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Showing papers on "Reflection (physics) published in 1975"


Journal ArticleDOI
TL;DR: In this paper, the nature of the characteristic wave motions is studied, and a characteristic receptance matrix for a characteristic wave is defined, and the equations governing the reflection process are set up, and used to formulate the equations for the natural frequencies and modes of a finite periodic system with arbitrary boundaries.

268 citations


Journal ArticleDOI
TL;DR: In this paper, a two-stream model for radiative transfer in an optically thin plane-parallel atmosphere is proposed, based on the dependence of the reflection and the transmission of the atmosphere on the angle of the incident radiation and on the angular dependence of a scattering phase function of the medium.
Abstract: The two-stream approximation has been applied to the equation of radiative transfer to obtain two–stream models for the transfer of radiation through an optically thin plane-parallel atmosphere. The models include the dependence of the reflection and the transmission of the atmosphere on the angle of the incident radiation and on the angular dependence of the scattering phase function of the medium. The two models arise from different methods for treating the incident radiation. It is shown that the models reduce to the thin-atmosphere approximation in the limit that the optical depth of the atmosphere approaches zero. In this limit the sign of the heating caused by the presence of a scattering and absorbing layer over a reflecting surface is derived. This reveals the importance of both the zenith angle and the angular dependence of the scattering phase function. The results obtained from the two-stream models are compared with those of numerical solutions to the equation of radiative transfer. I...

232 citations


Journal ArticleDOI
TL;DR: In this paper, a new ray model is presented for the reflection of electromagnetic radiation from the rough air-material interface of a randomly rough surface, where the surface is modeled as an ellipsoid of revolution.
Abstract: A new ray model is presented for the reflection of electromagnetic radiation from the rough air-material interface of a randomly rough surface. Unlike previous derivations that modeled the rough interface as consisting of microareas randomly oriented but flat (facets), this derivation models it as consisting of microareas not only randomly oriented but also randomly curved. Physically, the models are the same, but this new derivation leads to some new results. (1) For any given rough surface, there exists a single, optically smooth, curved surface of revolution of very restricted shape that will reflect radiation in the same distribution as that reflected by the rough interface. (2) Modeling that surface as an ellipsoid of revolution gives a surface-structure function that appears more accurate and useful than existing ones. (3) Unlike the facet derivations, this derivation lends itself to a normalization that gives the absolute, instead of just a comparative, reflectance-distribution function.

201 citations


Journal ArticleDOI
TL;DR: In this article, exact matrix equations for surface fields, as well as transmitted and reflected wave amplitudes are obtained for an interface having periodic height variation, in conjunction with the extended boundary condition, in which propagating waves are coupled with evanescent modes.
Abstract: Reflection behavior is examined for an interface having periodic height variation. Upon employing the Bloch theorem, in conjunction with the extended boundary condition, exact matrix equations are obtained for surface fields, as well as transmitted and reflected wave amplitudes. Tunneling considerations then lead to new energy constraints for problems of this type, in which propagating waves are coupled with evanescent modes. In the limit of surface corrugations shallow compared with impinging wavelength, analytic results are obtained confirming both the energy constraints and early computations by Rayleigh. Numerical results demonstrate the efficiency of the method.Subject Classification: 20.30.

196 citations


Proceedings ArticleDOI
01 Jan 1975
TL;DR: In this paper, a scalar theory of surface scattering phenomena has been formulated by utilizing the same Fourier techniques that have proven so successful in the area of image formation, and an analytical expression has been obtained for a surface transfer function which relates the surface micro-roughness to the scattered distribution of radiation from that surface.
Abstract: A scalar theory of surface scattering phenomena has been formulated by utilizing the same Fourier techniques that have proven so successful in the area of image formation. An analytical expression has been obtained for a surface transfer function which relates the surface micro-roughness to the scattered distribution of radiation from that surface. The existence of such a transfer function implies a shift-invariant scattering function which does not change shape with the angle of the incident beam. This is a rather significant development which has profound implications regarding the quantity of data required to completely characterize the scattering properties of a surface. This theory also provides a straight-forward solution to the inverse scattering problem (i.e., determining surface characteristics from scattered light measurements) and results in a simple method of predicting the wave length dependence of the scattered light distribution. Both theoretical and experimental results will be presented along with a discussion of the capabilities and limitations of this treatment of surface scatter phenomena.© (1977) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

