Relevant bibliographies by topics / Wide Angle Reflection/Refraction

Academic literature on the topic 'Wide Angle Reflection/Refraction'

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Published: 11 March 2023

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Journal articles on the topic "Wide Angle Reflection/Refraction"

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Rendleman, C. A., and F. K. Levin. "Reflection maxima for reflections from single interfaces." GEOPHYSICS 53, no. 2 (February 1988): 271–75. http://dx.doi.org/10.1190/1.1442462.

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At a workshop on refraction and wide‐angle reflections, Hilterman (1985) pointed out that, in contrast to the plane‐wave case, when there is a point source, a P-wave reflected from a plane interface attains its maximum amplitude at an offset greater than that corresponding to the critical angle (Figure 1). The same conclusion had been drawn earlier by Červený (1967). However, neither Červený’s results, which were based on very complicated mathematical expressions derived by Brekhovskikh (1960), nor Hilterman’s computer‐generated data shed light on the physics implied by the shifted maximum.
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Filatova, Elena, and Andrey Sokolov. "Effect of reflection and refraction on NEXAFS spectra measured in TEY mode." Journal of Synchrotron Radiation 25, no. 1 (January 1, 2018): 232–40. http://dx.doi.org/10.1107/s1600577517016253.

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The evolution of near-edge X-ray absorption fine structure in the vicinity of theK-absorption edge of oxygen for HfO2over a wide range of incidence angles is analyzed by simultaneous implementation of the total-electron-yield (TEY) method and X-ray reflection spectroscopy. It is established that the effect of refraction on the TEY spectrum is greater than that of reflection and extends into the angular region up to angles 2θc. Within angles that are less than the critical angle, both the reflection and refraction strongly distort the shape of the TEY spectrum. Limitations of the technique for the calculation of optical constants from the reflection spectra using the Kramers–Kronig relation in the limited energy region in the vicinity of thresholds are discussed in detail.
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Mereu, R. F. "The complexity of the crust from refraction/wide-angle reflection data." Pure and Applied Geophysics PAGEOPH 132, no. 1-2 (1990): 269–88. http://dx.doi.org/10.1007/bf00874366.

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Mereu, R. F. "The complexity of the crust and Moho under the southeastern Superior and Grenville provinces of the Canadian Shield from seismic refraction - wide-angle reflection data." Canadian Journal of Earth Sciences 37, no. 2-3 (April 2, 2000): 439–58. http://dx.doi.org/10.1139/e99-122.

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The major features of the individual velocity models, Poisson's ratio values, and crustal complexity derived from the interpretation of seismic data sets from four long-range seismic refraction - wide-angle reflection experiments are summarized. The experiments were conducted from 1982-92 in the southeastern portion of the Canadian Shield. In the conventional analysis of seismic refraction - wide-angle reflection data, only the onset times and amplitudes of the major arrival phases are used to derive seismic velocity models of the region under study. These models are over smoothed, have a number of intermediate discontinuities, are unable to explain the Pg coda, and bear very little resemblance to the models derived from the analysis of near-vertical seismic reflection data. In this paper some of the differences between seismic models derived from near-vertical reflection analysis and those from refraction analysis are reconciled from an analysis of the wide-angle reflection fields of the crustal coda waves that follow the first arrivals. This was done using a migration technique that to a first approximation maps the amplitudes of the record sections into a two-dimensional (2-D) complexity section. These new sections show significant lateral variations in crustal and Moho reflectivity and may be used to complement the 2-D velocity anomaly sections and near-vertical reflection sections. The method was based on a numerical study that showed that the coda can be explained with a class of complex heterogeneous models in which sets of small-scale, high-contrast sloping seismic reflectors are "embedded" in a uniform seismic velocity gradient field.
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Luetgert, James, and Carol E. Mann. "Avalon terrane in eastern coastal Maine: Seismic refraction-wide-angle reflection data." Geology 18, no. 9 (1990): 878. http://dx.doi.org/10.1130/0091-7613(1990)018<0878:atiecm>2.3.co;2.

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Pawlik, G., K. Tarnowski, W. Walasik, A. C. Mitus, and I. C. Khoo. "Liquid crystal hyperbolic metamaterial for wide-angle negative–positive refraction and reflection." Optics Letters 39, no. 7 (March 19, 2014): 1744. http://dx.doi.org/10.1364/ol.39.001744.

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Majdański, M. "The uncertainty in layered models from wide-angle seismic data." GEOPHYSICS 78, no. 3 (May 1, 2013): WB31—WB36. http://dx.doi.org/10.1190/geo2012-0280.1.

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The analytical method of estimating the uncertainty in layered models is addressed to models obtained using a layer-stripping modeling strategy or forward modeling. It is based on a simple principle of small error propagation. There are two variants of the method: a simplified one that includes refraction and vertical reflections and one that also includes wide-angle reflections. Both give a quantitative estimation for the existing models. To allow for a simple analytical estimation, refracted waves are described using a head-wave approximation in constant velocity layers; wide angle reflection paths are also simplified. In the case of trial and error forward modeling, this method can help determine how well the used parameterization is reflected in the data and avoid over-fitting the structures. This is especially important because the forward modeling is very subjective and there is no method to assess the parameterization without generating alternative models. For inversion problems using the layer-stripping method, the analysis allows for a correct propagation of errors and will help to evaluate the effect of including a priori information with known uncertainty. As a result, the layer-stripping modeling strategy is worse than simultaneous inversion for layered models because it gives larger uncertainties.
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Németh, Balázs, Ron M. Clowes, and Zoltan Hajnal. "Lithospheric structure of the Trans-Hudson Orogen from seismic refraction - wide-angle reflection studies." Canadian Journal of Earth Sciences 42, no. 4 (April 1, 2005): 435–56. http://dx.doi.org/10.1139/e05-032.

