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Showing papers in "Radio Science in 1985"


Journal ArticleDOI
TL;DR: In this paper, a new mapping function for the elevation angle dependence of the atmospheric delay is developed, and the delay predicted by this mapping function differs from ray trace results by less than approximately 5 mm, at all elevations down to 5 deg elevation, and introduces errors into the estimates of baseline length.
Abstract: Analysis of very long baseline interferometry data indicates that systematic errors in prior estimates of baseline length, of order 5 cm for approximately 8000-km baselines, were due primarily to mismodeling of the electrical path length of the troposphere and mesosphere ('atmospheric delay'). Here observational evidence for the existence of such errors in the previously used models for the atmospheric delay is discussed, and a new 'mapping' function for the elevation angle dependence of this delay is developed. The delay predicted by this new mapping function differs from ray trace results by less than approximately 5 mm, at all elevations down to 5 deg elevation, and introduces errors into the estimates of baseline length of less than about 1 cm, for the multistation intercontinental experiment analyzed here.

1,129 citations


Journal ArticleDOI
TL;DR: In this article, a practical atmospheric millimeter-wave propagation model (MPM) is proposed to predict attenuation for dry air at 2.5-430 GHz. But the model is limited to frequencies below 300 GHz and the number of spectroscopic parameters can be reduced to less than 200.
Abstract: A practical atmospheric Millimeter-Wave Propagation Model (MPM) is formulated that predicts attenuation. delay, and noise properties of moist air for frequencies up to 1000 GHz. Input variables are height distributions (0-30 km) of pressure, temperature, humidity, and suspended droplet concentration along an anticipated radio path. Spectroscopic data consist of more than 450 parameters describing local O2 and H2O absorption lines complemented by continuum spectra for dry air, water vapor, and hydrosols. For a model (MPM*) limited to frequencies below 300 GHz, the number of spectroscopic parameters can be reduced to less than 200. Recent laboratory measurements by us at 138 GHz of absolute attenuation rates for simulated air with water vapor pressures up to saturation allow the formulation of an improved, though empirical water vapor continuum. Model predictions are compared with selected (2.5-430 GHz) data from both laboratory and field experiments. In general, good agreement is obtained.

515 citations


Journal ArticleDOI
TL;DR: In this article, the effects of turbulence on the width of signal spectra received by these radars are discussed, and it is shown how turbulence intensities may be extracted from spectral width measurements.
Abstract: Radars operating in the frequency band between 2 MHz and several hundred megahertz are capable of supplying a large data base of measurements of turbulent energy dissipation rates in the middle atmosphere. So far this has not been achieved; only occasionally have such radars been used to produce estimates of turbulence intensities. In order to encourage a greater emphasis on this aspect of radar studies of the middle atmosphere, this review summarizes the various techniques which can be used to measure turbulent energy dissipation rates. It is shown how absolute measurements of backscatter cross section can be used to measure turbulence intensities. A new theory is presented which shows that the power backscattered from the mesosphere depends on the turbulent energy dissipation rate, the electron density gradient, the neutral density scale height, the total electron density and the temperature gradient. The effects of turbulence on the width of signal spectra received by these radars are discussed, and it is shown how turbulence intensities may be extracted from spectral width measurements. The importance of removing nonturbulent processes which also broaden the width of the power spectra, such as wind shear broadening and beam width broadening, are stressed.

368 citations


Journal ArticleDOI
TL;DR: In this paper, the authors review the theory and the observational evidence for both types of instabilities in the lower and middle atmosphere and show that convective instabilities predominate for high-frequency wave motions.
Abstract: Dynamical and convective instabilities are two mechanisms that contribute significantly to the dissipation of larger-scale motions and the generation of turbulence in the middle atmosphere. The former are normally due to enhanced velocity shears and/or a local minimum of the static stability either in the mean flow or associated with low-frequency wave motions. The most common dynamical instability is the Kelvin-Helmholtz (KH) instability which is often manifested in the atmosphere as a series of KH billows. Convective instabilities occur where the lapse rate becomes superadiabatic through the action of gravity waves and appear to predominate for high-frequency wave motions. This paper reviews the theory and the observational evidence for both types of instabilities in the lower and middle atmosphere.

