bluuebunny/crossref_metadata_2025 huggingface dataset:
Radar measurements of wind at Kwajalein
Authors: Crane Robert K.
Published: February 2008

The high‐power ALTAIR and TRADEX radars were used for high‐resolution wind measurements. Thin turbulent layers were observed in the stably stratified regions of the troposphere. The layers had thicknesses of the order of 100 m and vertical spacings of several hundred meters. Wind profiles were generated by interpolation using observed velocities in the layers. A detailed comparison between a wind profile constructed by using scattering from refractive index fluctuations produced by turbulence and a profile obtained from high‐resolution balloon observations showed good agreement between the two methods of observation. On the basis of the comparison, the uncertainty (accuracy) of the mean wind profile derived from turbulence measurements was estimated to be of the order of 0.3 m/s for each of the Cartesian horizontal wind components.
A model for attenuation by precipitation on a microwave earth‐space link
Authors: Misme Pierre , Waldteufel Philippe
Published: February 2008

A prior study shows that a precipitation model based on the concept of rain cells permits one to predict in a satisfactory way the attenuations occurring on a line‐of‐sight link at frequencies superior to a few gigahertz. The present work aims to extend this model for slanted paths. To begin with, various types of precipitation are identified. Then the effect of altitude on attenuation coefficients is looked into, allowance being made for changes in air density and temperature. Finally, the geometry of the model is adapted to slanted paths. Test comparisons reveal a fair agreement between observations and model predictions. A computing program permitting rapid calculations to be made is provided in an appendix.
Coherent wave propagation through a sparse concentration of particles
Authors: Brown Gary S.
Published: February 2008

The Foldy‐Twersky integral equation (FTIE) for the coherent field propagating through a sparsely populated, random, uncorrelated distribution of particles is solved to show that the average field inside any particle is a plane wave. This result is in conflict with the average single‐particle integral equation, which dictates that the average internal field cannot, in general, be a plane wave. The conflict is resolved by examining the conditions under which the average single‐particle‐scattering amplitudes resulting from the two integral equations are nearly equal. The major implications of this analysis are that (1) the classical Foldy result for the propagation constant of the coherent field follows directly from the FTIE and its implicit assumptions regardless of the electrical or physical properties of the particles and (2) the FTIE only applies to situations where the effects of multiple scattering upon the coherent field are negligible.
Ground‐based microwave radiometric retrieval of precipitable water vapor in the presence of clouds with high liquid content
Authors: Westwater E. R. , Guiraud F. O.
Published: February 2008

A dual‐channel microwave radiometer that measures precipitable water vapor and cloud liquid was operated during the 1979 Severe Storms and Mesoscale Experiment (Sesame). Conventional retrievals of vapor in the presence of clouds with high liquid content were not satisfactory. To correct these retrievals, an adaptive retrieval algorithm is developed and applied to the Sesame data. During clear conditions, or conditions of light clouds, the new recoveries are quite close to those obtained by conventional statistical inversion; however, during heavy liquid‐bearing clouds the recovered vapor agrees better with radiosonde data.
The dielectric properties of soil‐water mixtures at microwave frequencies
Authors: Wang J. R.
Published: February 2008

Recent measurements of the dielectric constants of soil‐water mixtures have shown the existence of two frequency regions in which the dielectric behavior of these mixtures was quite different. At the frequencies of 1.4–5 GHz there was strong evidence that the variation of the dielectric constant ε with water content W depended on soil type. While the real part of ε, ε′, for sandy soils rose rapidly with the increase in W, ε′, for the high clay content soils rose only slowly with W. As a consequence, ε′ was generally higher for the sandy soils than for the high clay content soils at a given W. On the other hand, most of the measurements at frequencies < 1 GHz indicated the increase of ε with W to be independent of soil types. At a given W, ε′ (sandy soil) ≅ ε′ (high clay content soil) within the precision of the measurements. These observational features could be satisfactorily interpreted in terms of a simple dielectric relaxation model suggested by Schwarz (1962), with an appropriate choice of the mean relaxation frequency ƒm and the range of the activation energy β. It was found that smaller ƒm and larger β were required for the high clay content soils than for the sandy soils in order to be consistent with the measured data. These requirements on ƒm and β were strongly supported by the observed dependence of the soil surface area per unit weight on the soil types.
Input impedance of vertical dipoles near a lossy half space
Authors: Metwally Ahmed D. M. , Mahmoud Samir F.
Published: February 2008

Exact solutions are derived for the input impedances of vertical magnetic and electric short dipoles over a lossy half space. The exact solution is expressed as a simple formula and a remainder, which takes the form of a rapidly converging series. Reduction to available approximate solutions in the literature under conditions of large dipole heights, large refractive index of the half space, or both is demonstrated. The derivation of new simple formulae that tend to the exact solutions when the refractive index of the half space approaches both limits of infinity or unity is of particular interest. Numerical examples are presented and compared with published results.
Estimation of the propagation delay through the troposphere from microwave radiometer data
Authors: Moran J. M. , Rosen B. R.
Published: February 2008

