Study On The Algorithms Of Velocity Analysis And NMO Correction For Vibroseis Data Processing

At present, as a non-explosive source, vibrator has smaller destruction and other advantages than explosive source, so it is widely used in urban exploration and shallow exploration. But when the various researches of the vibrator system and the field experiment are making a good program,the vibrators also face with an unprecedented specificity, which mainly reflect in the structure of the source, the source excitation signal, detection methods of seismic signal and data processing methods. On the one hand, for data processing in which, the different structures of the source and scanning signals make the original seismic records received on the ground are also different. But the conventional data processing using common software are usually for the pulse signal, so when processing the long sweep signal of vibrators, staff need to do some special processing such as relevant, high-end spectrum, the wavelet transform and so on using other software firstly, and then convert the processing results to the file format that the common software support, which will inevitably increase the workload of the staff seriously when deal with a large amount of data. On the other hand, the algorithms of some special processing methods used are complex, which make the computation large and the speed of execution slow. Therefore, in order to adapt to the particularities of vibrator data processing, it is necessary to develop an open seismic data processing software which is suitable for vibrators to enhance the efficiency. Considering overall, the software should have the characteristics like the Windows development platform, high processing speed, secondary development, in view of which we need to study on the every algorithms of the software data processing firstly. Based on the common ssing software both at home and abroad, aiming at the specificities of vibrators seismic data processing software, this paper introduced the total design of the primary function, the softweismic data-procesare configuration, the data structure and GUI interface firstly. And then, because the data processing for vibrators can be divided into the preprocessing, the substantial processing and the subservience processing,in which the substantial processing is again divided into the horizontal stack processing and the migration processing. And in this paper, all algorithms of the preprocessing and the horizontal stack were researched, in which the design of algorithms for the velocity analysis and the dynamic correction were studied on focus.About of the preprocessing module, in this paper, the algorithms design of which primarily include the import and export of the seismic data, the display of data, correlation, dynamic equalization and the sort of CDP trace, and the algorithms design of power spectrum and linear dimension frequency filtering were introduced also for the sake of filtering noise. In addition, this article also presented the processing results using these algorithms when applying to the simulation data and actual measured data, which prepared for the next algorithms design of velocity analysis and dynamic correction in horizontal stacking module.And for velocity in this paper, several common velocity analysis methods were compared, and considering the small computation and high processing speed that the vibroseis required, the method of velocity spectrum was selected to be the preferred velocity analysis method of the software. However, for the shallow seismic exploration of vibrators, the reflected wave is seriously interfered by the surface wave and other interference wave. So the sharp of the peak is not enough which make the velocity to pick up difficult, and the processing speed is low. To solve this problem, this paper introduced an improved velocity spectrum that includes the parameters optimization and the data optimization involved in the velocity analysis. And the parameters are about the time windowΔt0, sampling density of velocityΔνand the stack window of amplitude, the selection method of which is to test the parameters in a range from wide to narrow, and then determine the reasonable parameters. And because the energy of the disturbed wave is stronger than the reflected wave in the shallow seismic exploration, so the data optimization is about the energy balance between the deep layer and the shallow layer. In order to test the correctness of the improved velocity spectrum, this paper introduced the simulation of the seismic data in two seismic models, and processed it with the improved velocity spectrum method, the results showed that error rate of the velocity spectrum analysis for the simulation data is about 0.1 percent and the processing speed can be reduced to 1/10. Further, the improved velocity spectrum method was applied to process the wild seismic data of vibrators which was measured at Qinjiatun in the city of Changchun, and the velocity results were also used in the dynamic correction. All the results showed that the improved velocity spectrum method can effectively analyzed the correction velocity, and compared with the conventional velocity spectrum, the improved velocity spectrum can speed up the processing speed based on the effect of the velocity spectrum, and can make the operation time reduce to 1/20 around.Finally, based on the velocity analysis, the algorithms of dynamic correction and horizontal stacking have been introduced in this paper. Because the efficiency of the arithmetic for common dynamic correction is low, this is unsuitable for the vibroseis seismic data processing in PC environment. For this reason, a fast dynamic correction method called"group moving"was adopt instead of the common dynamic correction method using "point-by-point shifting". Fast dynamic correction divide all the sampling points into groups according to dynamic correction value, and the sampling points in one group have the same moving distance while in adjacent groups have a moving distance which differ a sample interval. Therefore, the dynamic correction using"group moving"instead of"point-by-point shifting"can improve the efficiency of operation. In order to test the correction of the algorithm,before using the dynamic correction and the horizontal stacking algorithms to process the wild data, this paper firstly introduced the processing of the simulation seismic data, and the results showed that the implementation time of procedures making use of the rapid dynamic correction can be reduced to 1/4 around. Based on the simulation, this paper referred to the dynamic correction and the horizontal stacking procession for the field vibrators seismic data measured at Qinjiatun in the city of Changchun using the velocity picked up from the velocity spectrum. And the results showed that the reflection lineups in shallow layer can be corrected even by the dynamic correction and the target reflector in shallow layer can also be clearly detected from the corresponding horizontal stacking time section, in addition, the horizontal stacking time section obtained by the algorithms in the paper had higher resolution than by other software, but there were still some problem of poor stack quality at the large offset and the deep zone need to be improved.