bluuebunny/crossref_metadata_2025 huggingface dataset:
Depolarization of 19 and 28 GHz earth‐space signals by ice particles
Authors: Cox D. C. , Arnold H. W. , Hoffman H. H.
Published: February 2008

Strong depolarization (sometimes > −20 dB) at 19 and 12 GHz occurring with low signal attenuation (often <1 dB) and associated with summer thunderstorms was described earlier. This paper describes winter observations at 19 and 28 GHz of what appears to be the same phenomenon. The depolarization is a few dB stronger at 28 GHz but is highly correlated between the two frequencies. The winter depolarization events appear when ground temperatures are near or below freezing and clouds are along the path. These events are caused by differential phase shift through ice crystals in the clouds.
Summary of the results of the Wisconsin Test Facility phasing anomaly investigations
Authors: Bannister Peter R.
Published: February 2008

Since 1974, many Wisconsin Test Facility (WTF) phasing anomalies have been observed. Among these anomalies are (a) ψ° phasing does not equal (360° − ψ°) phasing, contrary to the normal behavior of crossed dipoles; (b) the maximum field strength at any single receiving location does not occur when ψ = 0 or 180°; (c) the WTF antenna phasing shift appears to be −20° to −30°; (d) the WTF effective dipole moment does not appear to be independent of ψ; and (e)the WTF antenna phasing shift appears to be a function of azimuth angle. By a combination of near‐field and far‐field measurements, we have determined empirically a new WTF pattern factor that quantitatively describes these anomalies.
A transform‐pair relationship between incident and scattered fields from an arbitrary reflector
Authors: Ludwig Arthur C. , Brunstein Samuel A.
Published: February 2008

It is shown that a transform‐pair relationship exists between incident and scattered fields from an infinite, perfectly conducting reflector of arbitrary shape, when the physical optics approximation is applied. As an example of potential applications, this relationship is used to synthesize a reflector feed pattern required to produce a desired far‐field pattern from a given paraboloidal reflector.
Evidence for specular reflection from monostatic VHF radar observations of the stratosphere
Authors: Gage K. S. , Green J. L.
Published: February 2008

The received signal obtained on the vertical antenna of the 40 MHz Sunset radar often reveals an order‐of‐magnitude enhancement over the received signal obtained nearly simultaneously on an antenna pointed 30° from the zenith. The enhancement is most pronounced in regions of the atmosphere which are hydrostatically very stable. The enhanced vertical echoes are consistent with specular or partial reflection from thin stable laminae of radio index of refraction. An order‐of‐magnitude calculation is used to show that the expected reflectivity from a thin stable layer would easily be detected by the radar.
Pulsed electromagnetic radiation from a line source in a two‐media configuration
Authors: de Hoop A. T.
Published: February 2008

The pulsed electromagnetic radiation from a two‐dimensional line source in a lossless two‐media configuration is investigated theoretically. The author's modification of Cagniard's technique is used to derive closed‐form expressions for the electromagnetic field components anywhere in the configuration. Numerical results are presented pertaining to the incident, the reflected, and the transmitted wave for different positions of the source and the observer, as well as for different contrasts of the two media. Also, the corresponding total‐field plots are shown. In an appendix, the modified Cagniard contours pertaining to a lossless N‐media configuration are discussed and some two‐media modified Cagniard contours are shown.
Operator and diagram techniques for solving intensity moment equations in random media: Application to strong scattering
Authors: de Wolf D. A.
Published: February 2008

The moment equations for the intensity of an electromagnetic wave propagating in an almost‐transparent extended random medium are cast in an integral‐operator form. Transport equations and iterative series are derived. Solutions in several limits are given, and series of correction terms are discussed with use of diagram techniques. For simplicity, the treatment is restricted to plane waves, uniform isotropic turbulence, and only to the intensity covariance as far as correction terms are concerned.
Field penetration through small apertures: The first‐order correction
Authors: Van Bladel J.
Published: February 2008

The penetration of an incident wave through an aperture in a perfectly conducting screen is considered. The dimensions of the aperture are small with respect to the wavelength λ. The fields are expanded in a power series in jk, where k = 2π/λ. The zero‐order terms are well‐known: they require the solution of electrostatic or magnetostatic problems. The article is concerned with the first‐order terms. The integro‐differential equations for these terms are derived, and the diffracted field in the far‐field region of the aperture is investigated. The relevant multipole‐moments are evaluated.
Ray theory of electromagnetic surface‐wave modes in integrated optical systems
Authors: Blok H.
Published: February 2008