Uncertainty in the estimate of the microwave propagation delay through the troposphere is a principal limiting factor to the accuracy of measurements made with very long baseline interferometry. This uncertainty is due primarily to tropospheric water vapor, the total amount and vertical distribution of which are variable. Because water vapor both delays and attenuates microwave signals, the propagation delay, or wet path length, can be estimated from the microwave brightness temperature near the 22.235‐GHz transition of water vapor. We analyzed the data from a total of 240 radiosonde launches taken simultaneously at Chatham, Massachusetts, Albany, New York, and Portland, Maine, in 1974. Estimates of brightness temperature at 19 and 22 GHz and wet path length were made from these data. The wet path length in the zenith direction could be estimated from the surface water vapor density to an accuracy of 5 cm for the summer data and 2 cm for winter data. Using the brightness temperatures, the zenith wet path length could be estimated to an accuracy of 0.3 cm. Two dual‐frequency radiometers constructed by the National Radio Astronomy Observatory (NRAO) were rebuilt and used to determine how accurately the path length can be predicted from real radiometry data. These radiometers were capable of measuring the difference in the brightness temperatures at 30° elevation angle and at the zenith to an accuracy of about 1°K. In August 1975, 45 radiosondes were launched from Haystack Observatory over an 11‐day period. Brightness temperature measurements were made simultaneously at 19 and 22 GHz with the NRAO radiometers. The rms error for the estimation of wet path length from surface meteorological parameters was 3.2 cm, while from the radiometer brightness temperatures, the rms error was 1.5 cm.
Note on the Kirchhoff rough surface solution in backscattering
Authors: Fung A. K. , Eom H. J.
Published: February 2008

The purpose of this note is to demonstrate that an existing Kirchhoff solution by Beckmann and Spizzichino for the average backscattered power from a randomly rough surface correctly provides frequency dependence for a computer‐generated surface. In addition, it also approaches the geometrical optics solution in the high‐frequency limit. Results indicate that for backscattering near vertical incidence this solution is more general and useful for applications than the geometric optics solution (given by (5) in section 2).
Scattering of electromagnetic waves from random media with strong permittivity fluctuations
Authors: Tsang L. , Kong J. A.
Published: February 2008

All previous random media theories that have been applied to microwave remote sensing applications are only valid for cases of weak fluctuations of dielectric constant. By taking into proper account the singularity of the dyadic Green's function in the renormalization method, the low‐frequency limit of vector electromagnetic wave scattering from a random medium with large variance of permittivity function is studied. The strong fluctuation random theory is then applied to a ‘discrete scatterer’ problem in which the permittivity can assume only two values. It is then shown that the results of the strong fluctuation theory are consistent with those derived from discrete scatterer theory for all values of dielectric constants of the scatterers. Numerical results of the effective permittivity are illustrated for random media with isotropic and anisotropic correlation functions. It is shown that the results of the weak fluctuations theory differ significantly from those of the strong fluctuation theory. The second moment of the field in the backscattering direction is calculated using the distorted Born approximation and illustrated using parameters typically encountered in microwave remote sensing of vegetation.
Theorem on the maximum absorption of electromagnetic radiation by a scattering object of bounded extent
Authors: de Hoop A. T.
Published: February 2008

The absorption of electromagnetic energy by matter distributed in a predefined loading domain of finite extent is investigated in its general aspects. It is shown that under variation of the medium properties in the loading domain, the electromagnetic energy absorbed by the load can, at least in principle, be maximized. The maximization condition serves as constitutive relation, in a nonstandard form, for the relevant medium. The condition is a configurational property and is independent of the distribution of the sources that generate the exciting electromagnetic field.
The inverse medium (or inhomogeneous medium remote probing) problem and a closed‐form inverse scattering solution to the medium synthesis problem
Authors: Stone W. Ross
Published: February 2008

The exact inverse scattering theory of Bojarski is reviewed. It is shown how this theory can be applied to the problem of determining the generalized refractive index distribution of an inhomogeneous medium from measurements of the fields scattered by the medium. Questions of uniqueness, incomplete knowledge of the measured fields, and noisy measurements are discussed. The relationship between holography and inverse scattering is examined. The conditions under which holography can yield information about a scatterer, and the amount of information obtainable, are derived. The exact theory also applies to the general class of medium synthesis problems. An extension of the theory is presented which provides an exact, closed‐form solution to a wide class of synthesis problems.
The importance of coherence in inverse problems in optics
Authors: Ferwerda H. A. , Baltes H. P. , Glass A. S. , Steinle B.
Published: February 2008

A summary of current inverse problems of statistical optics is presented together with a short guide to the pertinent review‐type literature. The retrieval of structural information from the far‐zone degree of coherence and the (time‐averaged) intensity distribution of radiation scattered by a superposition of random and periodic scatterers is discussed.
Electromagnetic remote sensing of the temperature profile in a stratified medium of biological tissues by stochastic inversion of radiometric data
Authors: Edenhofer P.
Published: February 2008

