Showing papers on "Reflection (physics) published in 1979"

Seismic waves in a stratified half space.

Abstract: Summary. The response of a stratified elastic half space to a general source may be represented in terms of the reflection and transmission properties of the regions above and below the source. For P-SV and SH waves and both buried sources and receivers, convenient forms of the response may be found in which no loss of precision problems arise from growing exponential terms in the evanescent regime. These expressions have a ready physical interpretation and enable useful approximations to the response to be developed. The reflection representation leads to efficient computational procedures for models composed of uniform layers, which may be extended in an asymptotic development to piecewise smooth models.

Wave-equation datuming

Abstract: Wave-equation datuming is the name given to upward or downward continuation of seismic time data when the purpose is to redefine the reference surface on which the sources and receivers appear to be located. This technique differs from conventional datuming methods in the repositioning of seismic reflections laterally as well as vertically in response to observed time dips. The most interesting applications of the technique are those in which the redefined reference surface is an actual geologic interface having an irregular topography and a large velocity contrast. Wave-equation datuming can remove the deleterious effect such an interface has on seismic reflections originating below it. Wave-equation datuming also is applicable in seismic modeling.The computations required in wave-equation datuming are related to those of migration. The Kirchhoff integral formulation of the wave equation can provide a basis for computation to deal with the irregular surfaces and variable velocities that are central to the problem. The numerical implementation of the Kirchhoff approach can be reduced to an efficient procedure involving summations and convolutions of seismic traces with short shaping and weighting operators.

Ray interpretation of the material signature in the acoustic microscope

Abstract: The output voltage of the reflection acoustic microscope depends on the location on the object surface in a way that is characteristic of its elastic properties. We present a ray model showing that this dependence is due to interference between a narrow bundle of axial rays and rays associated with the leaky Rayleigh wave excited on the surface.

Velocity inversion procedure for acoustic waves

Abstract: An approximate solution is presented to the seismic inverse problem for two‐dimensional (2-D) velocity variations. The solution is given as a multiple integral over the reflection data observed at the upper surface. An acoustic model is used, and the reflections are assumed to be sufficiently weak to allow a “linearization” procedure in the otherwise nonlinear inverse problem. Synthetic examples are presented demonstrating the accuracy of the method with dipping planes at angles up to 45 degrees and with velocity variations up to 20 percent. The method was also tested under automatic gain control, in which case velocity estimates were lost but the method nonetheless successfully migrated the data.

Quantitative reflection contrast microscopy of living cells.

Abstract: Mammalian cells in culture (BHK-21, PtK2, Friend, human flia, and glioma cells) have been observed by reflection contrast microscopy. Images of cells photographed at two different wavelengths (546 and 436 nm) or at two different angles of incidence allowed discrimination between reflected light and light that was both reflected and modulated by interference. Interference is involved when a change in reflected intensity (relative to glass/medium background reflected intensity) occurs on changing either the illumination wavelength or the reflection incidence angle. In cases where interference occurs, refractive indices can be determined at points where the optical path difference is known, by solving the given interference equation. Where cells are at least 50 nm distant from the glass substrate, intensities are also influenced by that distance as well as by the light's angle of incidence and wavelength. The reflected intensity at the glass/medium interface is used as a standard in calculating the refractive index of the cortical cytoplasm. Refractive indices were found to be higher (1.38--1.40) at points of focal contact, where stress fibers terminate, than in areas of close contact (1.354--1.368). In areas of the cortical cytoplasm, between focal contacts, not adherent to the glass substrate, refractive indices between 1.353 and 1.368 were found. This was thought to result from a microfilamentous network within the cortical cytoplasm. Intimate attachment of cells to their substrate is assumed to be characterized by a lack of an intermediate layer of culture medium.

