bluuebunny/crossref_metadata_2025 huggingface dataset:
Multipole Methods for Scattering From a Conducting Cylinder Over a Dielectric Half‐Space
Authors: Kelly Kenneth R. , Schultz F. V.
Published: February 2008

Two different but equivalent multipole methods are applied to the problem of determining the scattering of an electromagnetic wave by a perfectly conducting cylinder over a dielectric half‐space. Numerical results are presented for different sets of parameter values. The results seem to be in good agreement with those obtained by geometrical optics methods for the high‐frequency case, and qualitative results can be obtained by a relatively simple procedure based on geometrical optics.
Theory of Midlatitude Sporadic E
Authors: Layzer David
Published: February 2008

A discussion of the observed properties of midlatitude sporadic E leads to the conclusion that vertical redistribution of neutral ionization is the only mechanism by which long‐lived metal ions can be concentrated into thin sheets extending over horizontal distances of several hundred kilometers. However, vertical ion transport occasioned by observed wind shears with vertical scales of a few kilometers fails to account for the vertical structure of E8 layers and their diurnal and seasonal variations. Experimental evidence indicates that, below 120 km, narrow layers of enhanced ionization coincide with abrupt changes in the magnitude and direction of the wind shear. These changes, marked by corners in the horizontal‐wind hodograph, occur over vertical intervals of 100 meters or less. Two alternative physical interpretations of these quasi‐discontinuities are discussed (I now regard my earlier suggestion that they represent gravity shocks as unlikely): stable contact discontinuities, across which the temperature and density (but not the vertical component of velocity and not the pressure) change abruptly; very narrow (Δz ≃ 10 meters) sheets of very high shear (dV/dz ≃ 0.1 sec−1). It is shown that in either case the layer could function as an effective ion trap. Strong and variable electric polarization fields, however, would interfere with the action of such a trap. Considerations related to the variable component of the polarization field provide a simple and straightforward qualitative explanation for the double‐peaked diurnal variation of intense summertime sporadic E, its seasonal variation, and its negative correlation with magnetic activity.
The Effect of a Buried Conductor on the Subsurface Fields for Line Source Excitation
Authors: Wait James R.
Published: February 2008

An approximate analytical method is presented for treating electromagnetic scattering from a slender cylindrical conductor buried in a homogeneous conducting half‐space. The excitation is by a uniform line source of current located on the surface. The solution is achieved by an iterative method that accounts for the interaction of the induced current in the cylinder and the air‐earth interface. It is shown that the cylindrical inhomogeneity will distort the profile of the subsurface magnetic field as the horizontal displacement is varied.
Antennas in Plasma: Characteristics as Functions of Frequency
Authors: Balmain K. G.
Published: February 2008

The literature on the subject is reviewed under the headings: anisotropic (cold) electron plasma, isotropic (warm) electron plasma, loop antennas, resonance rectification, and ion effects. Though the gap between theory and experiment has narrowed for most of these topics, understanding is still unsatisfactory at lower frequencies where ion motion cannot be neglected.
Electron Resonances Observed With Topside Sounders
Authors: Muldrew D. B.
Published: February 2008

Ionograms recorded with ionospheric sounders aboard rockets and satellites show signals (resonances) which can persist from a fraction of a millisecond to many milliseconds after the termination of the transmitted pulse. Many of the characteristics of the resonances at the plasma frequency ƒN, the upper‐hybrid frequency ƒT, the harmonic gyrofrequencies nƒB, where n ≥ 2, and the maximum frequencies of the Bernstein modes ƒQn can be explained by propagating electrostatic waves. At frequencies near ƒN, ƒT, and nƒB, electrostatic waves of slightly different frequencies generated by the transmitted pulse propagate in the ionospheric plasma, become reflected at distances up to several hundred meters away from the satellite, and return to the satellite, producing a continuous receiver response following the transmitted pulse. The resonance observed at the gyrofrequency ƒB is not yet understood. Nonlinear properties of the receiving system and/or the plasma can result in resonances observed at the sum and difference frequencies of the principal resonances. Other resoncance phenomena are also discussed.
The Transient Electromagnetic Response of a Spherical Shell of Arbitrary Thickness
Authors: Hill David A. , Wait James R.
Published: February 2008

Starting with the plane‐wave solution for scattering from a two‐layer sphere, the quasistatic response of a thin conducting shell is recovered analytically. Responses are also computed for shells of arbitrary thickness, and the range of validity of the thin‐shell approximation is determined. These results are extended to the time domain by a numerical inverse Fourier transform which yields the response to a step‐function incident field (magnetic or electric). It is found that under the thin‐shell approximation, the transient response has a simple single‐exponential form. This is modified to some extent when the arbitrary thickness of the shell is allowed for.
The EUV spectrophotometer on Atmosphere Explorer
Authors: Hinteregger H. E. , Bedo D. E. , Manson J. E.
Published: February 2008

