bluuebunny/crossref_metadata_2025 huggingface dataset:
Strong refraction near the Venus surface: Effects observed by descent probes
Authors: Croft Thomas A.
Published: February 2008

The high‐pressure atmosphere of Venus causes strong downward refraction of radio rays, with consequences that were evident in the telemetry signals from Pioneer Venus probes. As the probes descended, the strength of the direct signal to the earth gradually diminished because of the combined actions of absorption and refractive defocusing. Both phenomena became increasingly pronounced as penetration proceeded. Like occultation recordings of signal strength, these records too can be analyzed to yield a profile of atmospheric temperature versus altitude. During the final 30 km of descent, there was in addition to the direct signal a second measured component that traveled to the surface of Venus and from there scattered toward the earth. The strong atmospheric refraction played a key role leading to the strengthening (and hence the detectability) of these echoes. Surprisingly, it is found that such surface‐reflected signals provide a good indication of the horizontal winds existing at each altitude during the descent of the probes. Since the refraction is roughly the same in the visible band as it is at radio frequencies, there was some speculation that refractive effects might be visible in the images of the surface returned by the Soviet landers. No such effects were apparent. I demonstrate that the absence is attributable to limited visibility.
Measurements of electric and magnetic stray fields produced by various electrodes of 27‐MHz diathermy equipment
Authors: Kalliomaki P. L. , Hietanen M. , Kalliomaki K. , Koistinen O. , Valtonen E.
Published: February 2008

The present paper describes the results of measurements of electric and magnetic stray fields around three types of commercially available diathermy units with four very typical electrodes in six routine therapeutic treatments. The aim of the survey was to investigate the exposure to the physiotherapist and the exposure to unprescribed tissues. Field strengths were measured at 15 points close to the patient's body. At a distance of 0.6 m from the diathermy units the power density was less than 10 W/m2. With respect to stray fields the results showed that the diathermy devices are very similar but there are great differences between the electrodes during specific treatments. The results assist in selecting proper electrodes for various therapeutic treatments, as they indicate which electrodes would have minimal stray fields.
Interpretation of auroral radar experiments using a kinetic theory of the two‐stream instability
Authors: Schlegel Kristian
Published: February 2008

The evaluation of auroral radar measurements in terms of the Farley‐Buneman instability is reviewed and adjusted to recent observational (Te > Ti) and theoretical (propagation not exactly perpendicular to the magnetic field, high growth rates of the unstable waves) evidence that applies for the high‐latitude E region. The kinetic dispersion relation of the instability is studied in detail for a wavelength of 1 m in order to facilitate comparisons with the STARE auroral radar. The results of this new approach are compared with the results obtained with the simple dispersion relation which has so far been used to evaluate auroral radar experiments. It is shown that the new method results in considerably higher electron drift velocities in the case of strong convection. This means that with the former simple dispersion relation the electron drift velocities and electric fields have often been underestimated.
On the spectral expansion of the electric and magnetic dyadic Green's functions in cylindrical harmonics
Authors: Pearson L. Wilson
Published: February 2008

The expansions of the electric and magnetic dyadic Green's functions are constructed in terms of the solenoidal Hansen vector wave functions in cylindrical coordinates. A static term is shown to arise in the course of conducting the radial spectral integral. This pole term has apparently not been identified in previously published expansions and is similar to recently identified static terms in Cartesian and spherical wave function expansions. The integration in the longitudinal spectral variable is considered, too, and forms which offer two alternative integration paths are constructed.
Numerical calculations of low‐frequency TE fields in arbitrarily shaped inhomogeneous lossy dielectric cylinders
Authors: Hill S. C. , Durney C. H. , Christensen D. A.
Published: February 2008

The Galerkin method with subsectional linear basis and weighting functions is used to calculate the low‐frequency transverse electric fields in lossy dielectric cylinders. Arbitrarily shaped polygonal cells are employed to allow more accurate modeling of complex objects without excessive matrix sizes. To demonstrate the validity of the method, the analytical and numerical solutions are compared for triple‐layered concentric cylinders. The calculated fields in a model of the human torso exposed to a solenoidal field are also presented. Among other applications, the method should be useful for evaluating electromagnetic (em) biohazards, and for analyzing and designing dielectric antennas and hyperthermia applicators at low frequencies.
Reflection and transmission coefficients for local resonances in a cold magnetoplasma
Authors: van Duin Cornelis A. , Sluijter Frans W.
Published: February 2008

On the basis of the hypergeometric equation, a class of refractive index profiles has been generated that accommodates a local resonance and that is otherwise a monotonic transition from one limiting homogeneous region to another. The reflectivity and transmittivity then follow from the known circuit relations for solutions of the hypergeometric equation. The expressions found are compared with those obtained by Budden, based on a confluent hypergeometric equation.
The electromagnetic field in a layered earth induced by an arbitrary stationary current distribution
Authors: Kristensson Gerhard
Published: February 2008