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The Trans-Hudson Orogen (THO) is the world's largest Paleoproterozoic orogenic belt. Data from three refraction profiles are used to investigate its lithospheric structure in Saskatchewan and Manitoba. R1 crosses the orogen from the Hearne craton on the west to the Superior craton on the east; R2 and R3 are along the orogen. P-wave velocity structural models are generated using a ray-based technique. On line R1, higher crustal velocities in its eastern part coincide with rocks of the Flin Flon – Namew gneiss complex. Depth to Moho is in the 40–45 km range and equates to that from the reflection data, including a small crustal root below the Sask minicontinent. Along lines R2 and R3, depth to Moho varies from about 40 km up to 55 km at the north end of R2 and south end of R3. In general, variations in crustal velocity and depth to Moho do not correlate with the location and extent of geological domains; they appear to reflect the complex deformation and metamorphic history of the crustal rocks. Mantle velocities are high, ~8.2 km/s. However a limited area shows prominent velocity anisotropy, with values of 8.6 km/s along R2 and R3 and 8.1 km/s along R1. We speculate that the observed anisotropy represents an ~100-km-wide mantle suture zone resulting from the collision of Archean plates. The suture zone accommodated limited extensional deformation, associated with a counterclockwise rotation of the Superior plate, to generate the anisotropy. In this model, the lithospheric mantle of the THO internal domains and Sask craton are detached.
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Roberts, D. G., A. Ginzberg, K. Nunn, and R. McQuillin. "The structure of the Rockall Trough from seismic refraction and wide-angle reflection measurements." Nature 332, no. 6165 (April 1988): 632–35. http://dx.doi.org/10.1038/332632a0.

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Hole, J. A., R. M. Clowes, and R. M. Ellis. "Interpretation of three-dimensional seismic refraction data from western Hecate Strait, British Columbia: structure of the crust." Canadian Journal of Earth Sciences 30, no. 7 (July 1, 1993): 1440–52. http://dx.doi.org/10.1139/e93-124.

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As part of a multidisciplinary investigation of the structure and tectonics of the Queen Charlotte Basin and underlying crust, deep multichannel seismic reflection and coincident crustal refraction data were collected in 1988. Energy from the reflection air-gun array source was recorded at land sites at offsets appropriate to record crustal refraction and wide-angle reflection data. Refraction data recorded in a broadside geometry provide good three-dimensional coverage of western Hecate Strait. These data are modelled using tomographic inversion techniques to determine the three-dimensional velocity structure of the crust in this region. The one-dimensional average velocity increases rapidly with depth to 6.5 km/s at 7 km depth. Velocities from 7 to at least 12 km depth remain approximately constant and are associated with rocks of the Wrangellia terrane. Significant lateral velocity variations, including large differences in near-surface velocities attributable to surface features, relatively low velocities representing interbedded Tertiary sediments and volcanics, and a deep high-velocity anomaly that may represent the root of an igneous intrusion, are mapped. Wide-angle reflections from the Moho are used to determine the thickness of the crust. The Moho is at 29 km depth beneath the east coast of the Queen Charlotte Islands. This is deeper than the Moho observed below Queen Charlotte Sound and as deep as, or deeper than, that below Hecate Strait. Crustal thinning during Tertiary extension was thus greatest beneath the surface expression of the Queen Charlotte Basin, leaving the crust under the islands considerably thicker than under the basin. In an alternate or additional explanation, compression at the continental margin during the last 4 Ma may have been taken up by thickening or underplating of the continental crust beneath the islands. If the Pacific plate is subducting beneath the islands, the Moho observations constrain the slab to dip greater than 20–26°.
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Dissertations / Theses on the topic "Wide Angle Reflection/Refraction"

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Harsha, Senusi Mohamed. "Interpretation of Southern Georgia coastal plain velocity structure using refraction and wide-angle reflection methods." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/25886.

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Hananto, Nugroho. "Architecture and Evolution of North Sumatra Subduction Zone based on long Offset Seismic Reflection and Wide Angle Seismic Refraction / Reflection Data." Institut de physique du globe (Paris), 2011. http://www.theses.fr/2011GLOB1203.

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Hughes, Stephen. "Crustal structure of northeastern North America : results from the Ontario-New York-New England seismic refraction/wide-angle reflection experiment." Thesis, University of Leicester, 1992. http://hdl.handle.net/2381/35043.

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The Ontario-New York-New England seismic refraction/wide-angle reflection profile was acquired to investigate the deep structural interrelationships between the southeastern Grenville province and the western New England Appalachians. The Grenville province is characterized by 45 km thick crust, with an average crustal seismic velocity of 6.6 km/s and a Poisson's ratio of 0.28+0.01. In the mid-crust a laminated dome-like body is inferred to be composed of mafic cumulate sills on the basis of its high velocity (7.1 km/s) and Poisson's ratio (0.27). The lower crust is characterized by a velocity of 7.0 km/s which suggests a strongly mafic composition such as garnet pyroxene granulite. The Moho is a variable feature, characterized by en-echelon reflections suggestive of compositional interlayering. An anomalous mantle layer with a velocity of 8.6 km/s is proposed to represent an eclogized basaltic layer added to the lithosphere during Grenvillian orogenesis. The boundary between the Grenvillian craton and the western New England Appalachians is marked by an eastward dipping ramp structure which penetrates to a depth of 25 km where it soles out above a transitional mid-lower crustal interface. The New England Appalachians are characterized by an average crustal velocity of 6.4 km/s and a sharply reflective Moho delineating crustal thinning from 41 km to 37 km towards the Atlantic margin. The lower crustal velocity is 6.8 km/s, with a Poisson's ratio of 0.26+0.01. In contrast to the Grenvillian craton the seismic properties of the Appalachian lower crust are consistent with an intermediate composition interlaced with mafic sills related to extensional underplating and intrusion during the rifting of the Atlantic Ocean.
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Meléndez, i. Catalán Adrià. "Development of a New Parallel Code for 3-D Joint Refraction and Reflection Travel-Time Tomography of Wide-Angle Seismic Data. Synthetic and Real Data Applications to the Study of Subduction Zones." Doctoral thesis, Universitat de Barcelona, 2014. http://hdl.handle.net/10803/289786.