326 citations


Journal ArticleDOI
TL;DR: In this article, a coherent backscatter radar has been in operation at Goose Bay, Labrador, for the purpose of studying small-scale electron density structure in the high-latitude ionosphere.
Abstract: Since October 1983, a new coherent backscatter radar has been in operation at Goose Bay, Labrador, for the purpose of studying small-scale electron density structure in the high-latitude ionosphere This radar operates over a frequency band that extends from 8 to 20 MHz, and it uses an electronically phased array of 16 log-periodic antennas for both transmission and reception The radar transmits a seven-pulse pattern that enables one to determine 17-lag complex autocorrelation functions of the backscattered signals as a function of range and azimuth In this paper we present a complete description of the radar including explanations of the operation of the phasing matrix, the techniques of data acquisition and analysis as implemented in the radar microcomputer, and the possible on-line and automatic operating modes that may be instituted We also present examples of some of the initial results that we have obtained with the radar during the afternoon and late evening hours These examples include images of the two-dimensional distribution of small-scale structure and of their associated mean Doppler motion We also present examples of F region Doppler spectra derived from the complex autocorrelation functions These Doppler spectra show interesting differences from those of high-latitude E region irregularities

286 citations


Journal ArticleDOI
TL;DR: The MU (middle and upper atmosphere) radar of Japan is a 46.5-MHz pulse-modulated monostatic Doppler radar with an active phased array system as discussed by the authors.
Abstract: The MU (middle and upper atmosphere) radar of Japan is a 46.5-MHz pulse-modulated monostatic Doppler radar with an active phased array system. The nominal beam width is 3.6° and the peak radiation power is 1 MW with maximum average power of 50 kW. The system is composed of 475 crossed three-subelement yagi antennas and an equivalent number of solid state power amplifiers (transmitter-receiver modules). Each yagi antenna is driven by a transmitter-receiver module with peak output power of 2.4 kW. This system configuration enables very fast and almost continuous beam steering that has not been realized by other mesosphere-stratosphere-troposphere radars. Also, a variety of sophisticated operations are made feasible by dividing the antenna array into several independent subarrays. A brief description of the system, particularly its antenna and power amplifiers, is presented herein.

269 citations


Journal ArticleDOI
TL;DR: The MU radar of Japan uses an active phased array system with a 2.4kW peak power amplifier as mentioned in this paper, which attains a very fast and almost continuous beam steerability at the total peak radiation power of 1 MW.
Abstract: The MU (middle and upper atmosphere) radar of Japan uses an active phased array system. Each of 475 crossed three-subelement yagi antennas in a circular array is provided with a 2.4-kW peak power amplifier. This system configuration attains a very fast and almost continuous beam steerability at the total peak radiation power of 1 MW. A brief description of the in-house equipment is presented herein.

204 citations


Journal ArticleDOI
TL;DR: In this paper, the power, frequency shift, and spectral width of MST radar returns are compared in terms of statistical goodness of the estimators and computational convenience and simplicity, respectively.
Abstract: Processing techniques for the estimation of the power, the frequency shift, and the spectral width of mesosphere-stratosphere-troposphere (MST) radar returns are presented. The different techniques are compared in terms of statistical goodness of the estimators and in terms of computational convenience and simplicity.

163 citations


Journal ArticleDOI
TL;DR: In this paper, the authors examined the sensitivity of an evaporation duct model to meteorological measurements and found that the unexpectedly frequent occurrence of evapseoration duct heights greater than 40 m is related to thermally stable conditions in the atmospheric surface layer.
Abstract: The application of an evaporation duct model in operational and climatological assessments of propagation and the sensitivity of the model to meteorological measurements are examined. The unexpectedly frequent occurrence of evaporation duct heights greater than 40 m is related to thermally stable conditions in the atmospheric surface layer. The existence of stable conditions over the ocean is analyzed in terms of meteorological conditions and temperature measurement accuracies. Air-sea temperature differences measured by transiting ships are found to be biased toward stable conditions. The evaporation duct model is shown to be sensitive to this bias and yields high duct heights that are not supported by propagation measurements. A modified duct height calculation is proposed and applied to a radiometeorological data set.