A systematic ray theory of electromagnetic surface‐wave modes in integrated optical systems is presented. It is shown that in a slowly varying, horizontally layered optical waveguide the vertical components of the electromagnetic field satisfy two separate second‐order differential equations that correspond to TE and TM modes, respectively. In the horizontal direction, we develop a ray theory; in the vertical direction the application of the transverse resonance conditions leads to an eigenvalue problem. In the vertical direction the resulting solutions then behave as ordinary surface‐wave modes, while in the horizontal direction they possess all properties of two‐dimensional electromagnetic rays. The properties of the surface‐wave ray modes are discussed, in particular their propagation coefficients, for which a stationary expression (in the variational sense) is derived. Applications are briefly indicated.
Rough surface scattering of horizontally polarized waves and polarization dependence of backscatter cross section: Full wave solutions
Authors: Bahar E. , Rajan G. G.
Published: February 2008

Full wave solutions are presented for horizontally polarized waves scattered by rough surfaces. Complete expansions and exact boundary conditions are used in the analysis. These solutions are compared with the physical optics solution based on the local tangent approximation of the fields at the irregular boundary. Expressions for the backscatter cross section for both horizontally and vertically polarized waves are also compared with earlier solutions to this problem. The reciprocity relationship and the suitability of the approximate impedance boundary condition are examined, and special consideration is given to excitation and scattering at grazing angles. This work on irregular ground effects on radio wave propagation can be applied to problems of communication, navigation, positioning, and active remote sensing.
Parametric modeling of transient electromagnetic systems
Authors: Dudley D. G.
Published: February 2008

The modeling of a transient electromagnetic system as a single‐input, single‐output, linear, causal process is considered. Two canonical forms are discussed; one for impulse function input and the other for more general input. Expressions are derived for errors in the estimation of the model parameters caused by errors in the process data. It is shown that Prony's method is a special case of the impulse function model and that serious errors occur in attempts to apply the method in a noisy environment. It is also shown that least squares estimation of the model parameters produces biased results and that attempts to overcome this problem have led to nonlinear equation sets. Some recommendations are made concerning noise identification and filtering in order to improve results.
An asymptotic analysis of the scattering of plane waves by a smooth convex cylinder
Authors: Pathak P. H.
Published: February 2008

An approximate asymptotic high‐frequency result which is convenient for engineering applications is obtained for the field exterior to a smooth perfectly conducting convex cylinder when it is illuminated by a plane wave. This result is uniform in the sense that it remains valid within the transition regions adjacent to the shadow boundaries where the pure ray optical solution based on the geometrical theory of diffraction (GTD) fails, and it automatically reduces to the GTD solution exterior to the transition regions where the latter solution becomes valid. Furthermore, this result is expressed in the simple format of the GTD, and it employs the same ray paths as in the GTD solution. This uniform result is not valid in the close neighborhood of the cylinder; hence a separate asymptotic result is presented for this special case in a form which is also convenient for applications. The asymptotic results presented here are useful for predicting the patterns of antennas radiating in the presence of convex conducting cylindrical structures.
Mutual impedance between vertical dipoles over a flat earth
Authors: Richmond J. H. , Newman E. H.
Published: February 2008

The fields of a vertical dipole and the mutual impedance between vertical dipoles over a flat earth are expressed in terms of a Sommerfeld integral.
On low‐frequency propagation on a buried wire covered by a conducting jacket
Authors: Row R. V.
Published: February 2008

When a buried wire is jacketed by a high‐quality insulation, the propagation constant for the TM mode may be an order of magnitude greater than that of the insulation and many orders of magnitude less than that of the surrounding conducting medium. This is a well‐known result. It is shown here that if the conductivity (σ1) of the jacket is so large that σ1/ωε1, ≫ 1, then the propagation constant (k) approaches close to that (k2) of the external ground when σ1, is still several orders of magnitude less than (σ2) the conductivity of the ground. Whereas the voltage drop across the jacket is practically the entire voltage drop from the conductor to infinity for an insulating jacket, it is a negligible part of the drop when the jacket is a good conductor. This latter fact has an important impact when the results of theoretical models are compared with field data.
Atmospheric noise data for tropical regions
Authors: Aiya S. V. C.
Published: February 2008

The known unsatisfactory nature of atmospheric noise data based on pre‐1964 measurements for tropical regions is due to the inadequacy of the dynamic range of the measuring equipment in recording local storm noise. This high‐amplitude, highly impulsive noise arises from the electrical discharges inside the cloud at heights varying from about 3 to over 10 km above the mean sea level in the tropics. Direct ray reception of the radiation from such discharges is expected for source distances of the order of 300 km. The number of local storm days is experimentally found to be about three times the recorded number of thunderstorm days and can exceed 50% of the days of a season in the tropics. Electrical discharges corresponding to one lightning flash give rise to one noise burst in the receiver. The structure of such noise bursts and their amplitude and time characteristics have been studied. Highest amplitude noise present for 10% of the time in a short period of time like 5 min is the portion‐relevant for interference purposes, and this arises from the noise bursts described. Its short‐term characteristics are log normal. The long‐term characteristics of the short‐term mean values are also log normal. Consequently, noise data are furnished in terms of mean values and standard deviations. Along with such noise data, the required signal‐to‐noise ratios for different types of service are also given.
Generalized magnetoionic formulae for the propagation of radio waves in the F region of the ionosphere
Authors: Ramana K. V. V. , Rao D. N. Madhusudhana , Rao B. Jaganmohan
Published: February 2008