Some results are presented from investigations studying the process of inversion of multispectral microwave radiometric data to determine the subcutaneous temperature distribution in biological tissues. A transmission line concept is used to model a three‐layer planar configuration as typical for the tissue composition of a human upper arm (skin‐fat‐muscle). Computer‐simulated data are generated at 3, 5, and 10 GHz using the Rayleigh‐Jeans approximation and the radiative transfer approach. Starting from a characteristic temperature profile, the radiometric data set is inverted to yield reconstructed values of the profile. Using the process of stochastic inversion, it is shown how to compromise between penetration depths, temperature resolution, and confidence level of the temperature values retrieved.
A hybrid MM‐GTD technique for the treatment of wire antennas near a curved surface
Authors: Henderson L. W. , Thiele G. A.
Published: February 2008

The method of moments ((MM) and the geometrical theory of diffraction (GTD) are formally combined into a hybrid MM‐GTD technique. Wire type antennas are treated by the method of moments and their interaction with a large curved surface is accounted for through the GTD. Thus the mutual coupling between two dipoles in the presence of an infinitely long, perfectly conducting elliptic cylinder is analyzed for various orientations of the dipoles with respect to each other and with respect to the cylinder. Results are compared with an independent theory and with experimental data. Excellent agreement is shown, thereby demonstrating the accuracy of the hybrid MM‐GTD technique.
Frequency scaling of rain attenuation at centimeter and millimeter waves using a path‐averaged drop size distribution
Authors: Ihara Toshio , Furuhama Yoji
Published: February 2008

The applicability of several frequency scaling methods of rain attenuation is discussed based upon the cumulative distributions of rain attenuations at 81.8, 34.5, and 11.5 GHz measured in the same horizontal propagation path of 1.3 km for 1 year. A frequency scaling method (MISD) based upon the concept of a path‐averaged raindrop size distribution N−(D) is newly applied to statistical prediction of the attenuation and is shown to be effective at millimeter wave bands where attenuation changes remarkably depending upon the raindrop size distribution, although the usefulness of MISD has been verified for time‐sequential data. The size distribution determined from the statistical data at the three frequencies is given by N−(D) = 26,000 R−(−0.294)exp [−(5.6 R−0.283D)], 10 ≤ R− ≤ 70 mm/h, where R− is the path‐averaged rainfall rate in millimeters per hour and D is the diameter of a raindrop in millimeters. Frequency dependence of attenuation calculated by using this size distribution shows that the prediction of rain attenuation based upon the Laws and Parsons size distribution results in an underestimation at frequencies above 80 GHz.
Turbulence in deep radio occultations
Authors: Haugstad Bjarne S.
Published: February 2008

We investigate here the effect of turbulence in the focal region of spherical or weakly oblate refracting bodies by establishing weak scattering results for the scintillation index and power spectrum. If the spacecraft is a distance r⊥ from the focus in the plane of the sky, we find that initial focusing alone yields an increase in scintillation index proportional to r⊥−5/6. Still closer to the focus, where the semimajor axis of the atmospheric Fresnel zone has exceeded the outer scale of turbulence L0, the scintillation index reaches a plateau. In this regime of maximum scintillations, turbulence of the strength found above the earth's boundary layer, when scaled to the conditions of the focal evolute crossing during the recent Voyager 1/Jupiter encounter, yields a formal weak scattering scintillation index of ≃ 6 · 101. Such strong (saturated) scintillations may have contributed to the unsuccessful attempt to identify the evolute crossing in this case. An approximate calculation also shows that for reasonable solar‐spacecraft distances and probing wavelengths, irregularities in the solar corona plasma strongly affect both the maximum intensification and the signal coherence close to the gravitational focus of the sun. Use of extremely small wavelengths (≤10−4 m) seems necessary to achieve near optimal conditions for practically achievable solar‐spacecraft distances. The temporal power spectrum of the intensity scintillations is found to be band‐limited close to a focus, with both the bandwidth and the lower frequency boundary increasing rapidly as the focus is approached.
Bistatic radar reflectivities of Pruppacher‐and‐Pitter form raindrops at 34.8 GHz
Authors: Awaka Jun , Oguchi Tomohiro
Published: February 2008

This paper presents the bistatic radar reflectivities of raindrops with a real, nonspherical drop shape given by Pruppacher and Fitter. Calculations are carried out at 34.8 GHz. Comparison is made between the bistatic radar reflectivities of deformed raindrops and those of spherical raindrops. It is found that the difference between reflectivities is pronounced when the bistatic radar reflectivities are small.
Experimental investigation of ambient electromagnetic noise from 1.0 to 4.0 kHz in Italy and Norway
Authors: Dinger Robert J. , Meyers William D. , Davis John R.
Published: February 2008

