Point Ray Tracing Research Articles

Progress toward an acoustic point to point ray tracing method in a stratified atmosphere with wind

NASA is investigating acoustic propagation capabilities to accommodate a point to point propagation prediction scheme defining a ray between a specific source–observer pair in an inhomogeneous stratified atmosphere with wind. A 4D space-time ray method based on the null geodesic equations yields two main benefits over classical 3D Euclidian reduced ray equations: (1) it poses a valid two point boundary value problem for the rays connecting two locations; and (2) the solution method is valid throughout the whole domain including at ray turning points without the need for piecewise definitions. The resulting two point boundary value problem and the constant horizontal slowness vectors, which are a result of the stratified medium assumption, allow the desired (t, x, y, z) ray trace. The presentation highlights the equations and inputs required to solve the 4D ray trace. The solution to this two point boundary value problem will create the groundwork for efficient future NASA propagation codes.

Geological Structure Investigation of Shallow Layers by the Explosion Seismic Survey Tomographic Technique

The detailed P-wave velocity structure of the surface layers in the sea area off Kyushu, Japan, was analyzed using a three-dimensional (3-D) tomographic method for explosion seismic refraction and reflection surveys. Approximately 1,830 P-wave arrival times received from 15 rounds of explosion seismic surveys were used in the structural analysis of the two-dimensional (2-D) profile. The 3-D pseudo-bending technique, which is a fast algorithm for two point ray tracing, is used in forward modeling. The conjugate gradient (CG) algorithm was used to solve the discrete linearized equation of the travel-time residuals. The velocity structure obtained from the tomographic technique indicates heterogeneity in the lateral and vertical directions for seismic waves within in the study area. The sedimentary layer is thin near the coast and thickens gradually off the coast. The boundary contours of sedimentary layers reveal complicated serpentine curves. Lateral and/or vertical convex and concave structures are prominent in the contours. The scales of some concave and convex anomalous velocity structures are small; anomalous structures on a [Formula: see text] scale were identified. This might imply that a high resolution tomography imaging technique can be introduced in shallow-structure surveys. The explosion seismic survey tomographic technique characterizes the complicated structure, geometry and physical properties of abnormal objects well, and tomographic inversion of the explosion survey is available for detailed geological structure surveys and resource explorations, especially for resources such as oil, gas and minerals in complicated geological conditions. The calculated convergence velocity and stability of the tomography technique are also of a high standard.