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This dissertation is devoted to seismic tomography. I have implemented a new modelling tool for 3-D joint refraction and reflection travel-time tomography of wide-angle seismic data (TOMO3D). The reason behind this central objective is the evidence that the information based on 2-D seismic data does not allow to capture the structural complexity of many 3-D targets, and in particular that of the seismogenic zone in subduction margins. The scientific rationale for this statement, which justifies the central part of my thesis work, is based on the analysis of 2-D models obtained in the convergent margin of Nicaragua, a seismically active area where a textbook example of tsunami earthquake took place in 1992. In this application I modelled two perpendicular wide-angle seismic profiles for the characterisation of the overriding plate and the interplate fault. To do this, I applied TOMO2D, a state-of-the-art joint refraction and reflection 2-D travel-time tomography code. The inversion outcomes are two 2-D velocity models along both profiles, together with the 1-D geometry of the interplate boundary. In combination with other geophysical data measurements, namely coincident multichannel seismic profiles and gravity data, these models provide new constraints on the nature and structure of the margin, and in particular add new insights on the nucleation and propagation of the said earthquake and its tsunamigenic behaviour. Ultimately, this case study evidences the aforementioned limitations of 2-D modelling in the investigation of 3-D geological structures and phenomena. Following from this first application and with the idea of increasing the amount of data used in travel-time tomography, I focused on an a priori paradoxical phenomenon related to water-layer multiple phases, that under certain circumstances, is observed on wide-angle record sections. The interest of this study lies in the fact that this phenomenon can provide additional constraints on travel-time tomography models. First, I propose and corroborate the hypothesis explaining the apparent paradox, and then derive the most favourable geological conditions for the phenomenon to occur. Subsequently, the possibility to model this multiple-like phases is introduced in TOMO3D. The development of TOMO3D, which constitutes the core of my work, is founded on TOMO2D, from which it inherits the numerical methods for solving the forward and inverse problems. Source files have been rewritten, redefining and introducing the necessary variables and functions to handle 3-D data inversion. The tests made with the sequential version of the code emphasise the need of parallelisation for practicality reasons. Indeed, the increasing size of data sets along with the modelling of the additional spatial dimension results in computationally demanding inversions. Hence, I parallelised the forward modelling part of the code, which takes up to 90% of the computing time, with a combination of multiprocessing and message-passing interface extensions. Subsequently, the parallel version of TOMO3D is applied to a complex synthetic case simulating a subduction zone. This first 3-D application serves to evaluate the correctness of the code's programming, and as step-by-step description of the modelling procedure, with particular attention on the layer-stripping strategy used to successively model several reflectors. The outcomes demonstrate the ability of the code and the chosen inversion strategy to accurately recover the velocity distribution and the geometry of the two reflectors. Finally, TOMO3D is applied to a real 3-D wide-angle seismic data set acquired at the Pacific margin of Ecuador and Colombia to extract a 3-D velocity model of the overriding and incoming plates, which is then compared to previous results obtained with an extensively tested and used 3-D refraction travel-time tomography code (FAST). The comparison indicates that TOMO3D is more accurate than FAST but at the same time it is computationally more demanding. However, the parallelisation of TOMO3D allows using high-performance computing facilities, which is not the case of FAST or most of the existing codes.
Aquesta tesi està dedicada a la tomografia sísmica. Concretament, he implementat una eina de modelització 3D per a la tomografia conjunta de temps de trajecte de refraccions i reflexions (TOMO3D). La raó darrere d'aquest objectiu és l'evidència de que la informació basada en dades sísmiques 2D no permet copsar la complexitat de gran part dels cossos geològics, i en particular de la zona sismogènica en marges de subducció. El desenvolupament del TOMO3D es basa en el TOMO2D, un codi d'avantguarda per a la tomografia conjunta de refraccions i reflexions en 2D. Els arxius de codi han estat reescrits, redefinint i introduint les funcions necessàries per dur a terme la inversió 3D. Els testos fets amb la versió seqüencial del codi posen de manifest la necessitat de paral·lelització ja que l'increment de la mida dels conjunts de dades així com la modelització de la dimensió espacial afegida fan que les inversions siguin computacionalment exigents. La versió paral·lelitzada del TOMO3D ha sigut aplicada a un cas sintètic complex que simula una zona de subducció. Aquesta primera aplicació 3D serveix per avaluar la correcció de la programació del codi, i com a descripció pas a pas del procediment de modelització. Els resultats demostren la capacitat del codi per recuperar acuradament la distribució de velocitat i la geometria dels dos reflectors. Finalment, el TOMO3D és aplicat a un conjunt 3D de dades de sísmica de gran angle adquirit al marge pacífic d'Equador i Colòmbia per extreure'n un model 3D de la velocitat de les plaques cavalcant i subduïda, que és comparat amb el resultat obtingut amb un codi 3D de tomografia de temps de trajecte de refraccions (FAST). La comparació indica que el TOMO3D és més acurat que el FAST però al mateix temps és computacionalment més exigent. Tot i així, la paral·lelització del TOMO3D permet utilitzar plataformes de supercomputació, a diferència del que passa amb el FAST i la majoria de codis existents.
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Brancatelli, Giuseppe. "Analisi di dati acquisiti con OBS." Doctoral thesis, Università degli studi di Trieste, 2010. http://hdl.handle.net/10077/3458.

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2008/2009
Gli OBS (Ocean Bottom Seismometer) sono ampiamente utilizzati negli studi sismici crostali attraverso l’utilizzo delle registrazioni di onde rifratte e riflesse a grande offset (Wide Angle Reflection/Refraction, WAR/R). L'analisi di questi dati comporta, solitamente, l'impiego di modellistica diretta e/o inversa al fine di giungere alle velocità dei singoli strati e alle profondità delle interfacce. In questa tesi, invece, si presenta un approccio diverso che prevede: 1) costruzione di modelli di velocità dall’analisi dei segnali rifratti; 2) elaborazione dei dati OBS al fine di ottenere immagini sismiche a riflessione. In particolare, gli OBS e gli scoppi sono stati riportati ad uno stesso datum (superficie del mare), utilizzando il Wave Equation Datuming (WED). Dopo il WED è stato possibile applicare l'elaborazione tipica della sismica a riflessione. I profili OBS analizzati sono stati acquisiti nell'area dell'Arco Ellenico e, i risultati ottenuti, hanno permesso di riconoscere le strutture geologiche principali e i meccanismi dell’evoluzione tettonica. L'utilizzo del WED ha migliorato la risoluzione delle sezioni finali rispetto a quanto ottenibile con le correzioni statiche classiche. Per confronto è stata applicata la metodologia WED anche a dati simici ad alta risoluzione a terra, risolvendo problemi di correzioni statiche e di strutturazioni tettoniche apparenti nell'area della Bassa Pianura Friulana.
XXII Ciclo
1979
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Lester, W. Ryan. "Structure of the Chesapeake Bay Impact Crater from Wide-Angle Seismic Waveform Tomography." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/35090.

