The Chaos Characteristic And Modeling Study Of Ambient Noise In Land Seismic Exploration

Land seismic exploration is a common means and methods to find oil andgas fields. In the actual seismic data acquisition process, the desired signal willbe inevitably contaminated by random noise, and the signal-to-noise ratio ofseismic records will also be reduced by random noise, all that will influence theauthenticity and reliability of actual earthquake records. Therefore, we need toeffectively reduce random noise and improve the signal-to-noise ratio. Seismicexploration ambient noise as the main component of random noise, we need tohave a comprehensive understanding about it.Realistic noise generation system is a complex nonlinear system synthesizedby the geomorphic distribution, the coupling of vegetation and earth,underground medium and so on. Therefore, the seismic exploration ambient noisegenerated by external ambient noise source through this system must show strongnonlinearity. Chaos theory as an important part of the non-linear theory has beenwidely used in various fields since it was proposed. In this paper, we will studythe seismic exploration with the help of chaos theory.In the paper we study the chaos characteristic of the seismic explorationambient noise record got from the forest, the desert, the loess tableland, and themountain four measured areas. First, the study for quantitative analysis of thephase-state graph of the ambient noise record of four survey areas shows that thephase-state graph has strange attractor, and the ambient noise is determinedinitially with chaos characteristics. Next, we calculate the maximal Lyapunovcharacteristic exponent and correlation dimension of the ambient noise record ofsurvey areas. From the calculation results we can get that all the maximalLyapunov characteristic exponent of the ambient noise record are greater thanzero and the maximal Lyapunov characteristic exponent of different ambientnoise record is different. The result proves the seismic exploration ambient noisereally has chaos characteristics, and the chaotic extent of different ambient noiserecorded from different measured area is different. Statistical analysis of the maximal Lyapunov characteristic exponent show that the mountain’s average ofthe maximal Lyapunov characteristic exponent is largest, and next is the forest,the average of the desert and the loess tableland is equal and least. Through theanalysis the change curve of correlation dimension with the embeddingdimension of the ambient noise record of four surveyed areas, we can make surethat the ambient noise is generated by the chaos system not generated by therandom system. Finally, we analyze the reasons about the difference of chaoticextent of the ambient noise got from different survey area, and we consider thatthe main influence factors are geomorphic conditions, geological conditions andnatural conditions when the ambient noise is recorded.When we confirm the seismic exploration ambient noise has chaoticcharacteristics, we establish a mathematical model about the realistic noisegeneration system, and we choice the Duffing equation modeling the part of therealistic noise generation system with chaos characteristics. We get theparameters of Duffing equation about the forest and the desert by analyzing theinfluence of output with the Duffing equation parameters and the ambient noisegot from two survey areas. Then we get the input of chaos subsystem proceedfrom the frequency spectrum and the phase-state graph of the ambient noise, thefrequency spectrum express the frequency components and the phase-state graphexpress the chaos characteristic of the ambient noise, and analysis the differencebetween the input of two chaos subsystem. This work lay the foundation for thefurther study of the entire ambient noise generation system.In this paper, we study the chaos characteristic of the seismic explorationambient noise, it is a new understanding and complement of existing understandingof the seismic exploration ambient. Through studying the chaos characteristics,we can get more comprehensive understanding of the seismic exploration ambientnoise, and subtract the ambient noise from physical seismic exploration recordmore clearly.