Measurements have been made at sites in Italy and Norway of the spectral noise density, amplitude probability distribution (APD), and spectral content of ambient noise from 1.0 to 4.0 kHz. Analysis of the 120 days of recorded data included investigation of the noise diurnal variation, comparison of the APD's with two atmospheric noise models, and time domain excision of noise impulses to assess the reduction in noise achievable by nonlinear processing. The analysis of the diurnal variation suggested the existence of a large propagation anisotropy in the nighttime earth‐ionosphere waveguide at a frequency of 3 kHz, with east‐to‐west attenuation significantly lower than north‐south attenuation. Comparison of the APD's with the Field‐Lewenstein model and the Middleton model of atmospheric noise generally showed satisfactory agreement with both models. Processing of the recorded noise by clipping the large atmospheric noise impulses lowered the spectral noise density in Italy by an average of 6.7 dB (winter) and 3.3 dB (summer). A distinct spectral minimum in the vicinity of 3 kHz was always observable in Norway but was frequently not observable in Italy. The statistical distribution of the frequency of the Norway minimum had a peak near 3.6 kHz.
A UHF cross‐modulation D region heating experiment with aeronomic implications
Authors: Sulzer M. P. , Mathews J. D. , Tomko A. A.
Published: February 2008

A unique wave interaction experiment employing the Arecibo 2.0‐MW, 430‐MHz radar as disturbing or heating transmitter has been performed. The purpose of this experiment was to evaluate UHF electron heating effects and to extend the wave interaction technique to higher than usual heights (˜100 km). The heater beam used was much smaller in angular extent than the probing or wanted beam, yielding an unfavorable geometric weighting factor and making the experiment very sensitive to reflection properties of the E region. Nonetheless, wave interaction was easily detected using a completely digital signal processing technique. Comparison of experimental wave interaction results with a numerical model of the process indicates that lower thermosphere electron cooling rates are possibly too small by a factor of 4. Power spectra of the 3.155 MHz wanted signal (reflected from E region) amplitude fluctuations for ‘quiet’ and ‘disturbed’ days are also given.
Inference of refractivity profiles by satellite‐to‐ground RF measurements
Authors: Anderson K. D.
Published: February 2008

A technique is described to infer an estimate of the tropospheric radio refractive index distribution from earth‐based observations of a satellite‐borne beacon. This technique, known as the direct inference technique (DIT) predicts the refractivity profile by comparing the observed interference pattern, created as the satellite moves through low elevation angles, to patterns generated from a family of assumed refractivity profiles. It is shown that DIT correctly predicts the ducting environment for 12 of 22 satellite‐to‐ground RF measurements made during July and August 1978. Although the inferred profile geometry can differ significantly from the refractivity profile measured by an upper air sounding, the technique is moderately successful in predicting whether the true profile contains a ground‐based or elevated duct. However, the overall reliability of predicting the dominant features of the duct (e.g., refractive gradient through the trapping layer, top height of the duct) is not adequate for operational usage.
Modulation frequency wave generation by nonlinear interaction of high‐power RF radiation
Authors: Harker K. J. , Crawford F. W.
Published: February 2008

A theory has been developed to explain the observation at a ground station of a signal at the modulation frequency of a high‐power HF signal transmitted 180 km to the north of the station (Getmantsev et al., 1974). The theory is based on the following model. A modulated wave traveling in the ordinary mode traverses upward into the ionosphere and is reflected. At a short distance below the reflection layer, the carrier and one of the sidebands of which the modulated wave is composed interact to produce a whistler wave. The whistler generated by this mixing process then propagates to the ground where it is detected at the original modulation frequency.
Pulse‐to‐pulse correlation in satellite radar altimeters
Authors: Walsh Edward J.
Published: February 2008

Pulse‐to‐pulse correlation in satellite radar altimeters is examined to determine if range jitter in future altimeters could be reduced by increasing the pulse repetition frequency (PRF). Data from the Skylab radar altimeter is analyzed and compared with rules of thumb and the results of a Monte Carlo simulation. Altimeter range tracker configurations are reviewed and a simple curve is developed for the PRF below which decorrelation is assured. An adaptive PRF for future altimeters is recommended to conserve mission power while optimizing data collection during high‐sea states.
Automatic calculation of electron density profiles from digital ionograms: 2. True height inversion of topside ionograms with the profile‐fitting method
Authors: Xueqin Huang , Reinisch Bodo W.
Published: February 2008

An efficient electron density profile inversion algorithm is developed for use on automatically scaled digital topside ionograms. The profile‐fitting method described here models the topside ionosphere with a single polynomial, a method particularly suited for autoscaled data because it is not too sensitive to a certain amount of scatter in the h′(ƒ) data and it makes use of ordinary and extraordinary ray echoes. The program was applied to input data consisting of O and X trace segments obtained from automatic scaling of a number of digitized ISIS ionograms. It is shown that fully automatic calculation of the topside electron density profiles from digital topside ionograms can be performed in less than 10 s on a Cyber 71 computer.
On the analysis and interpretation of spaced‐receiver measurements of transionospheric radio waves
Authors: Rino C. L. , Livingston R. C.
Published: February 2008