An extreme ultraviolet (EUV) spectrophotometer for measurements of solar radiation at wavelengths ranging from 140 to 1850 Å will be included in the payload of each of the three Atmosphere‐Explorer (AE) missions, AE‐C, ‐D, and ‐E. The instrument consists of 24 grating monochromators, 12 of which can be telecommanded either to execute 128‐step scans each covering a relatively small section of the total spectrophotometer wavelength range or to maintain fixed (command‐selected) wavelength positions. The remaining 12 nonscan monochromators operate at permanently fixed wavelengths and view only a small fraction of the solar disk except for one viewing the whole sun in H Lyman α. Ten of the 12 scan‐capable monochromators also view the entire solar disk since their primary function is to measure the total fluxes independent of the distribution of sources across the solar disk. The narrow angular fields of view of the other monochromators allow good height resolution of atmospheric‐absorption analyses to be extended to altitudes as low as 90 to 100 km, based on occultation observations made near satellite sunrise and sunset.
Low‐energy electron experiment for Atmosphere Explorer‐C and ‐D
Authors: Hoffman R. A. , Burch J. L. , Janetzke R. W. , McChesney J. F. , Way S. H. , Evans D. S.
Published: February 2008

The low‐energy electron experiment will provide differential measurements of the energy influx and angular distributions of electrons and protons on the Atmosphere Explorer‐C and ‐D missions. The detectors consist of cylindrical electrostatic analyzers for species and energy selection and Spiraltron electron multipliers as particle sensors. The C version will contain three detectors, two measuring electrons and protons from 0.2 to 25 kev in 16 logarithmically‐spaced steps and one measuring 5 kev electrons continuously. Angular distributions will be acquired utilizing the spin of the spacecraft. The D version will contain 19 detectors, one proton‐stepped energy analyzer, and two electron‐stepped energy analyzers at two different angles, again over the energy range 0.2 to 25 kev. In addition it will contain 16 fixed‐energy detectors which will obtain high time‐resolution angular distributions in the spacecraft one‐revolution‐per‐orbit mode at five energies between 0.2 and 5 kev. Increase of these energies by a factor of 3.5 will be possible by ground command.
Digital‐correlation techniques in radio science
Authors: Hagen J. B. , Farley D. T.
Published: February 2008

Various digital techniques for estimating the autocorrelation function of a signal are analyzed, with emphasis on methods applicable to radio‐astronomy and incoherent‐scatter studies of the ionosphere. The importance of coarse (one‐ or two‐bit) quantization is stressed, as is the effect of oversampling, the use of a sampling interval less than the inverse of twice the signal bandwidth. For applications such as incoherent scatter in which the signal strength varies with range (i.e., time), multibit by one‐bit multiplication combined with oversampling is probably the optimum strategy, although it requires 32% more integration time than the full multibit by multibit technique. For very high speed sampling of a signal of which the mean amplitude is constant, a three‐level by three‐level technique offers many advantages. It is nearly as simple to implement as conventional one‐bit correlation but requires considerably less integration time to achieve equal statistical accuracy (only 26% more than full multibit correlation, when sampled at twice the Nyquist rate, as compared to 146% for a one‐bit correlator with sampling at only the Nyquist rate).
A new look at the thin‐plate scattering problem
Authors: Mittra, R. , Rahmat‐Samii, Y. , Jamnejad, D. V. , Davis W. A.
Published: February 2008

In this paper the H‐integral equation is investigated for the problem of plane‐wave diffraction by a thin plate. It is found that the limiting form of the H‐equation by itself is not complete unless the condition
is simultaneously enforced. By suitably combining the above‐mentioned equations, a new set of equations is derived for the two components of the surface current distribution on the plate. Several advantageous features of the new equations are pointed out, and numerical results based upon the use of these equations are presented for the thin‐strip and the square‐plate problems.
Plasma flow in the plasma sheet and its relation to substorms
Authors: Hones Edward W.
Published: February 2008

The substorm‐related thinning and thickening of the plasma sheet, processes that have been extensively studied at XSM≈ −18 RE, occur at all distances in the magnetotail beyond XSM ≈ −10 to −15 RE in most substorms. These processes involve rapid flow of plasma out of and into the magnetotail and suggest the formation of magnetic neutral lines, first near the earth and then far out in the tail during a substorm. Evidence for these processes is discussed.
The horizontal wire antenna over a conducting or dielectric half space: Current and admittance
Authors: King R. W. P. , Wu T. T. , Shen L.‐C.
Published: February 2008

The wave number, the distribution of current, and the admittance of a horizontal wire antenna over a homogeneous isotropic half space are determined when the complex wave number characteristic of the half space is large in magnitude compared with the real wave number of the air. The axial electric field at the surface of the half space is described. The properties of the antenna are obtained from those of the eccentrically insulated dipole in a general medium in the limit as the radius of the insulation is increased without limit while the distance of the dipole from the boundary is kept constant. Application of the new theory to the Beverage or wave antenna is discussed.
Radio frequency scattering from a heated ionospheric volume: 2, Bistatic measurements
Authors: Minkoff J. , Laviola M. , Abrams S. , Porter D.
Published: February 2008