182 citations


Journal ArticleDOI
TL;DR: Schroeder et al. as discussed by the authors showed that low-loss, high-scatter surfaces may be required for better concert−hall acoustics Surfaces shaped to give reflection coefficients according to such sequences show the expected high scatter in model experiments with microwavesSubject Classification: 5520, 5540
Abstract: Low−correlation sequences, such as ’’maximum−length’’ and Barker sequences and certain complex (magnitude one) sequences having flat power spectra, are ideally suited for designing surfaces of hard walls with highly diffuse reflections Recent subjective−preference evaluations [M R Schroeder, D Gottlob, and K F Siebrasse ’’Comparative Study of European Concert Halls’’, J Acoust Soc Am 56, XXX−XXX (1974)] indicate that low−loss, high−scatter surfaces may be required for better concert−hall acoustics Surfaces shaped to give reflection coefficients according to such sequences show the expected high scatter in model experiments with microwavesSubject Classification: 5520, 5540

155 citations


Journal ArticleDOI
TL;DR: In this article, the amplitude of seismic energy varies over a tremendous range and the amplitude-governing factors are primarily interested in are reflection coefficient, the interference of reflections from the top and base of a sand, and absorption.
Abstract: The amplitude of seismic energy varies over a tremendous range. Some of the factors responsible for such variation do not contain subsurface information; these include source strength and coupling, geophone sensitivity, array directivity, instrument balance, scattering in the near-surface, for example. Others depend on subsurface factors but do not convey information about lithology or hydrocarbon accumulation in a form from which we are able to extract it; these include spherical divergence, ray-path curvature, loss in transmission through intervening reflectors, peg-leg multiples, reflector rugosity, and curvature. The amplitude-governing factors we are primarily interested in are reflection coefficient, the interference of reflections from the top and base of a sand, and absorption.

115 citations


Journal ArticleDOI
TL;DR: In this paper, field measurements of multiple offshore bar spacing were compared to theory and wave measurements to corroborate the suggestion that bar formation and spacing are controlled by standing waves in the infragravity range (0.5-5 min).
Abstract: Field measurements of multiple offshore bar spacing were compared to theory and wave measurements to corroborate the suggestion that bar formation and spacing are controlled by standing waves in the infragravity range (0.5–5 min). Theoretical and experimental studies predict the reflection of progressive waves from a shoreline as standing waves. Associated drift in the bottom boundary layer is expected to produce sediment accumulation and bar formation under either the nodal or the antinodal points. Measurements of waves in the infragravity spectrum confirm the occurrence of such standing waves, and spacing of offshore bars in adjacent areas correlates well with the predicted position of the bars.

113 citations


Journal ArticleDOI
TL;DR: In this paper, a simple rearrangement of Kirchhoff's potential equation allows the reflection process to be evaluated as a convolution of the derivative of the source wavelet with a term called the wavefront sweep velocity, a measure of the rate at which the incident wavefront covers the reflecting boundary.
Abstract: A form of Kirchhoff’s wave equation is presented which is useful to the geophysicist doing an amplitude interpretation of seismic reflection data. A simple rearrangement of Kirchhoff’s retarded potential equation allows the reflection process to be evaluated as a convolution of the derivative of the source wavelet with a term called the “wavefront sweep velocity”. The wavefront sweep velocity is a measure of the rate at which the incident wavefront covers the reflecting boundary. By comparing wavefront sweep velocities for geologic models with different curvature, one obtains an intuitive feeling for the relation of diffraction and reflection amplitudes to boundary curvature. Also, from this convolutional form of the wave equation, the geometrical optics solution for the reflection amplitude is easily obtained. But more important, from the wavefront sweep velocity approach, a graphical method evolves which allows the geophysicist to use compass and ruler to estimate the effects of curvature and diffractio...

107 citations


Journal ArticleDOI
TL;DR: In this article, the authors consider a line-imaging migration process and find that the profile migration velocity depends not only on the true section velocity but also on certain geometrical factors which relate the profile direction to the structure.
Abstract: A reflecting interface with irregular shape is overlain by a material of constant velocity VT. Multifold reflection data are collected on a plane above the reflector and the reflector is imaged by first stacking then migrating the reflection data. There are three velocity functions encountered in this process: the measured stacking velocity VNMO; the true overburden velocity VT; and a profile migration velocity VM, which is required by present point‐imaging migration programs. Methods of determining VNMO and, subsequently, VT are well‐known. The determination of VM from VT, on the other hand, has not been previously discussed. By considering a line‐imaging migration process we find that VM depends not only on the true section velocity but also on certain geometrical factors which relate the profile direction to the structure. The relation between VM and VT is similar to, but should not be confused with, the known relation between VNMO and VT. The correct profile migration velocity is always equal to or gr...