A correlation analysis method developed by Armstrong and Coles has been applied to spaced‐ receiver data from the Wideband satellite. The method permits simultaneous estimation of the anisotropy and true drift of the diffraction pattern. The scintillation theory is applied to interpret the measured variations in anisotropy and pattern drift. The results show that in anisotropic media, there is a complicated interplay between apparent drifts and the anisotropy of the diffraction pattern that must be accommodated in spaced‐receiver data analyses. The method has been applied to verify the L‐shell aligned, cross‐field anisotropy of F region auroral zone irregularities.
Scientific and hygienic issues in biological research on microwaves: Toward rapprochement between East and West
Authors: Justesen Don R.
Published: February 2008

Many issues and controversies separate the experimental radiobiologist and the hygienist from the goal of attaining a concordant view of biological effects of exposure to microwaves and other radio‐frequency electromagnetic (RFEM) fields. Although the strongest notes of discord are struck by East‐West differences (e.g., recommended limits with respect to exposure of human populations to RFEM fields are generally orders of magnitude more stringent in the USSR than in the U.S.), there are discordant notes as well within national boundaries. To the end of achieving a better scientific grasp of problems and solutions the author discusses selected issues under the headings of semantics, tactics, logistics, and strategy. Among the topics discussed are problems of communication, physical measurements in relation to laboratory and regulatory practice, pitfalls of interdisciplinary research, and research needed to achieve ecologically valid data.
Eddy currents induced by RF magnetic fields in biological bodies
Authors: Lee Jen‐Hwang , Chen Kun‐Mu
Published: February 2008

A new theoretical method for determining the electric field or the eddy current induced by a uniform RF magnetic field or a beam of RF magnetic field in a biological body of rotational symmetry is presented. The body is subdivided into a number of circular rings with various radii and cross‐sectional areas. The induced electric field or eddy current in each ring is then numerically determined on the basis of the theory of vector potential and the moment method. Numerical examples are given, and the results based on the present theory are found to deviate significantly from the often used, quasi‐static solutions. An experiment was conducted to measure the electric fields induced by a UHF magnetic field in phantom biological models. The theory was verified by the experiment and the existing theoretical results.
Thermographic analysis of waveguide‐irradiated insect pupae
Authors: Olsen Richard G. , Hammer Wayne C.
Published: February 2008

Pupae of the insect Tenebrio molitor L. were thermographically imaged during waveguide irradiation through longitudinal slots. T. molitor pupae have been subjects of microwave‐induced teratology for a number of years, but until now the smallness of the insect has prevented detailed dosimetry. High‐resolution thermographic imaging equipment was used to obtain the magnitude and spatial distribution of absorbed microwave energy at three frequencies, 1.3, 5.95, and 10 GHz. The detail of the thermal images obtained is sufficient to show the differential heating of structures as small as a single insect leg. Results show that the electrical properties of the head, thorax, and abdomen are sufficiently different to seriously impair the usefulness of any theoretical dosimetric model of homogeneous composition. Some general features of correlation with a slab model in waveguide are given.
The response of mouse mammary tumor to microwave heating at 2.45 GHz
Authors: Robinson J. Eugene , Cheung Augustine Y. , Harrison George H. , Samaras George
Published: February 2008

We have conducted experiments quantitating the effects of microwave heating on the regrowth time of mammary tumors implanted on the flank of C3H mice. To minimize the size and shape dependence of the microwave heating, we immersed the tumors in tissue equivalent bolus and treated them with parallel opposed transverse electromagnetic applicators. The animals were not anesthetized during microwave irradiation. Two types of bolus were used: a semisolid gel and a temperature‐controlled solution of isotonic saline and alcohol. During tumor irradiation in the gel, temperatures were monitored adjacent to, but not inside of, the tumors. During irradiation in the liquid bolus, tumor temperatures were monitored for one out of each six animals per data point. Data from tumors treated in the semisolid bolus yielded lower regrowth slopes and higher intercepts than those heated by water baths. Both findings can be interpreted as indicating thermal nonuniformity of the microwave‐heated tumors. Plots of thermal sensitivity versus temperature are parallel to, but displaced from, those determined with water bath heating, suggesting that at least some small part of the tumor treated with microwaves was about 1°C lower than the target temperature. Tumors which were heated in the liquid bolus yielded regrowth curves consistent with homogeneous heating. A plot of thermal sensitivity versus temperature suggests that all parts of the tumors were at or slightly above target temperature. Regrowth time of the probed tumors was significantly greater than that of tumors in which no probe was present during microwave irradiation.
Electrical transient analysis for disseminated mineralization
Authors: Wait James R.
Published: February 2008

We present a short analysis of the electric transient response when a steady current in a frequency dispersive medium is interrupted. The model is a homogeneous host rock medium with a loading of spheroidally shaped metal ore grains. The latter can have a polarizable interface with the adjacent electrolyte. It is shown that the rate of decay of the electric field is more rapid for the smaller particles. Also, there is an optimum particle size if the area under the decay curve is to be maximized.
Inverting a dispersive scene's side‐scanned image
Authors: Harger Robert O.
Published: February 2008