The subject of this paper is to calculate the fields in a layered earth induced by a current distribution. A general formulation is presented, which contains very few restrictions of the current distribution. For the simplest current distributions (dipole, circular, and rectangular loops) we derive expressions for the fields, which contain a single integral (Sommerfeld type). Numerical computations are presented for the above mentioned sources, and some techniques for increasing the rate of convergence are discussed.
Microwave radio meteorology: Seasonal fading distributions
Authors: Schiavone James A.
Published: February 2008

Refractive fading can significantly impair service on terrestrial line‐of‐sight microwave transmission systems. Digital radio systems are particularly vulnerable to this fading which is produced by vertical gradients in the microwave refractive index. A characterization of the seasonal variation in fading and its dependence upon meteorological parameters provides the potential to improve transmission performance by better tailoring of transmission equipment design and usage to the amount of fading expected at a given location and time of year. In this work we study the seasonal variation in fading occurrence at Palmetto, Georgia, over a 28‐month period. The changes in the shapes of seasonal fading distributions as a function of fade threshold, path length, and antenna height are examined and interpreted meteorologically. The Palmetto distributions are compared with those measured at other worldwide locations and the year‐to‐year fading variability for Palmetto is estimated. The Palmetto studies show that mean monthly wind speed V is the best meteorological predictor of monthly accumulated time that signal is below −20 dB, t20, at Palmetto. The predictor is t20 = 17600 (12/V ‐ 1)2 and has a correlation coefficient of 0.88. Year‐to‐year variability in observed fading is greatest in early autumn when monthly accumulated 20 dB fading time differs by about 6000 s between years. Seasonal distribution shapes depend strongly on geographical location. The studies comparing different worldwide distributions show that 95% of the total annual fading occurs during the season experiencing monthly water vapor pressures > 10 mbars and that the peak in the seasonal fading distributions, outside of low latitude coastal regions, is associated with the months in the humid season when there is the least precipitation.
Dispersion characteristics for decaying or amplifying waves: 1. An observational approach
Authors: Vidmar R. J. , Crawford F. W. , Harker K. J.
Published: February 2008

One‐dimensional wave packets propagating through an infinite homogeneous medium may be characterized by three properties: group velocity, phase velocity, and growth or decay rate. Analysis of such wave packets excited by a periodic source maintained indefinitely, or by a transient source, e.g., a tone burst, establishes a local velocity computed in a manner similar to Brillouin's signal velocity as anenergy velocity. The expression for this depends on the types of source considered, and whether the plane wave components maintain their energy, decay, or amplify. In this paper, observational properties are deduced for wave packets which demonstrate that periodic and transient sources excite decaying and amplifying waves, with identical frequencies but with different local velocities, phase velocities, and growth or decay rates. An analysis of the amplifying waves in a beam‐plasma system is presented which exemplifies these source‐dependent properties.
Shadowing by non‐Gaussian rough surfaces for which decorrelation implies statistical independence
Authors: Bahar Ezekiel , Fitzwater Mary Ann
Published: February 2008

Expressions for the shadow functions are derived for a broad class of non‐Gaussian rough surfaces for which decorrelation of the surface heights implies statistical independence. The numerical results obtained for the backscatter shadow functions are compared with the shadow function for Gaussian surfaces and with recently published results for surfaces with an exponential joint height probability density that does not become statistically independent as the surface heights decorrelate. Contrary to earlier published results, it is shown that even for surfaces with large mean square slopes, the shadow function is not very sensitive to the precise form of the surface height density function assumed. This, however, does not mean that the rough surface scattering cross sections are insensitive to the assumed non‐Gaussian surface height probability density.
Rays and modes in a nonuniform troposphere
Authors: Kukushkin Alexander V. , Sinitsin Victor G.
Published: February 2008

A version of the hybrid (ray mode) representation of wave fields has been suggested which is convenient with refractive index profiles corresponding to simultaneously existing surface and elevated ducts. The field at the reception point is represented as a sum of normal modes peculiar to an isolated surface duct and an assembly of rays reflected from the elevated layer.
First bistatic oblique‐incidence ionograms between digital ionosondes
Authors: Wright J. W. , Kressman R. I.
Published: February 2008

Identical digital ionosondes (dynasondes) at Brighton Colorado and at White Sands Missile Range, New Mexico, 864 km distant, were synchronized for bistatic sounding in multifrequency and fixed frequency recording patterns. Three propagation modes are observed, identified, and reconciled with standard propagation theory; these include one‐hop propagation by sporadic E (Es) and the F region and two‐hop (F ‐ Es). Echo phase measurements at the four spaced antennas of the dynasonde receiving array permit echolocation calculations that are in good agreement with the path mid point, although effects of ionosopheric tilts and time variations are evident. These results encourage the concept of a global real time ionospheric monitoring network consisting of about 90 instruments that perform vertically incident and coordinated bistatic soundings, to yield a total of about 320 measurement ‘locations.’
Radiation properties of a vacuum‐insulated infinite flat slotted plate antenna in a cold isotropic homogeneous plasma
Authors: Beeckman P. A. , Weenink M. P. H.
Published: February 2008

