.
Published: February 2008

This paper reviews radar studies of the middle atmosphere at VHF and UHF frequencies. The mechanisms responsible for the scattering at both stratospheric and mesospheric heights are qualitatively discussed, and an attempt is made to evaluate the potential of the technique for inferring atmospheric parameters. A few applications of the technique to the study of atmospheric dynamics are then presented. Finally, some recommendations are made for future work.
An algorithm for retrieval of ocean surface and atmospheric parameters from the observations of the scanning multichannel microwave radiometer
Authors: Wilheit T. T. , Chang A. T. C.
Published: February 2008

The scanning multichannel microwave radiometer is a five‐frequency (6.6, 10.7, 18, 21, and 37 GHz), dual‐polarized microwave radiometer, which was launched in two separate satellites, Nimbus 7 and Seasat, in 1978. A formalism is developed which can be used to interpret the data in terms of sea surface temperature, sea surface wind speed, and the atmospheric content of water vapor and liquid water. It is shown with reasonable instrumental performance assumptions that these parameters can be derived to useful accuracies. Although the algorithms are not derived for use in rain, it is shown that at least token rain rates can be tolerated without invalidating the retrieved geophysical parameters.
Radio wave propagation in critical coupling media: Comparison of the generalized WKB and Katsenelenbaum's methods
Authors: Bahar E.
Published: February 2008

Adopting two basic concepts from the generalized WKB method, Katsenelenbaum claims to have obtained, in a simple manner, equations which would be more convenient and clear than the unwieldy and obscure results of the generalized WKB method and to have developed further these results. The purpose of this paper is to familiarize the reader with the versatility of the generalized WKB method and to examine in detail the claims by Katsenelenbaum. It is shown that all the coefficients in the generalized WKB equations (which are derived through a single transformation) have precise physical interpretations which can be verified independently. The generalized WKB method can be applied to dissipative or nondissipative media, with different types of turning points, for both vertically and horizontally polarized waves. This method has been used to obtain solutions to propagation problems for which no solutions are known in terms of listed mathematical functions, and it has also been applied to propagation in dielectric wave guides. Katsenelenbaum's analysis, which is restricted in scope, involves a series of transformations for the complex magnitude and (real) phase of the wave amplitudes. It is shown that there are errors in the coupling coefficients that appear in his equations and that they are not suitable at turning points, where most of the coupling between the upward and downward propagating waves occur. As a result his main result for the incremental reflection coefficient due to a small inflection in the permittivity profile is incorrect, even though he restricts his analysis to positive real (nondissipative) permittivity profiles.
Experimental study and theoretical model of high‐resolution radar backscatter from the sea
Authors: Lewis Bernard L. , Olin Irwin D.
Published: February 2008

The temporal characteristics of radar backscatter from the sea depend on the pulse width for surface resolutions less than about 20 m. While low‐resolution backscatter appears continuously noiselike, as the resolution is increased, the backscatter is punctuated by substantially quieter periods. This results in a noticeably ‘spikey’ characteristic. Measurements at 3 cm using several different pulse widths have been made near grazing incidence together with synchronized television views of the radar‐illuminated surface. These observations confirm that the largest backscatter is due to whitecaps. However, even the quieter periods disclose spikes, although they are about 3 orders of magnitude lower in power. A simple model of the salient scattering regions consists of a random collection of effective scattering centers which change in number with whitecap growth or decay. By comparing modeled surface realization with radar data it is concluded that the decorrelation time of the surface and scatterers within the surface are each about 10−2 s at X band.
A note on antenna models in a warm isotropic plasma
Authors: Singh Nagendra
Published: February 2008