Given the side‐scanned image of a scene characterized by a random, time‐varying reflectivity density, evolving in accordance with a dispersion relation, the linear, minimum mean‐square error estimator of the scene at a given time is found. The data are corrupted by additive, ‘white’ noise. The minimum mean‐square error does not depend on whether the real or the synthetic aperture technique is used or whether in the synthetic case, the ‘signal film’ or ‘complex’ image is the data. The effect of finite scanning velocity υ is to replace the white noise of spectral density ηo with a ‘colored’ noise of spectral density | ‐ υgx(k)/υ|ηo where υgx(k) is the group velocity directed along υ it is assumed that υgx(k)/υ < 1. The anomalous behavior when υgx (k) exceeds υ is noted.
Precision phase comparison via communication satellites using loop‐back tones
Authors: Yen J. L. , Lithopoulos E.
Published: February 2008

Phase comparison of remote oscillators by tone transmission via communication satellites is considered. By introducing loop‐back tones at each station to produce a virtual downlink frequency equal to the uplink frequency, the path phase between two stations is made independent of the direction of transmission. All nondispersive path effects are then canceled by using reverse path transmissions. The effective period for phase comparison is the mean period of the uplink and downlink transmissions. This represents a 2–order of magnitude increase in effective frequency over the previously used two‐tone method. The precision of phase comparison via satellites is now limited by uncertainties of ionospheric effects.
Radar cross section of a lightning element modeled as a plasma cylinder
Authors: Mazur Vladislav , Doviak Richard
Published: February 2008

The radar cross section of a lightning element modeled as a finite length plasma cylinder at an oblique angle of incidence is offered. The model is based on the exact solution of Maxwell's equations for a dielectric cylinder of Infinite length. Assumptions are made about reflection and transmission at joints between neighboring lightning elements. The proposed model is valid for cylinders with radii that are a small fraction of wavelength.
Oscillating bipolar electric field changes due to close lightning return strokes
Authors: Takagi Nobuyuki , Takeuti Tosio
Published: February 2008

We have recorded electric field changes due to close lightning return strokes during winter thunderstorms in the Hokuriku area, Japan. Oscillating bipolar field changes were sometimes recorded together with ordinary unipolar field changes as recorded in summer thunderstorms. In order to understand the reason for the appearance of an oscillating field change, we calculated the return stroke current along a lightning channel with a transmission line model and computed the field change due to the current at several distances. The calculation shows that the electric field due to nearby lightning (up to 30 km distant) oscillates because of the relatively small volume of the winter thundercloud.
Analytical expressions for the propagation characteristics of TM waves in nonlinear self‐focusing media
Authors: Liu F. S. , Joseph R. I.
Published: February 2008

Numerical results previously obtained by Miyagi and Nishida on the propagation characteristics of stationary TM waves in nonlinear self‐focusing media are shown to have simple analytic forms.
Scattering from randomly oriented circular discs with application to vegetation
Authors: Karam M. A. , Fung A. K.
Published: February 2008

A vegetation layer is modeled by a collection of randomly oriented circular discs over a half space. The backscattering coefficient from such a half space is computed using the radiative transfer theory. It is shown that significantly different results are obtained from this theory as compared with some earlier investigations using the same modeling approach but with restricted disc orientations. In particular, the backscattered cross‐polarized returns cannot have a fast increasing angular trend which is inconsistent with measurements. By setting the appropriate angle of orientation to zero the theory reduces to previously published results. Comparisons are shown with measurements taken from milo, corn and wheat and good agreements are obtained for both polarized and cross‐polarized returns.
An orbital diversity model for earth to space links under rain and comparisons with site diversity
Authors: Matricciani Emilio
Published: February 2008

Diversity systems are foreseen for earth to satellite links operating at frequencies above 10 GHz in localities with high rain‐induced attenuation. The paper discusses orbital diversity, which uses two satellites and an earth receiving site, through an analytical model for the rainfall random process. The model uses rain gauge measurements and radar‐derived information on the slant structure; it gives results that are similar to experimental data and physically meaningful. A comparison is also carried out with corresponding site diversity, and the procedure for computing both attenuation statistics is given. It is shown that orbital diversity may replace site diversity as far as rain attenuation is concerned and may give the same performance up to a certain limit of geometry which depends little on attenuation. It is also shown that site diversity gain can be converted to orbital diversity gain and that the geometrical parameters (site separation and angle aperture) which yield this conversion are related by linear relationships, which are independent of frequency.
An algorithm for estimating rain rate by a dual‐frequency radar
Authors: Fujita Masaharu
Published: February 2008

