| Around the first break tomography, in order to gain the velocity model of the near-surface,we ues the first break data.This paper studied the first break picking method of seismic data, improved the ray tracing algorithms, and put constrained methods in SIRT tomography inversion algorithm, and developed the tomographic imaging software. Using the model and real data on the software and we obtain good results.Firstly, this paper Studies and summarizes the first break picking of seismic data method. Summarizes the basic principles of ray tracing, in order to quickly and accurately to get the first break ray path and the first break time, this paper improved the method about high precision fast ray tracing with multi-retracing. View of the first break tomography method requires the speed and accuracy of the ray tracing, this paper uses several measures on the ray tracing algorithm and calculating efficiency to improve the ray tracing method. After improvement, the ray tracing method can meet the requirements of precision and speed to calculate quickly and accurately. Model test results prove that: the ray tracing method is a fast and effective, high accuracy first break ray tracing method, fully consistent with the first break tomography requirements.Based on the conclusion of several common principles of the inversion method, select the SIRT inversion method and programmed with C programming language. Add inversion relaxation factor to adjust the convergence rate, and also using a variety of reasonable and effective methods for restraint. These constraints include the range of velocity restriction, velocity extrapolating, velocity smoothing, layer constrained and so on. These constraints greatly improved the inversion accuracy and image quality of the SIRT method means. Model and actual data calculation shows that the inversion method is applicable.In this paper, the building of initial model is researched too, and gets several methods to build different initial modeling. It's good for raising the inversion's speed and reliability. In the model test and practical application, there are some rules about data processing and the choice of inversion parameters to follow .This paper summarizes some of them.Finally, we develop the tomography software using the QT programming language. We formed a flow of first break inversion, including data loading, data preprocessing, building the initial model, forward, inversion, QC, and displaying the maps. The system is running good and stable, the practical application also achieved good results. |