A variety of bistatic experiments which were carried out for the purpose of determining the scattering properties of the heated inospheric volume in the F layer over Platteville, Colorado, are described. Results are presented on the basis of which it was first determined that the center‐line scattering takes place from elongated field‐aligned scattering structures. Measurements are presented showing that, for the center‐line mode, the scattering of the incident signal consists, effectively, of specular reflections off the geomagnetic field lines.
HF‐VHF communications experiment using man‐made field‐aligned ionospheric scatterers
Authors: Barry G. H.
Published: February 2008

Scatter from man‐made, field‐aligned, F‐layer irregularities offers a means of over‐the‐horizon communication at VHF frequencies. Experimental data collected in 44 days of field operation in the autumns of 1972 and 1973 defines representative characteristics of signals transmitted over such a scatter circuit. A cloud of field‐aligned scatterers was created by the Platteville, Colorado, ionospheric modification facility; test transmitting sites were established in Texas and receiving sites in California. The data describe mean and peak cloud radar cross section, the dependence of cross section on heater power, heater modulation, time of day, and signal frequency, the circuit coherent and incoherent bandwidths, the signal amplitude statistics and spatial correlation, and the signal spectral spreading. The experiment also included the transmission of representative types of modulated signals including SSB voice, 100‐word/min FSK teleprinter data, 2400‐bit/sec data, 30‐kHz FM voice, and 3‐kHz FSK facsimile.
Arecibo heating experiments
Authors: Gordon W. E. , Carlson H. C.
Published: February 2008

Enhancements of various features of the incoherent scatter spectrum are observed when the ionosphere is illuminated with powerful, high frequency radio waves. The radio waves excite plasma instabilities producing lines or more complex spectral features near the local plasma frequency, at the local ion acoustic frequency, near the local gyrofrequency, and near twice the gyrofrequency. The enhancements occur in a thin slab as observed by the incoherent scatter radar and at both upshifted and downshifted frequencies with respect to the probing radar frequency. The enhancements are observed to vary with time when the excitation is held constant and is turned on or off.

The high power radio waves are produced by a 160 kw transmitter feeding a log‐periodic pair of curtains mounted at the focus of the 1000‐ft reflector and covering the frequency range from 5 to 12 MHz. The effects are observed with the incoherent scatter radar using the same reflector and with ionosondes and photometers.

The frequencies of the enhanced plasma line and the ion line and their relation to the pump (high frequency radio wave) frequency are predictable from available parametric instability theory. Other spectral features are being explained as the theory develops with the help of the observations. There remain some discrepancies, in particular the asymmetries in intensity, width, and fluctuations of the upshifted compared to the downshifted plasma lines.
Radar evidence of Fe+ in a sporadic‐E layer
Authors: Behnke Richard A. , Vickrey James F.
Published: February 2008

Incoherent scatter results are presented using compressed‐pulse techniques to study a sporadic‐E layer at Arecibo. Multiple Barker‐coded pulses were used to obtain the autocorrelation function of the Es layer. A 13‐bit code with a baud length of 4 μsec was employed, resulting in 600‐m height resolution. The observations are examined for the presence of Fe+ by least‐square fitting the measured autocorrelation functions to a library of theoretical ones. The analysis indicates that Fe+ dominates in the Es layer, usually providing about 70% of the ionization.
Low‐angle radar tracking errors induced by nonstratified atmospheric anomalies
Authors: Vickers William W. , López Manuel E.
Published: February 2008

Anomalous refractive profiles and inversion layer structures at the Western Test Range, Vandenberg, California, were measured using airborne sensors. When the marine inversion layer was traced inland, the refractive gradient was observed to undergo upward warping, waving, dilation, lensing, and splitting. Refraction corrections computed using airborne‐measured, full cross sections along the radar line of sight were at times more than twice as large as those corrections resulting from single‐point radiosonde or aircraft spiral inputs, which must assume a spherically stratified atmosphere. Ray‐tracing techniques could reliably predict the location of actually observed radio holes (areas where radar loss‐of‐lock occurs) only when inputs from full, three‐dimensional, airborne cross sections were used.
Impulse radar sounding in permafrost
Authors: Annan A. P. , Davis J. L.
Published: February 2008

A VHF impulse radar system operating on the ground is a viable technique for mapping the near‐surface geological structure and electrical properties of permafrost. A fixed antenna configuration transported over the surface yields a reconnaissance map of two‐way travel times for subsurface reflectors. Wide‐angle reflection and refraction (WARR) sounding determines propagation velocity versus depth when performed in layered areas. To obtain a WARR sounding, one measures travel time versus antenna separation. These techniques were field tested in the Tuktoyaktuk region of the Mackenzie River delta, N.W.T. Data recording was on a graphic display for initial field analysis and on analog magnetic tape for subsequent processing. Reconnaissance surveying has mapped structural features at various depths between 3 and 30 m. The electrical loss of the soils at a site limits the penetration depth. Clays and silts attenuate the radar signal more than sands and gravels. WARR soundings have determined dielectric constant versus depth in layered areas. While impulse radar is useful in delineating geological structure, core drilling is required to determine the geological composition.
Microwave radar wind measurements in the clear air
Authors: Chadwick R. B. , Moran K. P. , Strauch R. G. , Morrison G. E. , Campbell W. C.
Published: February 2008

