Research on the application of underwater node seismograph in land active source detection

Abstract

The precise timing of the active source excitation is very important. In order to obtain more accurate excitation timing, we debugged and installed the underwater node seismometer observation system in the Liujiaxia active source, and recorded the excitation data. Experiments show that the underwater node seismometer observation system can clearly record the excitation signal of the air gun source. At the same time, the ambient noise analysis was carried out for the observation data in calm. The noise power spectral density was lower than the NHNM noise curve, and the ambient noise value of each item was less than −120 dB. Compared with the ambient noise of the instruments erected on the shore, the noise recorded by the underwater seismometer was slightly higher than the noise of the onshore seismometer, which may be related to water waves, wind and ship navigation. Spectrum analysis of excitation data shows that the dominant frequency is within the range of 2～8 Hz, which is consistent with previous research results and can be used as one of the reference stations for recording active source excitation signal in Liujiaxia. The application of underwater node seismometer in land active source detection will be of certain value for improving the observation accuracy of air-gun active source and the construction of air-gun active source seismic monitoring system and data processing.

Keywords

• air-gun active source
• underwater seismograph
• ambient noise
• spectrum analysis