MODELING AND ANALYSIS OF AN ACOUSTIC CHANNEL WITH A MOVING SURFACE

2013 ◽  
Vol 21 (04) ◽  
pp. 1350015 ◽  
Author(s):  
YOUNGMIN CHOO ◽  
WOOJAE SEONG
Keyword(s):  
Travel Time ◽  
Ray Tracing ◽  
Path Dependence ◽  
Moving Surface ◽  
Modeling And Analysis ◽  
Surface Movement ◽  
Delay Times ◽  
Tracing Algorithm ◽  
The Difference ◽  
Ray Path

A ray tracing algorithm for moving surfaces is derived to enable the analysis of surface movement effects. For this, a ray tracing algorithm for frozen surface is modified. By comparing the results from frozen and moving surface ray models allows effects of a moving surface to be investigated. The surface movement effects can be seen with the difference between channel impulse responses from the frozen and moving surface ray models. For an investigation of ray path dependence of the surface movement effects, delay times of surface reflective paths from the two ray models are observed according to transmitted ping time. As the ray path from the source to surface gets longer, difference of travel time results from the two ray models increase. This fact indicates that surface movement effects depend on ray path, in particular travel time until a ray meets a surface.

Comparing Higher-dimensional Velocity Models for Seismic Location Accuracy using a Consistent Travel Time Framework

2021 ◽  
Author(s):  
Michael Begnaud ◽  
Sanford Ballard ◽  
Andrea Conley ◽  
Patrick Hammond ◽  
Christopher Young
Keyword(s):  
Travel Time ◽  
Ray Tracing ◽  
Seismic Velocity ◽  
3D Seismic ◽  
Location Accuracy ◽  
Velocity Models ◽  
Higher Dimensional ◽  
1D Model ◽  
Tracing Algorithm ◽  
2D And 3D

<p>Historically, location algorithms have relied on simple, one-dimensional (1D, with depth) velocity models for fast, seismic event locations. The speed of these 1D models made them the preferred type of velocity model for operational needs, mainly due to computational requirements. Higher-dimensional (2D-3D) seismic velocity models are becoming more readily available from the scientific community and can provide significantly more accurate event locations over 1D models. The computational requirements of these higher-dimensional models tend to make their operational use prohibitive. The benefit of a 1D model is that it is generally used as travel-time lookup tables, one for each seismic phase, with travel-time predictions pre-calculated for event distance and depth. This simple, lookup structure makes the travel-time computation extremely fast.</p><p>Comparing location accuracy for 2D and 3D seismic velocity models tends to be problematic because each model is usually determined using different inversion parameters and ray-tracing algorithms. Attempting to use a different ray-tracing algorithm than used to develop a model almost always results in poor travel-time prediction compared to the algorithm used when developing the model.</p><p>We will demonstrate that using an open-source framework (GeoTess, www.sandia.gov/geotess) that can easily store 3D travel-time data can overcome the ray-tracing algorithm hurdle. Travel-time lookup tables (one for each station and phase) can be generated using the exact ray-tracing algorithm that is preferred for a specified model. The lookup surfaces are generally applied as corrections to a simple 1D model and also include variations in event depth, as opposed to legacy source-specific station corrections (SSSCs), as well as estimates of path-specific travel-time uncertainty. Having a common travel-time framework used for a location algorithm allows individual 2D and 3D velocity models to be compared in a fair, consistent manner.</p>

Rapid solution of ray tracing problems in heterogeneous media

1980 ◽  
Vol 70 (4) ◽  
pp. 1137-1148 ◽  
Author(s):  
C. H. Thurber ◽  
W. L. Ellsworth
Keyword(s):  
Travel Time ◽  
Ray Tracing ◽  
Heterogeneous Media ◽  
Velocity Structure ◽  
Minimum Time ◽  
Local Minima ◽  
Complex Velocity ◽  
Efficient Manner ◽  
Tracing Techniques ◽  
Ray Path

abstract The determination of local earthquake hypocenters and orgin times from first-P-arrival times by Geiger's method requires a technique for finding the minimum travel time (and derivatives) between the source and the station. Sophisticated ray tracing techniques have been developed for this purpose for use in complex velocity structures. Unfortunately, the two common techniques, shooting and bending, are generally prohibitively expensive for routine use in data analysis. The bending method is also particularly vulnerable to the problem of local minima in travel time. A method has been developed known as the ray initializer, which can be used to circumvent these problems in many cases. First, the technique can find a reasonable estimate of the minimum-time ray path in a quick and efficient manner. The velocity in a region local to the source and receiver is laterally averaged to yield an approximate layered velocity model. One-dimensional ray tracing techniques are used to find the minimum-time path for this layered structure. The ray path estimate can then be used as the starting path in a bending routine, a procedure resulting in more rapid convergence and the avoidance of local minima. Second, the travel time found by numerical integration along the estimated ray path is an excellent approximation to the actual travel time. Thus, in many cases, the ray initializer can be substituted for a three-dimensional ray tracing routine with a tremendous increase in efficiency and only a small loss in accuracy. It is found that the location of an explosion, derived using the ray initializer, is nearly identical to a complete ray tracing solution, even for a highly complex velocity structure.