The properties of an infinite flat plate antenna in a cold isotropic homogeneous plasma are investigated for the case in which the antenna is excited by means of a delta function voltage source across the infinitely long and narrow slit. Special attention was paid to the influence of an insulating vacuum layer between the antenna and the plasma. The far field radiation pattern and the power transport into the plasma and along the plasma‐vacuum boundary are analyzed.
A rigorous analysis for the study of rain attenuation and depolarization statistics for terrestrial and earth‐space links
Authors: Kanellopoulos J. D.
Published: February 2008

A well‐known rigorous technique proposed by Lin for predicting rain attenuation statistics for terrestrial links has been modified in order to apply it to 5‐min point rainfall long‐term distributions and to include the case of earth‐space links. This same technique leads to the construction of an effective predictive model for the rain depolarization statistics. Comparison of the so‐obtained theoretical results with experimental data has been quite encouraging.
Nonlinear scattering from a plasma column: 2. Special cases
Authors: Crawford F. W. , Harker K. J.
Published: February 2008

A previous analysis of the scattered signal excited by nonlinear mixing of two plane waves normally incident on an infinitely long column of plasma is specialized to several simplified cases. Simplified expressions are derived for the nonlinear scattering coefficients in the long wavelength limit, and it is established that dipole and quadrupole components should predominate in the polar radiation pattern. The homogeneous column is treated as a limiting form of the general analysis, and is also studied in the long wavelength limit. The special case of second harmonic generation due to a single incident wave is treated in detail. Computations of nonlinear scattering coefficients, and the corresponding polar radiation pattern are presented. The results of the analysis are used to assess the feasibility of observing nonlinear scattering from meteor trails.
Observations of HF backscatter associated with the heating experiment at Tromsø
Authors: Hedberg Å. , Derblom H. , Thidé B. , Kopka H. , Stubbe P.
Published: February 2008

Backscatter echoes from a region modified by RF heating above Tromsø were observed at Kiruna on 3 and 7 MHz, at Lycksele on 14 and 17 MHz, and at Uppsala on 15.6 MHz. When the heater output is suddenly varied from off to on, the backscatter echoes appear and grow to an equilibrium value in some seconds and decay at turnoff but then in some tens of seconds. These rise and decay time constants are found to be frequency dependent, being longer at lower radar frequencies. The strongest echoes seem to be obtained when the F layer peak plasma frequency (f0 F2) is close to the heater pump frequency. Echoes are absent when the heater is operating in X mode. Variation of heater output from 100% to 12.5% of full power yields a corresponding variation in the received echo amplitude without noticeable threshold effects. Some Doppler shift measurements are also presented indicating that the modified region, as well as the background, for the days of observation has a radial motion toward north in the range 0–20 m/s as seen from Lycksele. Estimated wave propagation limitation for the 3 and 7 MHz backscatter set by the observed electron density profile indicates that on the days considered the radar reflecting volume may extend vertically from about 60 km below to 20 km above the estimated optimally heated level. Observations made are consistent if we assume a modified volume with a diameter of less than about 75 km and a vertical extent of 40–80 km composed of field‐aligned striations which grow and decay in accordance with the heater output power level.
Some properties of the auroral thermosphere inferred from initial EISCAT observations
Authors: Alcaydé D. , Fontanari J. , Bauer P. , de la Beaujardière O.
Published: February 2008

Using the equation of ion energy conservation, preliminary calculations of thermospheric neutral‐temperature profiles and atomic oxygen concentrations are made for 2 days of EISCAT incoherent scatter radar data. Since the original method currently applied at mid‐latitudes is not valid when joule heating of the ions occurs, we extended it to take joule heating into consideration. However, this new method is not valid if joule heating occurs simultaneously with electron heating by particle precipitation or photoelectrons. We show that the electron continuity equation around 200 km altitude can be applied to identify the periods of particle precipitation.
Studies of sporadic E (Es) associated with the main ionospheric trough
Authors: Rodger A. S. , Morrell C. , Dudeney J. R.
Published: February 2008

The occurrence of sporadic E (ES) under the main F region trough has been established using ionograms from a vertical incidence ionosonde at Halley Bay, Antarctica (76°S, 27°W; L = 4.2), a site well suited for such studies as the trough can be seen under a wide range of magnetic conditions and local times. Analysis shows that ES is very frequently observed under both the equatorward and poleward edges of the trough, as well as poleward of it. Before magnetic midnight, ES layers with semi‐thickness similar to those of the normal E layer are most common. This is in marked contrast to the layers seen after magnetic midnight which usually show the characteristics of thin ES layers. Additional information on the morphology and dynamics of ES layers associated with the main trough has been provided by detailed study of individual events using data from the British Antarctic Survey's advanced ionospheric sounder recently deployed at Halley Bay. A possible explanation of the observed change in the ES layer characteristics at about magnetic midnight is related to differences in the type and spectra of the precipitating particles. The effects of transport processes in the E region are also considered as a possible cause. It is shown that the redistribution of ionization by the convection electric field may be important.
Current and future programs for high‐latitude radio wave research
Authors: Greenwald R. A. , Hunsucker R. D.
Published: February 2008

