Showing papers in "Radio Science in 1982"
TL;DR: In this article, the radiation pattern of an infinitesimal electric dipole was calculated for the case where the dipole is vertically located on the plane interface of two dielectric half spaces.
Abstract: The radiation pattern of an infinitesimal electric dipole is calculated for the case where the dipole is vertically located on the plane interface of two dielectric half spaces and for the case where the dipole is lying horizontally along the interface. For the vertical case, it is found that the radiation pattern has nulls at the interface and along the dipole axis. For the horizontal case, it is found that the pattern has a null at the interface; that the pattern in the upper half space, whose index of refraction is taken to be less than that of the lower half space, has a single lobe whose maximum is normal to the interface; and that in the lower half space, in the plane normal to the interface and containing the dipole, the pattern has three lobes, whereas in the plane normal to the interface and normally bisecting the dipole, the pattern has two maxima located symmetrically about a minimum. Interpretation of these results in terms of the Cerenkov effect is given.
207 citations
TL;DR: In this paper, the attenuation function for multiple knife-edge diffraction is described and some example calculations are presented, in the form of a multiple integral, which is transformed into a series representation which is amenable to computer implementation.
Abstract: A recently derived attenuation function for multiple knife-edge diffraction is described, and some example calculations are presented. The function, in the form of a multiple integral, is transformed into a series representation which is amenable to computer implementation. A program has been written to compute the attenuation over propagation paths containing up to a maximum of 10 knife-edges. Attenuation curves for three example paths are presented showing the effects of multiple knife-edges on the received signal. A means of estimating the statistical distribution of attenuation for a given path from statistical knowledge of the atmospheric surface refractivity is suggested.
182 citations
TL;DR: In this paper, a simple attenuation model (SAM) is presented for estimating rain-induced attenuation along an earth-space path, which uses an effective spatial rain distribution which is uniform for low rain rates and which has an exponentially shaped horizontal rain profile for high rain rates.
Abstract: A simple attenuation model (SAM) is presented for estimating rain-induced attenuation along an earth-space path. The rain model uses an effective spatial rain distribution which is uniform for low rain rates and which has an exponentially shaped horizontal rain profile for high rain rates. When compared to other models, the SAM performed well in the important region of low percentages of time, and had the lowest percent standard deviation of all percent time values tested.
117 citations
TL;DR: An empirical model has been generated to estimate diversity gain on earth-space propagation paths as a function of earth terminal separation distance, link frequency, elevation angle, and angle between the baseline and the path azimuth.
Abstract: An empirical model has been generated to estimate diversity gain on earth-space propagation paths as a function of earth terminal separation distance, link frequency, elevation angle, and angle between the baseline and the path azimuth. This analysis utilized 34 diversity experiments which have been conducted in Canada, England, Japan, and the United States during the past decade. The resulting model reproduces the entire experimental data set with an rms error of 0.73 dB. The separation distance dominates the dependence of the diversity gain. The dependence on link frequency is small but significant. No identifiable dependence on baseline orientation was found.
111 citations
TL;DR: In this paper, a general review of cloud types and their water particle densities, attenuation and noise temperature calculations, and basic link signal-to-noise ratio calculations are presented for frequencies in the range 10-50 GHz.
Abstract: The microwave attenuation and noise temperature effects of clouds can result in serious degradation of telecommunications link performance, especially for low-noise systems presently used in deep-space communications. Although cloud effects are generally less than rain effects, the frequent presence of clouds will cause some amount of link degradation a large portion of the time. This paper presents a general review of cloud types and their water particle densities, attenuation and noise temperature calculations, and basic link signal-to-noise ratio calculations. Tabular results of calculations for 12 different cloud models are presented for frequencies in the range 10-50 GHz. Curves of average-year attenuation and noise temperature statistics at frequencies ranging from 10 to 90 GHz, calculated from actual surface and radiosonde observations, are given for 15 climatologically distinct regions in the contiguous United States, Alaska, and Hawaii. Nonuniform sky cover is considered in these calculations.
93 citations
TL;DR: The results of the comparison show that the new, two-component model performs as well as the other models for prediction on earth-satellite paths and the promise of the application of the new model to the unsolved problems of diversity improvement and interference prediction justifies the consideration of yet another model.