A model for predicting acoustic material signatures

Abstract: Unique acoustic material signatures (AMS) may be obtained in the reflection acoustic microscope. The proposed model shows that they result from interference between two components reradiated into the immerson fluid at the materials critical Rayleigh angle ϑR. The characteristic period ΔzN of this interference signature varies as the square of the Rayleigh wave velocity and is empirically given by ΔzN=λR/sinϑR, where λR is the Rayleigh wavelength. Materials covering a greater than 3 : 1 velocity range agree well with this physical model. Substitution of the longitudinal wave velocity in the expression extends the range of measurable AMS to acoustically slower materials. A variety of applications for AMS is suggested.

Optical switching device

Abstract: Respective end faces of two or more optical waveguides (23 to 29) are connected on one end face of a focussing rod lens (20) and a reflection means (21) having a reflection plane tilted with a specified angle (α) to the normal plane to the lens axis is disposed behind the other end face of the focussing rod lens (20) and angle of reflection plane of the reflection means (21) is varied by rotating the reflection means (21) around the lens axis (203) or by means of a piezo-electric driving device (30), thereby attaining selective switching of the waveguides (from 23 to selected one of 24 or 29) or varying the amount of rays to be transmitted through the waveguides (23 and 24 of FIG. 4), or thereby modulating the rays. By utilizing a semitransparent filter forming another tilted reflection plane, the amount of attenuation for different wavelength or connection of the waveguides are controlled separately.

Corrugated dielectric waveguides: A numerical study of the second-order stop bands

Abstract: A short description of a rigorous electromagnetic theory based on the numerical integration of a differential system is given. It allows the study of the stop-bands of a corrugated waveguide. Dispersion curves in the first and the second-order stop-bands are computed for various periodic waveguides. A selection rule due to the symmetry of the corrugation is found. The reflection of a plane wave by the guide is examined. It is demonstrated that under peculiar circumstances, the reflection coefficient has a modulus equal to unity.

A physical model for acoustic signatures

Abstract: A physical model is presented to explain the interference phenomenon that gives rise to the material‐dependent signature obtained from an acoustic reflection microscope. An approximate formula is derived for the peak separation of the characteristic response, and it agrees well with the experimental results.

An improved illumination model for shaded display

Abstract: To accurately render a scene, global illumination information that affects the intensity of each pixel of the image must be known at the time the intensity is calculated. In a simplified form, this information is stored in a tree of “rays” extending from the viewer to the first surface encountered and from there to other surfaces and to the light sources. The visible surface algorithm creates this tree for each pixel of the display and passes it to the shader. The shader then traverses the tree to determine the intensity of the light received by the viewer. Consideration of all of these factors allows the shader to accurately simulate true reflection, shadows, and refraction as well as the effects simulated by conventional shaders. Anti-aliasing is included as an integral part of the visibility calculations. Surfaces displayed include curved as well as polygonal surfaces.

First‐order reflection coefficient of surface acoustic waves from thin‐strip overlays

Abstract: The problem of surface‐wave reflection at thin‐strip overlays occurs frequently in signal‐processing devices. Grooved array reflectors employ strip overlays of the same material as the substrate, while metallic transducers incorporate strips of a material different from the substrate. A simple model for calculating the reflection coefficient of thin overlays is described, based on the normal‐mode analysis developed by Auld. Calculated values are in close agreement with reported experimental values for grooves in ST‐X quartz and Y‐Z lithium niobate, and for aluminum on ST‐X quartz.

The reflection of impulses from a nonlinear random sea

Abstract: A model of the reflection of radar impulses from the sea at near-vertical incidence is used to account for non-Gaussian ocean waves statistics. The joint probability density function (pdf), of wave height and slope, is calculated according to the theory of Longuet-Higgins (1963) on the distribution of variables in a 'weakly nonlinear' random era. The long-crested approximation is made, a Phillips wave spectrum is assumed, and the Gram-Charlier series is truncated after skewness terms. It is found that the height and height-slope skewness coefficients bear the ratio 1:2 and that the derived impulse response and conditional cross section versus wave height are in excellent agreement with previous observations. Finally, it is suggested that the empirically determined and theoretically predicted sea state bias be corrected for in the routine processing of satellite radar altimeter data.