This article is a summary of presentations made on the final day of the URSI International Symposium on “Radio Probing of the High‐Latitude Ionosphere and Atmosphere: New Techniques and New Results”. It was not possible to include all of the presentations made during that session, so the guest editors have attempted to give an overview on the status of new radio probing techniques already deployed and planned for the near future. Table 1 and the frontispiece to this issue briefly summarize the more important information available at the time of preparation of this article.
A note on the variational method (Rayleigh‐Ritz), Galerkin's Method, and the method of least squares
Authors: Sarkar Tapan K.
Published: February 2008

The variational method (Rayleigh‐Ritz), Galerkin's method and the method of least squares have been utilized extensively in electromagnetic theory to solve various field problems. In most cases, one makes a formal use of the techniques. In this paper, a tutorial approach has been taken to bring out the mathematical distinctions between the variational method (Rayleigh‐Ritz), Galerkin's method and the method of least squares. Examples have been presented to illustrate the strong and weak points of each of the techniques. Finally, the rates of convergence of the three techniques have been derived. It is hoped that with the appearance of this paper, application of a particular technique to solve an electromagnetic field problem would be more rigorous rather than formal.
Null field formulations for dielectric‐coated antennas
Authors: Aydin K. , Altintas A. , Hizal A.
Published: February 2008

Null field formulations utilizing a generalization of the extended boundary condition method of Waterman are presented for dielectric‐coated antennas of arbitrary but smooth shapes. Spherical, prolate spheroidal and spherically capped cylindrical antennas are solved as examples. Their power radiation patterns and input conductances are plotted as functions of coating thickness. The dielectric coating effectively increases the antenna size. Furthermore, it is shown that an eccentric coating can produce a considerable shift in the power radiation patterns.
Electromagnetic coupling characteristics of two half spaces through a waveguide with small apertures
Authors: Feng Deguang , Cheng David K.
Published: February 2008

The coupling problem between two half spaces that are connected by a section of a circular waveguide with a small aperture on both ends is solved by using an equivalent network representation. The conditions for aperture‐cavity resonances and the maximum field in the waveguide are determined. It is shown that, for certain combinations of aperture sizes, the maximum field is quite sensitive to the effective dielectric constant of the last half space. This phenomenon may be used to measure plasma density. The effects of off‐centered apertures are studied by the introduction of a reduction coefficient.
Emission measurements of 31.6 GHz absorption by atmospheric water vapor
Authors: Hogg D. C. , Guiraud F. O. , Westwater E. R.
Published: February 2008

The absorption by water vapor in the atmosphere was accurately measured at a frequency of 31.65 GHz (wavelength 9.48 mm). The data were obtained at three locations in the United States with total pressures of about 1010, 920, and 840 mbar. The continuum absorption (as differentiated from resonant absorption) was found to vary approximately as the square of the total surface pressure; the measurements and an associated modified formula for calculating the absorption are discussed. It is observed from the measurements that an additional term representing absorption by dimers is apparently not required.
Macroscopic Lagrangian description of warm plasmas: 2. Nonlinear wave interactions
Authors: Kim H. , Crawford F. W.
Published: February 2008

The macroscopic Lagrangian formulated in paper 1 is simplified to the adiabatic limit and expanded about equilibrium, to third order in perturbation, for three illustrative cases: one‐dimensional compression parallel to the static magnetic field, two‐dimensional compression perpendicular to the static magnetic field, and three‐dimensional compression. As examples of the averaged‐Lagrangian method applied to nonlinear wave interactions, coupling coefficients are derived for interactions between two electron plasma waves and an ion acoustic wave, and between an ordinary wave, an electron plasma wave, and an ion acoustic wave.
ULF/ELF electromagnetic fields produced in a conducting medium of infinite extent by linear current sources of infinite length
Authors: Inan A. S. , Fraser‐Smith A. C. , Villard O. G.
Published: February 2008

A previous analysis of a linear current source of finite length embedded in a conducting medium of infinite extent is extended to linear current sources of (1) infinite length and (2) semi‐infinite length. Electric and magnetic field expressions are derived, and the results are numerically evaluated for frequencies in the ULF/ELF bands. For convenience, some of the results are presented in a dimensionless form. A comparison is made between the electromagnetic fields produced by linear current sources of finite and infinite length, and it is shown that there is a relative enhancement in the electric field near the source of finite length. It is also found that an optimum frequency exists for the electric field produced by a linear current source of infinite length at which the field amplitude is a maximum at a fixed observation point. Some practical applications of our results are suggested.
The singularity expansion method and multiple scattering
Authors: Riley Douglas J. , Davis William A. , Besieris Ioannis M.
Published: February 2008