The electron‐transparent and electron‐reflecting models of antennas in a warm isotropic plasma are reexamined. It is shown that a purely electrical treatment of both the models without an explicit use of the boundary condition on electron velocity yields the same results as those previously obtained through an electromechanical treatment. The essential difference between the two models is that for the electron‐reflecting model, fields are nonzero only in the exterior region, while for the electron‐transparent model, they are nonzero both in the exterior and interior regions of the antenna. This distinction helps in clarifying some misconceptions about these models of antennas in warm isotropic plasma.
Finite element computation of microwave scattering by raindrops
Authors: Morgan Michael A.
Published: February 2008

Initial attention is directed toward summarizing the finite element method (FEM) analysis technique. This is followed by a discussion of exact lossy offset sphere verification tests as well as comparisons with oblate spheroid scattering results, as presented in two previous independent publications. The FEM is then applied to the computation of scattering by the theoretical raindrop shapes as derived by Pruppacher and Pitter. Vertical and horizontal polarizations are considered for 30‐GHz plane waves, having both 90° broadside and 50° canted arrival angles. Tabulated and graphical bistatic scattering results are presented, comparing the Pruppacher and Pitter drops with equivolume oblate spheroids.
A method for calculating rain depolarization distributions on microwave paths
Authors: Kanellopoulos John D. , Clarke Richard H.
Published: February 2008

Predictions of the long‐term statistics for rain depolarization are presented for terrestrial path lengths up to 4 km and for any type of linear polarization. Assuming a log normal form for the rain rate statistics, an approximate Gaussian model is deduced for the final cross‐polarization isolation (XPI) distribution in decibels. The parameters of the normal distribution are related to the parameters of the radio link and the rain rate distribution. Applications of this conclusion to the estimation of radio outage time due to interference are also presented for various cross‐polarization levels.
Structures of atmospheric precipitation systems: A global survey
Authors: Houze Robert A.
Published: February 2008

A survey of atmospheric precipitation systems, ranging from mid‐latitude cyclones and thunderstorms to tropical cloud clusters, hurricanes, and monsoons, shows that all these systems are well described in terms of the rather traditional concepts of stratiform and convective precipitation. In stratiform precipitation, ice particles grow as they drift downward from high levels and pass through a well‐defined melting layer. In convective precipitation, particles begin growing at low levels and are carried upward by strong updrafts and fall out in intense vertically oriented showers. Modern observations show that all the major types of precipitation observed over the globe can be and often are combinations of these two basic types of precipitation. Extratropical cyclonic precipitation is basically stratiform. However, it is typically intensified in regions called rainbands. Some rainbands are highly convective features which move through the basic stratiform precipitation. In other rainbands, shallow convective cells occur aloft and help to enhance the basic stratiform precipitation. Mid‐latitude thunderstorms and tropical precipitation systems are basically convective. However, stratiform precipitation can develop in the middle to late stages of development. This type of stratiform precipitation, which can become quite extensive in both tropical and mid‐latitude systems, apparently arises as groups or successions of active convective cells leave ice particles aloft to settle downward gradually after the cells' updrafts die out.
Modeling attenuation and phase of radio waves in air at frequencies below 1000 GHz
Authors: Liebe Hans J.
Published: February 2008

Moist air is characterized for the frequency range 1–1000 GHz as a nonturbulent propagation medium described by meteorological parameters. An adequate spectroscopic data base for air consists of three terms: (1) resonance information for 29 H2O lines up to 1097 GHz and 44 O2 lines up to 834 GHz in the form of intensity coefficients and center frequency for each line; (2) an empirical water vapor continuum spectrum; and (3) a liquid water attenuation term for haze and cloud conditions. This data base is the heart of two computer programs which calculate and plot attenuation rates (in decibels per kilometer), refractivity (in parts per million), and refractive dispersion (in parts per million). The first covers the troposphere and requires pressure, temperature, and relative humidity as input data. The second addresses isolated line behavior in the mesosphere wherein the geomagnetic field strength H is an additional input parameter due to the Zeeman effect of the O2 molecules. Each oxygen line splits proportionally with H into numerous sublines, which are juxtaposed to form Zeeman patterns spread over a megahertz scale. Patterns of three main polarization cases are considered. Various typical examples for a model atmosphere demonstrate the utility of the approach, provide new information, and underline the serious role that water vapor plays above 120 GHz.
Review of recent progress in ionospheric predictions
Authors: Davies Kenneth
Published: February 2008

