Illumination Analysis Based On Ray Tracing Theory

This paper focuses on the illumination analysis which is based on ray tracing theory. The principles utilized in this paper include the principle of ray tracing, the principle of Kirchhoff prestack depth migration and the theory of velocity smooth. The main thread of this paper is listed below:the principle of Kirchhoff prestack depth migration is the theoretical foundation of this paper, the target layer is determined according to the result of migration. The theory of velocity smooth is a useful tool. By velocity smoothing of a complicated velocity field, the quality of migration result and the continuity of ray tracing path can be improved. Ray tracing theory is another theoretical basis of this paper. According to the distribution of ray paths in the field, the energy of waves which distribute in the earth can be determined. By placing points averagely in the target lays which have poor imaging quality, and tracing the rays on the surface, we can get the distribution of rays on the surface, so that we can employ illumination analysis and observing system optimization.The principle of ray tracing utilized in this paper is based on the idea of Langan. In this theory, ray path is treated as a independent variable, the position, direction and travel time of ray are all expressed algebraically of arc of ray. In the past , Langan's theory of ray tracing was used to calculate the ray path and travel time. The theory of ray tracing is seldom used in illumination analysis, because illumination is a concept proposed in recent years.Illumination is used to analyze poor energy area and energy masked area. These areas seldom have good image quality because insufficient energy can reach these areas. We can uniformly cover these poor energy areas and assume that sufficient energy can reach, then perform ray tracing on the surface. According to the distribution of rays on the surface, we can determine the range of working place and the distribution of observing system, so that we can design distribution of shots and receivers in auxiliary. The acquired data in this method can have good image quality in theory, this is illumination works.The reason of research is ray tracing from the earth to surface,the illumination analysis and seismic survey optimal design are carried out by the ray tracing result, relying on the reciprocity principle of wave propagation, which is the same in theory with the method of placing shots on the surface, performing ray tracing downwards and reflecting on the target layer. The first method requires placing shots and receivers on the surface, performing ray tracing downwards, and getting the coverage of target layer according to the result of ray tracing. The second method uniformly covers the target layer, perform ray tracing upward, so that the observing system can be designed optimally according to the distribution of rays on the surface.Illumination technique is a tool which can be used in field data acquisition, data processing and interpretation. This paper only studies the usage in data acquisition, that is how to design seismic survey system optimally according to the method. Because the concept of illumination was proposed only a few years ago, there are large spaces for theoretical improvement, there is also large work to do on utilizing illumination analysis on model and practical data processing.