157 citations


Journal ArticleDOI
TL;DR: In this article, an investigation of the polar cap ionosphere near the peak of the last solar cycle identified polar cap F layer arcs and ionization patches as unique features, and as sources of severe scintillations observed on 250-MHz satellite beacon signals.
Abstract: An investigation of the polar cap ionosphere near the peak of the last solar cycle identified polar cap F layer arcs and ionization patches as unique features of the polar cap ionosphere, and as sources of severe scintillations observed on 250-MHz satellite beacon signals. The continuing investigations in January and December 1983 and January 1984 have shown that arcs and patches persist as the dominant features of the winter polar cap ionosphere during periods of low sunspot numbers. Improved ionospheric soundings made at Thule, Greenland (86°CGL), showed a clear diurnal variation for the occurrence of the patch-type ionization. Discussion of various possible mechanisms producing the observed ionization patches leads to the conclusion that the solar produced ionosphere equatorward of the dayside cusp is the source region of the ionization patches. Polar plasma convection transports this ionization across the cusp and the central polar cap. The local time dependence of the occurrence of the patches at Thule is shown to be a manifestation of the well-known universal time control of the polar cap F region. A strong positive solar cycle dependence of the scintillations was measured during three extended campaigns and confirms earlier measurements. The diurnal variation of scintillations is almost flat at solar maximum and has a local time variation very similar to that of the patch type ionization at solar minimum. Both arcs and patches contribute to substantial scintillations around solar maximum, while only the patches are responsible for the considerably weaker scintillations during solar minimum.

141 citations


Journal ArticleDOI
TL;DR: In this article, the authors describe the modeling of the average raindrop size distribution measured at Ile-Ife, a tropical station in South Western Nigeria, using a method of moment regression, which allows a single lognormal function to be accurately fitted over the entire range of rain rates measured, a convenient result for rain attenuation and scattering applications.
Abstract: The paper describes the modeling of the average raindrop size distribution measured at Ile-Ife, a tropical station in South Western Nigeria. The new “method of moment regression” employed is a systematic one that has allowed a single lognormal function to be accurately fitted over the entire range of rain rates measured, a convenient result for rain attenuation and scattering applications. The Marshall and Palmer law, frequently used for such calculations, has been shown to be inadequate as a model for this tropical station, especially at the high rain rates important for communications systems design. This result suggests that the similar Laws and Parsons dropsize distribution currently adopted by the International Radio Consultative Committee for estimating rain attenuation from 1 to 1000 GHz may not be adequate over such a large frequency range in such tropical locations. Some comparisons are also made with the lognormal models and modeling approaches of other workers. The results confirm the utility of the rain rate parameterization used in the model for Ile-Ife, while giving further support to the accuracy of the lognormal distribution.

Journal ArticleDOI
TL;DR: In this paper, cross sections of power spectral density for 1981 between 60-110 km for the 48- to 8 hour and 8- to 1-hour-period bands, and of mean square velocity components in the 10- to 60-min-period band, are compared to crosssections of mean wind.
Abstract: Cross sections of power spectral density for 1981 between 60–110 km for the 48- to 8 hour and 8- to 1-hour-period bands, and of mean square velocity components in the 10- to 60-min-period band, are compared to cross sections of mean wind. Individual spectra agree well in form and amplitude to similar spectra for other sites when averaged over the entire year, but there are substantial variations in power spectral density in each band over the year. In the 10-min to 8-hour-period band, minima in spectral densities follow the zero line of mean zonal velocity very closely, indicating strong gravity wave mean flow interactions. This, and the variation in gravity wave intensity in general, suggests that gravity wave momentum deposition plays an important role in balancing the heat and momentum budgets of the upper middle atmosphere.

Journal ArticleDOI
TL;DR: In this article, the authors used VHF radar measurements for the postset beam steering technique and for interferometer applications to study winds, waves, and turbulence in the stratosphere and mesosphere.
Abstract: Spaced antenna VHF radar measurements are utilized for the postset beam steering technique and for interferometer applications to study winds, waves, and turbulence in the stratosphere and mesosphere. Following a brief description of the basic instrumental setup and the off-line analysis method, some results are presented which demonstrate the consistency and applicability of these methods. Vertical velocity oscillations due to gravity waves are analyzed by means of the cross-spectrum technique. It is shown that phase differences of gravity wave oscillations, measured between vertical and two opposite, off-vertical postset beams, change their sign when the beam is swung back and forth. The same features of change of velocity sign are noticed when the mean wind is observed. The mean wind deduced with the postset beam steering technique is similar to the wind deduced with the spaced antenna drift technique and the independent radiosonde winds. Taking these results as justification for the applicability and feasibility of the postset beam steering method, the total wave vector and the intrinsic angular frequency of gravity waves in the stratosphere are deduced. Reasonable arguments are discussed to support the suggestion that these waves were generated in lower stratosphere wind shear regions and were attenuated little when propagating up to the middle stratosphere. Turbulence blobs in the mesosphere are tracked with the interferometer technique. It is shown that these blobs moved horizontally as well as vertically, a feature which cannot unequivocally be detected with conventional Doppler methods.