This paper reviews the state of ionospheric predictions following the Solar‐Terrestrial Predictions Workshop held in April 1979 at Boulder. The review includes: the various uses of the ionosphere, the physical bases, long‐term and short‐term variations, the techniques used for their prediction, and the current state‐of‐the‐art of ionospheric predictions. The different requirements of various users (system designers and planners) are discussed together with the needs for timely dissemination systems. Because ionospheric predictions and forecasts have been underway for many years, the advances have been of second order. The main advances include the incorporation of features such as the auroral oval, the magnetospheric cleft, the mid‐latitude trough, etc, the positions of which vary with local time and solar‐terrestrial activity. Other advances include: four‐dimensional models of the ionosphere, which yield electron density profiles useful in ray tracing; some new methods for predicting E layer and Es layer characteristics; transionospheric propagation, which requires prediction of total electron content; and scintillation characteristics. In recent years, advances have been made in the use of empirical and physical models of the ionosphere. Short‐term ionospheric forecasting has also progressed in recent years primarily through technological advances in data acquisition (e.g., satellite sensors), data processing (computers), and dissemination of information. Nevertheless, solar‐flare forecasting—a vital ingredient of magnetic/ionospheric storm forecasting—is still largely an art in which the forecasters' experience and skill, in recognizing and interpreting solar features, play the dominant role.
Coupled‐mode propagation in the ionospheric day‐night transition region
Authors: Überall Herbert , Nagl Anton , Seaborn J. B.
Published: February 2008

The height change of the ionosphere in the day‐night transition region leads to coupling and energy transfer between modes in propagating VLF and LF fields. This effect has often been evaluated on the basis of the ‘slab approximation,’ suppressing at the same time any reflected energy. In the present study, we treat this problem by the method of Pierce, in which reflections are properly taken into account as well as the gradual nature of the transition, hence leading to a more accurate evaluation of mode coupling. The details of the treatment are patterned after our previous application of the same method, and of our subsequent evaluation of mode coupling, for the problem of acoustic propagation in an under‐ocean sound channel.
Coherent wave attenuation by a random distribution of particles
Authors: Bringi V. N. , Varadan V. V. , Varadan V. K.
Published: February 2008

Coherent electromagnetic wave propagation in an infinite medium composed of a random distribution of identical, finite scatterers is studied. A self‐consistent multiple scattering theory using the T matrix of a single scatterer and a suitable averaging technique is employed. The statistical nature of the position of scatterers is accounted for by ensemble averaging. This results in a hierarchy of equations relating the different orders of correlations between the scatterers. Lax's quasi‐crystalline approximation is used to truncate the hierachy enabling passage to a homogeneous continuum whose bulk propagation characteristics such as phase velocity and coherent wave attenuation can then be studied. Three models for the pair correlation function are considered. The Matern model and the well‐stirred approximation are good only for sparse concentrations, while the Percus‐Yevick approximation is good for a wider range of concentration. The results obtained using these models are compared with the available experimental results for dielectric scatterers embedded in a host dielectric medium. Practical applications of this study include artificial dielectric (composites) and electromagnetic wave propagation through hydrometeors, dust, vegetation, etc.
Dependence of plasma line enhancement on HF pulse length and ionosphere preconditioning
Authors: Morales G. J. , Wong A. Y. , Santoru J. , Wang L. , Duncan L. M.
Published: February 2008

Recent ionospheric heating experiments at Arecibo demonstrate that the rapid growth of electrostatic plasma waves exhibits a remarkable dependence on HF pulse length and CW preconditioning. The effects are traceable to the generation of short‐scale distortions in the density profile near the plasma resonance.
An improved model for diversity gain on earth‐space propagation paths
Authors: Hodge D. B.
Published: February 2008