A modified linear travel-time interpolation ray tracing algorithm

2014 ◽  
Vol 50 (7) ◽  
pp. 426-434 ◽  
Author(s):  
Guo Yali ◽  
Han Yan ◽  
Wang Liming ◽  
Liu Linmao
Keyword(s):  
Travel Time ◽  
Ray Tracing ◽  
Tracing Algorithm

Tsunami Ray Tracing Method for Shortest Travel-Time Path

2021 ◽  
Author(s):  
Tung-Cheng Ho ◽  
Shingo Watada ◽  
Kenji Satake
Keyword(s):  
Travel Time ◽  
Ray Tracing ◽  
Tsunami Wave ◽  
Wave Theory ◽  
Ray Tracing Method ◽  
Tsunami Early Warning ◽  
Time Path ◽  
Long Wave ◽  
Ray Path ◽  
Tracing Method

<p>We propose a ray-tracing method to solve the two-point boundary value problem for tsunamis based on the long-wave theory. In the long-wave theory, the tsunami wave velocity is proportional to the square root of water depth, which is available from global bathymetric atlases. Our method computes the shortest travel times starting from each of the two given points and calculates the local ray direction to trace the ray path. We utilize an explicit, non-iterative tracing scheme that exhibits robust results and applies to any tsunami-accessible locations, and the global-shortest travel-time path is derived. In simple and real bathymetry cases, our method demonstrates stable results with neglectable low uncertainties. The ray-tracing method is then applied to analyze the path of tsunamis from different directions to four important bays in Japan. The result shows that tsunami ray paths are significantly influenced by local bathymetry, and some crucial structures, such as trench and trough, behave as the primary routes of this region. Deploying stations near these routes will be most beneficial for tsunami early warning. The existing tsunami-observing system off the Honshu area works well for tsunamis from the east side but slightly deficient for tsunamis from the west side. The far-field ray tracing shows that tsunamis traveling from Chile to Japan through two main routes—one via north Hawaii and the other via the south— depending on the location of the source.</p>

A fast algorithm for two-point seismic ray tracing

1987 ◽  
Vol 77 (3) ◽  
pp. 972-986
Author(s):  
Junho Um ◽  
Clifford Thurber
Keyword(s):  
Travel Time ◽  
Ray Tracing ◽  
Three Dimensional ◽  
Linear Interpolation ◽  
Geometric Interpretation ◽  
Approximate Algorithm ◽  
Velocity Models ◽  
Limit Test ◽  
Ray Path ◽  
Lateral Variations

Abstract A new approximate algorithm for two-point ray tracing is proposed and tested in a variety of laterally heterogeneous velocity models. An initial path estimate is perturbed using a geometric interpretation of the ray equations, and the travel time along the path is minimized in a piecewise fashion. This perturbation is iteratively performed until the travel time converges within a specified limit. Test results show that this algorithm successfully finds the correct travel time within typical observational error much faster than existing three-dimensional ray tracing programs. The method finds an accurate ray path in a fully three-dimensional form even where lateral variations in velocity are severe. Because our algorithm utilizes direct minimization of the travel time instead of solving the ray equations, a simple linear interpolation scheme can be employed to compute velocity as a function of position, providing an added computational advantage.

A New Ray Tracing Method Based on Linear Travel-Time Interpolation

2015 ◽  
Vol 743 ◽  
pp. 845-851
Author(s):  
L.J. Liu ◽  
Z.H. Xie ◽  
C. Yang
Keyword(s):  
Travel Time ◽  
Ray Tracing ◽  
Flaw Detection ◽  
Reverse Direction ◽  
Ray Tracing Method ◽  
Error Accumulation ◽  
Ray Path ◽  
Multiple Cells ◽  
Tracing Method ◽  
Background Area

In the application of industrial flaw detection, the materials to be detected are often a collection of a background area and a small amount of defect areas. In traditional linear travel-time interpolation (LTI) method, the assumption of travel-time linearity will lead to error accumulation when the rays go through multiple cells. In order to reduce the cumulative error in this application, a new ray tracing method is proposed based on linear travel-time interpolation. In our method, calculation points are located on the boundaries between different areas to determine the angle of refraction. Moreover, the minimum travel-time of each point is computed by multidirectional loop strategy, which will make the traced ray path conforms to the condition of minimum travel-time when ray transports from the reverse direction. The simulation results show that using the proposed method to calculate travel-times and paths of tracing rays, it is more rapid and accurate than traditional LTI method and cross-scanning LTI method.

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