94 citations


Journal ArticleDOI
Abstract: The reflection of a locally plane wave from a curved interface between two nonabsorbing dielectric media is investigated. Our analysis is applicable to an interface of general shape, defined at each point by the two principal radii of curvature. When the wave is incident from the denser medium at angles greater than the critical angle it is only partially reflected, due to a form of electromagnetic tunneling. Generalized Fresnel transmission coefficients and an extension of Snell's law are derived to account for this transmission into the less dense medium. Ray tracing can then be applied to determine such phenomena as the bending losses in optical slab waveguides, and the curvature loss of skew rays within straight optical waveguides of circular cross section.

Journal ArticleDOI
TL;DR: In this paper, a numerical method for solving linearized water wave problems with oscillatory time dependence is presented, where the diffraction problem for oblique plane waves incident upon an infinitely long fixed cylinder on the free surface is considered.
Abstract: This paper presents a numerical method for solving linearized water-wave problems with oscillatory time dependence Specifically it considers the diffraction problem for oblique plane waves incident upon an infinitely long fixed cylinder on the free surface The numerical method is based on a variational principle ezuivalent to the linearized boundary-value problem Finite-element techniques are used to represent the velocity potential; and the variational principle is used to determine the unknown coefficients in the solution throughout the fluid domain To illustrate this method, reflection and transmission coefficients and the diffraction forces and moment are computed for oblique waves incident upon a vertical flat plate, a horizontal flat plate and rectangular cylinders, where the comparison is made with the existing results by others

Journal ArticleDOI
TL;DR: In this article, a second-order theory for reflection and transmission of light by a slightly rough surface was developed, especially for a rough interface between vacuum and a freeelectron-like metal, where surface-plasma excitation can occur.
Abstract: A second-order theory is developed for the reflection and transmission of light by a slightly rough surface. The general results are discussed, especially for a rough interface between vacuum and a free-electron-like metal, where surface-plasma excitation can occur. The influence of the damping of the electron gas and of the shape of the roughness is discussed. Some different previous theories for reflection by a rough surface are shown to be limiting cases of the present theory.

Journal ArticleDOI
TL;DR: In this paper, an attempt has been made to establish an approximate method to calculate the resistance in crease of a full ship in regular oblique waves using a dynamometer, which was confirmed by the model test carried out in regular OO waves making use of a newly designed dynamometer.
Abstract: An attempt has been made to establish an approximate method to calculate the resistance in crease of a full ship in regular oblique waves. Applicability of this method was confirmed by the model test carried out in regular oblique waves making use of a newly designed dynamometer.Comparing the measured resistance increase and the computed one in accordance with the slender body assumption, fairly good agreement is shown as a whole except for the range of shorter wave length where the measured value is larger than the computed one. An approximate calculation method was proposed in consideration of the resistance increase due to the wave reflection at the blunt bow.It was shown that total resistance increase of a full ship in waves can be obtained approximately by the sum of the resistance due to ship motions and the wave reflection at the bow.


Journal ArticleDOI
TL;DR: In this paper, the velocity of the wave propagation in an inhomogeneous medium from the reflection coefficient (given for all frequencies) for a one-dimensional wave equation was studied.
Abstract: In this paper, we study the problem of obtaining the velocity of the wave propagation in an inhomogeneous medium from the reflection coefficient (given for all frequencies) for a one‐dimensional wave equation. Following the work of Kay and Moses, we reduce the problem to that of determining a ’’potential’’ for a Schrodinger‐type equation. However, in our work this ’’potential’’ depends quadratically on the wavenumber, and this dependence changes the structure of the spectral function and integral equations of the inverse problem. In the first part of the paper, we assume that the wave velocity c (x) has the same value at x=+∞ and at x=−∞. Then we relax this condition on c (x) and consider the cases where c (+∞) is different from c (−∞), but both quantities have well‐defined values. For certain types of velocities, we obtain the reflection coefficient analytically. We then use these reflection coefficients to get approximate solutions to the inverse problem. Finally, we present an example of a heterogeneous medium which is transparent for all frequencies of the incident wave.Subject Classification: 20.30, 20.35, 20.15.