An empirical model has been generated to estimate diversity gain on earth‐space propagation paths as a function of earth terminal separation distance, link frequency, elevation angle, and angle between the baseline and the path azimuth. This analysis utilized 34 diversity experiments which have been conducted in Canada, England, Japan, and the United States during the past decade. The resulting model reproduces the entire experimental data set with an rms error of 0.73 dB. The separation distance dominates the dependence of the diversity gain. The dependence on link frequency is small but significant. No identifiable dependence on baseline orientation was found.
Theoretical considerations for inverse scattering
Authors: Sabatier Pierre C.
Published: February 2008

Inversion theory is a guide for handling inverse problems rather than a set of inversion techniques. The usual ill‐posed character of inverse problems has first to be dealt with by reassessing the concept of solution and by giving a detailed answer to the basic mathematical questions of the solutions existence, uniqueness, construction, stability, and approximation. But this is not sufficient. If the results are to be used by physicists, they should take into account the fact that no physical problem can be given a complete study separately from all others. In other words, investigating mathematical questions, and in particular describing the sets of solutions, must be done in such.a way that physical motivations and physical considerations are always apparent. These remarks are illustrated by several examples taken from scattering theory.
Double series expansion of the Green's function for a perfectly conducting tubular cylinder of finite length
Authors: Lee Hung‐Mou
Published: February 2008

The kernel of the integrodifferential equations for the excited surface current distribution on a tubular cylinder is expanded in a complete set of orthogonal functions. The expansion coefficients are obtained explicitly as power series of the dimensions of the cylinder. As this kernel is a particular form of the free‐space Green's function, power series representations for the Green's function in other forms are also presented to facilitate direct applications to other problems.
Radiation from a moving point charge in a drifting anisotropic plasma
Authors: Yasumoto Kiyotoshi
Published: February 2008

The radiation from a moving point charge in an anisotropic cold plasma drifting uniformly along a finite external magnetic field is investigated. It is assumed that the charge is moving uniformly in the direction of the external magnetic field. In general, the radiation consists of two waves, i.e., the ordinary and extraordinary waves. The effects of the drift motion of the background plasma on the radiation characteristics of both waves are discussed in detail. It is found that as the drift velocity of the plasma increases and approaches that of the moving source, the radiated energy of the ordinary wave is resonantly enhanced and the Cerenkov ray becomes concentrated in the direction of the motion of the source.
Development of a minicomputer atmospheric noise model
Authors: Sailors D. B. , Brown R. P.
Published: February 2008

A practical but simplified atmospheric noise model in universal time for 1‐MHz Fam usable in estimating system signal‐to‐noise ratios in microminicomputer‐based HF propagation prediction systems is presented. Numerical mapping techniques were used to represent worldwide atmospheric noise in 24 numerical maps: one for each of six 4‐hour UT time blocks and each of four 3‐month periods. This representation results in a minimum reduction by one fifth in the number of coefficients necessary in computer memory over that of an earlier model in which the map represented an entire 24‐hour day. The simpler expression for the median noise levels (Fam) results in significant savings in computer code and time. Several versions were produced, each with a different number of coefficients (number of harmonics) in the Fourier representation for each time block. The number of coefficients ranged from 192 coefficients per time block for the most accurate versions to 35 coefficients for the least accurate. The accuracies were determined by calculating the rms residual between values of Fam used to develop the model and the corresponding values computed from each model. The most accurate model had an average rms error for all times and seasons of 1.3 dB, whereas the least accurate had a rms error of 4.5 dB. During summer, the worst season, the most accurate model had a rms error of 1.4 dB, whereas the least accurate had a rms error of 5.6 dB. The International Radio Consultative Committee noise data used to generate the models had an average standard deviation of the error at 1 MHz of 5.4 dB and an error of 6.7 dB during summer; the numerical map in use in current HF prediction programs has an average rms error of 1.7 dB and an error of 2.0 dB during summer. The locations of the maximum absolute deviations of the models were confined to a small region in central Africa.
Scattering cross section modulation for arbitrarily oriented composite rough surfaces: Full wave approach
Authors: Bahar Ezekiel , Rufenach Clifford L. , Barrick Donald E. , Fitzwater Mary Ann
Published: February 2008

