Study On Directionality Of Ambient Noise In Land Seismic Exploration

Seismic exploration is the most effective method in various geophysicalexploration methods of petroleum exploration. Artificial seismic exploration onland, collecting seismic data, and then processing the data can judge theunderground geological structure and buried oil. The whole process of the seismicexploration will be influenced by all kinds at any time. Noise suppression, tostrengthen the effective wave and to improve the signal-to-noise ratio of seismicdata has always been the goal of all kinds of technical methods in seismic signalprocessing. With the complexity of exploration area and the deepening of theformation, the seismic exploration has the higher request. In order to make betteruse of the various seismic processing technology, and expand new noisereduction measures, a more detailed and comprehensive investigation andanalysis on the characteristics of the noise is required.Ambient noise in land seismic exploration is a kind of inherent random noisein the exploration area, and it exist in the whole process of seismic exploration.Previous domestic and foreign scholars study the ambient noise confined to timestatistical properties such as mean, variance and correlation function. In recentyears,3-D seismic exploration technology has developed, and3-D spatial databody is obtained. So3-D space filtering technology become the hotspot.Therefore, the study of spatial property of ambient noise have also been putforward. This article introduces a spacial property from oceanography, which iscalled directionality, and studies the property preliminarily under the3-D seismicexploration observation system.Directionality of ambient noise reflects the propagation characteristics ofnoise. The waveform is mainly similar because of the same noise causes in theprocess of propagation, so we study the directionality of ambient noise byanalyzing waveform similarity of the noise data. The analysis of waveformsimilarity uses multi-channel relation theory, which is based on the principle oferror energy minimization. Use multiple standards such as energy ratio standard to measure the similar degree of part waveform of multichannel noise data. Webuild a model of directionality under the three dimensional seismic explorationobservation system. Assume a direction of propagation firstly, and then extractthe data collected by the receiver in noise propagation according to thearrangement situation of the receiver in each line and each channel. If thesimilarity of any part waveform is very high, we consider the noise is propagatedin the assumed propagation direction. That is to say the noise directivity is exist.According to the model of directionality of ambient noise in athree-dimensional seismic observation system, we do a lot of simulationexperiments. Firstly, we simulate the random signal with similar waveform,analyze similarity using multi-channel correlation, compute energy ratio standard,and verify the correctness of the theory. Secondly, we simulate multi-channelrandom signals, which has similar part waveform and time delay. Define a timewindow for scanning signal, extract the part signal within the time window, andanalyze the similarity of part waveform with multi-channel correlation. Theresults of experiments show that using time window to scan and extract data canget part waveform with high similarity in the random signal.Finally, we process the practical seismic data.3-D seismic exploration isused in desert region. We intercept the noise before arrival of multiple lines under3-D observation system, and set up the directionality model. Assume the noisepropagation, extract the actual noise data, use time window scanning andmulti-channel correlation analysis. Experiments prove that we can find the noisewith similar part waveform in the assumed propagation direction. So, wepreliminarily think that the directionality of ambient noise in land seismicexploration is exist.