The Study, Based On The Grid Before The Spherical Wave Ray Tracing Method

As a fast and effective approximative calculate method of wave field, raytracing has a very important meaning to the research of the seism wave theory and the seism wave's invention and excursion imaging process. The theory foundation of the raytracing is that under the conditions of high-frequency approximate the major energy of the seism wave transmits along the radial trace. The traditional raytracing methods comprise the try-shooting method of the initial value problem and the bending method of the border value problem. In recent years, the Kirchhoff's integral fore-stack depth migrations get much useful in the complex formation imaging. As one of its algorithm basses, the raytracing methods develop very fast. Large number of new algorithms different from the traditional ray-tracing methods have appeared. The main features of these methods are that they aren't limited by the descriptions of the travel-time and raytracing of the seism wave. They set out directly from the principle of Huygens and the Fermat theory and then descript the features of the seism wave fields by adopting the equivalent fore-waves.All traditional raytracing methods set out from the ray-equations and after divergence to the medium they get the travel-time and raytrace from the ray-equations. In the recent years, it concentrates primarily the calculations of the multivalue travel-times.The text expands two ray-tracing methods in common use, which is the finite difference method and the ordered wave front reconstruction method. They have resolved the defects of the traditional ray-tracing methods, but themselves have some defects.Basing on tallying up the other people's work, contraposing the virtues and the defects of in being, the characteristics of models of geological and seism waves spread under the ground in the practical exploration, we improved the method of Schneider. It based on the disciplinarian that seism waves spread with spherical surface waves in the isotopic medium. It regard local small area in the discrete medium as isotopic medium. We introduced a raytracing method of improved spherical surface fore-waves by a supposing of spherical surface waves, it is spherical surface fore-waves raytracing method basing on grid. We gained a calculate formula of seism waves travetime in any point of grid. We discussed the rationality of the new method. We also discussed the precision and efficiency of this method by calculating in several representative geologic models designed by equality and inequality medium by this method. We considered that the method of spherical surface waves raytracing basing on the grid combined the virtues of the grid method. It is precise and high efficient in calculating traveltime and raytrace. It is a perfect method of raytracing.