As a synthetic aperture radar scans different portions of a rough surface, the direction of the unit vector normal to the mean surface of the effective illuminated area (resolution cell) fluctuates. In this paper the modulation of the like and cross polarized scattering cross sections of the resolution cell are determined as the normal to it tilts in planes that are in and perpendicular to the fixed reference plane of incidence. By using the full wave approach, the scattering cross sections are expressed as a weighted sum of two cross sections. The first cross section is associated with scales of roughness within the effective illuminated area that are large compared to the radar wavelength, and the second cross section is associated with small‐scale spectral components within the resolution cell. Thus both specular point scattering and Bragg scattering are accounted for in a self‐consistent manner. The results are compared with earlier solutions based on first‐order Bragg scattering theory.
Some aspects of plasmapause probing by whistlers
Authors: Carpenter D. L.
Published: February 2008

A guide to the whistler literature is presented, with emphasis on whistler probing of plasma structure and motions near the plasmapause. Whistler probing experiments have identified several types of variations in plasmasphere radius with local time, including (1) variations of a few tenths of an earth radius over ∼ 20° longitude that appear to originate on the nightside of the earth during substorms; (2) a secondary maximum in plasmasphere radius near noon; (3) the duskside plasmasphere bulge. A variety of remarkable and as yet incompletely understood VLF propagation effects occur in the vicinity of the plasmapause, including a decrease in received whistler activity outside the boundary and unusual propagation features such as echoing above the half‐equatorial gyrofrequency on paths just outside the plasmapause. Whistlers provide important information on magnetospheric conditions during wave‐particle interaction periods, for example, on equatorial electron densities and path magnetic shell parameters needed in modeling studies of observed interactions.
High‐latitude ionospheric irregularities: A review of recent radar results
Authors: Hanuise C.
Published: February 2008

Ionospheric small‐scale irregularities are commonly detected with radar systems in both E and F regions from subauroral latitudes to the polar cap. In the E region, numerous observations performed at frequencies from HF to UHF have led to an understanding of the main features of the generating plasma instabilities. On the other hand, F region irregularities can only be detected with HF radars due to the aspect sensitivity of the echoes and the ionospheric refraction at these frequencies. Doppler studies have been performed only recently but have already shown that several well‐known plasma instability mechanisms can explain the observations. We review in this work the radar observations of these various natural irregularities with emphasis on the recent results and their implications for the theories of their generating mechanisms.
VHF radar signals scattered from the equatorial mesosphere
Authors: Royrvik Ola
Published: February 2008

Radio signals scattered from the equatorial mesosphere above Jicamarca, Peru have been studied. The scattered power level is dependent on look angle in the lower parts of the mesosphere. Indications are that this aspect sensitivity in the received signal cannot be adequately explained by specular reflection from stratified layers. Interferometer studies of the scattered signal have shown that there are structures in the mesosphere that have vertical velocity that varies in the horizontal direction within the antenna beam. The size of these structures is of the order of a few hundred meters. Considerations of vertical and horizontal scale sizes of these structures indicate that they are Kelvin‐Helmholtz billows drifting through the antenna beam.
Modeling of a tropical raindrop size distribution for microwave and millimeter wave applications
Authors: Ajayi G. Olalere , Olsen Roderic L.
Published: February 2008

