对齐误差对测试地震计自噪声的影响

本文在理论上研究了对齐误差对测试地震计自噪声的影响。指出对齐误差影响到2台仪器记录间的计算互功率谱密度, 进而影响到被测仪器记录间相干函数计算, 最终影响到被测仪器的自噪声计算。发现当存在对齐误差时, 在信噪比较高频段计算得到的自噪声水平比仪器的实际自噪声水平要高, 在一般的实际测试中可能高20 dB以上。为了消除对齐误差对自噪声测试的影响, 提出通过投影逆变换把观测记录变换到标准坐标系下, 再用变换后的观测记录来计算地震计自噪声。给出了基于以上思路和传感参数对比测试方法的地震计自噪声计算处理流程, 合成数据、 实际测试数据的处理检验计算结果表明, 本文方法可以有效克服地震计自噪声测试中对齐误差的影响。

Effect of Alignment Error on Estimation of Self-noise of Seismometer

The influence of alignment error on estimation of seismometer self-noise is theoretically studied in this paper. It is found that the alignment error affect calculated cross-power spectrum density between two records of 2 aligned instruments and then it affects the calculation of the coherence coefficient between the records of the instruments, and finally affects the estimated self-noise. It is found that the calculated self-noise is higher than the actual value in the higher frequency band when the alignment error exists, and may be more than 20 dB higher in practical test. To remove the influence of alignment error on calculated self-noise in test, it is proposed to transform the observation records to the standard coordinate system by inverse projection transformation, and use the transformed records to calculate the seismometer self-noise. The procedure is given to get self-noise without influence of alignment error based on the above idea and calculation of sensing data with side-by-side comparison. It is proved that the algorithm given in this paper is effective to overcome the influence of the alignment error on the seismometer self-noise test.