It is shown that an FM‐CW radar can be used as a Doppler radar to measure winds. A description of the processing used to measure Doppler shifts is included. An analysis of scattering by refractive‐index fluctuations shows that, under certain conditions, a Doppler FM‐CW radar should be able to measure winds continuously in the boundary layer. Experimental results comparing horizontal winds measured by a tethered balloon and the FM‐CW radar show very good agreement.
Analysis of semi‐infinite and finite thin‐wire antennas above a dissipative earth
Authors: Olsen Robert G. , Chang David C.
Published: February 2008

The problem of the reflection of current at the end of a semi‐infinite wire is solved using Wiener‐Hopf techniques. It is found that the end effect can be expressed as a single reflection parameter which is a function of the height of the wire, the electrical properties of the earth, and the frequency of the excitation. This simplification yields an accurate representation for the reflected current for points not very close to the end of the wire. Representation of the end effect in this manner leads to a simple theory for long finite horizontal antennas similar to that found in transmission line problems. Input conductance changes as a function of earth parameters for a resonant and an antiresonant antenna are then presented.
Anomalous radio wave absorption due to ionospheric heating effects
Authors: Graham Kristine N. , Fejer J. A.
Published: February 2008

An ionospheric volume in the F layer subjected to high power high frequency illumination is observed to be an effective scattering medium for radio signals. Experimental results are representative of a field‐aligned scattering geometry. Scatter of the incident wave into electrostatic waves by these strongly field‐aligned density irregularities is considered. This model explains the large decreases in radio wave reflectivity seen during the ionospheric modification.
Electromagnetic modeling of reflections inside an in situ gasified coal seam
Authors: Holmes John J. , Balanis Constantine A.
Published: February 2008

As an aid in the design of an electromagnetic system for the detection, monitoring, and mapping of the burn front of an underground (in situ) coal gasification process, an analytical model has been developed that will predict the electromagnetic field reflected from the gasified portion of the coal seam. The coal and gasified section have been modeled electrically as lossy media, surrounded above and below by relatively high conducting overburden and underburden. Vertical and horizontal electric and magnetic dipoles have been investigated, utilizing a geometrical optics formulation which also takes into account the physical roughness of the coal‐overburden (underburden) and coal‐gasified section boundaries. Indications are that a swept frequency monitoring system is capable of locating the burn front of the in situ gasification process, with the vertical electric dipole being the most attractive element.
Rain outage performance of tandem and route diversity systems at 11 GHz1
Authors: Drufuca G. , Torlaschi E.
Published: February 2008

Long distance radio systems at 11 GHz are considered with respect to rain outage. Conventional tandem systems and simple route diversity systems are analyzed and compared on the basis of rain attenuation statistics obtained from radar observations. The comparisons appear to be very favorable to diversity systems in terms of the number of repeaters. Unfortunately, the available descriptions of joint probabilities of attenuation for pairs of radio paths allow only conservative analysis of very simple diversity systems, so that effective designs are not yet possible. Therefore, the need for further investigations on intense precipitation patterns still exists.
Diagnosis of the turbulent state of ionospheric plasma by propagation methods
Authors: Yeh K. C. , Liu C. H.
Published: February 2008

An electromagnetic signal randomized by scattering from plasma irregularities and by subsequent diffraction in the nonrandom part of the medium is known to bear statistical information about the plasma turbulent irregularities. For example, if the turbulent spectrum is of the form κ−p in its wavenumber dependence, the received amplitude of the electromagnetic signal will fluctuate with a high frequency spectral asymptote of the form υ1−p. However, a power‐law turbulent spectrum of the form κ−p has certain nonphysical difficulties if cutoffs at both the inner scale and the outer scale are not introduced. In addition, in this paper it is shown that the mean arrival time and the mean square pulse width are rather sensitive to values of the outer and inner scales of ionospheric turbulence. Information concerning the values of these scales is rather meager at present. It is therefore suggested that pulsed experiments be made so that the inner scale and the outer scale can be determined. Possibilities of making similar measurements on a laboratory plasma are also implied.
Deposition of electromagnetic energy in animals and in models of man with and without grounding and reflector effects
Authors: Gandhi Om P. , Hunt Edward L. , D'Andrea John A.
Published: February 2008

Generalized curves are given for rates of whole‐body absorption of electromagnetic energy by models of human beings as a function of frequency. Exposures were made in free space, or when the model made electrical contact with the ground. The effects of the presence of reflecting surfaces also were analyzed. Peaks of absorption with and without a ground, are projected, respectively, to be (31 to 34 MHz) and (62 to 68 MHz) × (1.75/height of model in meters). Rates of energy deposition are given for models of man and for animals subjected to radiation at a power density of 10 mW/cm2 for the various conditions of exposure. At resonance, values of whole‐body absorption as high as 4,077 to 8,154 watts for the adult human being are predicted. The times‐to‐convulsion of ∼100‐g rats at power densities of 3 to 20 mW/cm2 confirmed predictions of extremely high rates of absorption in the presence of reflecting surfaces.
Comparison of the average specific absorption rate in the ellipsoidal conductor and dielectric models of humans and monkeys at radio frequencies
Authors: Massoudi Habib , Durney Carl H. , Johnson Curtis C.
Published: February 2008

