台网噪声评估及其对气枪震源激发效果影响的研究

Station network ambient noise level evaluation and its influence on air gun source excitation effect

为了研究背景噪声对长江地学气枪主动源实验激发效果的影响,收集了240个台站激发前72小时的背景噪声数据及20个定点激发的叠加结果进行实验分析.先剔除异常台站,按照国标将台网噪声水平划分为高、中、低3个等级进行评估,从而研究气枪波形信噪比与台站背景噪声的关系.结果表明:(1)台站接收能力与背景噪声水平密切相关;(2)气枪信号的信噪比在一定范围内受背景噪声的影响大于距离衰减的影响;(3)长江马鞍山—安庆流域段不同定点激发的场地条件基本一致;(4)随气枪信号叠加次数的增加,低噪台站的信噪比增长速度快于中、高噪台站,若想获得同样的叠加效果,高噪台站需要的叠加次数远大于低噪台站.

In order to study the influence of background noise on excited effect of air gun active source experiment in the Yangtze River,we collected and analyzed ambient noise data from 240 stations with 72 hours before air gun excited,and superposition results of 20 fixed points excitation.After removing the abnormal stations,ambient noise level of the seismic network was divided into three grades including high,middle and low based on international standard for the assessment,which were used to analyze the relationship between signal to noise ratio（SNR）of air gun waveforms and station ambient noise.The results showed that：（1） the station receiving ability is closely related to ambient noise level;（2）in a certain range,SNR of air gun signal is affected more by ambient noise than by the distance attenuation;（3） the field conditions of the different excited points are basically similar in Ma＇anshan to Anqing river basin of the Yangtze River;（4） with the increasing of air gun signal superposition times,SNR of low noise station is growing faster than that of high noise station,that is,the high noise station needs much more superposition times to get the same result.