A new application of the singularity expansion method (SEM) is explored. This application combines the classical theory of wave propagation through a multiple scattering environment and the SEM. The SEM is first reviewed and then applied to the single scatterer problem. This application is then extended to the multiple scattering case using both single and multiple interactions. A tensor form is used for the SEM description which leads to an associated tensor form of the solution to the multiple scattering problem with each SEM pole effect appearing explicitly. The coherent field is determined for both spatial and SEM parameter random variations.
Induced polarization response of disseminated mineralization for spheroidal geometries
Authors: Flanagan Peter W. , Wait James R.
Published: February 2008

An attempt is made here to model the complex resistivity effect which is utilized in the geophysical exploration for disseminated sulphide mineralization. A model of a hypothetical mineral grain is developed, and the complex resistivity of a medium loaded with such grains is studied. First, quasistatic electrical conditions (Wait, 1982) are used so that the problem can be solved by using potential fields. The equations are developed in spheroidal coordinates; however, a uniform nonconfocal grain surface impedance is used that does not allow a closed‐form solution (Wait, 1958, 1983α). Therefore, approximate solutions are obtained by using numerical techniques (Flanagan, 1983). Sample calculations of complex, frequency‐dependent resistivities of a hypothetical pyrite ore are presented. These calculations are based on experimentally determined surface impedance data for pyrite, taken from the literature (Olhoeft, 1982; Collett, 1959).
Calculated effects of traveling sporadic E on nocturnal ELF propagation: Comparison with measurement
Authors: Pappert Richard A.
Published: February 2008

A simple surface propagation model has been used to estimate the effects of a moving cylindrically symmetric, homogeneous, patch of sporadic E on propagation in the lower ELF band. Emphasis is on comparison with simultaneous Connecticut and North‐Atlantic reception of transmissions from the Wisconsin Test Facility (WFT) where nighttime propagation anomalies occurred 2–4 hours apart (Bannister, 1982). Ionospheric disturbances, travelling with a speed of order 100 km/hr and moving out of the geographic North‐Northwest, which cross both transmitter‐receiver great circle paths in such a way that they shadow the transmitter are found to be the most likely candidates for causing the delayed fades. Likely paths yield phase behavior which is in qualitative agreement with measurement. Patches with radii ≳0.5 Mm are required for the deepest fades.
High‐resolution probing of the HF ionospheric skywave channel: F2 layer results
Authors: Wagner L. S. , Goldstein J. A.
Published: February 2008

A computer‐controlled, coded‐pulse, step frequency, oblique sounder has been designed to probe the HF radio communication channel to a bandwidth of 1 MHz. The instrument monitors the complex pulse response of the channel over an extended period of time thus permitting simultaneous observation of the time and frequency behavior of the channel. A coherent time history presentation of the wide band data permits unequivocal identification of individual modes in situations involving several partially overlapping modes. Channel instantaneous bandwidth and mode Doppler shift can be estimated by inspection of the pulse response time history curves. Data presentation in the wide band time history format is also very informative in the description of signal fluctuation phenomena and in understanding their underlying causes. Measurements have been made over a short‐baseline (126 km), mid‐latitude path between an island off the southern California coast and the mainland. The response of the one‐hop F2 layer sky wave mode to a 1‐μs probing pulse is used to illustrate the unique capabilities of this instrument and the unusual effects that are observed with a high‐resolution probing pulse.
UHF/GHz scintillation observed at Ascension Island from 1980 through 1982
Authors: Mullen J. P. , MacKenzie E. , Basu Santimay , Whitney H.
Published: February 2008

Three years' scintillation measurements taken at Ascension Island have been reduced and are presented here. The 1.5‐GHz and 257‐MHz signals of Marisat were supplemented by 3.9‐GHz observations during January–May 1981. While their temporal patterns are similar to those found earlier in the Afro‐American zone, they exhibited unusually frequent occurrence of heavy scintillation at gigahertz frequencies often exceeding 30 dB at 1.5 GHz and 7 dB at 4 GHz. These patterns are attributed in part to the position of the station near the southern peak of the Appleton anomaly. Comparisons are made between these and similar observations taken at Hong Kong, near the northern peak of the anomaly.
The HiLat satellite mission
Authors: Fremouw E. J. , Carlson H. C. , Potemra T. A. , Bythrow P. F. , Rino C. L. , Vickrey J. F. , Livingston R. L. , Huffman R. E. , Meng C.‐I. , Hardy D. A. , Rich F. J. , Heelis R. A. , Hanson W. B. , Wittwer L. A.
Published: February 2008