Perturbation theory has been used to find the first‐order internal electric field, the SAR (specific absorption rate), the spatial variations of the SAR, and the maximum SAR in prolate spheroidal and ellipsoidal models of man and experimental animals during irradiation by an electromagnetic plane wave when the wavelength is long as compared to the dimensions of the exposed body. In our “conductor” model of man, conductivity is written explicitly in the curl H equation as: ∇ × H = σE + jω∈ E. In what we call the “dielectric” model, the conductivity is contained implicitly in the complex permittivity, so that the curl H equation is ∇ × H=jω∈E. The two models give different results for first‐order fields because the equations are expanded in a power series in k (k = ω√μ∈); in the conductor model σ enters into the zero‐order equations but in the dielectric model it does not. Because of the nature of the zero‐order equations, the expressions obtained from the conductor model are not valid as σ→0. We have found that the conductor model is valid only if ∈2 »ϵ1 where ϵ1 and ∈2, respectively, are the real and imaginary parts of the complex dielectric constant of the models. Consequently, some caution must be exercised in applying the results of perturbation theory as based on the conductor model. In this paper, the results of perturbation theory as applied to a lossy dielectric ellipsoidal model are described. The SAR in a dielectric ellipsoidal model of a rhesus monkey is calculated and compared with that of the conductor model. The SAR in the two models is found to be the same if the conduction current in the body is much larger than the displacement current. Although the conductor model is inaccurate for low values of conductivity, the equations are simpler than the ones for the dielectric model, and hence the conductor model is advantageous when valid.
Differential reflectivity and differential phase shift: Applications in radar meteorology
Authors: Seliga T. A. , Bringi V. N.
Published: February 2008

The differential scattering properties of classes of hydrometeors at linear orthogonal polarizations provide potentially important differences which may be exploited for radar measurements of precipitation. The ratio of the reflectivity at horizontal (ZH) and vertical (Zv) polarizations may be combined with other radar measurements such as absolute reflectivity and differential phase shift to determine drop size distributions. Previous model calculations of differential reflectivity ZDR = 10 log (ZH/Zy) were made using Gans' theory of scattering by spheroids. New calculations, using Waterman's T‐matrix method, are in excellent agreement with Gans' theory for raindrops at S‐band wavelengths. The ZDR‐differential phase shift combination, which need not depend on any absolute measurements, is shown to be a reasonable radar method for measuring two‐parameter raindrop size distributions. Finally, calculations of ZDR for oblate hailstones indicate the possibility of uniquely detecting large, dry hail when the hail is falling with preferred orientation.
The transient fields of simple radiators from the point of view of remote sensing of the ground subsurface
Authors: Botros Adel Z. , Mahmoud Samir F.
Published: February 2008

The electromagnetic transient response of electric line sources and current‐carrying loops above a two‐layered stratified ground is considered at both early and late times. The early time fields are obtained using the geometrical ray theory, while the late time fields are treated in a manner following the work of Wait, leading to closed‐form solutions. The limiting case of a homogeneous ground is considered by more exact means and comparisons are made with the case of late time response of the layered ground model. It is shown that the depth and the conductivity of the overburden layer may be detected from the behavior of the transient fields.
Path diversity for earth‐space communication links
Authors: Hodge D. B.
Published: February 2008

This paper contains the results of a radar study of path diversity performance on simulated earth‐space communication links in the presence of rainfall. The McGiIl University 3 GHz radar was used to obtain three‐dimensional fields of radar reflectivity. The radar reflectivities measured at resolution cells along the propagation paths of interest were converted to specific attenuation and these values of specific attenuation were then summed to yield the total path attenuation. This procedure was repeated along parallel earth‐space paths to yield the path diversity performance. The results for the Montreal area indicate that path diversity performance is mildly dependent upon the orientation of the propagation path and weakly dependent upon the baseline orientation of the ground diversity terminals.
On the determination and investigation of the terrestrial ionospheric refractive indices using GEOS‐3/ATS‐6 satellite‐to‐satellite tracking data
Authors: Liu Anthony S.
Published: February 2008

