Showing papers on "Reflection (physics) published in 1974"

Trench Slope Model

Abstract: New data demonstrate oceanic underthrusting and enable construction of a model of trench inner slopes. Magnetic, earthquake, and deep-penetration reflection seismic data supplemented by data from JOIDES drill holes, dredge hauls, and piston cores leave little room for doubt that thrusts and folds are the primary structures on the landward slopes of trenches, and, in accord with plate tectonics theory, they are considered to be caused by underthrusting of the oceanic plate beneath continents or island arcs. The seismic data and magnetic anomalies document continuation of the oceanic plate beneath the landward slope of the trench. These seismic data also show structural separation between the oceanic plate and overlying sediments and reveal that it is caused by thrusting and/or folding. The resultant uplift is documented by paleobathymetric and compaction studies of sediments from the slopes of several trenches and by surface motion associated with recent earthquakes.

Reflections, rays, and reverberations

Abstract: The connection is established between conventional matrix methods for layered media and the reflection and transmission properties of a single layer. This interrelation is then used to set up an iterative approach to the calculation of reflection and transmission coefficients in multilayered media. This approach lends itself to a ray interpretation and allows estimates of errors involved in taking truncated partial ray expansions to be made. The special effects due to a free surface are also considered.

Calculations on the Optical Modulation Transfer Function of the Human Eye for White Light

Abstract: Modulation transfer functions of the dioptrics of the human eye for white (equal energy distribution) light were calculated for different pupil sizes from experimental data on the aberrations. The largest aberration is the chromatic difference of focus. Since this aberration is well known quantitatively and is subject to small individual differences only, the calculated modulation transfer functions can be considered as representative for human eyes in general. The present calculations, the fundus reflection measurements of the line-spread function by Campbell and Gubisch [1], and the measurements of retinal scattering by Ohzu and Enoch [2] confirm each other. Modulation transfer functions were also calculated for just noticeable focusing errors, and may be informative on the tolerance limit to visual image quality. The calculations have been extended to the special conditions of vision at low luminances.

A theory of medium-scale traveling ionospheric disturbances

Abstract: Analysis of the excitation of atmospheric gravity waves leads to a hypothesis concerning the nature of medium-scale traveling ionospheric disturbances (TID's) and their relation to large-scale TID's Stationary phase techniques are used to derive the asymptotic fluctuations of velocity and electron density generated by a line source (eg, the auroral electrojet) Dissipation by viscosity and thermal conductivity is included in an approximate manner The gravity wave response includes a discrete spectrum of upper-atmospheric guided modes and a continuous spectrum of freely propagating waves; these two classes of waves can be associated with large-scale and medium-scale TID's, respectively The medium-scale TID's, in turn, are primarily composed of two families of waves: those that propagate obliquely upward from the source and reach the F region directly and those that propagate initially downward and reach the F region only after reflection from the earth For an E region source the earth-reflected waves appear as nearly monochromatic wave packets, whereas the direct waves appear for the most part as single pulses; this qualitative difference corresponds to J E Titheridge's observational distinction between periodic and nonperiodic TID's It is suggested that this dichotomy may imply the dominance of upper-atmospheric (as opposed to tropospheric) sources In this connection the average fluctuations of the auroral electrojet are shown to be sufficient to generate sizable medium-scale TID's that propagate to large horizontal distances with no loss of amplitude despite the absence of ducting mechanisms Such propagation is possible because amplitude attenuation due to cylindrical spreading is counteracted by the fact that the lower-frequency waves, which reach the F region at the greater horizontal distances, are generated with larger amplitudes Several properties of the calculated response, including the linear increase of period and wavelength with distance from the source, might be useful in future observational studies designed to identify the sources of medium-scale TID's

Two‐dimensional and three‐dimensional migration of model‐experiment reflection profiles

Abstract: A reflection profile represents an unfocused picture of the subsurface. In areas of rapid structural change, this unfocused picture may not reveal directly the true geometry of subsurface structures. Computer processing techniques, collectively called migration, have been used by many companies to focus 2-D reflection data. A description of the migration process can be given which allows immediate generalization to three-dimensions with arbitrary source and receiver positions.Reflection profiles digitally recorded in the laboratory over known acoustically semitransparent structural models establish the effectiveness of migration. Processed reflection data over 3-D models demonstrate that 3-D migration eliminates many of the lateral correlation ambiguities caused by 'sideswipes' and 'blind structures.'Structure maps developed from the results of 3-D migration of reflection data give a true and precise picture of 3-D models. When the same data are processed using 2-D migration, the mapped structures are distorted.In structurally complex areas it is desirable to collect 3-D reflection data. Single profiles cannot, and conventional grids may not, reveal adequate cross-dip information.