The complex refractive index of the ionized medium has been obtained by Sen and Wyller (1960) and Budden (1965) by taking into consideration the dissipation of the wave energy through electron‐molecule collisions. In the F region of the ionosphere, electron‐ion collisions play a dominant role rather than the electron‐molecule collisions. In this paper an effort has been made to arrive at the magnetoionic formulae by considering electron‐positive ion collisions. The resulting formulae are similar in form to those obtained by Budden (1965), but the dielectric tensor of the medium has a different value. As the effective collision frequency of the electron in the F region is much less than the probing frequency (usually, HF), an approximation to the dielectric tensor has been obtained which is free of Dingle integrals. Calculation of magnetoionic parameters using the approximate theory and Appleton‐Hartree formulae with the effective collision frequency resulted in reasonable agreement between the two methods.
Behavioral sensitivity of a domestic bird to 60‐Hz ac and to dc magnetic fields
Authors: Clarke Rex L. , Justesen Don R.
Published: February 2008

After conventional incubation (n = 2) or incubation in a 60‐Hz modulated 2450‐MHz microwave field (n = 2), four Leghorn chickens (Gallus gallus) of both genders were assessed for ability to perceive magnetic fields (dc at 4.0 milliteslas; 60‐Hz ac at 1.7 milliteslas rms) by the method of conditional suppression. Each bird operantly responded for rewards of grain while being subjected to a Pavlovian conditioning procedure in which a 90‐s presentation of an H field served as a conditional stimulus (CS) that terminated in a brief faradic shock to the feet, which served as the unconditional stimulus (US). Five to seven pairings of CS and US occurred aperiodically during daily, 60‐min sessions. A total of six tensession blocks of formal testing was conducted, two blocks with the ac field, two with the dc field, and two with a sham field in which the US alone was presented to provide control baselines of responding. Neither mode of incubation nor gender was a reliable source of variation, but highly reliable changes (Ps < 0.01) in the character of operant responding—increased variability—were observed during presentations of the ac or dc field. The domestic fowl may therefore share with several other avian species a sensitivity to H fields, although artifactual sensory cueing borne of vibration or heating of the H‐field source was not definitively ruled out. If real, the birds' sensitivity to the nominal dc field was probably associated with behavioral modulation – with incessant movement in the field by a chicken, especially of its head, during the operant‐respondent measures of conditioning. On the basis of our findings and those of other investigators, we believe that detection of H fields by avian species has its locus in the retina or in other neuroanatomical substrates of the visual system.
A power law fit to oxygen absorption at 60 GHz and its application to remote sensing of atmospheric temperature
Authors: Poon R. K. L.
Published: February 2008

The oxygen spectrum near 60 GHz is studied empirically with emphasis on its application to the passive remote sensing of the tropospheric and lower stratospheric temperature. For this purpose the oxygen absorption coefficient over a certain range of pressure p and temperature T is fitted to the power law form apx Ty, where a, x, and y are frequency‐dependent parameters. A root‐mean‐square relative error of 8% is obtained by best fitting the parameters to the theoretical absorption expressions proposed by Van Vleck and Weisskopf, Gross, and Rosenkranz. This provides a convenient basis for a quantitative comparison of the three theoretical expressions. The power law form also leads to a basic understanding of the remote sensing of the atmospheric temperature profile from airborne spectrometers. Such concepts as height selectivity and resolution can be naturally defined in terms of a, x, y, and the pressure scale height of the atmosphere. As a practical application it is shown how the power law form can help attack the forward and inverse problems in remote sensing. An example is given in treating satellite data from the Nimbus 5 microwave spectrometer.
The MST radar at Poker Flat, Alaska
Authors: Balsley B. B. , Ecklund W. L. , Carter D. A. , Johnston P. E.
Published: February 2008

We describe the basic configuration of the Poker Flat, Alaska, MST (mesosphere‐stratosphere‐troposphere) radar currently under construction by NOAA's Aeronomy Laboratory. This 50‐MHz coherent radar consists of a 4 × 104 m2 phased dipole array, a 6.4‐MW peak power transmitter system (consisting of 64 separate 100‐kW peak pulse power transmitter modules distributed throughout the array), and an on‐line Doppler analysis/data recording system. With some limitations the system will be capable of measuring winds, waves, and turbulence throughout the 1‐ to 100‐km height range. Data obtained from the portion of the Poker Flat system already in operation are presented and discussed.
Three‐dimensional wind measurements in the optically clear planetary boundary layer with dual‐Doppler radar
Authors: Kropfli R. A. , Hildebrand P. H.
Published: February 2008

