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

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.