On June 27, 1983, USAF satellite P83‐1 was launched from Vandenberg Air Force Base carrying the five ionospheric‐effects and diagnostic payloads of DNA's HiLat satellite mission. A Scout launch vehicle placed the satellite in an 800‐km circular orbit at an inclination of 82°. The HiLat experiments are as follows: (1) a VHF/UHF/L band coherent radio beacon for observing complex‐signal scintillation and total electron content; (2) a three‐instrument cold‐plasma package for measuring number density and temperature, their spatial fluctuations, and plasma convection velocity and its fluctuations; (3) an electron spectrometer for detection of precipitating and upwelling electrons with energies between 20 eV and 20 keV; (4) a three‐axis magnetometer; and (5) an optical assembly for imagery and spectrophotometry in the vacuum‐ultraviolet spectrum and for photometry at two visual wavelengths. With the exception of partial launch damage to the electron sensor (Langmuire probe) in the coldplasma package, all payloads initially operated as designed. After approximately 40 orbits of data collection, however, the imaging spectrophotometer failed. In spite of this failure, the optical instrument proved the concept of imaging the aurora, at vacuum‐ultraviolet wavelengths, under conditions of full sunlight. Its visual‐wavelength photometers continue to perform well, as do the other four HiLat payloads. This paper presents early observations from HiLat.
Ultraviolet remote sensing of the aurora and ionosphere for C3I system use
Authors: Huffman R. E. , Larrabee J. C. , LeBlanc F. J. , Meng C. I.
Published: February 2008

The operation of command, control, communications, intelligence (C3I) systems is improved by better methods of remotely sensing the normal ionosphere and disturbed ionospheric regions such as auroras. This paper describes an ultraviolet imager flown to study UV emission for passive ionospheric and auroral remote sensing. The ultraviolet imager launched on the U.S. Air Force Space Test Program P83‐1 satellite (HILAT) has been used for the investigation of high‐latitude polar ionospheric disturbances, together with other sensors of the Defense Nuclear Agency. This instrument obtained imagery of the earth's auroral and airglow activity with a 30‐A selectable spectral window in the vacuum ultraviolet wavelength range (1100 Å to 2000 Å). The experiment is designated the auroral/ionospheric mapper (AIM). It obtains an image using a mirror to scan repetitively across the ground track from the stabilized satellite in a polar orbit at about 830 km altitude. The intensity is measured by a photomultiplier tube at the exit slit of an Ebert‐Fastie spectrometer (⅛ m). The instrument also has two fixed wavelength nadir‐looking photometers at 3914 Å and 6300 Å with 10 Å spectral bandwidths. The capability of this sensor and initial observations of dayglow, limb brightening, and aurora will be presented. The images clearly demonstrate that auroral displays in the local summer polar region near solstice can easily be imaged at several wavelengths. The Rayleigh scattering and the photoelectron‐excited dayglow emission background, both produced by solar UV irradiation, do not have any significant effect on the monitoring of the aurora. Observations of ultraviolet emission intensities in the auroral oval and the polar cap region were made, all under full daylight conditions. Fine structures of different auroral forms were imaged with a spatial resolution of approximately 4 km × 20 km and sensitivity of approximately 50 rayleighs.
A high‐latitude phenomenological model of auroral precipitation and ionospheric effects
Authors: Miller K. L. , Vondrak R. R.
Published: February 2008

The real‐time distribution of high‐latitude ionization can be inferred by monitoring kilovolt electron precipitation. Several space‐based spectrophotometric imagers have been designed for this purpose. Assessment of the capabilities of specific satellite sensors requires a model of the spatial distribution of high‐latitude electron precipitation and its temporal variation. Because previous statistical models do not indicate the instantaneous spatial distribution of particle precipitation and resultant ionization, we have used an alternative phenomenological approach to model the high‐latitude ionosphere. This phenomenological model specifies the instantaneous pattern of high‐latitude kilovolt electron precipitation and related quantities such as ionization, conductivity, and auroral luminosities. The model specifies the temporal and spatial variations that occur during auroral substorms, based on the auroral morphology that has been deduced from optical and riometer studies. To illustrate the usefulness of the model for evaluating instrument performance, examples are shown of the simulated response of a satellite‐borne X ray imager.
The ionospheric contribution to the plasma environment in near‐earth space
Authors: Sharp R. D. , Lennartsson W. , Strangeway R. J.
Published: February 2008

Many C3I systems rely on satellites in geostationary and other near‐earth orbits that are largely within the earth's magnetosphere. It has only recently been observed that the ionosphere plays a major role in determining the hot plasma environment in which these satellites must operate. Spacecraft charging, radiation effects, and degradation of sensitive surfaces used in optical and thermal control systems are attributal to the interaction of spacecraft with this ambient hot plasma, and these effects are especially serious for the newer satellite systems designed to function in orbit for a decade or longer. Recent energetic ion mass spectrometer observations have shown that the hot magnetospheric plasma in the energy range from about 100 eV to about 30 keV contains a large and variable O+ fraction which is essentially all of ionospheric origin. The other principal constituent is H+ which can be either of ionospheric or solar wind origin. The O+/H+ ratio of the plasma is an important parameter in modelling the spacecraft‐plasma interactions to attempt to predict the magnitude of the above described effects. This report reviews the mass spectrometer observations by the International Sun Earth Explorer (ISEE 1) and the Spacecraft Charging at High Altitudes (SCATHA) satellites and examines the data for various signatures of the plasma sources. The relative contributions of the ionosphere and the solar wind to the plasma density are estimated in the altitude range from about 25,000 to 70,000 km on the basis of the ion composition. It is found that the ionosphere is an important or dominant source during both quiet and storm time conditions.
Large‐amplitude electric field fluctuations near the Harang discontinuity
Authors: Saflekos Nicolaos A. , Burke William J. , Fougere Paul F.
Published: February 2008