Journal ArticleDOI
TL;DR: In this paper, a model for Mesosphere - Stratosphere - Troposphere (MST) radar spectra is developed following the formalism presented by Pinkel (1981), and expressions for the one-dimensional spectra of radial velocity versus frequency and versus radial wave number are presented.
Abstract: A model for Mesosphere - Stratosphere - Troposphere (MST) radar spectra is developed following the formalism presented by Pinkel (1981). Expressions for the one-dimensional spectra of radial velocity versus frequency and versus radial wave number are presented. Their dependence on the parameters of the gravity-wave spectrum and on the experimental parameters, radar zenith angle and averaging time are described and the conditions for critical tests of the gravity-wave hypothesis are discussed. The model spectra is compared with spectra observed in the Arctic summer mesosphere by the Poker Flat radar. This model applies to any monostatic Doppler sounding system, including MST radar, Doppler lidar and Doppler sonar in the atmosphere, and Doppler sonar in the ocean.

Journal ArticleDOI
TL;DR: In this article, the authors discussed the possibility of incorporating differential reflectivity (ZDR) measurement in Doppler radars having fast scan capability, without compromising the accuracy of the spectral moment estimates.
Abstract: This paper discusses the possibility of incorporating differential reflectivity (ZDR) measurement in Doppler radars having fast scan capability, without compromising the accuracy of the spectral moment estimates. The presently established technique of ZDR measurement using alternate sampling of horizontally and vertically polarized signals (H and V) has long acquisition time and reduced maximum unambiguous velocity. It is shown that ZDR acquisition time can be reduced significantly by simultaneously sampling H and V signals and range averaging, which does not compromise spectral moments estimation capability and volume update time. An analysis of variance of ZDR suggests that accurate estimation of ZDR at scan rates of 18° s−1 is possible only if correlation between simultaneously received horizontally and vertically polarized echoes is better than 0.995. A theoretical investigation of all the factors that contribute to the decorrelation established that this indeed is the case for rain media. A scheme for ZDR measurement is suggested which uses +45° and −45° polarized transmissions alternately and simultaneous reception of H and V signals to compensate for bias error due to propagation. Further, a method for nearly eliminating the bias error due to receiver mismatch is suggested.

Journal ArticleDOI
TL;DR: In this paper, a surface field phase perturbation method for the calculation of the wave field scattered by a rough surface was proposed, which is based on the extinction theorem and uses a perturbations expansion of a function closely related to the complex phase of the surface field.
Abstract: We present initial results from the investigation of a surface field phase perturbation method for the calculation of the wave field scattered by a rough surface. This technique is based on the extinction theorem and uses a perturbation expansion of a function closely related to the complex phase of the surface field. This approach was suggested earlier, but we use the expansion in a different way. In the present work we consider only deterministic periodic surfaces, rough in one dimension, on which the total field is zero. We find that, for surfaces with modest slope and curvature, this technique can be used to calculate scattered fields even when surface relief is significant compared to the wavelength of the incident radiation.

Journal ArticleDOI
TL;DR: In this paper, the authors used dual bistatic radar and the Saskatoon MF radar to obtain horizontal scales, phase velocities and power spectral density cross sections of upper middle atmosphere gravity waves as determined from spaced wind speeds.
Abstract: Dual bistatic radar and the Saskatoon MF radar were used to obtain horizontal scales, phase velocities and power spectral density cross sections of upper middle atmosphere gravity waves as determined from spaced wind velocities. The wave scales averaged 60-110 km and varied from 44-210 km during the 10-100 min observation periods. The horizontal length scales varied directly with the length of the observation interval, while the phase speeds decreased as the observation interval increased. The rms velocity perturbations were about 5 m/sec. The associated vertical wavelengths were 30 and 6 km for the 10-100 min intervals. The power spectra densities obtained, when compared with similar data from previous compaigns, were found to vary on an annual basis. The spectral densities were noted to track the zero line of mean zonal velocity closely in the 10 min to 8 hr period bands. This last phenomena strongly indicates the occurrence of gravity wave mean flow interactions. 80 references.

