Showing papers on "Reflection (physics) published in 1986"

The Moho in the northern Basin and Range province, Nevada, along the COCORP 40°N seismic-reflection transect

Abstract: COCORP seismic-reflection profiles across Nevada at about 40°N image a prominent, essentially continuous band of reflectors at a two-way traveltime of 9 to 11 s. The approximate correspondence of this reflection time with estimates of the two-way traveltime to the Moho in this area provided by seismic-refraction data suggests that the prominent reflections are from the Moho. The relief on these reflectors (the “reflection Moho”) beneath Nevada, across a latitudinal transect of

X-ray diffraction of multilayers and superlattices

Abstract: Recursion formulae for calculating the reflected amplitude ratio of multilayers and superlattices have been derived from the Takagi-Taupin differential equations, which describe the dynamical diffraction of X-rays in deformed crystals. Calculated rocking curves of complicated layered structures, such as non-ideal superlattices on perfect crystals, are shown to be in good agreement with observed diffraction profiles. The kinematical theory can save computing time only in the case of an ideal superlattice, for which a geometric series can be used, but the reflectivity must be below 10% so that multiple reflections can be neglected. For a perfect crystal of arbitrary thickness the absorption at the center of the dynamical reflection is found to be proportional to the square root of the reflectivity. Sputter-deposited periodic multilayers of tungsten and carbon can be considered as an artificial crystal, for which dynamical X-ray diffraction calculations give results very similar to those of a macroscopic optical description in terms of the complex index of refraction and Fresnel reflection coefficients.

Reflection and refraction at the surface of a chiral medium: comparison of gyrotropic constitutive relations invariant or noninvariant under a duality transformation

Abstract: Fresnel amplitudes for specular reflection and refraction at the surface of an isotropic, intrinsically nonmagnetic chiral medium are derived for sets of constitutive relations that are invariant or noninvariant under a duality transformation of the electromagnetic fields. The invariant set leads to a differential reflection curve of incident left and right circularly polarized light that is null at normal incidence and peaks beyond Brewster’s angle; the noninvariant set leads to maximum differential reflection in the vicinity of normal incidence and extends over a wide range of incident angles. Both sets lead to effectively equivalent descriptions of standard optical rotation and circular dichroism.

Ambient illumination and the determination of material changes

Abstract: The task of distinguishing material changes from shadow boundaries in chromatic images is discussed. Although there have been previous attempts at providing solutions to this problem, the assumptions that were adopted were too restrictive. Using a simple reflection model, we show that the ambient illumination cannot be assumed to have the same spectral characteristics as the incident illumination, since it may lead to the classification of shadow boundaries as material changes. In such cases, we show that it is necessary to take into account the spectral properties of the ambient illumination in order to develop a technique that is more robust and stable than previous techniques. This technique uses a biologically motivated model of color vision and, in particular, a set of chromatic-opponent and double-opponent center-surround operators. We apply this technique to simulated test patterns as well as to a chromatic image. It is shown that, given some knowledge about the strength of the ambient illumination, this method provides a better classification of shadow boundaries and material changes.

Non-Lambertian Effects on Remote Sensing of Surface Reflectance and Vegetation Index

Abstract: This paper discusses the effects of non-Lambertian reflection from a homogeneous surface on remote sensing of the surface reflectance and vegetation index from a satellite. Remote measurement of the surface characteristics is perturbed by atmospheric scattering of sun light. This scattering tends to smooth the angular dependence of non-Lambertian surface reflectances, an effect that is not present in the case of Lambertian surfaces. This effect is calculated to test the validity of a Lambertian assumption used in remote sensing. For the three types of vegetations considered in this study, the assumption of Lambertian surface can be used satisfactorily in the derivation of surface reflectance from remotely measured radiance for a view angle outside the backscattering region. Within the backscattering region, however, the use of the assumption can result in a considerable error in the derived surface reflectance. Accuracy also deteriorates with increasing solar zenith angle. The angular distribution of the surface reflectance derived from remote measurements is smoother than that at the surface. The effect of surface non-Lambertianity on remote sensing of vegetation index is very weak. Since the effect is similar in the visible and near infrared part of the solar spectrum for the vegetations treated in this study, it is canceled in deriving the vegetation index. The effect of the diffuse skylight on surface reflectance measurements at ground level is also discussed.