Radar‐derived three‐dimensional wind fields were obtained near the Boulder Atmospheric Observatory tower during a planetary boundary layer (PBL) experiment called Phoenix in September 1978. A pair of closely spaced (12.3 km) Doppler radars observed the entire depth of the daytime PBL (˜2 km) over an area of ˜100 km2, with hundreds of velocity samples per km3, a radar resolution volume size of 150 m in all dimensions at the tower, and volume scan intervals of 50–180 s. The radar measurements obtained are compared with in situ measurements on aircraft, on the instrumented tower, and with other surface wind data. Preliminary results indicate that these data resolve wavelengths as small as 600 m and that the measurements are repeatable at each grid point to within 0.3 m/s. The radar‐derived wind fluctuations agreed with anemometer data on the tower to within 0.5 m/s and with data from an aircraft‐borne anemometer to within 1.0 m/s.
Long‐term measurements of Cn2 in the boundary layer
Authors: Chadwick R. B. , Moran K. P.
Published: February 2008

The results of a year‐long Cn2 measurement program to determine the feasibility for radar detection of hazardous wind shear are discussed. Monthly and hourly statistics of Cn2 are presented, and diurnal and annual cycles are identified. It is shown that Cn2 can be modeled as a one‐parameter log normal random variable.
D region absorption effects during high‐power radio wave heating
Authors: Tomko A. A. , Ferraro A. J. , Lee H. S.
Published: February 2008

Simultaneous solutions of the differential equations governing electron energy and power flow are used to study D region absorption effects arising from high‐power HF heating. It is shown that self‐absorption of the heating wave can severely limit HF heating of the upper ionosphere and that the power density available for heating above the D region saturates as the heating power is increased. Models of the electron temperature distribution under heated conditions are used to compute the change in two‐way integral absorption on a 2.4‐MHz diagnostic wave due to HF heating as a function of heating frequency. The predicted theoretical absorption change is found to agree with experimental results.
Transequatorial propagation through equatorial plasma bubbles—Discrete events
Authors: Heron M. L.
Published: February 2008

The discrete nature of VHF transequatorial propagation path openings is pointed out. These events are shown to be consistent with the concept of guided propagation inside equatorial plasma bubbles. The important prediction of this work is that observations on discrete transequatorial VHF links may be used to track the production and development of equatorial plasma bubbles.
Minimum redundancy linear arrays for a large number of antennas
Authors: Ishiguro Masato
Published: February 2008

A linear array that achieves maximum resolution for a given number of antennas is advantageous in earth‐rotation aperture synthesis. This type of array is called a minimum redundancy linear array; it is obtained by reducing redundant spacings present in the array. Various methods are examined to find optimum arrays for a large number of antennas. From the systematic analysis of regular patterns in these arrays, a possibility of generalizing optimum arrays is suggested. Optimum configurations could also be used for distributing stations in an aperture synthesis array.
Time cells for adaptive prediction of total electron content
Authors: Donatelli D. E. , Allen R. S.
Published: February 2008

Adaptive procedures, using multiplicative and additive prediction functions of the standard deviation of the observations, are analyzed to estimate and compare their effectiveness in correcting for ionospheric variability in time delay and range measurements. The adaptive algorithms use real time measurements to reduce rms errors in ionospheric predictions. Total electron content data from Hamilton, Massachusetts, for 1969–1976 are used to evaluate diurnal, seasonal, and solar cycle impact on radar, navigation, and communication systems. Time cells are defined from the growth rate of rms residual error. Significant reductions in rms error are achieved in daytime, at solar maximum, when time delay and range errors are greatest, using a multiplicative prediction function.
The determination of the direction of arrival of an interference field
Authors: Lai Hang H. , Dyson John D.
Published: February 2008

The problem of resolving the complex interference field at a receiving site, that is caused by multimode propagation at high frequencies, into the individual plane wave components and determining the direction of arrival of these components is considered. The method developed is based on Prony's algorithm. To illustrate the effect of noise on the solution, a first‐order linearized model of a statistical study of a two plane wave problem for this conventional Prony's method is presented. A modification of Prony's technique, an eigenvalue approach, allows one to analytically determine the number of waves in the problem, and this approach is less susceptible to the effect of noise. Data obtained from a controlled experiment when a signal from a distant source was repeated and retransmitted at a different location verify that the system as well as the algorithm is capable of resolving waves coming from different directions. Experimental evidence related to multimode as well as single‐mode propagation coming from the same source has been obtained.
Propagation effects on a coherent polarization‐diversity radar
Authors: Metcalf James I.
Published: February 2008

Differential propagation effects are a key element in the design and use of dual‐channel radars for meteorological measurements. Particularly in the case of circularly polarized signals, these effects determine the maximum ranges to which certain measurement objectives can be accomplished. For various purposes one may want to assume either that propagation effects are negligible or that they dominate backscattering effects in the received signals. Approximate and exact representations of the averaged signal parameters and the spectral functions are given for cases in which propagation effects are predominant. The cross‐spectrum of the two received signals and the spectral power ratio can be used under some conditions to separate scattering and propagation effects.
An Analysis of short pulse and dual frequency radar techniques for measuring ocean wave spectra from satellites
Authors: Jackson Frederick C.
Published: February 2008