Journal ArticleDOI
TL;DR: In this paper, a direct vision type high-frequency Doppler frequency sounder and a setup of a high frequency sounding array at the northern part of Taiwan Island were presented.
Abstract: A development of a direct vision type high-frequency Doppler frequency sounder and a setup of HF Doppler frequency sounding array at the northern part of Taiwan Island were presented. By use of all typhoons that occurred in 1982 and 1983, the detectability of the typhoon-generated acoustic-gravity waves by use of this HF Doppler frequency sounding array was presented. The results show that the acoustic-gravity waves generated by a typhoon can be detected by this sounding array; however, the detectability is only 2 out of 12.

Journal ArticleDOI
TL;DR: In this paper, the relationship between the observed wind fluctuation spectrum and the wave spectrum was derived based on acoustic-gravity wave theory and radar observation principle, and the theoretical results can be used to interpret the observational data as well as to derive parameters for the model wave spectrum.
Abstract: Recently, gravity waves and two-dimensional turbulence have been proposed as possible causes for the observed mesoscale wind fluctuations in the atmosphere. In order to use wind velocity data measured by MST radars to investigate atmospheric gravity wave spectra, it is important to apply the correct relation between the observed wind fluctuation spectrum and the wave spectrum. In this paper, based on acoustic-gravity wave theory and radar observation principle, this relationship is quantitatively derived for the general case of acoustic-gravity waves. Examples are given to show how the theoretical results can be used to interpret the observational data as well as to derive parameters for the model wave spectrum. From the theoretical results, tests for the consistency of the gravity wave model for atmospheric wind fluctuations will be proposed.

Journal ArticleDOI
TL;DR: In this paper, the authors show that the density irregularities are convected by the dc electric field and that the instabilities are of the gradient drift type, and they also suggest that these irregularities are field-aligned structures, as evidenced by their ducting effect on downgoing ELF hiss.
Abstract: Electron density irregularities at medium scale (from a few kilometers to tens of kilometers) have been observed in the high-latitude topside F region by the satellite Aureol 3. These irregularities are field-aligned structures, as evidenced by their ducting effect on downgoing ELF hiss. It is often observed that the density enhancements have an asymmetrical structure in the direction perpendicular to the magnetic field. On one side of the density enhancement, an intense electrostatic turbulence is observed together with large density fluctuations. The other side is usually steeper and appears stable. These observations suggest that the density irregularities are convected by the dc electric field and that the instabilities are of the gradient drift type.

Journal ArticleDOI
TL;DR: In this article, the authors used the MST radar at Poker Flat, Alaska, over the past 5 years to determine the kinetic energy density (Joules per m−3) height profiles in the troposphere, stratosphere and mesosphere.
Abstract: Continuous observations of the wind field obtained using the MST radar at Poker Flat, Alaska, over the past 5 years enable a determination of kinetic energy density (Joules per m−3) height profiles in the troposphere, stratosphere and mesosphere. Three specific frequency intervals of the horizontal wind velocity spectrum are processed to yield height profiles of kinetic energy density corresponding roughly to periods of gravity waves, tides and planetary waves (although the wind fluctuations do not necessarily correspond to wavelike processes). Preliminary results of this analysis are presented here for both summer and winter periods.