Journal ArticleDOI
TL;DR: In this article, the reflection of electromagnetic waves from a smooth conducting surface at high frequencies is studied and the incident and reflected fields are expanded in asymptotic series of the form E = exp [iks(r)]\Sigma\min{m=0}max{\infty}(ik)^{-m}e_{m}(r), where s is the phase function, and e is the amplitude vector.
Abstract: The reflection of electromagnetic waves from a smooth conducting surface at high frequencies is studied in this paper. Both the incident and reflected fields are expanded in asymptotic series of the form E = exp [iks(r)]\Sigma\min{m=0}\max{\infty}(ik)^{-m}e_{m}(r) , where s is the phase function, and { e_{m} } are amplitude vectors. Explicit formulas based on a ray technique are given for calculating the first two orders of the electric field, magnetic field, and surface current. When the conducting surface is a paraboloid (or a sphere) and the incident field is a plane wave in its axial direction, our solution recovers the exact solution (or the first two orders of the exact asymptotic solution), As a special case, our result is compared with the work of Schensted. It appears that the latter is only partially correct.

Journal ArticleDOI
TL;DR: In this article, the main peaks of the angular distribution of atoms inelastically reflected from a crystal surface are associated with analytical critical points of the surface phonon dispersion curves, particularly those of Rayleigh and Lucas modes.
Abstract: The main peaks of the angular distribution of atoms inelastically reflected from a crystal surface are shown to be associated with analytical critical points of the surface phonon dispersion curves, particularly those of Rayleigh and Lucas modes. Because of such a relation, the frequencies and wave vectors of these modes could be measured by analyzing the shift of the peaks under a change of the angle of incidence.

Patent
03 Oct 1975
TL;DR: In this paper, the authors present a method to provide a guided wave antenna having a radiation pattern which can be controlled electronically, by control signals derived from a computer or any other suitable source.
Abstract: The present invention makes it possible to provide a guided wave antenna having a radiation pattern which can be controlled electronically, by control signals derived from a computer or any other suitable source. In this way, the directional characteristics of the antenna can be adjusted and/or scanned rapidly, without any mechanical manipulation of the antenna. In one embodiment, a guided radio wave is launched along an antenna surface having an array of elements which provide variable non-uniform surface impedance adapted to be controlled by electronic signals. For example, each variable impedance element may comprise a wave guide section having one end leading from the antenna surface. Each wave guide section may include a solid-state electronic reflection amplifier having charcteristics which can be varied by supplying control signals to the amplifier, to vary the magnitude and phase angle of the wave reflected from the reflection amplifier. By changing the control signals supplied to any particular reflection amplifier, it is possible to cause attenuation or amplification and phase shift of the guided wave as it passes across the particular wave guide section. A wide variety of solid-state electronic control elements may be provided along one or more surfaces of the antenna. In another embodiment, a wave traveling in a closed subsurface wave guide is coupled into the guided wave open surface structure, using an array of wave guide elements containing electronically controllable amplifiers and phase shifters.

Journal ArticleDOI
01 Nov 1975
TL;DR: In this article, a uniform asymptotic solution was obtained for the propagation near an isolated caustic of water waves on a slow irrotational current, where there was no restriction to straight caustics or to steady currents.
Abstract: A uniform asymptotic solution is obtained which describes the propagation near an isolated caustic of water waves on a slow irrotational current. Unlike earlier work there is no restriction to straight caustics or to steady currents.