Global duricrust on Mars: Analysis of remote-sensing data

Abstract: A study is conducted of the infrared thermal emission, radio thermal emission, and radar reflection data sets with the objective to obtain a simple and self-consistent model for the Mars surface. The results are compared with in situ observations at the Viking Lander sites. Attention is given to thermal inertia values, the abundance of surface rocks, radar/thermal correlations, diurnal temperature deviations, and radio emission data. It is suggested that all of the global remote-sensing data sets considered can be reconciled on the basis of variations in the degree of formation of a case-hardened crust or duricrust. On the other hand, no other model which has been proposed in conjunction with any individual data set can satisfy all of the constraints discussed.

Nonspecular phenomena in beam fields reflected by multilayered media

Abstract: Past studies have shown that beams reflected by a single dielectric interface exhibit lateral and focal shifts under total-reflection conditions or angular shifts if a partial reflection regime is maintained. We investigate these effects for Gaussian beams incident upon multilayered media by using an analysis that treats the three beam-shifting phenomena in a unified manner. This approach reveals a novel fourth effect that manifests itself as an expansion or a reduction of the beam waist. All the four nonspecular phenomena are evaluated for typical layered configurations, and simple approximate relations are derived. The results show that the reflected beam fields may be considerably different from those predicted by geometrical optics if incidence occurs at an angle around which the reflectance function varies rapidly.

Optics of Floquet-Bloch waves in dielectric gratings

Abstract: The behavior of light in dielectric gratings is discussed in terms of the optical Floquet-Bloch waves (or modes). The emphasis is on the development of a good physical understanding of the nature of these waves, using the wavevector diagram to summarize their spatial dispersion and spectra. It is shown that Floquet-Bloch theory offers some advantages conceptually over the commonly used coupled-wave theory, because the rays of the Floquet-Bloch waves (given by their group velocities) play the same role in a periodic medium as do those of plane waves in isotropic or graded-index media. The effect on power conservation of truncating the Floquet expansions for the Floquet-Bloch waves is considered in detail. Using the greater intuitive power of Floquet-Bloch theory, it is shown (in contrast to recent claims to the contrary) how rigorous coupled-wave theory can be applied to symmetrical reflection gratings, and secondly how the light in these gratings can be viewed in terms of the multiple-beam interference of Floquet-Bloch waves, leading to behavior reminiscent of a low-finesse Fabry-Perot cavity.

The Effect of the Marginal Ice Zone on the Directional Wave Spectrum of the Ocean

Abstract: During the MIZEX-84 experiment in the Greenland Sea in June–July 1984, a cooperative program was carried out between the Scott Polar Research Institute (SPRI) and the Institute of Oceanographic Sciences (IOS) to measure the change in the directional character of the ocean wave spectrum in the immediate vicinity of the ice edge. The aim was to extend one-dimensional spectral measurements made hitherto so as to study in full the processes of reflection and refraction Directional spectrum analysis of these records shows that (i) significant reflection of wave energy occurs at the ice edge (detected using Long-Hasselmann analysis); (ii) within the ice the directional spectrum at high frequencies, where attenuation is rapid, broadens to become almost isotropic; whereas (iii) the directional spectrum at swell frequencies, where the attenuation is slower, becomes initially narrower before broadening more slowly than the high frequency energy. An explanation of these effects is offered in terms of scatte...