A four‐frequency moment characterization of backscatter from the near‐vertical is applied to an analysis of the short pulse (SP) and dual frequency (DF) microwave techniques. It is found that (1) the range reflectivity modulation spectrum closely approximates the directional wave slope spectrum. Harmonic distortion is small and is a minimum near 10° incidence. (2) The SP measurement SNR (signal‐to‐noise ratio) is typically 20–30 dB greater than the narrowband DF SNR. The difference in SNR is the ratio of the range beam extent to pulse length, minus the ratio of beam‐limited to pulse‐limited Doppler spreads. It is concluded that narrowband DF measurements are basically impractical. To be practical, the DF technique must be ‘widebanded.’ SP measurements on the other hand are found to be practical, using existing space‐qualified microwave hardware.
On detecting reflections in presence of scattering from amplitude statistics with application to D region partial reflections
Authors: Rastogi P. K. , Holt Olav
Published: February 2008

In many radar experiments which use transmission or scattering of radio waves through a random medium, the received signal is modeled as a reflected sine wave of amplitude A in a scattered narrow‐band Gaussian random process of variance 2σ2. In this model the received signal amplitude has a Rice family of distribution characterized by a parameter α = A/σ. It is shown that amplitude statistics cannot be used to discriminate weak reflections from scattering (α < 0.5). Behavior of mean, skewness, and kurtosis of the normalized signal amplitude is examined for a constant and an intermittent reflected component. It is shown that intermittency has a strong effect on these. Applications to a D region partial‐reflection experiment at Tromsø are briefly discussed. It is shown that, at least in some simple cases, enhanced reflections arise from the top and bottom parts of turbulent layers.
Inversion of one‐dimensional scattering data using Prony's method
Authors: Miller Edmund K. , Lager Darrel L.
Published: February 2008

A one‐dimensional configuration is the simplest geometry to invert, yet it has practical application to such problems as scattering from inhomogeneous half spaces and propagation on nonuniform transmission lines. Whether the medium parameters vary continuously or discretely with position, the problem's numerical description can usually be developed in finite‐difference approximation. As such, the scattered and transmitted fields can be represented as exponential series, whose exponents are related to the electrical thicknesses of the layers which make up the model. If the exponents or poles are derivable from field data, then the inverse problem is formally solvable. This paper considers application of Prony's method, a procedure for obtaining the poles of exponential signals, to such one‐dimensional problems. Analysis of both time‐domain and frequency‐domain data is studied. The effects of the medium characteristics, number of layers, and other factors are examined. It is concluded that Prony's method has merit for certain classes of one‐dimensional inverse problems.
Automatic calculation of electron density profiles from digital ionograms: 1. Automatic O and X trace identification for topside ionograms
Authors: Reinisch Bodo W. , Xueqin Huang
Published: February 2008

This first paper in a series of three describing the automatic processing of digital ionograms discusses the scaling of topside ionograms in a ground‐based minicomputer. The objective is to automatically obtain the vertical electron density profiles. The topside ionogram scaling algorithm finds the resonance and cutoff frequencies and the vertical O and X echo traces. Application of the scaling algorithm to digitized ISIS 1 and 2 ionograms illustrates its performance and demonstrates the feasibility to automatically scale topside ionograms. The ISIS studies show that polarization tagging of the O and X signals should be done in a digital satellite sounder to assure successful, real time scaling of complex ionograms.
Attenuation with distance and wind speed of HF surface waves over the ocean
Authors: Forget P. , Broche P. , de Maistre J. C.
Published: February 2008

An HF monostatic experiment is performed in order to evaluate the relative attenuation with distance of radio waves propagating in the ground wave mode over the sea surface, at 7 and 14 MHz. Clear evidence of the wind speed (causing the sea roughness) influence arises from the data, particularly at 14 MHz. The results are compared to Barrick's theoretical calculations, and a good agreement is found for the values of attenuation rates (in decibels per kilometer) and their variation with the wind speed in the upwind/downwind case. Some discrepancies in the data are partially interpreted as due to a fetch influence upon the radar cross section.
Dielectric properties of thawed active layers overlying permafrost using radar at VHF
Authors: Arcone Steven A. , Delaney Allan J.
Published: February 2008