When the radio link between two satellites (GEOS‐3/ATS‐6) is intercepted by the Earth's ionosphere and neutral atmosphere, a change in the Doppler frequency results. Travel through the atmosphere causes the Doppler phase to be advanced in the ionosphere's portion and retarded in the neutral portion of the atmosphere. Analysis of the shortening and lengthening of the phase of the Satellite‐to‐Satellite Tracking (SST) data that passed within 40–700 km above the Earth's surface during its ATS‐6 to GEOS‐3 to ATS‐6 path, caused by the atmosphere, results in refractivity versus height profiles. The SST Doppler data were used directly to adjust the GEOS‐3 orbit. Perturbation from the Moon, Sun, and a 15th‐order/degree Earth gravity field were included in the orbit solution. This orbit was continued through the occultation period and a model ionosphere was estimated by a least‐squares adjustment of the Chapman ionosphere parameters from the SST data residuals. The refractivity profile obtained by this model ionosphere was compared to a refractivity profile obtained by a direct integral inversion of the SST data residuals. Systematic differences between the two methods were caused by orbital errors, which propagated into the solution. The SST data yielded refractive index profiles in a novel economical manner because no additional or special on‐board equipment were required.
Delay and Doppler power spectra of a fading ionospheric reflection channel
Authors: Malaga Alfonso , McIntosh Robert E.
Published: February 2008

The time and frequency selective behavior of a fading HF ionospheric reflection channel is considered in this paper. Both deterministic and random spatial and temporal variations of the ionosphere and the troposphere are included in determining the multipath delay and Doppler frequency spreading of a channel in which the signals are reflected off of a multilayered ionosphere. An example which illustrates the diffuseness of the multipath and Doppler spectra under typical propagation conditions is given.
Numerical analysis of three‐dimensional arbitrarily‐shaped conducting scatterers by trilateral surface cell modelling
Authors: Wang J. J. H.
Published: February 2008

A new technique has been developed to calculate the scattering characteristics of a three‐dimensional arbitrarily‐shaped conducting body. The analysis employs a moment method which divides the surface of the scatterer into trilateral surface cells. The physical‐optics type of current on each cell has been utilized to form the set of basis functions. A generalized computer program has been written and has been tested on the case of a sphere to demonstrate the numerical advantages of the present technique as compared with other existing surface‐type integral approaches and wire‐grid modelling techniques.
Interdisciplinary and international contributions to research on biological effects of electromagnetic waves: Past performances and future challenges
Authors: Johnson Curtis C.
Published: February 2008

From lessons learned in the late 1960s and early 1970s, skilled teams of interdisciplinary investigators have formed that are making technical and scientific contributions to knowledge of the biological response to non‐ionizing electromagnetic radiations. Examples of technological advances in the US and other Western nations are nonperturbing thermal sensors, and dosimeters for measuring whole‐body absorption of energy and for determining differential uptake of energy in tissues of interest. These advances have enabled considerable gains in knowledge and prediction of energy capture by human and infrahuman bodies as functions of wavelength and orientation of an object in the field. Complementing these advances are those by Eastern investigators, who have performed many epidemiological surveys and have pioneered studies of behavioral and nervous reactions to long‐term, low‐level irradiation. The resulting accretion of data, including those from international programs of scientific exchange, will help provide a sound basis for standards of safety and for beneficial applications of radio frequency energy. Especially promising in the area of medicine are microwave techniques for non‐invasive diagnostic “imaging” of deep tissues, and for treatment of cancer.
Impedance measurements of Deception Island as a natural very‐low‐frequency antenna
Authors: Morgan M. G.
Published: February 2008

In 1960 I suggested that Deception Island, near the northern end of the Antarctic Peninsula, might serve as a useful naturally resonant VLF slot antenna. Connection across the island was subsequently made and impedance measurements were obtained. Contrary to theoretical predictions by Galejs and by Staras, a strong resonance was obtained. However, it occurred at 9.5 kHz, rather than at 5 kHz as anticipated. This is ascribed to a short, low cut through one of the arms of the island which otherwise range from 500 to 1000 ft high. A composite transmission line model is constructed to represent the data. A first approximation to the efficiency suggests that it is in the range of 10–25%.
Summary of extremely low frequency (ELF) field strength measurements made in Connecticut during 1975
Authors: Bannister Peter R.
Published: February 2008

Both 42‐ and 76‐Hz, horizontal, magnetic‐field‐strength measurements (amplitude and relative phase) were made in Connecticut during 1975. These measurements were taken to further investigate sunrise, daytime, sunset, nighttime, and seasonal extremely low frequency (ELF) propagation variations. The transmission source for these 1.6‐Mm range measurements was the US Navy ELF Wisconsin Test Facility. It was determined from these measurements that (1) ELF nighttime propagation is much more variable than daytime propagation, (2) the “Halloween effect” was observed for the sixth consecutive year, and (3) phase velocity changes during pure nighttime propagation conditions occasionally appear to be greater than changes associated with the sunrise‐sunset terminators crossing the transmitter or receiver locations.
On some effects observed during powerful VLF wave action on the ionosphere
Authors: Molchanov O. A. , Resnikov A. E. , Fligel D. S.
Published: February 2008

The results of observations of the amplitude variations of pulses transmitted by a powerful VLF transmitter (ƒ = 15 kHz) at different distances are given. The duration of the pulses varied from 5 to 120 sec. The observed variations may be explained as the self‐action of a powerful wave in the lower ionosphere.
Collisionless damping of Alfvén waves in an inhomogeneous plasma: Solution of the initial value problem
Authors: Abels‐van Maanen A. E. P. M. , Weenink M. P. H.
Published: February 2008