Resonance theory of acoustic waves interacting with an elastic plate

Abstract: Sound transmission and reflection properties of an elastic layer immersed in a fluid are analyzed by extending the resonance formalism, previously developed by us for the case of a fluid layer [J. Acoust. Soc. Am. 65, 9–14 (1979)]. Resonance expressions for the transmission and reflection coefficients have been obtained both in terms of the frequency‐thickness variable and of the angle‐of‐incidence variable. The resonance positions and widths are explicitly obtained from real equations in terms of given material quantities. Comparison of the resonance theory and exact calculations are given for a steel plate immersed in water. The resonance formalism results show excellent agreement with exact theory in all cases. Interferences between overlapping resonances are clearly identified and analyzed. An examination of the limiting form of the y resonances confirms previous empirical findings of other researchers concerning the frequency‐thickness behavior of the poles and zeroes of the Rayleigh and Lamb resonan...

The Rayleigh hypothesis in the theory of reflection by a grating

Abstract: In this paper, the Rayleigh hypothesis in the theory of reflection by a grating is investigated analytically. Conditions are derived under which the Rayleigh hypothesis is rigorously valid. A procedure is presented that enables the validity of the Rayleigh hypothesis to be checked for a grating whose profile can be described by an analytic function. As examples, we consider some grating profiles described by a finite Fourier series. Numerical results are then presented.

Occurrences, Properties, and Predictive Models of Landslide-Generated Water Waves

Abstract: Large water waves generated by landslides impacting with a body of water are known from Disenchantment and Lituya Bays, Alaska; Vaiont reservoir, Italy; Yanahuin Lake, Peru; Shimabara Bay, Japan; and many fiords in Norway. The combined death toll from these events most likely exceeds 20,000 people. Such waves may be oscillatory, solitary, or bores and nonlinear mathematical theories or linearizing assumptions are thus needed to describe their wave amplitudes, celerities, and periods. In this paper the following approaches are compared: (1) the Noda simulation of a vertically falling and horizontally moving slide by linearized impulsive wave theory and estimation of nonlinear wave properties; (2) the Raney and Butler modification of vertically averaged nonlinear wave equations written for two horizontal dimensions to include three landslide forcing functions, solved numerically over a grid for wave amplitude and celerity; (3) the empirical equations of Kamphuis and Bowering, based on dimensional analysis and two-dimensional experimental data; and (4) an empirical equation developed in this report from three-dimensional experimental data, i.e., log(η max /d) = a + b log(KE), where a, b = coefficients, η max = predicted wave amplitude, d = water depth, and KE = dimensionless slide kinetic energy. Beyond the slide area changes in waveform depend upon energy losses, water depth and basin geometry and include wave height decrease, refraction, diffraction, reflection, and shoaling. Three-dimensional mathematical and experimental models show wave height decrease to be a simple inverse function of distance if the remaining waveform modifiers are not too severe. Only the Raney and Butler model considers refraction and reflection. Run-up from waves breaking on a shore can be conservatively estimated by the Hall and Watts formula and is a function of initial wave amplitude, water depth, and shore slope. Predicted run-ups are higher than experimental run-ups from three-dimensional models. The 1958 Lituya Bay and 1905 Disenchantment Bay, Alaska events are examined in detail, and wave data are developed from field observations. These data and data based on a Waterways Experiment Station model are compared to wave hindcasts based on various predictive approaches, which yield a large range of predicted wave heights. The most difficult problems are in matching the exact basin geometry and estimating slide dimensions, time history, and mode of emplacement. Nevertheless, the hindcasts show that the mathematical and experimental model approaches do provide useful information upon which to base engineering decisions. In this regard the empirical equation developed in this report is at least as satisfactory as existing methods, and has the advantage of requiring less complicated input data.

Tropopause detection by partial specular reflection with very-high-frequency radar.

Abstract: The tropopause can be detected and its altitude determined routinely with the use of meter-wavelength, very-high-frequency radar. At meter wavelengths and at vertical incidence, the tropopause is revealed by partial specular reflection from stable atmospheric layers. The echoes received at vertical incidence as a result of partial specular reflection are greatly enhanced over echoes received at oblique incidence arising from turbulent scatter. Very-high-frequency radars utilizing partial specular reflection promise a major advance in the remote sensing of the atmosphere.