Effects of interplanetary shock waves on energetic charged particles

Abstract: Experimental data on the influence of interplanetary perpendicular and oblique shock waves on the ambient energetic protons are presented along with a theoretical analysis of the acceleration of particles in almost perpendicular shock waves. It was found that low-energy protons can be accelerated in perpendicular shock waves by repeated crossings of the shock front up to a maximum energy given by the product of their initial energy times the ratio of the magnetic fields. High-energy protons need to stay at the shock front for longer times than low-energy protons in order to reach the same relative energy gain. In the theoretical study of proton acceleration at almost perpendicular shock waves, it was found that protons reflected at shock waves with the angle between the upstream magnetic field and the shock normal greater than about 80 deg achieve large energy gains at the shock front. The larger this angle, the higher the energy gain. However, the reflection and energization of protons at these shock waves is not 'instantaneous', neither is it a one-step process: it is performed through repeated crossings of the shock front.

Wave Transmission through Porous Structures

Abstract: Assuming long, normally incident waves on a homogeneous porous structure of rectangular cross section, a simple explicit solution for the transmission and reflection coefficients are obtained from a linearized theory. The relationship between the nonlinear flow resistance in the porous medium and its equivalent linear form is obtained in explicit form. Empirical relationships for the nonlinear flow resistance are reviewed and are shown to lead to acceptable estimates of the hydraulic properties of a porous medium. Using the empirical relationships for the hydraulic properties of a porous material in conjunction with the explicit simple solution for the reflection and transmission coefficients leads to results comparable to the results of other more time-consuming procedures.

Standing waves on beaches

Abstract: Simultaneous measurements of run-up spectra and nearshore wave spectra associated with standing waves have been made on a natural beach. Digital wave staffs and bottom-mounted pressure sensors were placed in a line at various distances offshore from a digital run-up meter. The run-up meter, which measured the position of the edge of the water, consisted of a series of electrical contacts suspended above the beach face and spaced 30 cm apart. Because of the possible influence of nonlinear interactions on the spectra, bicoherence was estimated, and the frequency range appropriate to a linearized model was defined. In this low-frequency region of the spectrum the cross-spectra phase angles between data records had values near 0 or π at frequencies of high coherence. The energy spectrum levels and the observed phase differences between records were in good agreement with the linear shallow water wave theory (Lamb, 1932) for standing waves on a plane beach. The general reflection coefficient for the data, estimated from the disagreement between data and standing wave theory, was found to be approximately 0.7. This result indicates that the theory of Miche (1944) for reflection from a plane beach predicts a reflection coefficient that is too high by a factor of approximately 1.5.

Physics of Sound in Marine Sediments

Abstract: I. Theory.- A. Derivation.- A Review of the Derivations of the Formulas for the Acoustical Properties of Liquid-Solid Mixtures.- Acoustic Waves in Saturated Sediments.- B. Interpretation.- Acoustic and Mechanical Loading of Marine Sediments.- Influence of Anisotropy and Soil Structure on Elastic Properties of Sediments.- The Seismic Wide Angle Reflection Method in the Study of Ocean Sediment Velocity Structure.- Sonobuoy Measurements in Thin Layers.- II. Applications.- The Interaction of Underwater Acoustics and Marine Geophysics.- Underwater Sound Transmission Through the Ocean Floor.- Geoacoustic Models of the Sea Floor.- Sound Propagation Calculations Using Bottom Reflection Functions.- III. Measurement Techniques.- Nonlinear Acoustics and Its Role in the Sedimentary Geophysics of the Sea.- Near-Bottom Acoustic Observations of Abyssal Topography and Reflectivity.- Remote Sediment Classification Potential of Reflected Acoustic Signals.- Measurement of Viscoelastic Properties of Sediments Using a Torsionally Vibrating Probe.- A Method for Measuring In Situ Acoustic Properties During Sediment Coring.- IV. Measurement Results.- Acoustic Estimates of the Topography and Roughness Spectrum of the Sea Floor Southwest of Iberian Peninsula.- Acoustical Characteristics of the Sea Floor: Experimental Techniques and Some Examples from the Mediterranean Sea.- Statistical Correlation of Physical Properties and Sound Velocity in Sediments.- Preliminary Study of Global Sediment Sound Velocities from Sonobuoy Data.- Measurements of Reflectivity by Explosive Signals.