This paper concerns an estimation algorithm of rain rates for a dual‐frequency radar at rain‐attenuating bands. The estimations are made based on the concept of least squares. In the algorithm, the ratios of received echo powers at adjacent range bins at each frequency are used to eliminate some unknown and/or undetermined factors, such as radar calibration factors. The algorithm, which is applicable when a part of echoes at one frequency is missing due to rain attenuation, is also developed. In the estimation algorithm, the relationship between specific attenuation and rain rate (k‐R relationship), and that between effective Z factor and rain rate (Z‐R relationship), are assumed to be expressed by the usual power law form. The k‐R relationships are fixed; however, the Z‐R relationships are expressed by the least squares regression form in terms of the measured quantities and the rain rates. The results of computer simulation experiments are described to demonstrate the validity of the present algorithm.
The impact of ice along satellite‐to‐earth paths on 11‐GHz depolarization statistics
Authors: Stutzman W. L. , Bostian C. W. , Tsolakis A. , Pratt T.
Published: February 2008

This paper summarizes measurements of ice depolarization made using a unique facility consisting of a dual‐site (7.3‐km site spacing), dual‐circularly polarized, low‐elevation angle (10.7°) receiving system for the SIRIO 11.6‐GHz beacon. Significant depolarization (cross‐polar discrimination as low as 10 dB) in the absence of attenuation occurred relatively frequently. However, the impact of the ice on the cross‐polar discrimination statistics for a 6‐month time period was small.
Introduction
Authors: Hunsucker Robert D. , Greenwald Raymond A.
Published: February 2008

This special issue of Radio Science contains papers presented at the URSI International Symposium on Radio Probing of the High‐Latitude Ionosphere and Atmosphere: New Techniques and New Results held in Fairbanks, Alaska, August 9–13, 1982. This symposium was sponsored by the International Union of Radio Science, Commissions G and H, the University of Alaska, USNC/URSI, U.S. Air Force Geophysics Laboratory, the National Science Foundation and Alascom, Inc.

Ninety‐seven papers were presented at the symposium, of which some were already in the publication process and some were not submitted for publication in this issue of Radio Science. The papers were submitted to Radio Science following announcements in the symposium brochure, EOS, and Radio Science.
EISCAT: An updated description of technical characteristics and operational capabilities
Authors: Folkestad Kristen , Hagfors Tor , Westerlund Svante
Published: February 2008

This paper describes the European Incoherent Scatter Installations in North Scandinavia. Technical characteristics are given and the procedures designed for preparing and running experiments are outlined. Features of a set of adopted standard programmes and the method of data analysis are sketched along with the principles established for allocating observing time. The paper briefly reviews the operation of the facility so far and presents some results which underline the experimental capability of the system.
Early MITHRAS results: The electric field response to substorms
Authors: de la Beaujardière O. , Holt J. , Nielsen E.
Published: February 2008

The MITHRAS data base offers a unique opportunity to observe simultaneously the auroral‐zone ion convection pattern with three radars, widely separated in longitude. We attempt to separate local‐time versus universal‐time effects in a study of the electric field signature associated with substorms. Preliminary results indicate that this signature is similar at a given local time, regardless of the longitude of the station. In the dawn and dusk sectors the electric field is intensified, whereas around noon and midnight the electric field appears to reverse during a substorm. The potential drop across the polar cap can be estimated from the potential across the auroral oval. The radar data agree well with the relationship found by Reiff and co‐workers between the solar wind energy parameter ε and the cross‐tail potential.
Estimation of turbulent energy dissipation, winds, and ionospheric structure from Dynasonde measurements
Authors: Wright J. W. , Hunsucker R. D.
Published: February 2008

A sample of Dynasonde observations at Cleary, Alaska, of the daytime E region, in ionogram and Kinesonde observing modes, is shown to satisfy analysis criteria leading to winds and turbulence. The wind effects on the ionization distribution in the E region are shown to be consistent with the “wind shear” process for the sporadic E phenomenon at this large magnetic dip (76.5°). The lifetime of neutral atmospheric density fluctuations is deduced using standard phase screen diffraction arguments and is shown to yield plausible values for the energy rate of turbulent eddy diffusion. This suggests the value of a more systematic and long‐term Dynasonde measurement program dedicated to studies of the turbopause.
Impedance of a plane capacitor immersed in a beam‐plasma system and in a streaming plasma
Authors: Fujita Takao , Adachi Saburo
Published: February 2008

The impedance of a plane capacitor in a cold electron beam‐electron plasma system is investigated theoretically. A radiation resistance results from excitations of two beam modes. It is found that the resistance becomes negative in a frequency range below an electron plasma frequency owing to the effect of a two‐stream instability. As a special case, the impedance in a streaming collisionless plasma which includes no stationary plasma component is also discussed. This impedance is found to be very similar to the impedance for the stationary plasma having an equivalent collision frequency.
Pulse length dependence of radar signal strengths for Fresnel backscatter
Authors: Hocking W. K. , Röttger J.
Published: February 2008