The paper describes the modeling of the average raindrop size distribution measured at Ile‐Ife, a tropical station in South Western Nigeria. The new “method of moment regression” employed is a systematic one that has allowed a single lognormal function to be accurately fitted over the entire range of rain rates measured, a convenient result for rain attenuation and scattering applications. The Marshall and Palmer law, frequently used for such calculations, has been shown to be inadequate as a model for this tropical station, especially at the high rain rates important for communications systems design. This result suggests that the similar Laws and Parsons dropsize distribution currently adopted by the International Radio Consultative Committee for estimating rain attenuation from 1 to 1000 GHz may not be adequate over such a large frequency range in such tropical locations. Some comparisons are also made with the lognormal models and modeling approaches of other workers. The results confirm the utility of the rain rate parameterization used in the model for Ile‐Ife, while giving further support to the accuracy of the lognormal distribution.
Reflection of high‐frequency radio waves in inhomogeneous ionospheric layers
Authors: Davies Kenneth , Rush Charles M.
Published: February 2008

Formulas are given for the calculation of rays in model ionized layers in which the variation of the square of the refractive index is expressed separately in terms of the horizontal (x, y) and vertical (z) coordinates. Examples of three‐dimensional paths in linear‐parabolic layers are presented showing reflections in the horizontal, as well as the vertical, direction. To illustrate long‐distance transequatorial propagation the equatorial anomaly is simulated by two elliptic cylinders with axes parallel to the equator. Sample calculations show that in this model the ground range can increase as the angle of elevation at the ground increases.
Propagation of electromagnetic waves through geological beds in a geophysical probing environment
Authors: Chew W. C. , Anderson B.
Published: February 2008

In geophysical probing, a borehole is often drilled in the earth, and the environment probed with electromagnetic waves. When such a borehole transverses a complex geological environment, the effect of the inhomogeneous medium on the propagation of electromagnetic waves needs to be understood. In this paper we present two methods with which the effect could be assessed in a two‐dimensional inhomogeneous environment. The first technique illustrates a generalized Hankel transform method. The second technique shows the use of the semianalytic method to solve a two‐dimensional inhomogeneity problem. Comparison with the finite element method showed 200 times improvement in computational speed. The method is general and may be extended to application in the field of optics, microwaves and millimeter waves.
Simultaneous observation of precipitating atmosphere by VHF band and C/Ku band radars
Authors: Fukao Shoichiro , Wakasugi Koichiro , Sato Toru , Tsuda Toshitaka , Kimura Iwane , Takeuchi Norio , Matsuo Masuru , Kato Susumu
Published: February 2008

Multifrequency meteorological radar observations provide more detailed information on precipitation than single‐frequency observations. However, these observations have been generally limited to the microwave range. This paper describes a simultaneous observation of precipitating atmosphere by using the VHF band radar and the microwave C/Ku band radar. The frequency difference makes it possible to discriminate atmospheric scattering from precipitation scattering. The preliminary result shows that (1) VHF echoes stronger than those expected from the clear atmosphere condition are received from precipitating atmosphere and (2) the intensity of VHF scattering strongly depends on precipitation structures.
The MU radar with an active phased array system: 2. In‐house equipment
Authors: Fukao Shoichiro , Tsuda Toshitaka , Sato Toru , Kato Susumu , Wakasugi Koichiro , Makihira Tsuneichi
Published: February 2008

The MU (middle and upper atmosphere) radar of Japan uses an active phased array system. Each of 475 crossed three‐subelement yagi antennas in a circular array is provided with a 2.4‐kW peak power amplifier. This system configuration attains a very fast and almost continuous beam steerability at the total peak radiation power of 1 MW. A brief description of the in‐house equipment is presented herein.
Observations of mesospheric wind velocities: 1. Gravity wave horizontal scales and phase velocities determined from spaced wind observations
Authors: Meek C. E. , Reid I. M. , Manson A. H.
Published: February 2008