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The Chesapeake Bay impact structure is one of the largest and most well preserved impact structures on Earth. It has a unique morphology composed of an inner crater penetrating crystalline basement surrounded by a wider crater in the overlying sediments. In 2004, the U.S. Geological Survey conducted a seismic survey with the goals of constraining crater structure and in support of the drilling of a borehole into the deepest part of the crater. Travel-time and waveform inversion were applied to the data to produce a high-resolution velocity model of the crater. Low-fold reflection processing was also applied. Northeast of the crystalline crater, undeformed, eastward-sloping crystalline basement is ~1.5 km deep. The edge of the inner crater is at ~ 15 km radius and slopes gradually down to a depth of 1.5 - 1.8 km. A central peak of 4-5 km radius rises to a depth of ~0.8 km. Basement velocity in the crystalline crater is much lower than undeformed basement, which suggests ~10% fracturing of the crater floor, and up to 20% fracturing of the central uplift. A basement uplift and lateral change of velocity, interpreted as the edge of the transient crater, occurs at a radius of ~ 11 km. Assuming a 22 km diameter transient crater, scaling laws predict a ~30 km diameter crater and central peak diameter of 8-10 km. This indicates that post-impact collapse processes that created the ~ 30 km diameter crystalline crater were unaffected by the much weaker rheology of the overlying sediments.
Master of Science
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Oueity, Jounada. "Near-vertical and wide-angle seismic reflection studies of the Moho and sub-crustal lithosphere in NW Canada." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/28903.

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High quality, coincident near-vertical incidence (NVI) and refraction/wide-angle seismic reflection data (R/WAR) acquired along a profile in the Northwest Territories are used to study the nature of the Moho and subcrustal reflectors. First, we re-examine distinct subhorizontal reflections on NVI data in the uppermost mantle that were interpreted previously as a separate feature from a relict subducted slab. Using forward and inverse traveltime modeling of both data sets along the crooked line, we investigate the origin of the reflections. Our results demonstrate that the subhorizontal reflectors are the continuation of the relict subducted slab, which extends laterally for 300 km at depths from 35 to 90 km. Its base is the source of the R/WAR reflections. The apparent flattening is an artifact of projecting a 3-D geometry onto a 2-D cross section. The shallowly subducted slab probably contributed to the thickening and stabilization of the sub-crustal lithosphere in the region. Second, we examine the detailed structure of the Moho and propose a possible scenario for its formation and evolution. Strong Moho reflections are observed on the NVI data (shot gathers and stacked section). The WA data are characterized by a ~0.5 s coda trailing the PmP (Moho) phase. For analysis of these observed data, we follow two approaches, forward and inverse modeling. In forward modeling, we calculate wide-angle and near-vertical synthetic seismograms using 1- and 2-D wave propagation algorithms. Comparison between synthetic and observed data for shot gathers was made possible through development of a novel noise-removal technique using the curvelet transform. For the inverse method, we use a statistical analysis approach based on the von Karman autocorrelation function. Our results indicate that the Moho is a finite-thickness (~3 km), heterogeneous transition zone. The heterogeneities can be described by laterally discontinuous layering, lamellae structure with randomly distributed ellipses or a von Karman distribution with a lateral correlation length of 936 m. The transition zone separates the lower crust with a lateral correlation length of 732 m from the uppermost mantle with a correlation length of 261 m. The Moho is interpreted as a thermal/metamorphic front, a regional décollement, or both.
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Biari, Youssef. "Structure profonde de la marge Nord-Ouest Africaine." Thesis, Brest, 2015. http://www.theses.fr/2015BRES0080/document.

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La marge NE Américaine est une des marges les mieux étudiées au monde, elle a fait l’objet de plusieurs études géophysiques. En comparaison, la marge africaine reste peu étudiée car uniquement deux campagnes océanographiques y ont été menées : la campagne Sismar (2001) au large de la Meseta et la campagne Dakhla (2002) au large du Sahara. La structure profonde de la marge canadienne est connue grâce aux profils de sismique grand-angle SMART-1, 2 et 3. Le premier objectif du projet MIRROR était d’acquérir des profils combinant sismique grand-angle et sismique réflexion sur un segment homologue au profil SMART-1. La comparaison entre les segments homologues de ces deux marges ayant pour but de mieux comprendre le mode d’ouverture de l'océan Atlantique Central. Une comparaison entre les modèles Sismar, Dakhla et Mirror montre que la croûte continentale est plus épaisse au nord et s'amincit vers le sud. La largeur de la zone de transition est plus étroite au sud et les profils Sismar sont localisés sur un bassin sédimentaire posé sur une croûte continentale très amincie. La comparaison avec la marge homologue montre que l'épaisseur, la structure de la croûte continentale et la zone d'amincissement sont très semblables. Par contre, il existe une zone de manteau exhumé et serpentinisé sur le profil Canadien qui n'a pas d’homologue sur la marge africaine. De plus, l'épaisseur de la croûte océanique est différente avec 8 km sur la côte africaine et seulement 3-4 km sur la marge canadienne. Plusieurs hypothèses ont été proposées pour expliquer cette différence (a) une différence d’âge entre les deux croûtes (b) un épaississement lié au passage du point chaud des Canaries (c) une accrétion asymétrique
The NE American margin represents one of the best studied margins in the world, it was the subject of several scientific programs. In comparison, the conjugate NW African margin remains fairly unknown, only two deep seismic cruises were acquired: the SISMAR cruise (2001) offshore the Meseta and the DAKHLA cruise (2002) offshore the Sahara. The deep structure of the Canadian margin is known due to the SMART wide-angle seismic profiles 1, 2 and 3. The first objective of the MIRROR project was to acquire combined wide-angle and deep reflection seismic data offshore a segment conjugate to the SMART-1 profile. The comparison between the homologous segments of these two margins aimed to better understand the opening mechanism of the Central Atlantic Ocean. A comparison between Sismar, Dakhla and Mirror models shows that the continental crust is thicker in the north and thins toward the south. The width of the transition zone is narrower south and Sismar profiles are located on a sedimentary basin placed on a very thinned continental crust. Comparing the Mirror profile with that of the Canadian conjugate margin (Smart 1) shows that the thickness, the structure of the continental crust and the thinning is very similar. However, zones of exhumed and serpentinized mantle were imaged along the Canadian profile that have no conjugate on the African margin. Moreover, the thickness of the oceanic crust is variable with 8 km on the African side and only 3-4 km on the Canadian margin. Several hypotheses have been proposed to explain this difference (a) an age difference between the two types of crust (b) thickening associated with the passage of the Canary hotspot (c) an asymmetric accretion or (d) an accretion at slow to ultra-slow speading centers
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Bouyahiaoui, Boualem. "Structure profonde et réactivation de la marge est-algérienne et du bassin adjacent (secteur d'Annaba), contraintes par sismique réflexion multitrace et grand-angle terre-mer." Thesis, Nice, 2014. http://www.theses.fr/2014NICE4116/document.