Variable reflection effect driving mirror - has adjustable filter in front of mirror, with photocells to adjust transmission and set relative intensity of reflected light

Abstract: The interior driving mirror is covered with a variable transmission plate (2) linked to a control circuit. A photo-detector (7) behind the plate adjusts the transmission so that the reflected light does not dazzle the driver. A second photocell (14) outside the mirror sets the relative intensity of the reflected light w.r.t. the ambient illuminations and is not dazzled by following headlights.

Theoretical reflection seismograms for elastic media

Abstract: Theoretical seismograms for an explosive source in a multilayered elastic medium are constructed by Fourier synthesis and plane wave superposition. The calculation scheme which builds up a reflection matrix layer by layer in the frequency and wave number domain allows the inclusion of attenuation and a choice of the level of internal multiples in each layer. Comparative calculations of theoretical seismograms for an elastic model and in the acoustic approximation, neglecting shear, show that the main differences arise at large offsets. The inclusion of shear waves leads to lower reflected P wave amplitudes at the end of the spread but only small amounts of converted phases.

Reflection and transmission coefficients for seismic waves in ellipsoidally anisotropic media

Abstract: The deficiency of an isotropic model of the earth in the explanation of observed traveltime phenomena has led to the mathematical investigation of elastic wave propagation in anisotropic media. A type of anisotropy dealt with in the literature (Potsma, 1955; Cerveny and Psencik, 1972; and Vlaar, 1968) is uniaxial anisotropy or transverse isotropy. A special case of transverse isotropy which assumes the wavefronts to be ellipsoids of revolution has been used by Cholet and Richard (1954) and Richards (1960) in accounting for the observed traveltimes at Berraine in the Sahara and in the foothills of Western Canada. The kinematics of this problem have been treated in a number of papers, the most notable being Gassmann (1964). However, to appreciate fully the effect of anisotropy, the dynamics of the problem must be explored. Assuming a model of the earth consisting of plane transversely isotropic layers with the axes of anisotropy perpendicular to the interfaces, a prime requisite for obtaining amplitude dist...

Seismic imaging of deep crust

Abstract: We introduce here an integral two‐dimensional (2-D) scheme for the processing of deep crustal reflection profiles. This approach, in which migration occurs before stacking, is tailored to the unique character of the data in which nonvertically propagating energy is as important as vertically propagating energy. Since reflector depths range beyond 30 km, the horizontal displacement of reflections which occurs in migration can be as large as reflector depths; under these circumstances, the common‐midpoint (CMP) stack is inadequate. In our scheme, each common‐source trace gather is transformed into a set of traces (beams) corresponding to set of different incidence angles. A correction for wavefront curvature similar to the normal moveout (NMO) correction yields traces (focused beams) which are focused at image points along the direction of arrival. While the method is equivalent to the Kirchhoff integral migration method, and therefore to any complete continuation method, it gives rise to an intermediate da...

On the synthesis of realistic Sea States in a laboratory flume

Abstract: Background report on how to make realistic waves in laboratory flumes, including the method of splitting wave signals into incoming and reflecting waves

Composite optical element having controllable light transmission and reflection characteristics

Abstract: A three layer composite optical structure wherein a first layer is a substrate having surface variations holographically formed therein that contain phase information of a light pattern or object desired to be reconstructed from the element by reflection, a thin substantially uniform layer of material coated over that surface variation, and a third layer that overcoats the thin layer in order to form a substantially uniform thickness composite structure. The indices of refraction of the overcoating and the substrate are made substantially the same so that light transmitted through the element is neither diffracted nor refracted. The thin intermediate layer is disclosed to be either reflective metal or a substantially transparent layer having an index of refraction substantially different from that of the other two layers. Such an element has applications in sunglasses or as an addition to car or other windows.