Reflection of thermoelastic waves at a solid half-space with thermal relaxation

Abstract: The thermal and elastic plane wave motion of small amplitude in a homogeneous, isotropic and thermally conducting solid which occupies a half-space is considered. The presence of the thermal waves effect change in the angle of emergence.

Electromagnetic fields in spatially dispersive media

Abstract: The structure of the electromagnetic field in a spatially dispersive model medium occupying a plane parallel slab is obtained, free of several customary ad hoc assumptions made in other theories. The model medium is characterized by a dielectric response function appropriate to the neighborhood of an isolated-exciton transition frequency. The exact mode expansion for the electromagnetic field in the slab is derived and it is found that, unlike in the case of an unbounded medium, a single plane wave cannot be generated in the slab. An elementary solution (a single mode) is found to consist, in general, of six plane waves (four transverse and two longitudinal ones), coupled by two linear relations. These relations are shown to be equivalent to two nonlocal boundary conditions (of the form encountered in connection with the Ewald-Oseen extinction theorem in molecular optics), which the nonlocal contribution to the induced polarization must satisfy on the faces of the slab. This result resolves a long-standing controversy about the nature of the so-called additional boundary conditions that are generally believed to be required for solving problems of interaction of an electromagnetic field with a spatially dispersive medium. The results are applied to the problem of refraction and reflection on a spatially dispersive model medium occupying a half-space and a generalization of the classic formulas of Fresnel are obtained. The behavior of the reflected and transmitted waves as functions of the angle of incidence and of the frequency are illustrated by several figures. Our results are shown to differ from those obtained by Pekar in a well-known paper. The difference is traced to the nature of the additional boundary conditions postulated by Pekar; they are found to be inconsistent with the additional boundary conditions that we derive as an exact consequence of Maxwell's theory. Comparisons with several other theories, especially with those of Sein and Birman and of Maradudin and Mills are also made.

Analysis of Gaussian beam propagation and diffraction by inhomogeneous wave tracking

Abstract: Inhomogeneous waves behave locally like A(r) exp[ikS(r)], where A and S are spatially dependent complex amplitude and phase functions, and k is the (large) free-space wavenumber. A previously developed asymptotic theory for high-frequency propagation and scattering of such waves is here applied to the propagation and scattering of paraxial Gaussian beams. Attention is given to Gaussian beams in free space, to beams in a lens-like medium with parabolic variation of the refractive index, and to beam reflection by a cylindrical obstacle. In the latter instance, the obstacle size may be comparable to the incident beamwidth, thereby introducing substantial distortion into the reflected beam. The results obtained from the asymptotic theory are verified by comparison with rigorously derived solutions, thereby confirming the validity of the theory, which can also be applied to more general medium and obstacle configurations.

Gaussian Beam Interaction with a Planar Dielectric Interface

Abstract: The problem of electromagnetic Gaussian beam scattering from a planar interface separating two lossless dielectric media is considered. Employing a modal plane wave expansion and the continuity of the fields across the boundary, the reflected and transmitted beams are obtained using the Fresnel approximation, and a Taylor series expansion of the reflection and transmission coefficients, for both polarizations. Particular emphasis is given to the beam shift of both the reflected and refracted beams, the change in width of the transmitted beam, and the behavior at polarizing incidence.

The Physical Basis for Analysis of the Depth of Absorbing Species Using Internal Reflection Spectroscopy

Abstract: Internal reflection spectroscopy is discussed for a nonuniform distribution of an absorbing species. Although some distributions cannot experimentally be distinguished from others, if one assumes a distribution, information about depth and concentration can be obtained by making measurements at several angles of incidence. A practical method is proposed and demonstrated for obtaining thickness and concentration for an assumed step profile.