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Dans ce travail de thèse, nous analysons la structure crustale de la marge est-algérienne et du bassin adjacent (région d’Annaba), à partir d’un ensemble de nouvelles données acquises durant la Campagne SPIRAL’2009 incluant un profil sismique terre-mer de ~240 km de long, des lignes sismiques réflexion pénétrante 360-traces, et des profils gravimétriques et magnétiques. Nous avons par ailleurs disposé pour cette étude de données complémentaires incluant notamment un ensemble de profils de sismique réflexion offrant des résolutions complémentaires. La structure crustale ainsi établie nous permet de discuter les nombreux modèles cinématiques d’ouverture du bassin est-algérien proposés dans la littérature, afin de caler dans le temps la formation du bassin par rapport à la collision. Elle permet également de discuter la localisation de la déformation liée à la réactivation de la marge, par rapport aux grands domaines lithosphériques du système marge-bassin, afin de mieux comprendre les modalités de l’inversion. Dans le bassin profond, la modélisation directe des temps d’arrivée et des amplitudes des ondes réfractées et réfléchies met en évidence une croûte océanique anormalement mince de 5-5.5 km d’épaisseur, composée de deux couches. La première, de 2.2 km d’épaisseur, montre des vitesses comprises entre 4.8 à 6.0 km/s impliquant un fort gradient; la seconde de 3.3 km d’épaisseur, présente des vitesses comprises entre 6.0 à 7.1 km/s et un plus faible gradient de vitesse. La modélisation des temps d’arrivées des ondes S fourni pour cette couche un coefficient de Poisson de 0.28, indiquant qu’elle est majoritairement constituée de gabbros
In this study, we determine the deep structure of the eastern Algerian basin and its southern margin in the Annaba region (easternmost Algeria), to better constrain the plate kinematic reconstruction in this region. This study is based on new geophysical data collected during the SPIRAL cruise in 2009 that included a wide-angle, 240-km-long, onshore-offshore seismic profile, multichannel seismic reflection lines, and gravity and magnetic data, which was complemented by the available geophysical data for the study area. The analysis and modeling of the wide-angle seismic data using travel-times and amplitudes, and integrated with the multichannel seismic lines, reveal the detailed structure of an ocean-to-continent transition. In the deep basin, there is an ~5.5-km-thick oceanic crust that is composed of two layers. The upper layer of the crust is defined by a high velocity gradient and P-wave velocities between 4.8 km/s and 6.0 km/s from the top to the bottom. The lower crust is defined by a lower velocity gradient and P-wave velocity between 6.0 km/s and 7.1 km/s. The Poisson ratio in the lower crust deduced from S-wave modeling is 0.28, which indicates that the lower crust is composed mainly of gabbros. Below the continental edge, a typical continental crust with P-wave velocities between 5.2 km/s and 7.0 km/s from the top to the bottom shows a gradual seaward thinning of ~15 km over an ~35-km distance
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Laurencin, Muriel. "Etude de la géométrie, de la nature et des déformations de la zone de subduction des Petites Antilles du Nord." Thesis, Brest, 2017. http://www.theses.fr/2017BRES0096/document.

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Dans les zones de subduction, la géométrie du slab est l'un des paramètres qui contrôle les déformations tectoniques de la marge, le couplage et le potentiel sismogénique. La subduction des Antilles résulte du chevauchement de la plaque Caraïbe vers le NE sur les plaques Amériques, à une vitesse de convergence de 2 cm/an. La sismicité est hétérogène et augmente localement sous la plateforme des Iles Vierges. D’une obliquité croissante vers le nord, cette zone est favorable à un partitionnement dont les déformations sont très peu observées. Ces travaux ont permis de confirmer un substratum d’une affinité de croûte océanique épaissie par un panache mantellique et faiblement épaissi par le magmatisme formant les arcs volcaniques Deux structures accommodant le partitionnement de la déformation ont été mis en évidence. La faille de Bunce est une faille décrochante sénestre de 850 km s’étendant d’Hispaniola jusqu’à Barbuda découplant le prisme d’accrétion du substratum. Le Passage d’Anegada, dont nous avons découvert son extension vers le NE, entaille profondément l’avant-arc. Formé par extension due à la collision du Banc des Bahamas sur le nord de la marge caribéenne, ces structures sont réactivées en décrochement sénestre compatible avec du partitionnement. Les caractéristiques d’une dorsale lente (core complexe et grain océanique) entrant en subduction sont imagées pour la première fois. Elles affectent probablement la morphologie du prisme d’accrétion et le potentiel sismogène. Là où les séismes et les déformations de partitionnement (Passage d’Anegada) s'accentuent localement, le slab est moins profond. Ainsi, le couplage interplaque pourrait augmenter localement et favoriser l'activité sismique et le partitionnement tectonique sous le Passage d'Anegada
In subduction zones, the 3D geometry of the plate interface is one of the key parameters that controls margin tectonic deformation, interplate coupling and seismogenic behavior. The North American plate subducts below the Caribbean plate with a convergence rate of 20 mm/y. The seismic activity is heterogeneous and increases locally under the Virgin Islands platform. The northward increasing convergence obliquity is favorable in partitioning which deformations were not really observed. This PhD confirms that the forearc crust is a crust of oceanic affinity thickened by hotspot magmatism and poorly affected by subduction magmatism. Two structures accommodating the partitioning of the deformation were identified. The Bunce Fault is a 850-kmlength sinistral strike-slip fault extending from Hispaniola to the east of Barbuda decoupling the accretionary prism from the Caribbean substratum. The Anegada Passage, whose extension towards the NE is highlighted, entailed deeply the forearc. The structures are reactivated in sinistral strike-slip faults compatible with the partitioning of the deformation after formation in extension due to the collision of the Bahamas Bank with the northern margin. We image for the first time the characteristics of a slow ridge formation (partly complex core and partly oceanic grain) entering in subduction. It affects the morphology of the accretion prism and probably the seismogenic potential of the subduction interface. We have highlighted a shallower slab which is located under the NE Anegada Passage and where earthquakes and partitioning deformations increase locally. Thus, the shallowing slab might results in a local greater interplate coupling favoring seismic activity and tectonic partitioning beneath the Anegada Passage
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Books on the topic "Wide Angle Reflection/Refraction"