Abstract: A two-component rain model has been developed for calculating attenuation statistics. In contrast to most other attenuation prediction models, the two-component model calculates the occurrence probability for volume cells or debris attenuation events. The model performed significantly better than the International Radio Consultative Committee model when used for predictions on earth-satellite paths. It is expected that the model will have applications in modeling the joint statistics required for space diversity system design, the statistics of interference due to rain scatter at attenuating frequencies, and the duration statistics for attenuation events.
90 citations
TL;DR: In this paper, the authors compared the absorption coefficient (7.5 g/m/cubed water vapor at 290 K) and approximately the same for total zenithal attenuation.
Abstract: Calculations are presented for atmospheric absorption and radiation emission for several atmospheric conditions and elevation angles. The calculations are for frequencies in the 1 to 340 GHz frequency range. The calculations are compared to those from other models. Agreement is found to within 15% for absorption coefficient (7.5 g/m/cubed water vapor at 290 K) and approximately the same for total zenithal attenuation. The attenuation and gaseous emission noise curves defined by the International Radio Consultative Committee are found to have minor inconsistencies.
85 citations
TL;DR: In this article, a review of the application of the phase screen model to the interpretation of data from the Defense Nuclear Agency's Wideband satellite (international designation P76-5), which was operational from May 1976 until August 1979, is presented.
Abstract: Phase screen models have been used for nearly three decades to facilitate the application of the scintillation theory to data interpretation. Only recently, however, as large amounts of multifrequency phase-coherent beacon data have been analyzed, has the full potential of the model been realized. This paper presents a review of the application of the phase screen model to the interpretation of data from the Defense Nuclear Agency's Wideband satellite (international designation P76-5), which was operational from May 1976 until August 1979. The signal structure and experiment configuration allowed measurements of temporal, spatial, and frequency coherence for a wide variety of scintillation conditions. The derived scintillation parameters are in excellent agreement with the phase screen theory. Moreover, the inferred irregularity structure has been confirmed by recent in situ measurements. The principal results can be summarized with simple algebraic formulas for the scintillation level, spatial/temporal coherence, and frequency coherence or coherence bandwidth. With appropriate manipulations, the formulas fully accommodate the propagation angle dependence in highly anisotropic media.
81 citations
TL;DR: A parameter estimation technique that parameterizes the first three-spectral moments corresponding to the desired stratospheric signals as well as a few Taylor series coefficients of the auto-correlation function of the clutter is presented.
Abstract: The 430 MHz, 2 MW radar at the Arecibo Observatory is currently being used as a stratospheric-troposheric (ST) radar. One of the problems in the automatic analysis of the signals come from the very large amplitude of the ground clutter echoes. The problem is agravated by the fading of these signals, which makes it difficult to discriminate them from the desired stratospheric returns. A parameter estimation technique that parameterizes the first three-spectral moments corresponding to the desired stratospheric signals as well as a few Taylor series coefficients of the auto-correlation function of the clutter is presented. The three first moments can be obtained in this manner even in the presence of clutter 50 dB stronger. The technique automatically takes care of instrumental and processing biases. Spectrum aliasing presents no problem. A sequence of fine altitude and high temporal resolution wind profiles is presented, showing the potential of the instrumental and technique for the study of stratospheric dynamics.
74 citations
TL;DR: In this paper, the authors present observations of turbulence-induced tropospheric phase fluctuations measured at 5 GHz on the near-vertical paths relevant to many astronomical and geophysical measurements.
Abstract: The article presents observations of turbulence-induced tropospheric phase fluctuations measured at 5 GHz on the near-vertical paths relevant to many astronomical and geophysical measurements. The data are summarized as phase power spectra, structure functions, and Allan variances. Comparisons to other microwave observations indicate relatively good agreement in both the level and shape of the power spectrum of these tropospheric phase fluctuations. Implications for precision Doppler tracking of spacecraft and geodesy/radio interferometry are discussed.
73 citations
TL;DR: In this article, a simple curve is developed for the PRF below which decorrelation is assured, and an adaptive PRF for future altimeters is recommended to conserve mission power while optimizing data collection during high-sea states.
Abstract: Pulse-to-pulse correlation in satellite radar altimeters is examined to determine if range jitter in future altimeters could be reduced by increasing the pulse repetition frequency (PRF). Data from the Skylab radar altimeter is analyzed and compared with rules of thumb and the results of a Monte Carlo simulation. Altimeter range tracker configurations are reviewed and a simple curve is developed for the PRF below which decorrelation is assured. An adaptive PRF for future altimeters is recommended to conserve mission power while optimizing data collection during high-sea states.