The initial value problem of the linearized ideal MHD equations for a low‐β plasma in an inhomogeneous magnetic field is solved for a broad class of initial conditions. The validity of the solutions breaks down after a time, which is determined by the magnitude of the initial conditions. The energy is transported to the inhomogeneous region. The mechanism described here could therefore possibly be used for shaping of the plasma temperature profile.
A first‐order theory on wave depolarization by a geometrically anisotropic random medium
Authors: Tan H. S. , Fung A. K.
Published: February 2008

A vector theory of wave scattering from a random medium has been developed using the first‐order renormalization theory. It is demonstrated with a chosen anisotropic correlation function that this first‐order theory can lead to cross‐polarized backscatter when the correlation function of the permittivity fluctuations is not required to have symmetry with respect to the plane of incidence. It is also found that while, in general, 12 modes may exist in the random medium (after excluding the evanescent modes), only two propagating modes are dominant and satisfy the radiation condition. When the correlation function is isotropic in the azimuth, there is no coupling between polarization components, and only one dominant propagating mode may exist for a given incident polarization. Approximate closed form expressions for the scattering coefficients are obtained for the anisotropic correlation function. The effects of anisotropy on the angular behaviors of the scattering coefficients are illustrated.
The spectral measurement of plasma lines
Authors: Showen R. L.
Published: February 2008

A method for measuring the critical frequencies of the ionospheric layers to accuracies better than 1 kHz is presented. The method depends on the fact that the intensity of the incoherent backscatter plasma line is a function of the electron number density scale height. At the peak or valley of a layer, more electrons are resonant within a specific frequency resolution cell. When fine‐frequency measurements are made of the echo from a long radar pulse, the abrupt signal intensity variations as a function of the frequency permit accurate determination of the critical frequencies. Measurements with the Arecibo Observatory 430‐MHz radar of the peak densities show that fluctuations of the order of 0.005% can be detected. The integration time must not be longer than a few seconds or frequency smearing caused by ionospheric changes occurs. Comparison of the upshifted and downshifted plasma line frequencies demonstrates the effect of different reception wavelengths on the resonant frequency and also permits determination of the electron drift velocity.
A review of satellite time transfer technology: Accomplishments and future applications
Authors: Cooper Robert S. , Chi Andrew R.
Published: February 2008

A brief review of the research accomplishments by NASA in meeting the needs of the space program for precise time in satellite tracking is presented. As a major user of precise time signals for clock synchronization of NASA's worldwide satellite tracking networks, the agency provided much of the necessary impetus for the development of stable frequency sources and time synchronization technology. The precision in time required for both satellite tracking and space science experiments has increased at a rate of about 1 order of magnitude per decade from 1 ms in the 1950's to 100 μs during the Apollo era in the 1960's to 10 μs in the 1970's. In the 1980's, when the Tracking and Data Relay Satellite System (TDRSS) comes into operation, satellite timing requirements will be extended to 1 μs and below. These requirements are needed for spacecraft autonomy and data packeting which are now in active planning stages.
An integral‐equation approach to long‐wave propagation in a nonstratified earth‐ionosphere waveguide
Authors: Field E. C. , Joiner R. G.
Published: February 2008

This paper presents a method for analyzing long‐wave propagation under conditions where the properties of the earth‐ionosphere waveguide change markedly over lateral distances comparable with a wavelength or Fresnel zone. The method is most useful for extremely low frequencies (ELF). To facilitate numerical solution, the lateral wave equation is transformed into an integral equation that accounts for most full‐wave properties, including diffraction around localized disturbances and reflection from lateral gradients. Approximate solutions show that full‐wave methods must be used to account for lateral gradients transverse to the propagation path if the effective width of a localized ionospheric disturbance is less than about two‐thirds the width of the first Fresnel zone. In that situation the lateral WKB approximation significantly overestimates the corresponding propagation anomaly when the disturbance is centered near the propagation path and underestimates the anomaly when the disturbance is centered far off path. Numerical solutions for disturbances having gradients in the direction of propagation reveal pronounced standing wave patterns if the waveguide properties change markedly over a lateral distance equal to about one‐sixth of a wavelength.
Effects of microwave radiation on erythrocyte membranes
Authors: Liu L. M. , Nickless F. G. , Cleary S. F.
Published: February 2008

Suspensions of rabbit, human, and dog erythrocytes were irradiated by S‐band microwaves in a WR‐284 waveguide chamber for a period of 20 minutes or three hours. The release of K+ and hemoglobin, and the osmotic fragility of the cells, were assayed to determine the effects of microwave and conventional heating on erythrocyte membranes. Conventional heating and microwave radiation resulted in sample temperatures that ranged from 25 to 44°C. There were no statistically significant differences between freshly prepared cells that were irradiated and those heated in a temperature‐controlled water bath at energy absorption rates near 200 mW g−1 for three‐hour exposures at a frequency of 3.0 GHz, and near 80 and 100 mW g−1, respectively, for frequencies of 2.45 and 3.95 GHz. Freshly prepared suspensions of rabbit erythrocytes and ouabain‐treated suspensions were also exposed to 3.0‐GHz microwaves at an absorption rate of 170 mW g−1 for 20 minutes or for three hours. No statistically signficant differences were detected between irradiated and water‐bath‐heated samples. In addition, effects of 3.0‐GHz microwaves on rabbit erythrocytes that had been held for seven days at 4°C prior to three hours of exposure were studied at a range of absorption rates to 170 mW g−1; no statistically significant effects of microwave irradiation were observed compared with the water‐bath‐heated controls although both modes of heating induced permeability changes relative to room‐temperature controls.
Errors in magnetic direction finding due to nonvertical lightning channels
Authors: Uman M. A. , Lin Y. T. , Krider E. P.
Published: February 2008

