The Research On Spatiotemporal Characteristics Of The Land-Seismic-Exploration Random Noise

Land-seismic-exploration is one of the most important methods for the mineral prospecting. Due to the complexity of surface and near-surface conditions, we need to improve the seismic-exploration technology to detect the resources in deep and irregularlayers. In the procedures of seismic-exploration(acquisition, processing and interpretation), seismic data processing is very important. Especially, suppression effect of random noise impacts on the subsequent series of processes, including velocity analysis,migration imaging and inversion. However, when the seismic data is collected in the field,the detectors receive the seismic record contains a lot of random noise information,especially when the exploration target is more complex, the signal is very weak and the noise is strong, the overall record has low signal noise ratio. How to suppress random noise under the condition of low SNR is particularly important for seismic exploration.Due to the low signal noise ratio, the signal energy is weak. The systematic research on spatiotemporal characteristics of the land-seismic-exploration random noise can effectively suppress random noise to guide the random noise suppression method’s selection, improvement and suppression strategies. Until now, the characteristics of the random noise have not been deeply studied. It has been the obstacles for the increasing signal noise ratio of seismic records and the the improving of the seismic-exploration random noise attenuation methods. For improving the noise attenuation techniques, the proper understandings about the properties of the seismic-exploration random noise are acquired. From this viewpoint, the research about the characteristics of the seismic random noise has a great significance.In this dissertation, we mainly focus on the time domain, space domain and spatiotemporal characteristics of the seismic-exploration random noise. The Gaussianity,stationarity, linearity, power spectral density and similitude of the seismic-exploration random noise is investigated. We compare random noise spatiotemporal distribution characteristics in different acquisition environment(grassland, desert, hilly areas, forest belt), and analyze the relationship between the environment and the spatiotemporal characteristics of random noise. On this basis, the influence of the complexity of the environments and the noise duration on the spatiotemporal characteristics of the random noise is analyzed. Furthermore, we explain the accurateness of our findings by taking the noise generating mechanism and environment features into consideration.The main findings of this dissertation are summarized as follows:By applying the Shapiro-Wilk testing methods and the analyzing of the high-order moments, the Gaussianity of the seismic-exploration random noise is studied. In this study,the kurtosis and the skewness of the seismic-exploration random noise is investigated. Theresults show that the seismic-exploration random noise has a great difference from the Gaussian process. On this basis, we apply the Shapiro-Wilk testing methods to scientifically study the Gaussianity of the random noise. The results indicate that the Gaussianity of the random noise has a great relationship with the properties of the collected environments. The seismic-exploration random noise in a simple environment is always superior to the noise in a complex environment in terms of the Gaussianity. By analyzing the Gaussianity testing results, we obtain that the portions of the non-Gaussian noise data are very huge. It means that the seismic-exploration random noise is a non-Gaussian process.Our dissertation is one of the first attempts to investigate the stationarity of the random noise by applying the stationarity testing methods based on time-frequency(TF)analysis and surrogates. At the same time, we test the stationarity of the random noise with different duration. The basic idea of the testing methods is to assess the stationarity of the testing series by compare its TF features with those of its surrogates. We analyze the properties of the random noise in different environments. The results of our study suggest that the seismic-exploration random noise is not stationary. The properties of the noise change with the time-length of the noise and complexity of the acquired environments.The results indicate the stationarity of the noise in a simple environment is superior to that of the noise in a complex environment. Besides, we also compare the stationarity of the noise in different time-length. Based on this, it is shown that short noise is always more stationary than the long one. We also use some experiments to prove the correctness of our findings.In this dissertation, the Thomson’s PSD estimation method is used to analyze the power spectral density(PSD) of the seismic-exploration random noise. In this dissertation,we use Thomson’s PSD estimation method to investigate the spectral properties of the random noise. The results indicate that the noise is not a white noise process. The spectral of the noise is related to the features of acquired environments. The energy of the noise in a simple environment, e.g. desert and grassland, is concentrated in low frequencies. Thus,it can be seen as low-frequency-narrow-band color noise. However, the noise in a complex environment, e.g. forest belt and hilly areas, has more energy in high frequencies. In contrast, the noise in those environments is wide-band. It can be viewed as wide-band color noise. In addition, we also investigate the similitude of the seismic-exploration random noise. Our findings indicate the similitude of the noise changes with the properties of the acquired environment conditions. There is similitude existed in the random noise records from a simple environment. However, it is not obvious for the noise in a complex environment. On this basis, we combine the features of the acquired environment and the results of the stationarity analysis to give a reasonable explain to the findings in similitude analysis.In this dissertation, the Delay Vector Variance(DVV) and Quantified Delay VectorVariance(QDV) methods is used to investigate the linearity of the seismic-exploration random noise. We analyze the linearity of the noise data collected in the different environments. The results show that the seismic-exploration random noise cannot be simply classified as a linear process or a non-linear process. The linearity of the seismic-exploration random noise has a strong relation with the collected environment conditions. For a simple environment, the linearity of the random noise is great, and it can be seen as a linear process. However, for a complex environment, there are some non-linear components existing in the random noise. From this view, the seismic-exploration random noise in a complex environment should be considered as the production of a non-linear process.In this study, we scientifically investigate the Gaussianity, stationarity, linearity,power spectral density and similitude of the seismic-exploration random noise. We check the characteristics of the random noise collected in the different geology environments,and compare the corresponding results of the different noise data. On this basis, we obtain the general understandings about the spatiotemporal characteristics of the seismic-exploration random noise. The results indicate that the traditional understandings about the seismic-exploration random noise characteristics have their own limitations. The characteristics of the seismic-exploration random noise have strong relationship with the collected environment conditions. Moreover, the noise durations also have influence on the properties of the random noise. On this basis, we prove the correctness of our findings by the theoretical analysis and the proper experiments. In general, the findings of our dissertation provide a new understanding about the seismic-exploration random noise characteristics. The findings of our dissertation can also be used as the theoretical foundations for improving the denoising techniques and modeling research for the seismic-exploration random noise. In conclusion, our study has the great practical significance and application potentials.