TL;DR: In this paper, an efficient electron density profile inversion algorithm is developed for use on automatically scaled digital topside ionograms and profile fitting method described here models the top-side ionosphere with a single polynomial, a method particularly suited for autoscaled data.
Abstract: An efficient electron density profile inversion algorithm is developed for use on automatically scaled digital topside ionograms The profile-fitting method described here models the topside ionosphere with a single polynomial, a method particularly suited for autoscaled data because it is not too sensitive to a certain amount of scatter in the h′(ƒ) data and it makes use of ordinary and extraordinary ray echoes The program was applied to input data consisting of O and X trace segments obtained from automatic scaling of a number of digitized ISIS ionograms It is shown that fully automatic calculation of the topside electron density profiles from digital topside ionograms can be performed in less than 10 s on a Cyber 71 computer
TL;DR: In this paper, a generalized spectral extension of the uniform GTD is used to determine the contribution from the doubly diffracted ray, where the edge of one wedge is illuminated by the shadow boundary field of the other.
Abstract: A solution is obtained for the high-frequency scattering by a pair of parallel wedges where the edge of one wedge is illuminated by the shadow boundary field of the other. A generalized spectral extension of the uniform GTD is used to determine the contribution from the doubly diffracted ray. Expressions for the diffracted field are given for plane, cylindrical, and spherical wave illuminations. Incidence oblique to the edges is also considered. These expressions reduce to a closed form at the shadow boundaries and outside the overlapping transition regions where the results coincide with those obtained by the uniform GTD augmented by slope diffraction. The solutions to the scalar problems are then used to derive a dyadic diffraction coefficient for the doubly diffracted field, in the ray-fixed coordinate system. The general expressions presented here directly apply to the diffraction by half planes, strips, and joined wedges (thick edges) where the number of terms involved significantly reduces.
TL;DR: In this article, it was shown that the one-dimensional corrugated surface can be solved by using two scalar functions: the components of the electric and magnetic fields along the row direction of the surface, and appropriate boundary conditions to obtain simple matrix equations.
Abstract: Electromagnetic waves scattered from a periodic dielectric and perfectly conducting surface are studied for a general angle of incidence. It is shown that the one-dimensional corrugated surface can be solved by using two scalar functions: the components of the electric and magnetic fields along the row direction of the surface, and appropriate boundary conditions to obtain simple matrix equations. Results are compared to the case where the incident angle wave vector is perpendicular to the row direction. Numerical results demonstrate that energy conservation and reciprocity are obeyed for scattering by sinusoidal surfaces for the general case, which checks the consistency of the formalism.
TL;DR: In this paper, the authors present a new technique to obtain sea surface wind speeds from HF sky wave radar backscatter spectra, which uses sea state parameters obtained with an appropriate inversion technique, together with relevant empirical/theoretical relationships on the growth of a wind generated sea.
Abstract: The ability to obtain sea surface wind speeds from HF sky wave radar backscatter spectra is important if such a radar is to make a meaningful contribution to a meteorological or oceanographic observation network. Since the radar measures wave parameters only, wind vectors must be inferred from the wave measurements in the light of what knowledge we have concerning the processes of wave generation. Previous attempts to extract wind speeds have proved unsatisfactory for a variety of reasons. We present here a new technique to enable such a derivation, which uses sea state parameters obtained with an appropriate inversion technique, together with relevant empirical/theoretical relationships on the growth of a wind-generated sea. The procedure is illustrated with a Doppler spectrum obtained during the JASIN experiment, and some comparisons made with other JASIN surface data.
TL;DR: In this article, a simple formula was derived as an approximation for the general exact integrals for the radial component of the electric field generated by a horizontal electric dipole in a half-space of water or earth near its boundary with air.
Abstract: A new simple formula is derived as an approximation for the general exact integrals for the radial component of the electric field generated by a horizontal electric dipole in a half-space of water or earth near its boundary with air. The field in the water or earth is investigated as a function of radial distance from the source for er = 80, 20, and 4, over wide ranges of conductivities and frequencies. Special attention is paid to the ranges in which the direct wave from the dipole produces an interference pattern of standing waves when it interacts with the lateral wave. For selected values of the parameters the radial electric field computed from the new simple formula is compared with the field evaluated numerically from the exact integrals. The agreement is excellent when the ratio of wave numbers characteristic of the denser half-space and air is large, quite good even when this ratio is as small as 2.