Acoustic reflection from elastic spheres. I. Steady‐state signals

Abstract: Measurements are made of the acoustic reflected pressure from aluminum and tungsten‐carbide spheres for ka values between 5 and 20. Only the farfield monostatic case is considered. Experimental values are compared to a harmonic‐wave solution. Excellent agreement is observed when the wave speeds in the sphere material are adjusted by an amount smaller than the known uncertainty in the wave‐speed values in the solids. The position of rapid changes in the reflection solution with ka is found to be very sensitive to shear‐wave speed and insensitive to longitudinal‐wave speed. The sensitivity to ambient temperature of the position of a selected minimum in the reflection solution is examined computationally for an aluminum sphere. A shift in the value of ka at which a minimum is calculated is also observed experimentally. Long pulses are used to approximate steady‐state conditions and agreement with the steady‐state theory shows that this approximation is adequate.

Application of complex ray tracing to scattering problems

Abstract: Representations and geometric constructions associated with complex points, complex lines, and complex rays are introduced. They are applied to the problem of scattering of an evanescent plane wave by a conducting circular cylinder. This problem has an exact solution, which provides a check of the validity of complex ray tracing and suggests more general applications. An important role is played by the transformation that maps the point of reflection, on the complex extension of the scattering surface, onto the trace in real space of the complex reflected ray. For the particular problem considered, the phase and amplitude of the reflected field are computed and the "phase paths" and "phase fronts" are constructed. The reflected field and phase paths obtained in this manner are not to be taken in their entirety because some reflection points are not "illuminated" by the incident wave, and because the reflector may be only part of the cylinder. Tentative selection and truncation rules are used which yield good agreement with the exact solution over some regions. The disagreement, where it occurs, comes-as it does for real rays-from neglecting the diffracted field such as the creeping waves around smooth surfaces and, in the case of truncation, the edge waves from the discontinuity. Some consideration is given to scattering by an arbitrary smooth conductor. Some problems peculiar to the use of complex rays are stated.

Reflection of clusters of helium, hydrogen, and nitrogen as function of the reflector temperature

Abstract: Clusters of helium, hydrogen, and nitrogen are reflected at a polished stainless steel plate at temperatures ranging from 80 to 550 K. The incident clusters contain on the average about 1.5×105 atoms of helium or molecules of hydrogen or 104 molecules of nitrogen, as measured by time‐of‐flight mass spectrometry. The angular distributions of the average sizes, the velocities, and the molecular intensities of the reflected cluster beams show that in the investigated range of reflector temperatures the reflection of the helium clusters corresponds to the hydrogen cluster reflection at higher reflector temperatures while the nitrogen cluster reflection corresponds to the hydrogen cluster reflection at lower reflector temperatures. The transition between the two regimes of reflection as observed with hydrogen clusters is marked by an optimum reflector temperature leading to a maximum intensity of the reflected beam, a minimum loss of clustered material, and a distinct angular separation of incident cluster sizes. At a grazing incidence angle of 84.3° the measured optimum reflector temperature for the hydrogen cluster reflection is 215 K and increases with decreasing angle of incidence. The two regimes of high‐temperature and low‐temperature reflection of clusters exhibit close phenomenological relationship to the regimes of thermal and structure dominated scattering of atoms from single crystal planes. In both cases the transition region is characterized by a maximum angle of reflection and a minimum divergence of the reflected beam. The features of high‐temperature cluster reflection are explained by a semiempirical model based on the evaporation recoil of the cluster molecules ablating after contact with the comparatively hot reflector surface.

Rayleigh‐wave reflection from groove and step discontinuities

Abstract: In an important new class of signal‐processing devices using elastic surface waves, the reflection of a Rayleigh wave from grooves is a key feature. In the present paper, a boundary‐perturbation technique is employed to determine the reflection of a Rayleigh wave from either a shallow groove or a low step in the surface of an isotropic elastic half‐space. Comparison with available experimental data for the case of the rectangular groove and step yields excellent agreement.