Horizontal scales and phase velocities of upper middle atmosphere (60–110 km) gravity waves determined from preliminary analysis of spaced wind observations obtained with a dual bistatic radar (Gravnet), based on and operated together with the Saskatoon MF radar are presented. In the observed period range of 10–100 min, horizontal scales increase from values of ∼44 km at 10 min to ∼211 km at 100 min, while observed phase speeds decrease from values of ∼72 m/s at 10 min to ∼34 m/s at 100 min. Typical rms perturbation velocities are ∼5 m/s. Calculation of intrinsic wave parameters indicates that in the intrinsic period range of 10–100 min, horizontal scales increase from values of ∼68 km at 10 min to ∼119 km at 100 min, with intrinsic phase speeds of ∼93 m/s at 10 min and ∼20 m/s at 100 min. The corresponding values of vertical wavelength are 30 km and 6 km, respectively.
Advanced sounding: 2. First results from an advanced chirp ionosonde
Authors: Poole A. W. V. , Evans G. P.
Published: February 2008

A BR Communications “chirp” ionosonde has been modified to allow the measurement of the phase of ionospherically reflected echoes. The use of a dual‐channel receiver and microprocessor‐based control allows phase comparisons of temporally and spatially diverse echoes from which Doppler velocity, angle of arrival, and polarization mode can be evaluated, in addition to group range and amplitude. A test study of the ionosphere at Grahamstown is described.
A research‐oriented ionosonde with directional capabilities
Authors: Bowman G. G. , Hainsworth D. W. , Dunne G. S.
Published: February 2008

A recently developed ionosonde (called a disonde) designed for low‐budget research projects, is described briefly. It is capable of measuring the comparative signal strengths and the angles of arrival of signals returning from the ionosphere. In addition, phase‐path information is available. The capabilities of the system are illustrated by some sample recordings and there is some discussion on these recordings. In addition, the capacity of this system (and a similar system which it replaced) to obtain research results is illustrated by discussing some results already produced.
Airborne measurements of the ocean radar cross section at 5.3 GHz as a function of wind speed
Authors: Feindt Folkart , Wismann Volkmar , Alpers Werner , Keller William C.
Published: February 2008

Measurements of the normalized radar cross section (NRCS) at 5.3 GHz (C band) of the sea surface as a function of wind speed and direction are presented. The data were obtained by a coherent scatterometer mounted on a small two‐engine airplane performing circle flights over the Atlantic. Our data show that the wind speed exponent at 5.3 GHz is typically 20% smaller than at 13.9 GHz (Ku band). Furthermore, the upwind/crosswind ratio of the NRCSs at C band is typically 20% smaller, and the upwind/downwind ratio typically 30% smaller than at Ku band.
Effective propagation constants in dense random media under effective medium approximation
Authors: Zhu P. Y. , Fung A. K. , Wong K. W.
Published: February 2008

The effective medium approximation is applied to study the effective propagation constants in a dense random medium. The dyadic Green's function is introduced to establish the effective medium approximation formalism for electromagnetic waves. The multiple scattering equations and the Lippmann‐Schwinger equations for the transition operator are obtained in the configuration average form. The dispersion equations of multiple scattering is derived by using a standard method in quantum mechanics. To obtain an expression for the effective propagation constants the matrix elements of the configuration average dyadic transition operator are calculated in momentum representation. Numerical illustrations are carried out to demonstrate the difference in the effective propagation constants between the use of this approximation and the well‐know quasicrystalline approximation. A comparison is made with measured loss tangent in dry snow.
Reflection of electromagnetic plane waves from a moving ferrite surface
Authors: Mueller R. S.
Published: February 2008

The power reflection coefficient is derived for an electromagnetic H wave incident on a semi‐infinite magnetized ferrite medium, moving perpendicular to the plane of incidence. Both the speed of the moving media and the anisotropy of the ferrite contribute to hybrid modes of the reflected and transmitted electromagnetic field components. Double refraction at an anisotropic boundary is not new but what is interesting in this article is the effect of the speed of the moving ferrite on both the propagation constants and the power reflection coefficient.
A general theory of the interaction of electromagnetic waves with isotropic, horizontally layered media1 (Summary)
Authors: Walsh J. , Donnelly R.
Published: February 2008

