The Study Of Passive Imaging Method Of Seismic Interferometry

Seismic interferometry is a new method of seismic exploration which isprevalent in recent years. It is based on the reciprocity equations of convolution andcorrelation types. With the seismic interferometry technology, new seismic data canbe synthesized from the original data, which have higher SNR and resolution.Passive seismic imaging is one of important applications of seismic interferometry.In conventional seismic exploration, multiple waves, background noise, tremorcaused by natural earthquake are regarded as noise, reducing the SNR, making theresolution decline. But in fact, these noises also contain much useful informationwhich can be used. Passive imaging of seismic interferometry is just the method thatuses the microseisms or background noise to image the underground geologicalstructure. Since the power of seismic signal form the passive sources is weaker thanthat from the artificial source, the SNR of the passive data is pretty low. It is difficultto process them directly. Through the seismic interferometry, we can reconstruct thedata to get new data so that it can avoid the effect of certain complex medium andcomplex sources. At the meantime, the synthesized data have higher SNR and canreflect locality properties of some complex geological structure.In this paper, we investigate the theoretical principle of seismic interferometry;analyze the relationship between time shift and correlation. The math basis ofseismic interferometry is the reciprocity equation. We derive the reciprocityequations of convolution and correlation types. These two equations are thefoundational equation for the seismic interferometry that varieties of applications ofinterferometry are based on. We simply the reciprocity with far-field approximateand illustrate the physical significances of two types of reciprocity equations.We illustrate the some applications of seismic interferometry in detail. The mainaim of seismic interferometry is to synthesize the new data by constructing theoriginal data which can better reflect the geological information of the medium,increasing the SNR and resolution. In this paper, we investigate the theories of VSPâ†'SSPcorrelation transform,VSPâ†'SWPcorrelation transform,SSPâ†'SSPtransform and VSPâ†'VSPcorrelation transform. Analyze theadvances of transformed data to the original data. At the meanwhile, we explore theissues that might be encountered when the seismic interferometry is applied to theactual field. Finally, we study the one of the most important application ofinterferometry——passive imaging of seismic interferometry; We investigate theprinciples of passive imaging of interferometry. Based on the reciprocity ofcorrelation type, we derive the foundational equation of seismic passive imaging,that is the relationship between the transmission and reflection. We synthesize thevirtual sources gather by numerical simulation. After processing, we get the stackprofile, through the contrasting to model, verify the feasible of the passive imagingof seismic interferometry. We change the distribution of sources to explore theeffects of imaging results. We investigate the relationship between the seismicwavelet and imagine results. Then we study the effects of reception time on theimaging results the analogy among the results of numerical simulation. Finally, weexplore the application to the complex medium through the numerical simulation forcomplex medium.