甚宽频带地震计自噪声测试方法对比

Comparison of self-noise measurement methods for very broadband seismometers

在河北红山巨厚沉积与地震灾害国家野外科学观测研究站,对JS-120型甚宽频带地震计采用2台和3台地震计同址比测法进行同址比测。选取连续600小时观测数据样本,基于分频带概率统计法,提取自噪声优势概率典型值,分析测试结果差异。结果表明,3台法可通过互功率谱之比校正地震计之间传递函数的差异,得到的自噪声水平比2台法更低,结果更加稳定;当比测地震计之间性能存在差异时,自噪声较高的地震计会影响记录的相干性,导致其他地震计自噪声结果偏高;由于安装过程中存在不一致性,在接近二类海洋噪声频段的0.1—1 Hz频带,地震计自噪声功率谱曲线形态发生变化,且2台法表现更明显;在0.04 Hz以下的低频段,地震计自噪声水平较高,与观测背景噪声接近,在进行低噪声科学实验观测场地遴选和背景噪声水平评估时,应考虑低频段地震计自噪声的影响。

A collocation test for the JS-120 very broadband seismometers was conducted with the methods of two and three seismometers at the Hebei Hongshan National Observatory on Thick Sediments and Seismic Hazards.We selected 600 hours of continuous observation record samples and extracted typical self-noise values with advantage probability based on the sub-band probability statistics method to analyze differences in test results.The results show that the three seismometers method can correct the transfer function difference between seismometers through the ratio of cross-power spectra,and the result is lower and more stable than the two seismometers method.When the performance of seismometers differs,seismometers with higher self-noise will affect the coherence of the records,leading to higher self-noise results for other seismometers.Due to inconsistencies in the installation process,the shape of the seismometers’self-noise power spectrum curves change in the range of 0.1 to 1 Hz close to the secondary microseism frequency band,and the performance of the two seismometers method is more obvious.In the low-frequency band below 0.04 Hz,the seismometer self-noise level is relatively high,which is close to the observation ambient noise.The influence of seismometer self-noise in the low-frequency band should be considered when the selection of observatories for scientific experiments with low noise and the evaluation of ambient noise level was conducted.