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J, Moses Michael, and Geological Survey (U.S.), eds. Wide-angle seismic recordings obtained during the tact multichannel reflection profiling in the northern Gulf of Alaska. Menlo Park, Calif: U.S. Dept. of the Interior, U.S. Geological Survey, 1990.

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Brocher, Thomas M. Wide-angle seismic recordings obtained during the tact multichannel reflection profiling in the northern Gulf of Alaska. Menlo Park, Calif: U.S. Dept. of the Interior, U.S. Geological Survey, 1990.

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Brocher, Thomas M. Wide-angle seismic recordings obtained during the tact multichannel reflection profiling in the northern Gulf of Alaska. Menlo Park, Calif: U.S. Dept. of the Interior, U.S. Geological Survey, 1990.

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Brocher, Thomas M. Wide-angle seismic recordings obtained during the tact multichannel reflection profiling in the northern Gulf of Alaska. Menlo Park, Calif: U.S. Dept. of the Interior, U.S. Geological Survey, 1990.

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Riahi, M. Ali. Crustal two- and three-dimensional models of the Gulf of Bothnia area based on wide-angle and normal-incidence seismic data. Uppsala: Acta Universitatis Upsaliensis, 1995.

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J, Moses Michael, and Geological Survey (U.S.), eds. Onshore-offshore wide-angle seismic recordings of the San Francisco Bay Area Seismic Imaging Experiment (BASIX): The five-day recorder data. Menlo Park, Calif: U.S. Dept. of the Interior, U.S. Geological Survey, 1993.

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Brocher, Thomas Mark. Onshore-offshore wide-angle seismic recordings of the San Francisco Bay Area Seismic Imaging Experiment (BASIX): The five-day recorder data. Menlo Park, Calif: U.S. Dept. of the Interior, U.S. Geological Survey, 1993.

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Brocher, Thomas M. Onshore-offshore wide-angle seismic recordings of the San Francisco Bay Area Seismic Imaging Experiment (BASIX): The five-day recorder data. Menlo Park, Calif: U.S. Dept. of the Interior, U.S. Geological Survey, 1993.

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Novak, Olaf. A wide-angle seismic study of the SE-flank of the Kenya Rift in corporating a multidisciplinary interpretation. Dublin: University College Dublin, 1997.

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Brocher, Thomas Mark. Onshore-offshore wide-angle seismic recordings of the San Francisco Bay Area Seismic Imaging Experiment (BASIX): Data from the Northern California Seismic Network. Menlo Park, Ca: U.S. Dept. of the Interior, U.S. Geological Survey, 1994.

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Book chapters on the topic "Wide Angle Reflection/Refraction"

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Rumpel, Hanna-Maria, Claus Prodehl, Catherine M. Snelson, and G. Randy Keller. "Results of the CD-ROM project seismic refraction/wide-angle reflection experiment: The upper and middle crust." In The Rocky Mountain Region—An Evolving Lithosphere: Tectonics, Geochemistry, and Geophysics, 257–69. Washington, D. C.: American Geophysical Union, 2005. http://dx.doi.org/10.1029/154gm20.

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Snelson, Catherine M., G. Randy Keller, Kate C. Miller, Hanna-Maria Rumpel, and Claus Prodehl. "Regional crustal structure derived from the CD-ROM 99 seismic refraction/wide-angle reflection profile: The lower crust and upper mantle." In The Rocky Mountain Region—An Evolving Lithosphere: Tectonics, Geochemistry, and Geophysics, 271–91. Washington, D. C.: American Geophysical Union, 2005. http://dx.doi.org/10.1029/154gm21.

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Epili, Duryodhan, and Robert F. Mereu. "The GLIMPCE seismic experiment: Onshore refraction and wide-angle reflection observations from a fan line over the Lake Superior Midcontinent Rift System." In Properties and Processes of Earth' Lower Crust, 93–101. Washington, D. C.: American Geophysical Union, 1989. http://dx.doi.org/10.1029/gm051p0093.

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Garrett, Steven L. "Reflection, Transmission, and Refraction." In Understanding Acoustics, 513–42. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-44787-8_11.

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Abstract The behavior of one-dimensional waves propagating through media that are not homogeneous will be the focus of this chapter. We start with an examination of the behavior of planewaves impinging on a planar interface between two fluid media with different properties and then extend that analysis to multiple interfaces and to waves that impinge on such an interface from an angle that is not perpendicular to that surface. The extent of those boundaries separating regions with different acoustical properties will be much larger than the wavelength of the sound. Many cases to be examined here will assume that the extent of the boundary is infinite and the wave incident on such an interface will be both reflected back into the medium from which it originated and be transmitted into the second medium on the other side of the interface. This exploration concludes with consideration of wave propagation through a medium whose properties change slowly and continuously through space resulting in curved ray paths. If the variation of sound speed is linear with height or depth, then the ray paths are arcs of circles. Complicated sound speed profiles will be approximated by piecewise-linear segments that have constant sound speed gradients.
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Neurieder, P. "Seismic Standard Software in Refraction and Wide-Angle Applications." In Joint Interpretation of Geophysical and Geological Data Applied to Lithospheric Studies, 71–91. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3590-0_5.

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Braile, L. W., and C. S. Chiangl. "The continental Mohorovičič Discontinuity: Results from near-vertical and wide-angle seismic reflection studies." In Reflection Seismology: A Global Perspective, 257–72. Washington, D. C.: American Geophysical Union, 1986. http://dx.doi.org/10.1029/gd013p0257.