Journal ArticleDOI
TL;DR: In this paper, the authors consider plane-wave motion at normal incidence in an horizontally layered system sandwiched between the air and the basement rock, and they propose a process dynamic predictive deconvolution.
Abstract: Dynamic predictive deconvolution makes use of an entire seismic trace including all primary and multiple reflections to yield an approximation to the subsurface structure. We consider plane-wave motion at normal incidence in an horizontally layered system sandwiched between the air and the basement rock. Energy degradation effects are neglected so that the layered system represents a lossless system in which energy is lost only by net transmission downward into the basement or net reflection upward into the air; there is no internal loss of energy by absorption within the layers. The layered system is frequency selective in that the energy from a surface input is divided between that energy which is accepted over time by net transmission downward into the basement and the remaining energy that is rejected over time by net reflection upward into the air. Thus the energy from a downgoing unit spike at the surface as input is divided between the wave transmitted by the layered system into the basement and the wave reflected by the layered system into the air. This reflected wave is the observed seismic trace resulting from the unit spike input. From surface measurements we can compute both the input energy spectrum, which by assumption is unity, and the reflection energy spectrum, which is the energy spectrum of the trace. But, by the conservation of energy, the input energy spectrum is equal to the sum of the reflection energy spectrum and the transmission energy spectrum. Thus we can compute the transmission energy spectrum as the difference of the input energy spectrum and the reflection energy spectrum. Furthermore, we know that the layered system acts as a pure feedback system in producing the transmitted wave, from which it follows that the transmitted wave is minimum-delay. Hence from the computed energy spectrum of the transmitted wave we can compute the prediction-error operator that contracts the transmitted wave to a spike. We also know that the layered system acts as a system with both a feedback component and a feed-forward component in producing the reflected wave, that is, the observed seismic trace. Moreover, this feedback component is identical to the pure feedback system that produces the transmitted wave. Thus, we can deconvolve the observed seismic trace by the prediction-error operator computed above; the result of the deconvolution is the wave-form due to the feedforward component alone. Now the feedforward component represents the wanted dynamic structure of the layered system whereas the feedback component represents the unwanted reverberatory effects of the layered system. Because this deconvolution process yields the wanted dynamic structure and destroys the unwanted reverberatory effects, we call the process dynamic predictive deconvolution. The resulting feedforward waveform in itself represents an approximation to the subsurface structure; a further decomposition yields the reflection coefficients of the interfaces separating the layers. In this work we do not make the assumption as is commonly done that the surface as a perfect reflector; that is, we do not assume that the surface reflection coefficient has magnitude unity.

Journal ArticleDOI
17 Jan 1975-Nature
TL;DR: In this article, a new effect was proposed for obtaining effective interaction between coherent light waves and free electrons, and potential applications of the effect are optical electron accelerators (linac)1,2 and optical amplifiers3.
Abstract: A NEW effect is proposed for obtaining effective interaction between coherent light waves and free electrons. Potential applications of the effect are optical electron accelerators (linac)1,2 and optical amplifiers3.

Journal ArticleDOI
S. E. Elliott1, B. F. Wiley1
TL;DR: The possibilities inherent in reflection amplitude anomalies or bright spots on seismic cross-sections as indications of gaseous hydrocarbons have stimulated widespread interest as discussed by the authors, and laboratory measurements were made on specimens of compacted Ottawa sand of approximately 30 percent porosity.
Abstract: The possibilities inherent in reflection amplitude anomalies or “bright spots” on seismic cross‐sections as indications of gaseous hydrocarbons have stimulated widespread interest. To help evaluate these possibilities, laboratory measurements were made on specimens of compacted Ottawa sand of approximately 30 percent porosity. The measurements were made at five different water saturations (0 percent and 100 percent, and approximately 9 percent, 45 percent, and 85 percent) and net confining pressures to 10,000 psi. The gas was air. Measurements were made with acoustic pulses with a peak frequency of about 700 khz.

Journal ArticleDOI
TL;DR: The instrumentation that was developed in the Physikalisch-Technische Bundesanstalt for measuring the spectral radiance factor beta(lambda) for the d/O and 45/0 geometries and in principle also for the inverseGeometries is described.
Abstract: The standards necessary for transferring the reflection scale must meet certain requirements. First, the present paper discusses the question of how far these requirements are met by the materials now used for realizing the reflection standards. Then the instrumentation is described that was developed in the Physikalisch-Technische Bundesanstalt for measuring the spectral radiance factor beta(lambda) for the d/O and 45/0 geometries and in principle also for the inverse geometries. How these measurements are made so that the values obtained for a material standard are related to the perfect reflecting diffuser as the primary standard is discussed.

Journal ArticleDOI
TL;DR: In this article, it was shown that specular second-harmonic emission from a dense, inhomogeneous plasma produced by laser irradiation of plane solid targets occurs on oblique reflection of a $p$-polarized light wave, in agreement with theoretical predictions.
Abstract: It is experimentally shown that specular second-harmonic emission from a dense, inhomogeneous plasma produced by laser irradiation of plane solid targets occurs on oblique reflection of a $p$-polarized light wave, in agreement with theoretical predictions.