On-resonant phase-conjugate reflection and amplification at 10.6 microm in inverted CO(2).

Abstract: We have obtained phase-conjugate reflection and amplification with an effective reflectivity exceeding unity by redirecting the output of a TEA CO(2)-laser oscillator into its own gain medium. The intense counterpropagating waves within the laser were coupled through the saturated medium to provide the nonlinearity in a process analogous to degenerate four-wave mixing.

Reflection and transmission of discontinuity waves through a shock wave. General theory including also the case of characteristic shocks

Abstract: An incident wave creates a discontinuity in the acceleration of the shock front. The amplitudes of the reflected and transmitted waves are also determined. Special attention is given to the case of the weak shocks and the characteristic shocks.

The origin of fine scale acoustic stratigraphy in deep-sea carbonates

Abstract: In this paper we investigate the origin and geologic significance of the closely spaced high-frequency subbottom acoustic reflectors characteristic of pelagic carbonates. A detailed survey was conducted of a small area in the equatorial Pacific with the Marine Physical Laboratory's Deep-Tow instrument package, providing high-resolution 4-kHz profiles and precise positioning of core samples. The cores were sampled at closely spaced intervals for sound velocity and saturated bulk density. Acoustic impedances were calculated, and a reflection coefficient log determined for the upper 10 m of the sediment column. The reflection coefficient log revealed no interfaces with large reflection coefficients that correlated with the reflectors seen on the Deep-Tow 4-kHz seismic profile. The calculated reflection coefficients were very low (typically 10−3–10−5) and varied about a wavelength that was on the order of the wavelength of the 4-kHz pulse, implying that interference plays a role in the composition of the seismic record. Convolving the outgoing 4-kHz pulse with the reflection coefficient log generated a synthetic seismogram that very closely resembled the 4-kHz reflection profile. Varying the frequency of the outgoing pulse changed the amplitude and position of the reflectors seen on the synthetic seismograms. Thus we conclude that the reflectors seen on the 4-kHz seismic profile were not caused by discrete geologic horizons but rather are the result of the interference of many small layers.

Transport scattering coefficients from reflection and transmission measurements

Abstract: Moments of the emerging distributions for the one‐speed homogeneous slab albedo problem are manipulated to provide a scheme for calculating the expansion coefficients of the scattering kernel of the medium. Simple equations for the highest‐order and next‐highest‐order coefficients are given, and suggestions for their possible use in experiments are provided.

Velocity Determination from Seismic Reflection Data

Abstract: The determination of the gross velocity distribution in the ground from CDP reflection data depends primarily on the determination of the velocity producing maximum coherency in the stacked data. This stacking velocity is a mathematical quantity which has no physical significance. The interval and average velocities describe meaningful physical parameters and are related to the maximum coherency stacking velocity through the r.m.s. velocity. The relationship between these velocities is illustrated. The limitations to the horizontal resolution of the velocity tool are discussed.

Detection of subsurface defects by reflection interference

Abstract: A process for detecting defects in a multiply layered light transmitting structure, comprising illuminating the surface of the structure with a beam of light at an angle of incidence to the structure at which at least a portion of the beam will be reflected, and detecting the intensity of the reflected beam to locate subsurface as well as surface anomalies in the structure.

Small-signal wavefront reversal in nonthreshold reflection from a Brillouin mirror

Abstract: A method is proposed and implemented for small-signal wavefront reversal during stimulated Brillouin scattering in an optical waveguide. This method may find applications in the wavefront reversal of nanosecond pulses.

Method and apparatus for measurement of reradiation in particle flow cell systems

Abstract: Measurement of the energy and direction of radiation, typically scattered light, produced by particles passing through an optical sensing zone is improved in focusing of the scattered light and flexibility in the choice of focal length for positioning of photoresponsive devices. The improvement is obtained by collimating the collected scattered light entering a deviating device, typically a fresnel prism, and then focusing the emerging separate, independent beams for measurement. Collimation can be obtained using optical elements including lens systems or reflective systems such as those employing parabolic reflection.