The nature of the non‐gaussianity of primary reflection coefficients and its significance for deconvolution*

Abstract: One of the important properties of a series of primary reflection coefficients is its amplitude distribution. This paper examines the amplitude distribution of primary reflection coefficients generated from a number of block-averaged well logs with block thicknesses corresponding to 1 ms (two-way time). The distribution is always essentially symmetric, but has a sharper central peak and larger tails than a Gaussian distribution. Thus any attempt to estimate phase using the bi-spectrum (third-order spectrum) is unlikely to be successful, since the third-order moment is almost identically zero. Complicated tri-spectrum (fourth-order spectrum) calculations are thus required. Minimum Entropy Deconvolution (MED) schemes should be able to exploit this form of non-Gaussianity. However, both these methods assume a white reflectivity sequence; they would therefore mix up the contributions to the trace's spectral shape that are due to the wavelet and those that are due to non-white reflectivity unless corrections are introduced. A mixture of two Laplace distributions provides a good fit to the empirical amplitude distributions. Such a mixture distribution fits nicely with sedimentological observations, namely that clear distinctions can be made between sedimentary beds and lithological units that comprise one or more such beds with the same basic lithology, and that lithological units can be expected to display larger reflection coefficients at their boundaries than sedimentary beds. The geological processes that engender major lithological changes are not the same as those for truncation of bedding. Analyses of sub-sequences of the reflection series are seen to support this idea. The variation of the mixing proportion parameter allows for scale and shape changes in different segments of the series, and hence provides a more flexible description of the series than the generalized Gaussian distribution which is shown to also provide a good fit to the series. Both the mixture of two Laplace distributions and the generalized Gaussian distribution can be expressed as scale mixtures of the ordinary Gaussian distribution. This result provides a link with the ordinary Gaussian distribution which might have been expected to be the distribution of a natural series such as reflection coefficients. It is also important in the consideration of the solution of MED-type methods. It is shown that real (coloured) primary reflection series do not seem to be obtainable as the deconvolution result from MED-type deconvolution schemes.

Profile-measuring light probe using a change in reflection factor in the proximity of a critical angle of light

Abstract: A profile-measuring light probe includes: an illuminator for irradiating a fine spot of light on a subject to be measured; an objective lens for forming an image of the fine spot on an image plane; and a relay lens for converting the light from the fine spot into a generally parallel ray. Further, the light probe includes a window plate constituted by an entrance prism for taking in the generally parallel ray emitted from the relay lens; a flat glass for subjecting the taken-in ray to multiple internal reflections and transmitting the same, and an exit prism for outputting the ray thus transmitted to the outside. The light probe measures the distribution of light quantity of the light emitted from the window plate to thereby measure a profile of the subject to be measured. With the above-described arrangement, it becomes possible for the light probe to perform the measuring through the utilization of a change in reflection factor of a light inciding in the proximity of a critical angle without using a critical angle prism.

Development of a Three-Dimensional Noncontact Digital Optical Profiler

Abstract: A noncontact three-dimensional optical profiler for measuring surface roughness is described. The system consists of a reflection microscope, Mirau interferometer with a reference surface mounted on a piezoelectric transducer, CID detector array, frame grabber, and micro-computer. Interferometric phase-shifting techniques are used to obtain surface height information. The height measurements areprocessed by a computer to obtain topographical statistical parameters, which are useful in predicting tribological and magnetic performances of the head-media interface in magnetic storage systems. Sample data are presented for magnetic media (tape, floppy disk, and rigid disk), a magnetic head, a silicon wafer, and a glass slide.

Ultrasonic reflection mode imaging of the nonlinear parameter B/A: I. A theoretical basis

Abstract: The theoretical basis of a new method for obtaining both reflection and transmission mode images of the nonlinear parameter B/A is given. An expression for the instantaneous (not cumulative) phase shift in a sinusoidal probe waveform due to nonlinear interaction with an arbitrary pump waveform propagating in the opposite direction is derived. This instantaneous phase shift is proportional to the convolution of the pump waveform with the spatial distribution of the nonlinear parameter B/A along the propagation path of the pump and interacting probe. The instantaneous phase of the probe can be obtained in real time giving a measure of the variation of B/A along an image line.