01 Nov 1975
TL;DR: The planetary electron reflection magnetometry (PERM) as mentioned in this paper is a method for measuring the magnitude, direction, and scale size of magnetic fields near the surface of the moon and other planetary bodies with weak and small-scale-size surface fields.
Abstract: The paper describes the technique of planetary electron reflection magnetometry (PERM), a method for measuring the magnitude, direction, and scale size of magnetic fields near the surface of the moon and other planetary bodies with weak and small-scale-size surface fields. It is noted that the PERM technique is based on the ability of magnetic fields to reflect charged particles. A qualitative account of the implementation of the technique is presented along with some results obtained by the Apollo 15 and 16 Particles and Fields subsatellites. The quantitative aspects of PERM are treated by examining solutions to the equation of motion of a charged particle in a magnetic field, computing reflection coefficients on the basis of trajectory calculations, and determining the direction of the lunar surface magnetic field. The sensitivity of the PERM technique is calculated, and effects of lunar electric fields and spacecraft potentials on the measurements are described. Extension of the technique to Mars and Venus is discussed.

Journal ArticleDOI
TL;DR: In this article, it was shown that abrasion of the plate surfaces does not suppress specular reflection of phonons, contrary to the behavior in crystalline materials, which reinforces the suggestion that nonspecular reflection at crystal surfaces is caused primarily by lattice defects.
Abstract: Thermal-conductance measurements on thin Mylar and glass plates indicate that abrasion of the plate surfaces does not suppress specular reflection of phonons, contrary to the behavior in crystalline materials. This reinforces the suggestion that nonspecular reflection at crystal surfaces is caused primarily by lattice defects---defects which are absent in amorphous materials.

Journal ArticleDOI
TL;DR: A complete analysis of the propagation characteristics of a ray through an axially symmetric graded-index medium is carried out in the geometrical optics approximation, and two constants of the motion are shown to exist and be invariant when reflection occurs on the core-cladding interface of cladded graded index fibers.
Abstract: A complete analysis of the propagation characteristics of a ray through an axially symmetric graded-index medium is carried out in the geometrical optics approximation. First, two constants of the motion are shown to exist for a ray propagating in an infinite medium. Secondly, these constants of the motion are shown to be invariant when reflection occurs on the core-cladding interface of cladded graded index fibers. This conservation law allows the study of the propagation characteristics of a ray through a fiber even though its trajectory may be discontinuous because of reflection at the core-cladding interface. The temporal behavior of various cladded parabolic-index fibers is given by their impulse responses when excited uniformly by parallel beams under different input angles. Rays are shown to propagate in two different ways: a reflected type of propagation takes place through reflections on the core-cladding interface, and a selfocusing type of propagation where rays go through the fiber core without touching the cladding.

Journal ArticleDOI
TL;DR: In this paper, the authors used a highly parallel exploring beam which was obtained by selecting the central part of the wave fan to study the dynamical diffraction phenomena of neutrons, and measured the rocking curve of the Bragg-case diffraction which was very close to the intrinsic diffraction curve of silk hat type with the reflection per cent of about 100%.
Abstract: Dynamical diffraction phenomena of neutrons are studied with a highly parallel exploring beam which is obtained by selecting the central part of the wave fan. The 111 reflection of silicon single crystals is used with neutron wavelengths of 0.86A and 1.50A. (i) The rocking curve of the Bragg-case diffraction which is very close to the intrinsic diffraction curve of silk hat type with the reflection per cent of about 100% is measured with the double-crystal arrangement of parallel setting. The angular spread of the exploring beam, 0.065'', is used, which is 1/8.5 times the half-value width of the intrinsic curve. (ii) The minute deviation angle of the beam, 0.032'', refracted by a wedge-shaped germanium crystal is measured with the double-crystal arrangement of parallel setting, where the deviation angle is magnified to 59' in the wave fan of the second crystal. (iii) By using a neutron interferometer the change in the optical path due to a wedge-shaped material inserted is measured.

Journal ArticleDOI
TL;DR: In this article, statistical properties of the ground diffraction pattern formed by ionospherically reflected radio waves are used to examine models of the angular spectra of reflections from the ionospheric D-region.
Abstract: Statistical properties of the ground diffraction pattern formed by ionospherically reflected radio waves are used to examine models of the angular spectra of reflections from the ionospheric D-region. In the daytime two distinct height regions characterized by differing reflection mechanisms are identified within the D-region. Below 85 km the angular spectrum of reflected waves frequently contains coherent components, whereas a spectrum of incoherent or randomly phased components is characteristic of reflections from the region above 85 km. There is evidence which suggests the presence on many occasions of isolated moving reflectors in the reflecting 'ionospheric screen' . . Both the mean angular spread and the fading speed of waves partially reflected from the D-region show an increase with increasing height of reflection.