The Study And Application Of Noise Suppression Method In Seismic Exploration

With the generation and rapid development of digital signal processing, it is widelyused in the biomedicine, image video, radar, communication, aerospace and geophysicalexploration and so on. Seismic exploration is the primary exploration method in geophysics.Seismic data which are contaminated by noise can't be directly used for inversion andinterpretation. In order to obtain results of the inversion and interpretations more accurateand reliable, the signal to noise ratio of seismic data need to be improved by digital signalprocessing.From the perspective of digital signal processing, seismic noise reduction methods andtechniques of research began in the 1960s. From the beginning of digital Wiener filteringmethod introduced to seismic exploration, denoise technology rapidly developed andgradually formed the basic theory of digital signal processing in seismic. Seismic noiseincludes random noise and coherent noise. The random noise has not fixed frequency,certain apparent velocity and direction of propagation and it appears random in the entireseismic record. Its frequency band is very wide. So it is difficult to attenuate by thedifference of frequency and direction of propagationbetween the random noise andreflected signal.Wiener filter is the earliest and most classic method to suppress random noise inseismic. It require to known the correlation or spectrum characteristics of signal and noise.In fact, it is difficult to obtain the correlation or spectral, so the result of Wiener filter is notsatisfactory. At the same time, Wiener-Hoff equation is an ill-posed problem. In order toovercome the ill-posed, the classic method for solving Wiener-Hoff equation includes thespectral factorization and Bode-Shannon method (pre-whitening method). The thinking ofregularization is introduced to improve these shortcomings of Wiener filter in this thesis.The regularization is the general method for solving the ill-posed problem. At the sametime, the Wiener filter response can be constrained by regularization term when thecorrelation or spectrum is estimated inaccurately. The goal is to let the filter response asclose as possible to the optimal Wiener filter response. In the one-dimensional case, weproposed the regularization constraint term about the first derivative of estimated signal. We derived the impulse response and frequency response of Wiener filter under theconstraint. The regularization parameter is discussed and given the analysis formula withthe actual. The analysis formula makes the regularization constraint Wiener filter moreeasily achieved. In the two-dimensional case, we proposed the regularization constraintterm about the gradient of estimated signal. We derived the constraint Wiener filterfrequency response in the thesis. We test the 1D constraint Wiener filter with synthetic andactual data, the results show that 1D constraint Wiener filter has more force capacity indenoising than Wiener filter. The reflection signal loss less after 1D constraint Wienerfiltering than after Wiener filtering, especially for high frequency signal.The coherent noise has significant kinematic characteristics, certain frequency andapparent velocity. Such as ground-roll, multiple, sound, and industrial electricity, etc.Ground-roll is main coherent noise in land seismic exploration. It's serious interferencewith the signal to noise ratio. Therefore, the suppression of ground-roll is an important partin seismic exploration.Ground roll is a particular type of Rayleigh wave that occurs in the zone of lowvelocity near the surface and has high amplitude, low frequency and low velocity. Groundroll is also dispersive and its distribution likes a broom in the form of near a straight line.Current processing methods of eliminating ground roll include frequency filtering, FKfiltering and Radon transform and so on. The correlation between ground roll and reflectedsignal and the frequency band which is always overlaped, lead to the reflection signallossing with different degrees in frequency filtering or FK filtering. Radon transform isbased on the linear of Ground roll in seismic records. In Radon domain, ground roll is"energy point", it can be clearly separated form reflection signal. However, due to theendpoint effect and cut-off, the ground-roll can not completely suppressed and thereflection signal is distorted.Trace transform is a developing pattern recognition method in recent years. It has beensuccessfully used for object recognition. The Radon transform is a special case of the Tracetransform, that is to say trace transform is the generalization of Radon transform. Its featureis that the different functional defined on the line set can be choose. But the Radontransform is an integral operation on the line set.In the thesis a new method based on trace transform is proposed for suppressingground roll. This method is integral operation of directional derivative of function along the line set, called directional derivative trace transform. The inverse directional derivativetrace transform is derived by using the properties of Fourier transform and Hilberttransform. Its purpose is to reconstruct the original function. The directional derivativetrace transform of seismic records is composed of two parts, one part mainly is representground roll; the other part mainly is represent reflection signal (relative to the first part). Inthe Radon domain the ground roll and reflection signal is a whole. Because of the endpointeffect and the overlaps of ground roll and a few reflection signals, it is difficult toaccurately determine the scope of the ground roll. So the ground roll can't be completelysuppressed. The endpoint of ground roll will remaining and few reflection signals will alsobe suppressed. However, in the trace domain the seismic record consists of two parts.According to the two parts ground roll can be more accurately determined, which makes theground roll suppressed more thoroughly. In the thesis presents the formula of determiningthe scope of ground roll is presented and the law of choice parameter is illustrated byexperiments of different models.In order to understand the ground roll in detail, the ground roll generation, propagationand characteristics are discussed in detail in the thesis. The seismic record that containsground roll is simulated from simply to complexly. Using the directional derivative tracetransform to suppress the ground roll in difference models. The analysis of waveform andspectrum before and after ground roll attenuation shows that the proposed method caneffectively suppress the ground roll and the effect is better than Radon transform. Theeffectiveness of the proposed method is also proved by law data processing.