In a recent series of papers a model was developed to explain the strengths of VHF radio echoes backscattered from the atmosphere. The model assumed that a process called ‘Fresnel scattering’ was operating. One feature of the model was the proposal that the scattered signal power should be proportional to the square of the radar pulse length (Δr) used. This paper reexamines that proportionality and concludes that for conditions of Fresnel scattering, the scattered power should rather be proportional to the pulse length. It is then shown that under conditions more general than those proposed in these earlier works, the pulse width dependence is more complex than either (Δr) or (Δr)2. These revised assumptions are more appropriate to the real atmosphere and may help explain some experimental results. Experimental data and computer simulations are also discussed.
Analysis of scalar wave scattering from slightly rough random surfaces: A multiple scattering theory
Authors: Ito Shigeo
Published: February 2008

This paper presents an analytical approach to the problem of scalar wave scattering from a slightly rough random surface with the Dirichlet or the Neumann boundary condition. The Green's function method is employed to analyze statistical characteristics of waves including multiple scattering. The integral equations for the first and second moments of scattered waves are derived in a unified form for both boundary conditions. Iterative solutions for the intensity of coherent and incoherent waves are then obtained and are shown to satisfy energy conservation. The effects of multiple scattering due to surface roughness are incorporated systematically into those solutions through an effective surface impedance. Numerical results of the first‐order solutions for the incoherent wave show that even for slightly rough surfaces multiple scattering effects are pronounced in the Neumann case at near‐grazing incidence when the correlation length of the surface height is smaller than the wavelength. In the Dirichlet case, such effects appear at angles near normal incidence, but are not so significant. The results obtained herein are also compared with those previously obtained under the same perturbation boundary condition.
Orthogonal mappings of time‐harmonic electromagnetic fields in inhomogeneous (bi)anisotropic media
Authors: Suchy K. , Altman C. , Schatzberg A.
Published: February 2008

If the electromagnetic field vectors and constitutive tensors of a (bi)anisotropic medium are mapped as the position vector with an orthogonal mapping, then another system of Maxwell's equations is obtained from the original one as well as a corresponding Green's tensor. If a similar mapping is applied on the transposed constitutive tensors and the adjoint field vectors, then yet another system of Maxwell's equations is obtained. Its Green's tensor is related to the original Green's tensor by a reciprocity theorem. Various examples are given for uniaxial media.
Investigation of a surface field phase perturbation technique for scattering from rough surfaces
Authors: Winebrenner Dale , Ishimaru Akira
Published: February 2008

We present initial results from the investigation of a surface field phase perturbation method for the calculation of the wave field scattered by a rough surface. This technique is based on the extinction theorem and uses a perturbation expansion of a function closely related to the complex phase of the surface field. This approach was suggested earlier, but we use the expansion in a different way. In the present work we consider only deterministic periodic surfaces, rough in one dimension, on which the total field is zero. We find that, for surfaces with modest slope and curvature, this technique can be used to calculate scattered fields even when surface relief is significant compared to the wavelength of the incident radiation.
Theoretical prediction of the operational characteristics of a double polarized microwave communication system
Authors: Kanellopoulos J. D.
Published: February 2008

In this paper, a general analysis is proposed for the prediction of the operational characteristics of a double polarization microwave communication system where the dominant factor for degradation has been taken to be the rainfall. This analysis can be considered as an improved version of previous techniques dealing with the same subject. One of the features of the paper is the analytical examination of the spatial inhomogeneity of the rain medium as it affects the joint statistical analysis between rain attenuation and depolarization.
Measurements of irregularities in the mid‐latitude ionosphere with a radio interferometer
Authors: Knowles Stephen H. , Matsakis D.
Published: February 2008

Radio astronomy interferometers have potential use for systematic monitoring of medium‐scale irregularities in the ionosphere. In this article, precepts for their use are derived, and preliminary analysis of data samples from interferometers at Green Bank, West Virginia, and Magdalena, New Mexico, is presented. A typical differential electron content of about 1015/m2 over a 35‐km baseline is observed. A day‐night correlation with TEC values is observed; we found the nighttime ionosphere to be more disturbed during high geomagnetic activity. Ionospheric irregularities are observed to persist over periods of an hour or longer.
Construction of a model of equatorial scintillation intensity
Authors: Aarons Jules
Published: February 2008

By using a 5‐year series of observations at 254 MHz taken at Huancayo, Peru, an analytical equation has been developed to yield scintillation excursions in decibels as a function of solar flux, magnetic index, local time, and day of the year; the equation, while characterizing the parameters given for the region surrounding the magnetic equator and for the Atlantic sector, has serious limitations in its application at other latitudes, other frequencies, and other longitudes in the equatorial region. Current available models of electron density and total electron content are inadequate to explain the differences between high levels of scintillation activity in years of high solar flux over the anomaly region relative to that of the magnetic equator. Newer models under development go further towards explaining levels of fading. Excursions levels of the order of 28 dB and greater have been observed in the anomaly region, while only 8–9 dB excursions have been noted at 1.6 GHz on the magnetic equator. The longitudinal characteristics indicate differences in activity over various regions of the earth particularly relative to solstice scintillation occurrence. Characteristics of the patches, such as intervals between patches and differing propagation paths when transmitting from multiple satellites, can be used to move information through the ionosphere even during nights of intense scintillations.