排序方式： 共有8条查询结果，搜索用时 15 毫秒
1
1.
The numerical tracing of short ray segments and interpolation of new rays between these ray segments are central constituents of the wavefront construction method. In this paper the details of the ray tracing and ray-interpolation procedures are described. The ray-tracing procedure is based on classical ray theory (high-frequency approximation) and it is both accurate and efficient. It is able to compute both kinematic and dynamic parameters at the endpoint of the ray segments, given the same set of parameters at the starting point of the ray. Taylor series are used to approximate the raypath so that the kinematic parameters (new position and new ray tangent) may be found, while a staggered finite-difference approximation gives the dynamic parameters (geometrical spreading). When divergence occurs in some parts of the wavefront, new rays are interpolated. The interpolation procedure uses the kinematic and dynamic parameters of two parent rays to estimate the initial parameters of a new ray on the wavefront between the two rays. Third-order (cubic) interpolation is used for interpolation of position, ray tangent and take-off vector from the source) while linear interpolation is used for the geometrical spreading parameters. 相似文献
2.
Three observational data sets are used to construct a continuous record (1850-2001) of April ice edge position in the Barents Sea: two sets of Norwegian ice charts (one from 1850 to 1949 and the other from 1966 to 2001) and Soviet aircraft reconnaissance ice extent charts from 1950 to 1966. The 152-year April ice extent series is subdivided into three sub-periods: 1850-1899, 1900-1949 and 1950-2001. For each of these study sub-periods, a mean April ice edge and a set of anomalies (differences in position between a given April and the mean April ice edge) are computed. The calculations show the mean ice edge position retreated north-eastward over the 152-year period, with the greater retreat seen in the changes from the 1850-1899 sub-period to the 1900-1949 sub-period. The distribution of the standard deviation of the ice edge anomaly over the linear distance along the mean ice edge shows no substantial difference between any of the three periods of the study. Within each study period, the maximum variation is observed in the sector bounded by the 25°E and 49° E meridians, which covers the main pathway of the warmer water flow from the Norwegian Sea. 相似文献
3.
Gjøystdal Håvar Iversen Einar Laurain Renaud Lecomte Isabelle Vinje Vetle Åstebøl Ketil 《Studia Geophysica et Geodaetica》2002,46(2):113-164
Throughout the last twenty years, 3D seismic ray modelling has developed from a research tool to a more operational tool that has gained growing interest in the petroleum industry. Various areas of application have been established and new ones are under development. Many of these applications require a modelling system with flexible, robust and efficient modelling algorithms in the core. The present paper reviews the basic elements of such a system, based on the open model concept and the wavefront construction technique. In the latter, ervený's dynamic ray tracing is an intrinsic part. The modelling system can be used for generating ray attributes and synthetic seismograms for realistic 3D surveys with tens of thousands of shots and receivers. Moreover, some other types of application areas are illustrated: Production of Green's functions for prestack depth migration and hybrid modelling (combined ray and finite-difference modelling), attribute mapping and illumination analysis, both for survey planning and interpretation. Finally, the concepts of isochron rays and velocity rays related to seismic isochrons have been introduced recently, with very interesting future applications. 相似文献
4.
T. Vinje 《Applied Ocean Research》1991,13(6):297-306
5.
A new 3D wavefield modelling approach based on dynamic ray tracing is presented. This approach is called wavefront construction, and it can be used in 3D models with constant or smoothly varying material properties (S- and P-velocity and density) separated by smooth interfaces. Wavefronts consisting of rays arranged in a triangular network are propagated stepwise through the model. At each time step, the differences in a number of parameters are checked between each pair of rays on the wavefront. New rays are interpolated whenever this difference between pairs of rays exceeds some predefined maximum value. A controlled sampling of the wavefront at all time steps is thus obtained. Receivers are given multiple-event values by interpolation when the wavefronts pass them. The strength of the wavefront construction method is that it is robust and efficient. 相似文献
6.
T. E. Vinje 《Meteorology and Atmospheric Physics》1967,16(1):31-43
Summary Micrometeorological measurements made at Norway Station, Antarctica, indicate that the exchange of sensible heat between air and snow is excecuted by the aeration. The existence of a laminar sub-layer over permeable snow is in this connection questionable. A zig-zag profile found in the mean vertical distribution of the temperature near the surface indicates that the turbulence in this layer is systematized. From the temperature profile we have estimated the vertical displacement of the elements, and in connection with measurements of the frequency of temperature variations near the surface, we have calculated the heat transfer in the air. An expression for the eddy heat transfer coefficient which contains fairly well defined quantities and proportions has been derived.
With 1 Figure 相似文献
Zusammenfassung Aus mikrometeorologischen Messungen auf der Norway Station, Antarctica, wird gefolgert, daß der Austausch von fühlbarer Wärme zwischen Luft und Schnee durch Bodenatmung vor sich geht. Die Existenz einer laminaren Grenzschicht über einer porösen Schneedecke wird in diesem Zusammenhang bezweifelt. Die vertikale Temperaturschichtung der bodennahen Luftschicht zeigt ein Zickzack-Profil und deutet darauf hin, daß die Turbulenz in dieser Schicht systematische Züge enthält. Aus den Temperaturprofilen wird die vertikale Verschiebung der Turbulenzelemente geschätzt. Die gemessene Frequenz der Temperaturschwankungen in der bodennahen Luft ermöglicht die Berechnung der Größe des Wärmeaustausches. Abschließend wird ein Ausdruck für den turbulenten Wärmeaustausch-Koeffizienten abgeleitet, der verhältnismäßig wohldefinierte Größen und Verhältnisse enthält.
Résumé Sur la base de mesures micrométéorologiques effectuées à Norway Station, Antarctique, on déduit que l'échange de chaleur sensible entre l'air et la neige s'effectue par le truchement de la respiration du sol. On met alors en doute l'existance d'une couche limite laminaire au-dessus d'une couverture poreuse de neige. L'étagement vertical des températures dans les couches d'air voisines du sol présente un profil en zig-zag. Par conséquent, la turbulence montre, dans cette zone, des traits systématiques. Par le moyen des profils de température, on estime le déplacement vertical des éléments de turbulence. La fréquence mesurée des variations de température au voisinage du sol permet de calculer l'importance des échanges de chaleur. On en tire, pour terminer, une expression du coefficient d'échange turbulent de la chaleur, expression qui contient des grandeurs et des relations relativement bien définis.
With 1 Figure 相似文献
7.
8.
1