A general formulation of the problem of determining the electromagnetic field resulting from a finite electromagnetic source placed above a horizontally layered isotropic medium is presented. A solution to the problem is given in terms of two‐dimensional Fourier transforms. The solution has the following properties: the source field is arbitrary, the resulting electric field intensity is found directly as a function of the source field intensity, and the boundary conditions evolve directly from the technique in the form of auxiliary equations.
Propagation of surface waves on a thin resistive sheet or a coated substrate
Authors: Richmond Jack H.
Published: February 2008

This paper considers the surface waves which can propagate on a thin homogeneous dielectric slab of infinite extent, with thickness d, permittivity ε1, and conductivity σ when the ambient medium is free space. Contour plots are included to present numerical data on the surface wave parameters (attenuation constant and phase velocity) over a range of thickness d and surface resistance Rs where Rs = 1/(σd). Data are given for surface waves having parallel polarization, as well as those having perpendicular polarization. The thin resistive sheet is also available as a coating on one surface of a low‐loss dielectric substrate. Numerical data are presented for this structure as well, and it is found that the surface wave properties are similar on the two forms with one exception. The zero‐order surface waves propagate on the homogeneous resistive sheet even when the frequency, the thickness, or the surface resistance is reduced without limit. On the coated substrate, however, the zero‐order surface wave with perpendicular polarization cuts off and disappears when Rs is reduced to a certain small value. As it is reduced still further, the zero‐order mode is replaced with a succession of higher‐order modes.
Wave packets of lateral waves due to a vertical monopole: Experiment and theory
Authors: Brown M. F.
Published: February 2008

A wave packet or pulse comprised of a distribution of single‐frequency lateral waves due to a vertical monopole is analyzed. The Fresnel‐integral terms in the Fourier transform of a general formula for E2z(ρ, z, ω), the vertical electric‐field component in air, are represented using confluent hypergeometric functions. A wave packet of lateral waves is calculated for a pulsed short bare monopole at the boundary between a pair of Earth's material regions and compared with experimental measurements.
An approximate method for solving the vector radiative transfer equation in discrete random media
Authors: Ito Shigeo , Oguchi Tomohiro
Published: February 2008

Analytical expressions for the specific intensity of circularly polarized optical waves propagating in discrete random media are obtained by approximately solving the vector radiative transfer equation. The proposed method extends the solution for scalar waves to include polarization effects and facilitates calculations of multiply scattered incoherent intensities over a wide range of optical depths. To derive simple analytical solutions for given particle sizes, we first separate the first‐order solution or small‐angle solution from the solution to be obtained. We then expand the remainder, which includes the higher order multiple scattering, in terms of the generalized spherical functions. The first two terms of the expansion are retained, and the resulting vector diffusion equation is solved analytically. Approximate solutions for both the copolarized and cross‐polarized specific incoherent intensities are shown to be in good agreement with numerical solutions for almost arbitrary optical depths.
A comparative numerical study of several techniques for modeling a horizontal wire antenna over a lossy half‐space
Authors: Karwowski Andrzej , Michalski Krzysztof A.
Published: February 2008

The electric‐field integral equation for the current on a thin, horizontal wire antenna radiating above a lossy half‐space is solved by the method of moments, with the effect of interface included via the Sommerfeld integrals, the well‐known reflection‐coefficient approximation and the high‐contrast approximation. A modified implementation of the reflection‐coefficient approximation is suggested, which makes this technique reasonably accurate for antennas near the interface. A comparison is made between the methods for several cases of practical interest. The high‐contrast approximation is shown to be superior to the reflection‐coefficient approximation.