We present theory to show that errors in lightning magnetic direction finding due to nonvertical source orientations are minimized by detecting the field from the lowest possible channel section. For 99 cloud‐to‐ground lightning channels photographed in Arizona, 45 exhibited a bottom few hundred meters within about 8° of the vertical, the standard deviation of the distribution of lower‐channel tilt angles being about 18°. These experimental results, coupled with theory, suggest that if a wideband gated direction finder is used, polarization errors due to nonvertical sources can be kept less than 1° for lightning beyond 10 km.
High‐altitude resolution stratospheric measurements with the Arecibo 430‐MHz radar
Authors: Woodman R. F.
Published: February 2008

The potential of the Arecibo 430‐MHz radar for the study of stratospheric dynamics and turbulence has been recently established. In the past the instrumented resolution of the system has been larger than 300–600 m. The present paper describes instrumental modifications which have enabled us to obtain a resolution of 150 m, the maximum allowed by the transmitter bandwidth. Such a gain in resolution is very important for stratospheric studies, since it is expected that turbulence occurs at these altitudes in layers with thickness between a few tens to a few hundred meters. Furthermore, a complementary coded pulse scheme has been used for the first time. Such a code has the advantage of generating no pulse side lobes, an important property for defining the quiet regions existing in between turbulent layers. Decoding is performed digitally. The high data processing rate is taken care of by the use of a preprocessor. Power spectra of the signals corresponding to 256 altitudes are evaluated on line by means of an array processor peripheral connected to the processing computer. Useful echoes have been obtained from 10 km to about 30 km. The existence of layers of turbulence has been demonstrated, and their separation has been determined, but the thickness of some of them has still not been fully resolved. The separation of the layers varies as a function of altitude, changing from a few hundred meters at lower stratospheric heights to a few kilometers at 25‐ to 30‐km altitudes. The results obtained show the importance of high resolution when using radars to obtain wind information from the Doppler shift of turbulence echoes.
Analysis of linear antenna systems: A different approach
Authors: Walsh John , Srivastava S. K.
Published: February 2008

An alternative to the classical methods of analysis of linear antenna systems is proposed. The practice of solving an integral equation directly for an unknown current distribution is replaced by that of solving an integral equation for an unknown intermediate function. This intermediate function is shown to be the forcing function of a differential equation whose closed‐form solution yields the unknown current distributions. Numerical results based on the method and contained in this paper compare favorably with those of other investigators both theoretically and by measurement. The method exhibits a convergence rate far superior to that of the classical Pocklington formulation when simple approximating functions and point matching are used, yet the flexibility of the Pocklington formulation is retained. The method is well behaved numerically and convenient for computation.
Radiative transfer theory for active remote sensing of a layer of small ellipsoidal scatterers
Authors: Tsang L. , Kubacsi M. C. , Kong J. A.
Published: February 2008

The radiative transfer theory is applied within the Rayleigh approximation to calculate the backscattering cross section of a layer of randomly positioned and oriented small ellipsoids. The orientation of the ellipsoids is characterized by a probability density function of the Eulerian angles of rotation. The radiative transfer equations are solved by an iterative approach to first order in albedo. In the half space limit the results are identical to those obtained via the approach of Foldy's and distorted Born approximation. Numerical results of the theory are illustrated using parameters encountered in active remote sensing of vegetation layers. A distinctive characteristic is the strong depolarization shown by vertically aligned leaves.
Scattering cross sections for random rough surfaces: Full wave analysis
Authors: Bahar Ezekiel
Published: February 2008

The full wave approach developed earlier to evaluate the radiation fields scattered by deterministic two dimensionally rough surfaces is used here to determine the scattering cross sections for random rough surfaces. The medium below the irregular boundary is characterized by complex permittivity and permeability. For slightly rough surfaces, the full wave solutions for the incoherent scattered fields are shown to be in agreement with the perturbation solution. However, when the major contributions to the scattered fields come from the region of the rough surface around the stationary phase (specular) points, the full wave solutions are in agreement with the physical optics solutions. Thus the full wave solutions which reduce to the perturbation, the physical optics, and the geometrical optics approximations in special cases precisely determine the limitations of these approximations and reconcile the differences between them. The full wave solutions satisfy duality, reciprocity, and realizability relations in electromagnetic theory, and they are invariant under coordinate transformations.