TL;DR: In this paper, a vectorial-wave finite-element method was proposed to calculate the propagation characteristics of axially nonsymmetrical fibers. But this method is restricted to single-mode optical fiber and the field outside the central core region is expanded by a series of modified Bessel functions.
Abstract: In an axially symmetrical single-mode optical fiber, the polarization plane of the propagated HE11 mode is subject to unstable rotation due to slight changes in ambient conditions. Such an instability can be prevented by making the refractive index distribution in the fiber axially nonsymmetrical. This paper describes a two-dimensional, vectorial-wave finite-element method calculation of the propagation characteristics of such axially nonsymmetrical fibers. It is an improved version of Yeh's program; the field outside the central core region is expanded by a series of modified Bessel functions. Some numerical examples are described.
TL;DR: In this article, the authors combined the benefits of high-frequency-resolution Alouette 2 analog sounder data with advanced digital graphics techniques to study simulated waveparticle interactions in the ionosphere.
Abstract: Several hundred topside ionograms were used to study simulated wave-particle interactions in the ionosphere. The study combined the benefits of high-frequency-resolution Alouette 2 analog sounder data with advanced digital graphics techniques. The study shows that the sounder phase can cause significant plasma heating when the plasma parameter is confined to specific ranges. The observations support the Harris instability generation process and the nonlinear Landau damping maintaining process for long-duration diffuse resonances. The observations also suggest that the so-called Q resonances have characteristics which imply that generation processes in a sounder-stimulated plasma turbulence may be involved.
TL;DR: In this paper, the authors proposed an approximate method for analyzing the discontinuities in slab dielectric waveguides based on replacing the unbounded configuration by a corresponding periodic multilayer structure.
Abstract: We propose an approximate method, of general applicability, for analyzing the discontinuities in slab dielectric waveguides. The method is based on replacing the unbounded configuration by a corresponding periodic multilayer structure. Hence the entire spectrum becomes discrete, and this makes the problem easier. The characteristic equation for the modal solution in a periodical multilayer dielectric waveguide is expressed in a matrix form which can be readily solved with a computer. In order to solve the discontinuity problems of slab waveguides, we expressed the reflected and transmitted fields by truncated modal expansions. The unknown amplitudes of the reflected and transmitted modes are determined by the boundary conditions. Numerical results are graphically shown including the cases which have been difficult to analyze by other methods. The accuracy of our results is checked by evaluating the relative errors and comparing with other available results.
TL;DR: In this paper, a self-consistent multiple scattering theory using the T matrix of a single scatterer and a suitable averaging technique is employed to account for the statistical nature of the position of scatterers is accounted for by ensemble averaging.
Abstract: Coherent electromagnetic wave propagation in an infinite medium composed of a random distribution of identical, finite scatterers is studied. A self-consistent multiple scattering theory using the T matrix of a single scatterer and a suitable averaging technique is employed. The statistical nature of the position of scatterers is accounted for by ensemble averaging. This results in a hierarchy of equations relating the different orders of correlations between the scatterers. Lax's quasi-crystalline approximation is used to truncate the hierachy enabling passage to a homogeneous continuum whose bulk propagation characteristics such as phase velocity and coherent wave attenuation can then be studied. Three models for the pair correlation function are considered. The Matern model and the well-stirred approximation are good only for sparse concentrations, while the Percus-Yevick approximation is good for a wider range of concentration. The results obtained using these models are compared with the available experimental results for dielectric scatterers embedded in a host dielectric medium. Practical applications of this study include artificial dielectric (composites) and electromagnetic wave propagation through hydrometeors, dust, vegetation, etc.
TL;DR: In this paper, multiple scattering calculations of rain effects were studied on the basis of calculating the incoherent intensity at 30, 60, 90, and 120 GHz, where the Mie solution and the Laws-Parsons distribution were used to determine scattering and absorption characteristics.