The reflection and ducting of atmospheric acoustic-gravity waves

Abstract: A simple form is derived for the differential equations governing the propagation of acoustic–gravity waves in an atmosphere whose temperature and horizontal wind velocity vary in an arbitrary mann...

Acoustic reflection from elastic spheres and rigid spheres and spheroids. II. Transient analysis

Abstract: Curves relating the reflected acoustic pressures to frequency for a rigid sphere and spheroid and for elastic spheres of aluminum, brass, and tungsten carbide in water are obtained. Experimental measurements using single short acoustic pulseforms are compared with theory. Excellent agreement is obtained for the limited ranges of ka over which the experiments were done. Only the case of monostatic reflection is considered.

Amplitudes of horizontally refracted Love waves

Abstract: Love-wave transmission and reflection are studied numerically for a vertical interface between two layered models. By a new method of approximation, the transmission and reflection coefficients can be computed for propagation directions differing from normal incidence. We consider the Love mode as a superposition of propagating plane SH waves in a surface layer and an inhomogeneous plane SH wave falling off with depth in the half-space below. The method is based on satisfying all boundary conditions on the vertical interface and computing the coupling between the interface stress displacement pattern and the transmitted/reflected Love modes. The computations are done rapidly on a small computer. The transmission coefficients change rapidly with period. For propagation from ocean to continent, they increase with decreasing periods in the interval 60 to 20 sec. The opposite trend is found for propagation from continent to ocean. The amplitude transmission coefficient curves show almost no dependence on the angle of incidence except for large angles. The fine structure of the curves is similar to that for plane SV waves incident on an interface between two homogeneous elastic media. Love-wave amplitude observations at OBS on the ocean bottom northwest of San Francisco and at BKS in Berkeley also show these trends as a function of period and of angle of incidence.

The damping of core waves

Abstract: Attenuation in the core is examined by using spectral ratios of seismic core waves. In the outer core a Qα of 5000–10,000 is obtained from the amplitude radio P7KP/P4KP. From the PKIKP/PKP amplitude ratio, Qα in the inner core has a value between 120 and 400. An unusual result is that P7KP is consistently higher in frequency than P4KP, which may indicate frequency-dependent reflection and transmission coefficients at the mantle-core boundary for rays that nearly graze the core.

The dispersion relation of surface plasmons on rough surfaces

Abstract: The dispersion relation of surface plasmons ω(kperpendicular) on rough silver surfaces has been measured by the reflection method and the light scattering method. The resonances (minimum reflection intensity and maximum scattering intensity) are in general displaced to higher kperpendicular-values compared with smooth surfaces, and the halfwidth of the resonances increases with roughness.

Reflection of a Gaussian ultrasonic beam from a liquid‐solid interface

Abstract: A Gaussian distribution of amplitudes in an ultrasonic beam reflected from liquid‐solid interfaces is used in the reexamination of the concept of “beam displacement” which occurs at the angle of excitation of surface waves on the interface. Experimental results show that the energy of the reflected beam is redistributed into two or more beams at (or near) this angle. The theory of Brekhovskikh has been extended to include both a Gaussian input beam and the second derivative of the phase shift upon reflection. Reasonable agreement is obtained between theory and experiment for water‐aluminum and water‐brass interfaces. For water‐beryllium and water‐stainless steel the agreement is fair.

Closed-Form Mathematical Solutions to Some Network Analyzer Calibration Equations

Abstract: A general evaluation procedure is described for calibration of a linear complex reflectometer (network analyzer) and for two-port measurements. New closed-form formulas and procedures are given for two practical cases: 1) calibration or measurement with two known standards and a sliding termination; 2) calibration or measurement by one standard and two different sliding terminations. The reflection coefficient magnitudes and phases of these sliding terminations need not be known. The closed-form formulas make it possible to determine calibration constants by direct calculation without approximations or complicated multivariable iterations.

Method for coating anti-reflection film on surface of optical material

Abstract: A method for coating silicon oxide SiO film and silicon dioxide SiO2 film on the surface of transparent optical material of glass or syntheic resin whose refractive indices are varied by changing the condition of vapor-deposition, under a predetermined condition of vapor-deposition so as to form a firm and durable anti-reflection film.