Recently, much attention has focused on physical mechanisms responsible for the formation and evolution of the plasma density irregularities in the F region ionosphere that disrupt communications at high latitudes. The polar orbiting S3–2 satellite with its complement of high resolution of plasma, particle and field detectors provides useful information on the dynamics of some irregularities. This study focuses on plasma density and electric field measurements taken as the satellite flew poleward along the Harang discontinuity during a substorm. The position of the Harang discontinuity is established from simultaneous ground magnetometer measurements and DMSP imagery. The plasma density showed a distinct maximum near the poleward boundary of auroral electron precipitation that was two orders of magnitude higher than in the trough and in the (winter) polar cap. Very intense (>100 mV/m) electric field fluctuations were detected along the steep, equatorward, plasma density gradient near the poleward boundary of the oval. Power spectral densities of these fluctuations did not obey expected power laws but had strong spectral lines between 1 and 16 Hz that do not seem to map to the peak of the F‐layer. This suggests a magnetospheric source for at least some high‐latitude electric field irregularities. Simultaneously measured spectra for plasma densities consistently showed k−2 power laws over the 0‐ to 8‐Hz range. This is consistent with the predictions of nonlinear, gradient drift theory.
Results from the SEEP active space plasma experiment: Effects on the ionosphere
Authors: Imhof W. L. , Gaines E. E. , Voss H. D. , Reagan J. B. , Datlowe D. W. , Mobilia J. , Helliwell R. A. , Inan U. S. , Katsufrakis J. , Joiner R. G.
Published: February 2008

An active satellite‐ground coordinated space plasma experiment was conducted from May to December, 1982, in which electrons were precipitated from the radiation belts into the ionosphere by the controlled injection of VLF signals from ground‐based transmitters. The results confirm the hypothesis that electrons can be precipitated from the radiation belts by ground‐based VLF transmitters, and they provide information relating to the effects of such precipitation on the ionosphere. The ionization produced in the atmosphere of the northern hemisphere at L = 2.3 by the modulated signals from ground‐based VLF transmitters was shown to be as great as one ion pair/cm3 s at 80 km altitude. The ionization at comparable positions produced by naturally occurring electron precipitation varies greatly, and can be as low as 0.1 ion pair/cm3 s, but is also sometimes larger than 100 ion pairs/cm3 s at times of lightning flashes.
Microwave antenna temperature of the earth from geostationary orbit
Authors: Njoku Eni G. , Smith Ernest K.
Published: February 2008

The microwave antenna temperature of the earth has been computed for the case of a communication satellite antenna viewing the earth from geostationary orbit. An earth‐coverage beam is assumed and detailed computations are performed to account for varying land‐ocean fractions within the field of view. Emission characteristics of the earth's atmosphere and surface are used with an accurate radiative transfer program to compute observed brightness temperatures. Values of 250 to 290 K commonly used for antenna temperature in satellite communication noise calculations are found to be over conservative estimates, with more realistic values lying in the 60–240 K range depending on frequency and subsatellite longitude. These values also depend on assumptions concerning antenna beam coverage. Variations in atmospheric and surface conditions, and variations in antenna beam shape (as distinct from coverage), affect the computed results by less than ≃ 10 K.
The influence of metallic ions on the plasma instabilities in the high‐latitude E region
Authors: Schlegel Kristian
Published: February 2008

Metallic ions like Mg+ and Fe+ can be quite abundant at E region heights during meteor showers. Since their mass is significantly different from the mass of the “normal” E region ions like NO+ and O2+ the E region plasma will behave quite differently in the presence of these ions. As a consequence, the results of the dispersion relation of the modified two stream and the gradient drift plasma instability, occurring in the high latitude E region, are significantly different from the “normal” case. Some of these results are presented and the implications for the interpretation of auroral radar results (STARE) are discussed.
Foil clouds as a tool for measuring wind structure and irregularities in the lower thermosphere (92–50 km)
Authors: Widdel H. U.
Published: February 2008

Improvements of observation techniques allow a detailed interpretation of results obtained by radar tracking of a descending foil cloud (“chaff”) target. Preposition is that the aerodynamic characteristics of the chaff is properly matched to the environment and that the size of the chaff cloud is kept small during deployment. By this, uplift motions seen at certain height levels could be identified as real motions not caused by radar tracking errors. Further, effects believed to be caused primarily by laminar separation of flow and not by turbulence were observed. This is illustrated by some results obtained during the MAP/WINE campaign winter 1983/1984 over Andenes (Northern Norway).
Ray‐tracing in a two‐dimensional ionosphere
Authors: LaBahn R. W.
Published: February 2008