Abstract: The multiple scattering calculations of rain effects are studied on the basis of calculating the incoherent intensity at 30, 60, 90, and 120 GHz. The Mie solution and the Laws-Parsons distribution are used to determine scattering and absorption characteristics. The equation of transfer and the Stokes parameters are used to determine incoherent intensities for the horizontal and vertical polarizations. The ratio of the copolarized incoherent intensity to the copolarized coherent intensity is defined as the incoherent copolarized discrimination. The ratio of the cross-polarized incoherent intensity is defined as the incoherent cross-polarized discrimination. These ratios are calculated in terms of copolarized attenuation, rain rate, and field of view. The results show that multiple scattering effects may become significant during heavy rains.
TL;DR: In this paper, the radio refractive index is calculated by summing the refraction due to the infrared resonances of the water vapor monomer, and it is shown that this calculated refraction agrees well with measured values, its temperature dependence departs significantly from the measured variation with temperature.
Abstract: : The radio refractive index is calculated by summing the refraction due to the infrared resonances of the water vapor monomer. Although this calculated refraction agrees well with measured values, its temperature dependence departs significantly from the measured variation with temperature. The rotational resonances of water vapor give a contribution to the radio refractive index that does not vary precisely as e/T (expn 2); theoretical reasons are given for this departure from the classical refraction by permanent dipoles.
TL;DR: In this paper, a theory is presented and a model is developed to predict the effects of foliage on a line-of-sight propagating field and the effective fractional volume of foliage comprising the Rayleigh components is constructed as a function of frequency using forest stand table data.
Abstract: A theory is presented and a model is developed to predict the effects of foliage on a line-of-sight propagating field. In view of the sparse concentration of foliage, the Foldy-Twersky theory for wave propagation through discrete random media is used to obtain the complex propagation constant for the coherent field. On the basis of the measurements of Stutzman et al. (1979), the dominant foliage components are taken to be Rayleigh-like in their scattering and absorbing characteristics. The effective fractional volume of foliage comprising the Rayleigh components is constructed as a function of frequency using forest stand table data. Trunks and branches are modeled as Rayleigh cylinders; leaves are ignored because of their small total volume. The model fails above the frequency for which the effective fractional volume goes to zero. The model provides reasonably good agreement with propagation measurements and is capable of explaining some of the observed polarization effects.
TL;DR: In this paper, the scaling of top-side ionograms in a ground-based minicomputer is described, and the scaling algorithm finds the resonance and cutoff frequencies and the vertical O and X echo traces.
Abstract: This first paper in a series of three describing the automatic processing of digital ionograms discusses the scaling of topside ionograms in a ground-based minicomputer. The objective is to automatically obtain the vertical electron density profiles. The topside ionogram scaling algorithm finds the resonance and cutoff frequencies and the vertical O and X echo traces. Application of the scaling algorithm to digitized ISIS 1 and 2 ionograms illustrates its performance and demonstrates the feasibility to automatically scale topside ionograms. The ISIS studies show that polarization tagging of the O and X signals should be done in a digital satellite sounder to assure successful, real time scaling of complex ionograms.
TL;DR: In this paper, a correlation analysis method developed by Armstrong and Coles has been applied to spaced-receiver data from the Wideband satellite to verify the L-shell aligned, cross-field anisotropy of F region auroral zone irregularities.
Abstract: A correlation analysis method developed by Armstrong and Coles has been applied to spaced- receiver data from the Wideband satellite. The method permits simultaneous estimation of the anisotropy and true drift of the diffraction pattern. The scintillation theory is applied to interpret the measured variations in anisotropy and pattern drift. The results show that in anisotropic media, there is a complicated interplay between apparent drifts and the anisotropy of the diffraction pattern that must be accommodated in spaced-receiver data analyses. The method has been applied to verify the L-shell aligned, cross-field anisotropy of F region auroral zone irregularities.
TL;DR: In this paper, the propagation of electromagnetic waves in media with various horizontal layers has been analyzed and the electromagnetic fields outside the source region were obtained from the dyadic Green's functions for the case of media with three and four layers.
Abstract: The propagation of electromagnetic waves in media with various horizontal layers has been analyzed. The electromagnetic fields outside the source region were obtained from the dyadic Green's functions for the case of media with three and four layers and for horizontal and vertical electric dipoles. These results agree with those obtained using Hertz potentials. One of the major results is a generalization of the dyadic Green's functions for solving the problem of media with N horizontal layers.
TL;DR: In this paper, the state of the art in the calculation of electromagnetic wave scattering by hydrometeors is discussed, including point-matching, T matrix, unimoment, and Fredholm integral equation.