Field measurements of the dielectric constant of thawed active layers of up to 1 m in depth at four sites in Alaska have been made using short‐pulse ground radar whose returns were received in the near‐field radiation zone. Three sites consisted of saturated silts with varying amounts of organic material, and the fourth site was a moist sand. The reflector returning the radar signals was the active layer/permafrost interface. Analysis of the waveforms showed that all the materials were nondispersive over the radar pulse bandwidth (75–225 MHz), and this was confirmed by time domain reflectometry (TDR) studies of field samples. The average dielectric constants were between 23 and 34 for the silts, which averaged between 45 and 50% water by volume, while the sandy site gave an average value of about 12 for a probable water content of about 23% by volume. These values are very similar to the laboratory work of others and were also confirmed by TDR. The high dielectric constants of the saturated materials allowed accurate profiling of active layer depth, and an example is presented. More detail would probably be achieved with a higher‐frequency radar.
A simple model for the estimation of rain‐induced attenuation along earth‐space paths at millimeter wavelengths
Authors: Stutzman W. L. , Dishman W. K.
Published: February 2008

Design of millimeter wave satellite communication systems must include accurate estimates of the excess attenuation caused by rain. This paper presents a model for estimating the slant path attenuation due to rain. The model is both conceptually and computationally simple, allowing the system designer to easily obtain estimates of link outages caused by rain attenuation. Estimates of attenuation as a function of point rain rate require only the operating frequency, elevation angle, and earth station latitude and altitude. An exponentially shaped spatial rain rate profile is used. The attenuation values as a function of point rainfall rate are coupled with a point rainfall rate distribution to calculate the attenuation distribution (percentage of time that a given attenuation level is exceeded during a year). The rain rate distribution can be obtained from local data sources or can be estimated from global rainfall models. Comparisons of estimated attenuation with measured data from experiments across the world are presented. The level of agreement between model predictions and experimental data is also examined for other models available in the literature.
The effect of microwave radiation (1.0 GHz) on the blood‐brain barrier in dogs
Authors: Chang Barbara K. , Huang Andrew T. , Joines William T. , Kramer Richard S.
Published: February 2008

Although a disruptive effect of low‐level microwave (MW) radiation on the blood‐brain barrier (BBB) of small laboratory animals has been suggested by a number of authors, the relevance of these studies to larger animals has received little attention. Using 131I albumin as our tracer molecule and cannulation of the cisterna magna and of the femoral vein to permit multiple sampling of cerebrospinal fluid (CSF) and plasma, we have studied the effects of microwave radiation on the BBB in dogs. Measurement of the CSF/plasma distribution ratio (cmpCSF/cmpplasma) of 131I albumin was carried out over a 5‐hour period after exposure of the dog's head for 20 minutes to various power densities of continuous wave microwave at a constant frequency of 1.0 GHz. Control animals (n = 11) were subjected to the same experiment, but received no MW exposure. No effect on the BBB was observed in two dogs each at the following power densities: 2, 4, 10, 50, and 200 mW/cm2. Eleven dogs were exposed to 30 mW/cm2, and, within this group, there were two animals in which the penetrance of the BBB by the 131I albumin was increased 4–5 times over controls, and two additional animals which showed twofold to fourfold increased penetrance. However, the CSF : plasma distribution ratios of the remaining animals receiving 30mW/cm2 did not differ statistically from controls. The results obtained in the four dogs experiencing a postmicrowave alteration of the blood‐brain barrier suggest that, for the dog, a microwave ‘window’ effect may be operating very near 30 mW/cm2.
Effective electrical properties of heterogeneous earth models
Authors: Wait James R.
Published: February 2008

An attempt is made to examine critically the basic formulations of current flow in heterogeneous media such as brine‐ saturated rocks with the grains having a regular form. The pore space dependence on the conductivity and permittivity is given special attention. The extension of the small volume loading mixture formulas to large volume loading is carried through explicitly, following the procedure of Bruggeman, Hanai, Cohen, Sen, and others. We indicate that the particle shape plays a major role.
A study of the various methods for computing electromagnetic field utilizing thin wire integral equations
Authors: Sarkar Tapan K.
Published: February 2008

In this paper we analyze the numerical aspects of the various methods that have been utilized to analyze thin wire antennas. First, we derive the properties of the operators for Pocklington's and Hallen's integral equation. On the basis of these properties, we discuss the various iterative methods used to find current distribution on thin wire structures. An attempt has been made to resolve the question of numerical stability associated with various entire domain and subdomain expansion functions in Galerkin's method. It has been shown that the sequence of solutions generated by the iterative methods monotonically approaches the exact solution provided the excitations chosen for these problems are in the range of the operator. Such a statement may not hold for Galerkin's methods if the inverse operator is unbounded. Moreover, if the excitation function is not in the range of the operator, then the sequence of solutions forms an asymptotic series. Examples have been presented to illustrate this point.
Radio science and oceanography
Authors: Shearman E. D. R.
Published: February 2008