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Nowack, Robert L. "Applications of Inverse Methods to the Analysis of Refraction and Wide-Angle Seismic Data." In Inverse Problems in Wave Propagation, 395–417. New York, NY: Springer New York, 1997. http://dx.doi.org/10.1007/978-1-4612-1878-4_20.

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Mereu, Robert, Dapeng Wang, and Oliver Kuhn. "Evidence for an inactive rift in the Precambrian from a wide-angle reflection survey across the Ottawa-Bonnechere graben." In Reflection Seismology: The Continental Crust, 127–34. Washington, D. C.: American Geophysical Union, 1986. http://dx.doi.org/10.1029/gd014p0127.

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Mereu, Robert. "The Heterogeneity of the Crust and its Effect on Seismic Wide-Angle Reflection Fields." In Heterogeneity in the Crust and Upper Mantle, 257–79. Boston, MA: Springer US, 2003. http://dx.doi.org/10.1007/978-1-4615-0103-9_10.

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Rokhlin, S. I., T. K. Bolland, and L. Adler. "Effects of Reflection and Refraction of Ultrasonic Waves on the Angle Beam Inspection of Anisotropic Composite Material." In Review of Progress in Quantitative Nondestructive Evaluation, 1103–10. Boston, MA: Springer US, 1987. http://dx.doi.org/10.1007/978-1-4613-1893-4_126.

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Conference papers on the topic "Wide Angle Reflection/Refraction"

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"Workshop 6—Refraction and wide-angle reflections." In 1985 SEG Technical Program Expanded Abstracts. SEG, 1985. http://dx.doi.org/10.1190/1.1892767.

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Botelho, Marco A., Irshad R. Mufti, and Vicente P. Neto. "Multishot prestack depth migration: An application on wide‐angle reflection and refraction GPR data." In SEG Technical Program Expanded Abstracts 1998. Society of Exploration Geophysicists, 1998. http://dx.doi.org/10.1190/1.1820166.

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Jiao, Lingxiu, Wooil Moon, and W. Kinsner. "Detection of refraction and wide angle reflection signals using the variance fractal dimension trajectory technique." In SEG Technical Program Expanded Abstracts 1997. Society of Exploration Geophysicists, 1997. http://dx.doi.org/10.1190/1.1885646.

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Jiao, Lingxiu, and Wooil M. Moon. "3-D seismic modelling using Lithoprobe AGT’92 high resolution seismic wide angle reflection and refraction data in Sudbury, Ontario, Canada." In 6th SAGA Biennial Conference and Exhibition. European Association of Geoscientists & Engineers, 1999. http://dx.doi.org/10.3997/2214-4609-pdb.221.055.

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Barr, Sandra, H. Ruth Jackson, Deping Chian, John Shimeld, Chris E. White, and Matthew Salisbury. "CONTRASTS IN CRUSTAL CHARACTER BETWEEN MEGUMA AND AVALONIA BASED ON WIDE-ANGLE SEISMIC REFLECTION/REFRACTION PROFILES ALONG THE SCOTIAN MARGIN AND ACROSS NOVA SCOTIA, CANADA." In Northeastern Section - 57th Annual Meeting - 2022. Geological Society of America, 2022. http://dx.doi.org/10.1130/abs/2022ne-374511.

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Matsui, Yutaka, and Yukinori Iizuka. "Basic Performance of Normal Incidence Method for Inspection of Middle Zone of Wall Thickness of LSAW Steel Pipes." In 2016 11th International Pipeline Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/ipc2016-64328.

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This paper describes the performance of the ultrasonic normal incidence method as a technique for inspection of the middle zone of wall thickness of LSAW (Longitude Submerged Arc Welding) steel pipes. Generally, the tandem method is applied to LSAW seam inspection of the middle zone of wall thickness. However, it is difficult to adjust the locations and angles of each probe. Therefore, the normal incidence method using one probe for inspection of the middle zone of wall thickness was studied. Because the probe arrangement is simple, it is possible to reduce the time and effort required to adjust the probe location and angle. In the normal incidence method, it is possible to transmit and receive a mirror reflection because the ultrasonic wave is transmitted perpendicularly to a planar flaw under a high refraction angle. As a result of comparison experiments of the normal incidence method and tandem method, the amplitude of the echo from flat bottom drilled hole (F.B.H.) is 12dB higher in the normal incidence method than in the tandem method. The normal incidence method also has wide area sensitivity in the circumferential direction, however, the amplitude of the reflection echo changes ±25% when the incidence angle of the pipe changes ±0.3°. Thus, in practical applications, strict control of the deviation of the pipe incidence angle is necessary. This suggests that the reliability of this technique can be improved by compensating for sensitivity variations, for example, fluctuations associated with tracking backlash.
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Wadhwa, Abhishek, and Sung-Yong Park. "Optical Analyses of Microfluidic Tunable Liquid Prisms for Enhanced Solar Energy Collection." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-37797.

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We present optical analyses of a microfluidic tunable liquid prism to find its optimized configuration that can achieve wider beam steering as well as less reflection loss and eventually maximize solar energy capture without mechanical tracking. For this study, four different prism configurations are compared from single to quad-stacked ones with various refractive indices of the liquids filled in the prism. Its beam steering capability can be improved by increasing the refractive index ratio between the liquids used and by using higher number of the stacked prisms. The quad-stacked prism is able to steer incoming sunlight with an incident angle of a α ≤ ± 75° at an apex angle of φ ≤ ± 30°, which represents more than 5 times improvement, when it is compared to the single prism using the same liquids. For appropriate liquid material selection, the effect of refractive index ratio, r = n2/n1, on beam steering was additionally studied. However, one considerable issue is the fact that the better beam steering, the more reflection loss. This is because both higher number of interfaces and larger refractive index ratio make more reflection at each of the interfaces. Our reflectance analysis showed that the quad prism performs inferior to the double prism until α = ± 32°, while being of superior beam steering performance. To further reduce the solar energy loss through the quad prism, a modified configuration is proposed with a thin film added to the interfaces. 50 % of the total reflection was reduced. Our technology promises an alternative to a low-cost and high-efficiency solar tracking system capable of beam steering as wide as ± 75° and reflection loss as low as 4.5%, during all daily tracking of the sun.
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Hadley, G. Ronald. "Comprehensive device simulation via solution of the 2-D Helmholtz equation." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oam.1992.mw4.