Journal ArticleDOI
TL;DR: In this paper, the impact of multipath effects on the group delay measurement was analyzed and data analysis procedures were developed for minimizing the impact on group delay measurements, including low-pass filtering, day-to-day correlation, and calibration to relative differential carrier phase advance measurements by using subsets of the absolute ionospheric group delay data.
Abstract: Signals from the Global Positioning System (GPS) satellites can be used to make measurements of absolute ionospheric group delay and relative phase advance. These ionospheric parameters have wide application in providing corrections for military systems requiring knowledge of ionospheric time delay and phase scintillation, such as satellite detection radars. Multipath effects from the local environment of the receiving antenna can cause severe contamination of ionospheric group delay measurements made with GPS pseudorandom noise receivers. Measured variations in the multipath effects in some typical clean and reflective environments are presented and shown to be consistent with signal analysis for pseudorandom noise receivers. Measured single reflector multipath is analyzed briefly and shown to correlate well with calculations. Since antennas must frequently be located in environments that are much less than ideal, data analysis procedures were developed for minimizing the impact of multipath on the group delay measurement. These include low-pass filtering, day-to-day correlation, and calibration to relative differential carrier phase advance measurements by using subsets of the absolute ionospheric group delay data. Results of these processes as applied to the test data from various multipath environments are presented.

Journal ArticleDOI
TL;DR: The first long-term measurements of phase scintillations at high latitudes from a quasi-stationary Air Force satellite at 250 MHz were reported in this paper, where the measurements were made from Goose Bay, Labrador covering the corrected geomagnetic latitude range of 64°-72°N and Thule, Greenland covering the correction geOMagnetic latitude ranges of 85°-89°N.
Abstract: The first long-term measurements of phase scintillations at high latitudes from a quasi-stationary Air Force satellite at 250 MHz are reported. The measurements were made from Goose Bay, Labrador covering the corrected geomagnetic latitude range of 64°–72°N and Thule, Greenland covering the corrected geomagnetic latitude range of 85°–89°N. Data from December 1979, March–April 1980 and March–April 1982 are presented from both stations. The sunspot numbers during these specific time periods were approximately the same. The scintillation magnitudes were higher during the vernal equinox at both stations than during the winter solstice. The Goose Bay data showed a well ordered diurnal variation with a nighttime maximum and daytime minimum, whereas the Thule data showed no such ordering. The limited phase scintillation data set from Thule is augmented by intensity scintillation measurements made during 1979–1982 using the same quasi-stationary satellites. The long-term Thule data shows that the major variation in scintillation activity is annual with minimum scintillations observed in the local summer, as was determined earlier by Aarons et al. (1981). In contrast to the pronounced annual variation, the dependence of overall scintillation activity on sunspot cycle is not greatly evident during 1979–1982 when the sunspot number varied approximately between 100 and 200. It was found that both Goose Bay and Thule could show phase scintillations of the order of 10 rad (with 82-s detrend period) even during magnetically quiet times. One such case study, conducted during March 1982, is presented and second-order parameters such as phase aad intensity spectral strengths and slopes and intensity decorrelation times are discussed for this event at both stations. The use of geostationary satellite data shows the importance of enhanced magnetospheric convection velocities on the observation of large phase scintillation values at both sites. This underscores the need for incorporating irregularity dynamics in the currently developed static models of ionospheric scintillation.

Journal ArticleDOI
TL;DR: In this article, the authors examined the spectrum of atmospheric motions over the range of periods from a few minutes to many hours that have been made with ST/MST radars in the past 5 years.
Abstract: We consider the observations of the spectrum of atmospheric motions over the range of periods from a few minutes to many hours that have been made with ST/MST radars in the past 5 years. This range of periods includes the periods associated with buoyancy waves and the scale of atmospheric motions often referred to by meteorologists as the mesoscale. We consider the spectra of both horizontal and vertical velocities and examine their interpretation in terms of buoyancy wave theory and turbulence theory. To help in interpreting these spectra we present some recently determined aircraft wavenumber spectra. It is found that radar and aircraft horizontal wind spectra are in reasonable accord with expectations from quasi two-dimensional turbulence theory. The vertical velocity spectra are believed to be due to waves. Comparison of the energy levels and shapes of the horizontal and vertical velocity spectra are not consistent with existing models of internal wave spectra. However, it is possible that these inconsistencies arise from Doppler-shifting effects that are not taken into account in existing internal wave models. Nevertheless, we stress that all the observations we have examined support the hypothesis that quasi two-dimensional turbulence coexists with a nearly universal spectrum of buoyancy waves.