Reflection and transmission of an obliquely incident wave by an array of spherical cavities

Abstract: A plane wave is incident on a doubly periodic array of spherical cavities in an elastic solid. The cavities are of equal radius d, and their centers are located in a single plane, the x1x2 plane, at positions x1=ma, x2=nb. The propagation vector of a plane, time‐harmonic, incident longitudinal wave is located in the x1x3 plane. The scattering problem is formulated rigorously by taking advantage of the geometrical periodicity. The reflected and transmitted longitudinal and transverse wave motions may be expressed as superpositions of an infinite number of wave modes, each with its own cutoff frequency. Reflection and transmission coefficients have been defined as integrals over a single cavity in terms of the displacement components and auxiliary surface traction terms on the surface of the cavity. The system of singular integral equations for the displacement components has been solved numerically by the boundary integral equation method. Curves show the reflection and transmission coefficients for the re...

Observations on intensity oscillations in reflection high‐energy electron diffraction during epitaxial growth of Si(001) and Ge(001)

Abstract: Intensity oscillations have been found in the specular beam of reflection high‐energy electron diffraction patterns during growth of Si(001) and Ge(001) by molecular beam epitaxy. The reported results demonstrate the dependence of the amplitude and damping of the oscillations on different parameters such as substrate temperature, electron beam angle of incidence, and azimuth.

Convergent‐beam reflection high‐energy electron diffraction (RHEED) observations from an Si(111) surface

Abstract: Conditions for the intensity enhancement of a Bragg reflection are investigated through convergent-beam (CB) reflection electron diffraction experiments. This intensity enhancement is of great interest for reflection electron microscopy of surfaces. Comparison of CB reflection diffraction patterns with CB transmission diffraction patterns shows a very similar enhancement which can be explained by Bloch waves. The observed surface diffraction parabolae are closely related to Kikuchi envelopes. The intensity enhancement can be interpreted as a channelling phenomenon.

Theory and application of antiscattering single layers: antiscattering antireflection coatings

Abstract: We recall the analytical expression that gives, for a rough surface illuminated at normal incidence, the light scattered in the half-space containing the specular reflection direction. Two cases are studied: the bare substrate and the substrate coated with one transparent layer. It is shown, for this specular direction, that the light scattered from a single layer can be equal to zero (perfect antiscattering) in certain conditions relative to the roughnesses of the two layer interfaces. Data calculation proves that this antiscattering effect occurs in all directions of the half-space of the reflected light. The experimental results are in good agreement with this theoretical analysis for five different dielectric materials. This study brings out most information about the grain of the material, which is responsible for the residual roughness.

Reflection of Heavy Ions

Abstract: The backscattering of heavy ions from surfaces is investigated by computer simulation (TRIM.SP). The particle and energy reflection coefficients are shown to scale with the ratio of target mass to ion mass as well as with the reduced energy e for e>0.02 and for normal incidence. At lower energies not only the scaling breaks down but also the effect of a chemical binding influences the reflection coefficient. The calculated data include also the dependence of the reflection coefficients on the angle of incidence as well as angular and energy distributions. Simulated results are in reasonable agreement with those from analytical theory and experiment.

Water Waves Over Ripples

Abstract: The interaction of small amplitude water waves with a patch of bottom ripples is studied using the Boundary Integral Equation Method (BIEM). Normal and oblique wave incidence is examined for reflection coefficients and the laboratory data of Davies and Heathershaw are compared to the numerical results, with the conclusion that the analytical model of Davies and Heathershaw overestimates the reflection coefficient at resonance. Comparison of BIEM results for oblique incidence is made with an extension of the recent work of Mei showing good agreement, even for large amplitude ripples.

Arsenic-induced intensity oscillations in reflection high-energy electron diffraction measurements

Abstract: A technique of arsenic‐induced RHEED intensity oscillations has been used to accurately measure arsenic incorporation rates as a function of substrate temperature during the homoepitaxial growths of both GaAs and InAs by molecular beam epitaxy (MBE). Measurements were made at growth temperatures from 350 to 650 °C and at arsenic fluxes of 0.1 to 10.0 monolayer/s. The method measures only the arsenic actually incorporated into the growing film and does not include the arsenic lost in splitting the arsenic tetramers or lost by evaporation from the sample.