The three main radio techniques for remote sensing of the ocean surface, microwave radar, microwave radiometry, and dekametric or HF radar, are surveyed. The generation and characterization of wind waves and swell on the ocean surface, and the first‐order mechanism of Bragg resonant scattering of radio waves by such surfaces are outlined. Doppler HF radar techniques, ground wave and sky wave, developed for utilization of this effect to sense remotely wave, wind direction and surface current velocity are reviewed. Second‐order scattering effects, hydrodynamic and electromagnetic, are also present, and their signatures on the Doppler echo spectrum of an HF radar permit measurement of wave height, wavelength spectrum and directional spectrum. Finally, the scattering mechanisms relevant in satellite‐borne microwave radar are outlined. Bragg resonance occurs with short waves, these being modulated by the longer gravity waves of practical interest. The potential of the radar altimeter, scatterometer and synthetic aperture radar for global ocean surveillance is illustrated by examples from the satellite.
Radio noise fields generated by corona streamers on a power line
Authors: Olsen Robert G.
Published: February 2008

A theory of the radio noise field generated by corona on a single conductor transmission line with an earth return is presented. Each corona streamer is modeled as an electric dipole driven by a current pulse. The electromagnetic fields generated both directly by the corona streamers and by the currents induced on the transmission line by the streamers are calculated. The equivalent vertical electric field (after averaging over the ‘random’ properties of the corona and assuming a perfectly conducting earth) is then calculated and compared to the commonly used quasi‐static approximation to this field. For points electrically close to the conductor, the equivalent vertical electric field decays more rapidly than predicted by the quasi‐static theory. In the far field the opposite is true.
A differential‐Doppler study of traveling ionospheric disturbances from Millstone Hill
Authors: Evans J. V. , Holt J. M. , Wand R. H.
Published: February 2008

From January 1971 to March 1973, five satellites of the Navy Navigation Series (Transit) in polar orbits at 1000 km altitude were tracked from Millstone Hill to secure differential‐Doppler measurements of N‐S gradients in the ionosphere. In all, over 2000 passes were observed, encompassing all local times and seasons. All of the differential‐Doppler records have been scanned to secure statistical information on the incidence, wavelength, amplitude, and location of the traveling ionospheric disturbances detected. Most of the TID's had wavelengths in the range of 150–350 km and were seen to the south of the station, suggesting that they were traveling from north to south. The incidence peaked at 60% of all passes at 0800 local time and dropped to less than 5% for a few hours before sunrise. The seasonal variation is less clear‐cut, but the incidence seems to be increased in winter and the equinoxes and reduced in summer. This may be simply a consequence of the dependence of the detectability on total content. While the character of the fluctuations and a north‐to‐south motion would be consistent with a source in the auroral ionosphere, there seems to be no increase in incidence during magnetically disturbed times. Moreover, in summer the waves are seen equally to the north and the south of the station. It seems possible that there may be many sources for these waves distributed in latitude and that the observed locations are controlled by the filtering effects of F region winds.
Nonlinear scattering from a plasma column: 1. Theory
Authors: Crawford F. W. , Harker K. J.
Published: February 2008

An analysis is presented of the scattered signal excited by nonlinear mixing of two plane waves normally incident on an infinitely long column of plasma. A general solution is developed for the polarization in which the electric field vectors of the waves are perpendicular to the column axis and the column is assumed to be radially inhomogeneous. The special case of second harmonic generation due to a single incident wave is treated in detail.
Calculation of ice depolarization on satellite radio paths
Authors: Tsolakis A. , Stutzman W. L.
Published: February 2008

In this paper, theoretical methods are presented for calculating the depolarization of ice clouds. Rayleigh scattering from single particles is used. A general theory is introduced that includes distributions of ice particle shapes and orientation angles for both single and multiple scattering. It is shown that the more accurate multiple scattering formulation yields cross‐polar discrimination values significantly worse than those for single scattering over the 10‐ to 30‐GHz band for high ice content. Comparisons are made to measurements using the SIRIO satellite.
A design for an automatic HF radio system
Authors: Elvy S. J.
Published: February 2008

Microprocessor control systems, coding schemes, and modern communications equipment suggest new possibilities for the operation of HF radio systems. This paper describes a design concept for an automatic radio system, intended to overcome some of the traditional difficulties experienced with HF communications and to provide new capabilities including selective calling and automatic connectivity. The design incorporates a passive frequency selection technique using built‐in ionospheric prediction data and real time monitoring of channel interference levels.
Passive monitoring of the ionosphere
Authors: Paul Adolf K.
Published: February 2008

The increasing congestion in some portions of the radio spectrum, especially in the AM band, makes it virtually impossible to obtain information about the ionosphere in those bands by conventional sounding. This raises the question, if ionospheric information can be obtained in a passive mode by measuring the angle of arrival of signals transmitted by stations of known location over a short or medium length path involving ionospheric reflection. No difficulties are expected if only one wave is observed at the receiving site. If the signal can propagate over two different paths, the two superimposed waves can be separated numerically in amplitude and direction of arrival, provided that amplitude and phase are recorded at four spaced receiving antennas. It appeared that the ionospheric sounding facility at Brighton, Colorado, had the capability to test this principle. Several tests showed that the high data quality makes this approach very promising. The two‐wave separation, however, could not be tested, since the two receiving antenna pairs are sampled in sequence, and ionospheric changes cause already significant changes in the phase relation of the two waves over periods much shorter than the sampling interval of 20 ms. The relevance of these tests to direction finding will also be discussed.
Comparison of HF oblique transmissions with ionospheric predictions
Authors: Millman George H. , Swanson Roger W.
Published: February 2008