Journal ArticleDOI
TL;DR: In this paper, a VHF-UHF imaging system for applications to the reconstruction, with a high temporal resolution, of the two-dimensional spatial structure of lightning has been implemented and the interferometric technique used for obtaining high resolution and low ambiguities is presented, and the influence of source and system parameters on the location accuracy, ambiguity removal, and reconstruction of source structure is discussed.
Abstract: A VHF-UHF imaging system for applications to the reconstruction, with a high temporal resolution, of the two-dimensional spatial structure of lightning has been implemented. The interferometric technique used for obtaining high resolution and low ambiguities is presented, and the influence of source and system parameters on the location accuracy, ambiguity removal, and reconstruction of source structure is discussed.

Journal ArticleDOI
TL;DR: In this article, the radial wave number spectra of wind fluctuations obtained from heights near the mesopause by the Poker Flat, Alaska, mesosphere-stratosphere-troposphere (MST) radar running in a high spatial resolution mode (300 m).
Abstract: We present radial wave number spectra of wind fluctuations obtained from heights near the mesopause by the Poker Flat, Alaska, mesosphere-stratosphere-troposphere (MST) radar running in a high spatial resolution mode (300 m). The spectra are of radial wind fluctuations along one vertical and two oblique (15° zenith angle) beams measured at heights of 82–88 km during summer. The oblique wave number spectra have amplitudes that are within a factor of 3 of each other and appear to follow power laws with exponents in the −2 to −2.8 range. In order to infer what portion of the spectral amplitude can be attributed to gravity waves, the ratio of oblique to vertical amplitudes is compared with the ratio predicted by the gravity wave model of VanZandt. The observations are found to be consistent with the model, suggesting that gravity waves are the dominant motion in the high-latitude summer mesosphere.

Journal ArticleDOI
TL;DR: In this paper, three closely spaced vertical clear-air radar sites were installed and operated in Southern France during the Alpex experiment, which was designed to determine atmospheric wave parameters in the troposphere and lower stratosphere.
Abstract: Three closely spaced vertical clear-air radar sites were installed and operated in Southern France during the Alpex experiment. This United States-France cooperative effort was designed to determine atmospheric wave parameters in the troposphere and lower stratosphere. In this report we describe the experiment, give an overview of the data and present vertical wind speed power spectra. We also show spatial coherences obtained between heights and between radar sites.

Journal ArticleDOI
TL;DR: In this article, a modified Fresnel scatter model was proposed to better account for the pulse width dependence and height dependence of backscattered power observed at vertical incidence at lower VHF.
Abstract: This paper presents a modified Fresnel scatter model and compares the revised model with observations from the Poker Flat, Alaska, radar, the sounding system (SOUSY) radar, and the Jicamarca radar. The modifications to the original model have been made to better account for the pulse width dependence and height dependence of backscattered power observed at vertical incidence at lower VHF. Vertical profiles of backscattered power calculated using the revised model and routine radiosonde data show good agreement with observed backscattered power profiles. Relative comparisons of backscattered power using climatological data for the model agree fairly well with observed backscattered power profiles from Poker Flat, Jicamarca, and SOUSY.

Journal ArticleDOI
TL;DR: The full MU radar system has been in operation since late 1984 as discussed by the authors, and among various possible observations, the standard tropospheric, stratospheric and mesospheric observations have been carried out so far.
Abstract: The full MU (middle and upper atmosphere) radar system has been in operation since late 1984. Among various possible observations, the standard tropospheric, stratospheric, and mesospheric observations have been carried out so far. Preliminary results of turbulence observations are presented. These observations demonstrate the capability of this system and also reveal some basic scattering properties.

Journal ArticleDOI
TL;DR: In this article, the effect of the inhomogeneous medium on the propagation of electromagnetic waves in a two-dimensional environment was analyzed using generalized Hankel transform and semianalytic method.
Abstract: In geophysical probing, a borehole is often drilled in the earth, and the environment probed with electromagnetic waves. When such a borehole transverses a complex geological environment, the effect of the inhomogeneous medium on the propagation of electromagnetic waves needs to be understood. In this paper we present two methods with which the effect could be assessed in a two-dimensional inhomogeneous environment. The first technique illustrates a generalized Hankel transform method. The second technique shows the use of the semianalytic method to solve a two-dimensional inhomogeneity problem. Comparison with the finite element method showed 200 times improvement in computational speed. The method is general and may be extended to application in the field of optics, microwaves and millimeter waves.