The quasi‐parabolic method is adapted to ray‐trace through a medium with horizontal gradients in electron density. The resulting method is and applicable to any model ionosphere without the requirements for numerical derivatives. Example calculations are given for model ledges and troughs and an average worldwide ionospheric model.
MST radar detection of middle atmosphere tides
Authors: Forbes Jeffrey M.
Published: February 2008

Meterological and dynamical requirements pertaining to the specification of middle atmosphere tides by the MST radar technique are outlined. Major issues addressed include (1) the extraction of tidal information from measurements covering a fraction of a day, (2) the ramifications of variability on the determination and interpretation of tides, (3) required temporal and spatial resolutions, (4) desired global distributions of MST radars, so as to complement existing MST, meteor wind, and partial reflection drift radar locations.
Electric dipole fields over a quarter space earth inhomogeneity and application to ice hazard detection
Authors: Ryan J. , Walsh J.
Published: February 2008

An analysis of the fields generated by an electric dipole over a quarter space earth inhomogeneity is carried out. The results of this analysis have a particular application to the long‐range detection of ice hazards such as multiyear ice, pressure ridges and icebergs. Navigation through Arctic regions and exploration in ice‐infested waters are severely limited by the inability of conventional microwave marine radar to provide adequate detection capability. The analysis is based on a method of space and electric field decomposition in which Heaviside functions are used to decompose a three‐dimensional space into regions having different electrical properties. The region above z = 0 represents free space and the region below represents two semi‐infinite homogeneous media. Maxwell's equations are used to derive a partial differential equation for the electric field for the complete space. This partial differential field equation is decomposed into three field equations, one for each region, and a boundary equation. The boundary equation represents the conditions which the electric field must satisfy at each of the interfaces. In this manner, this technique provides its own boundary conditions. Selecting the appropriate spherical Green's function, the resultant convolution type integral equations are simplified by using the boundary equation to eliminate half of the unknowns and taking the two‐dimensional (spatial) Fourier transform. By assuming the refractive indices of the media below are large and taking the source field as the far field of a vertical electric dipole, the three field equations are reduced to a single algebraic equation. This equation is inverse Fourier transformed, and the resultant convolution integral equation is written in operator notation. The operator is formally inverted in the form of a Neumann series. By utilizing stationary phase integration and the Laplace transform, the series may be summed to give either the propagated field or the backscattered field.
Current theoretical attempts toward synchronization of a global satellite network
Authors: Skalafuris Angelo J.
Published: February 2008

When relativistic effects become important, synchronization of clocks in Keplerian orbit is formally a problem of synchronization in noninertial frame of reference. Although such a procedure is impossible from basic principles, even the synchronization in approximation has never been treated in the historical literature of relativity. In recent times a number of papers have appeared which touch upon this subject; however, those communications are not entirely in agreement with one another over the procedure. This paper attempts to clarify what each author has done and delineates the differences and questions left open by their individual procedures. Finally, a number of specific questions are enumerated which, if thoroughly researched, could resolve the controversy which appears to surround current attempts at relativistic synchronization of clocks orbiting the earth.
Effects of antenna element structure on element properties and array pattern of a planar phased array
Authors: Fukao Shoichiro , Sato Toru , Hojo Hiroshi , Kimura Iwane , Kato Susumu
Published: February 2008

A numerical consideration is performed on degradation of element properties and array patterns of a planar phased array owing to the effects of antenna element structure. By using a crossed 3‐subelement Yagi antenna specially designed for the VHP‐band MST radar in Japan (the MU radar) as a model of antenna element, the following two subjects are investigated: (1) mutual coupling effects induced by deviation of the intersecting point of a pair of crossed subelements from each subelement center, and (2) effects of vertical current which flows on the mast supporting the antenna subelements. It is concluded that neither of them provide significant degradation of either element properties or array patterns. Although this conclusion is derived for specific phased arrays composed of specific antenna elements, it will be essentially valid for ordinary planar phased arrays composed of dipoles or Yagi antennas.
Directional slope distributions of wind‐disturbed water surface
Authors: Haimbach Stephen P. , Wu Jin
Published: February 2008

Probability‐density functions of directional slopes of the wind‐disturbed water surface were measured with an optical scanner. The upwind‐downwind and crosswind components of mean‐square slopes were found to vary with the logarithm of wind‐friction velocity. The angular variation of mean‐square slopes was found to follow an elliptical, Gaussian joint probability‐density function, with its variance again related to the wind‐friction velocity.
A sleeve monopole antenna in a warm plasma
Authors: Egashira S. , Morita Y.
Published: February 2008

A sleeve monopole antenna whose length is comparable to a plasma wavelength has been studied both theoretically and experimentally in the frequency region for which there is electron plasma wave propagation. In taking account of Landau damping, it is found that if the sleeve length is larger than 25 Debye lengths, for the monopole of length 4 cm with a radius of 1 mm, then the input impedance becomes insensitive to further increase in sleeve length. The theoretical input impedances are found to be in good quantitative agreement with the experimental results.