High‐frequency oblique transmissions made for a short period of time during the maximum phase of the past solar cycle are compared with the frequencies predicted utilizing the ITS‐78 and the IONCAP (ionospheric communications analysis and prediction) ionospheric prediction programs developed by the Institute for Telecommunication Sciences. The external atmospheric noise levels predicted by the ITS‐78 program are also compared with experimental data. The measurements conducted in the northeastern U.S. reveal that, for undisturbed solar‐geophysical conditions, the experimental data are in good agreement with the theoretical predictions.
The behavior of the backscattered power from an intensely turbulent ionosphere
Authors: Yang C. C. , Yeh K. C.
Published: February 2008

Experimental evidence based on ionospheric scintillation observations has revealed the importance of multiple scattering at a frequency as high as gigahertz. In most cases, even though the scattering is intense, the scattered energy is concentrated mainly in the forward direction. Making use of these observations, a scattering theory is developed in this paper that takes into account both multiple scattering and Fresnel diffraction. It shows that both of these effects will reduce the backscattered power when the irregularity spectrum is Gaussian, but will leave the backscattered power unaltered, except for a 3‐dB enhancement, when the irregularity spectrum follows a power law. This enhancement of radar returns subtends a narrow cone centered in the backward direction. Numerical investigations show that the width of the enhancement cone is controlled by the intensity of multiple scattering, i.e., a change of parameter to increase multiple scattering will decrease the width of the enhancement cone.
Observations of the radio noise background in the frequency range 150–180 kHz
Authors: Knowles S. H. , Kelly F. J. , Waltman W. B. , Odenwald S.
Published: February 2008

Observations were made of the radio noise background in the frequency range 150–180 kHz to provide reference data for the design of the ground wave emergency network system. These observations were undertaken at Nanjemoy, Maryland, during early summer 1983 and included 41 days of data recording. The noise environment was found to be dominated by impulsive thunderstorm noise. A typical nighttime mean noise power spectral density was 1×10−15 W m−2 Hz−1 (noise factor of 107 dB above kT0), while a typical daytime level was at least 14 dB quieter. However, the daytime level was at times significantly higher, especially during the presence of a local thunderstorm front. During local thunderstorm activity, impulses with peak power spectral density of 1×10−14 W m−2 Hz−1 were observed frequently, while the most energetic pulse detected during our monitoring period had a peak power spectral density of 6.8×10−14 W m−2 Hz−1 (Fa = 125 dB). Sample amplitude probability distributions and time probability distributions are presented for day/quiet, night, and thunderstorm conditions. Agreement with the mean noise level predictions of CCIR report 322 is satisfactory within the accuracy limits of the CCIR data.
Detection of local and long‐path VLF/ELF radiation from modulated ionospheric current systems
Authors: Lunnen R. J. , Ferraro A. J. , Lee H. S. , Allshouse R. , Carroll K. , Werner D. , Collins T. W.
Published: February 2008

This paper describes the local and long‐path very low frequency/extremely low frequency (VLF/ELF) radiation produced by modulation of the ionospheric current systems during high frequency (HF) heating of the ionospheric D region and very high frequency (VHF) heating of the equatorial electrojet. A brief description of the theory and the geometry of the heating experiment is followed by a discussion of local VLF/ELF radiation detected near the HF transmitter locations at Arecibo, Puerto Rico, and at the Jicamarca Radar Observatory near Lima, Peru. Long‐path detection of VLF/ELF radiation initially recorded on a path from Tromso, Norway, to the Pennsylvania State University in 1981 is updated with current experimental long‐path results over paths between Jicamarca, Peru, and Salinas, Puerto Rico, as well as Arecibo, Puerto Rico, to the Pennsylvania State University.
Geometrical theory of a one‐dimensional microstrip resonator: The effect of topside charges and currents
Authors: Chang David C. , Kuester Edward F. , Mahnad Ali R.
Published: February 2008

The effects of fields which penetrate from underneath a microstrip patch antenna to the top of the patch can affect the resonance condition for this antenna. Previous cavity models for the rectangular patch have ignored this effect. In this paper, we present an analysis of a one‐dimensional microstrip resonator where topside effects are accounted for. The influences on the unloaded radiation Q and on the resonant frequency are examined as functions of the substrate permittivity.
Spectral moment estimation in MST radars
Authors: Woodman Ronald F.
Published: February 2008

Processing techniques for the estimation of the power, the frequency shift, and the spectral width of mesosphere‐stratosphere‐troposphere (MST) radar returns are presented. The different techniques are compared in terms of statistical goodness of the estimators and in terms of computational convenience and simplicity.