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The simulation of photonic circuit elements, such as diode lasers, waveguides, couplers, and turning mirrors, has in the past depended to a great extent upon the use of the paraxial beam propagation method. This method, although easy to use and efficient in terms of computer resources, is entirely inadequate to model many of the devices now being fabricated, because of the restricting assumptions employed in its derivation. In order to overcome these limitations, we solve the 2-D (or 3-D) harmonic Helmholtz equation prior to the introduction of restrictions, resulting in a formulation that includes the following three important features: (1) treatment of adjacent regions of widely different indices of refraction, (2) wide-angle (non-paraxial) beam propagation, and (3) reflection. The solution is obtained by using an iterative technique in order to minimize the required storage. Although the method is numerically intensive at present, future progress in solution techniques coupled with the advent of larger and faster computers is expected to make this method more attractive for a variety of applications. We illustrate the capability of this technique by solving several problems of interest, including energy loss resulting from propagation through a large-angle Y-guide splitter, reflectivity of a facet-terminated waveguide, and the performance of waveguides etched with both first and second order Bragg gratings.
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Edgerton, Robert F. "Optical Characterization of TiO2 and SiO2 in Single Films and Double Layer Stacks." In Optical Interference Coatings. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/oic.1992.othd5.

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We have been sputtering TiO2 and SiO2 for use in wide-band anti-reflection coatings on glass. We have made a study of the the optical properties of single material depositions of each of the constituent films on Corning 7059 and Silicon Wafer substrates. We have also taken some of the TiO2 depositions and deposited a SiO2 film on top of them during the same run in which the individual SiO2 sample was deposited. We are interested in knowing if the optical properties of the TiO2 or the SiO2 are affected by the deposition of SiO2 on top of the TiO2. Optical studies have been made of the six types of samples: SiO2, TiO2, and SiO2/TiO2 on the 7059 glass and Silicon wafers. Data has been taken with a Variable Angle Spectroscopic Ellipsometer (VASE ref. 1) from 300nm to 1000nm in wavelength and at a variety of angles of incidence from 50 to 80 degrees. In addition transmission and reflection data near normal incidence has been taken using a VW reflection accessory on a CARY 17DI dual-beam spectrophotometer from 350 nm to 750 nm. First the TiO2 ellipsometric data was analysed. The TiO2 was sufficiently transparent in the visible and near infrared that it was possible to set the extinction coefficient to zero and solve for the index of refraction and physical thickness of the sample. Having established a value for the physical thickness, the ellipsometric data, Psi and Delta, was used to find the value of n and k at each wavelength by a recursive process. After making many studies of several different samples of TiO2, it was found that the simplest way to characterize a particular sample of TiO2 was as a mixture of two extreme material types labeled TiO2 (Low Index) and TiO2 (High Index). We have used the effective medium approximation (EMA) to combine them and use the volume fraction of the TiO2 (Low Index) that is mixed into the TiO2 (High Index) as the adjustable parameter, vf10.
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Antonov, Alexander A., and Maxim V. Gorkunov. "Dielectric Fourier Metasurfaces for Wide-Angle Reconfigurable Anomalous Refraction." In Novel Optical Materials and Applications. Washington, D.C.: OSA, 2021. http://dx.doi.org/10.1364/noma.2021.noth2d.3.

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Reports on the topic "Wide Angle Reflection/Refraction"

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Riedel, M., M. M. Côté, P. J. Neelands, G. Middleton, G. Standen, R. Iuliucci, M. Ulmi, et al. 2012 Haida Gwaii Mw 7.7 earthquake response - ocean bottom seismometer relocation and geophone orientation analysis and quality control of wide-angle P-wave refraction data. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 2014. http://dx.doi.org/10.4095/295551.

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Keen, C. E. Conversion of seismic-reflection time to depth for the Labrador margin, Davis Strait, and Baffin Bay, offshore northern Canada and Greenland, using sonic logs, checkshot surveys, and wide-angle seismic velocities. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 2019. http://dx.doi.org/10.4095/315016.

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Wilson, D., Michael Shaw, Vladimir Ostashev, Michael Muhlestein, Ross Alter, Michelle Swearingen, and Sarah McComas. Numerical modeling of mesoscale infrasound propagation in the Arctic. Engineer Research and Development Center (U.S.), October 2022. http://dx.doi.org/10.21079/11681/45788.

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The impacts of characteristic weather events and seasonal patterns on infrasound propagation in the Arctic region are simulated numerically. The methodology utilizes wide-angle parabolic equation methods for a windy atmosphere with inputs provided by radiosonde observations and a high-resolution reanalysis of Arctic weather. The calculations involve horizontal distances up to 200 km for which interactions with the troposphere and lower stratosphere dominate. Among the events examined are two sudden stratospheric warmings, which are found to weaken upward refraction by temperature gradients while creating strongly asymmetric refraction from disturbances to the circumpolar winds. Also examined are polar low events, which are found to enhance negative temperature gradients in the troposphere and thus lead to strong upward refraction. Smaller-scale and topographically driven phenomena, such as low-level jets, katabatic winds, and surface-based temperature inversions, are found to create frequent surface-based ducting out to 100 km. The simulations suggest that horizontal variations in the atmospheric profiles, in response to changing topography and surface property transitions, such as ice boundaries, play an important role in the propagation.
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Keen, C. E., K. Dickie, L. T. Dafoe, T. Funck, J. K. Welford, S A Dehler, U. Gregersen, and K J DesRoches. Rifting and evolution of the Labrador-Baffin Seaway. Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/321854.

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The evolution of the 2000 km long Mesozoic rift system underlying the Labrador-Baffin Seaway is described, with emphasis on results from geophysical data sets, which provide the timing, sediment thickness, and crustal structure of the system. The data sets include seismic reflection and refraction, gravity, and magnetic data, with additional constraints provided by near-surface geology and well data. Many features that characterize rift systems globally are displayed, including: wide and narrow rift zones; magma-rich and magma-poor margin segments; exhumation of continental mantle in distal, magma-poor zones; and occurrences of thick basalts, associated with the development of seaward-dipping reflectors, and magmatic underplating. The magma-rich regions were affected by Paleogene volcanism, perhaps associated with a hotspot or plume. Plate reconstructions help elucidate the plate tectonic history and modes of rifting in the region; however, many questions remain unanswered with respect to this rift system.
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