Abstract: This paper is concerned with the state of the art in the calculation of electromagnetic wave scattering by hydrometeors. Four methods currently being used are briefly described (point-matching, T matrix, unimoment, and Fredholm integral equation), and aspects of their computational implementation are reviewed and compared. The ranges of validity of three types of approximation are discussed—those with respect to size, orientation, and frequency. Finally, scattering patterns from various sizes of spheroidal raindrop at 11.7 GHz are briefly discussed.
TL;DR: In this paper, the concept of energy balance is applied to compute the total loss (or extinction) resulting from a partially polarized plane wave impinging upon a scatterer, and it is shown that under the far-zone condition, the application of the stationary phase approximation leads to an expression relating the total losses to the Stokes parameters of the incident wave and the forward scattering amplitudes of the scattered wave.
Abstract: The concept of energy balance is applied to compute the total loss (or extinction) resulting from a partially polarized plane wave impinging upon a scatterer. It is shown that under the far-zone condition, the application of the stationary phase approximation leads to an expression relating the total loss to the Stokes parameters of the incident wave and the forward scattering amplitudes of the scattered wave. This relation may be referred to as the vector forward scattering theorem. For a linearly polarized incident plane wave, the result reduces correctly to the standard forward scattering theorem in the literature.
TL;DR: In this article, a least square solution for antenna gains and an analysis of the variation of the signal-to-noise ratio over the channels of a spectral line correlator system are presented.
Abstract: The frequency responses of the receiving channels of a radio astronomy synthesis array and, in particular, the variations between them for different antennas are factors that limit the accuracy and sensitivity of the instrument. A response that approximates a rectangular passband as closely as possible is advantageous from considerations of maximizing sensitivity within a given frequency band and minimizing the smearing of detail in the outer regions of a map. Tolerances on slopes, ripples, and other bandpass distortions can be determined by examining their effects with regard to loss in sensitivity and the introduction of errors in the assignment of complex gain factors for individual antennas by using calibration observations. These calibration errors are generally larger in amplitude than in phase and their effect is usually more serious than the loss in sensitivity. Velocity dispersion in waveguide transmission systems and the accuracy in adjustment of compensating time delays also affect the phase responses of the signal channels, and examination of these effects also leads to limits on system design parameters. Implementation of the tolerances derived, including some details of the filter specifications, is discussed for the very large array radio telescope of the National Radio Astronomy Observatory. Appendices contain an algorithm for performing a least squares solution for antenna gains and an analysis of the variation of the signal-to-noise ratio over the channels of a spectral line correlator system.
TL;DR: The results would indicate that the thresholds for convulsions induced by short exposures of the brain to high energy pulses are dependent only on the deposited energy and temperature rise.
Abstract: Previous studies have indicated that auditory responses could be evoked in the head of animals exposed to 500-μs-wide or less microwave pulses of relatively small absorbed energies (5–180 mJ/kg). These studies were extended using an exposure system capable of locally exposing the head and especially the brain of the animal to a single 915-MHz pulsed magnetic field with sufficient intensity to produce a specific absorption rate level as high as 4×105 W/kg for any pulse width. When the animal was exposed to various pulse widths (1μs to 360 ms) and power levels (2–10 kW), the animal displayed no reaction other than that due to the hearing effect until the peak absorbed energy density in the brain exceeded 28 kJ/kg, or an absorbed energy in the head of 680 J, regardless of peak power or pulse width. Thermographic and thermocouple measurements indicated a maximum temperature rise of 8°C or final maximum brain temperature of 46° −46.5°C at the reaction level. The reaction consisted of petit or grand mal seizures lasting for 1 min after exposure, followed by a 4- to 5-min unconscious state during which normal reflexes were displayed. There was a decrease in heartbeat rate in the exposed unanesthetized animals. After the period of unconsciousness the rats recovered without apparent effect from the exposure. Measurements indicated that the brain temperature returned to baseline level within 5 min after exposure and the animals began moving when the brain temperature returned to within 1°C of their normal values. These results would indicate that the thresholds for convulsions induced by short exposures of the brain to high energy pulses are dependent only on the deposited energy and temperature rise. Histological examinations of some of the animal brains indicated some demyelination of neurons 1 day after exposure and some microfocal glial nodules in the brain 1 month after exposure.