Borehole logging method for fracture detection and evaluation

Abstract: In a method for locating fractures in subsurface earth formations traversed by a borehole a first signal is generated representative of low frequency Stoneley waves (that is tube waves) propagating along the borehole from a source mounted in a logging tool. A second signal is generated by an array of detectors on the tool, representative of low frequency Stoneley waves propagating along the borehole and arising from reflection from fractures of the waves propagating from the source. An indication of the presence of fractures is derived by deconvolving the second signal with the first signal and identifying the time and magnitude of the peak value of the envelope of the deconvolved signal. The variation that would be expected in the presence of fracture and the actual variation are compared and a fracture detected when the actual and expected variations match. Alternatively the first and second signals can be cross-correlated and the time of the peak negative value of the cross-covariance determined. The width of a fracture can also be found, by estimating the fracture reflectivity R" for a range of possible fracture widths w according to the equation ##EQU1## where Hn.sup.(1) is the nth order outgoing Hankel function; F is Stoneley wave frequency; S is Stoneley wave slowness; a is the borehole radius; and a is a term related to borehole fluid viscosity (typically set equal to unity). The value of w yielding an estimated value of reflectivity closest to the value derived from the magnitude of the envelope of the deconvolved signal is taken as being indicative of the fracture width.

Seismic reflection investigations of sinkholes beneath Interstate Highway 70 in Kansas

Abstract: Seismic reflection studies were performed across actively developing sinkholes located astride Interstate Highway 70 in Russell County, Kansas. Results indicate that high‐resolution seismic reflection surveys are useful in the subsurface investigation of some sinkholes. In particular, we were able to delineate the subsurface vertical and horizontal extent of the sinkholes because of the excellent acoustical marker‐bed characteristics of the Stone Corral anhydrite. The seismic reflection evidence presented here, combined with borehole information from 1967, suggest that the Stone Corral anhydrite has been down‐dropped within one of the sinkholes as much as 30 m in 13 years. The seismic reflection method is potentially useful in engineering studies of other sinkholes and karst features. The seismic data presented here were obtained in the presence of relatively heavy highway traffic (i.e., up to a few dozen vehicles per minute) using the MiniSOSIE recording technique.

Seismic Wave Propagation In Stratified Media

Abstract: Publisher Summary This chapter focuses on elastic wave propagation in stratified media. The development of the theory of elastic wave propagation in stratified media has been strongly influenced by the problems of seismic wave propagation and the nature of the seismograms recorded from earthquakes. For purely analytic developments of elastic wave propagation, the level of manageable algebraic complexity is reached in a model with one or two uniform layers overlying a uniform half space. This chapter shows how the excitation of elastic waves, within a horizontally stratified structure, can be conveniently developed in terms of reflection and transmission matrices. This procedure has allowed the construction of the full response of the medium or approximations with desired properties so that theoretical seismograms may be calculated for realistic distributions of elastic parameters. Although this development has been for isotropic media, nearly all the results apply directly to the case of full anisotropy if 3 × 3 reflection and transmission matrices allowing coupling between all wave types are employed. This development of the wavefield for both source and receiver within the stratification may be used for other classes of wave propagation.

Nonlinear reflection and refraction of planar ion-acoustic plasma solitons.

Abstract: Experimental observations on the reflection and refraction of a planar ion-acoustic soliton from a metallic mesh electrode are performed in a uniform double-plasma device. Reflection and refraction angles are observed to depend on the incident wave amplitude, showing a nonlinear Snell's law.

Goos–Hänchen beam shift at total internal reflection with application to spatially dispersive media

Abstract: In this paper the Goos–Hanchen beam displacement at total internal reflection is reviewed. The basic theory of the beam shift is discussed from a classical approach, and measurement of the shift is discussed. Other experimental results are outlined. The theory of finite beam shift at total internal reflection is summarized. An application to nonlocal media is discussed. Finally, recent developments are outlined with implication for beam shifts in spatially dispersive media.