High-frequency parasitic modes of superconducting gravimeters
High-frequency parasitic modes of superconducting gravimeters
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DOI：
10.1007/s00190-008-0253-6
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发表时间：
2009-05-01
影响因子：
4.4
通讯作者：
Imanishi, Yuichi
中科院分区：
文献类型：
--
作者：
Imanishi, Yuichi
超导重力仪(SG)在100点左右存在一种被称为寄生模式的长周期仪器噪声，其确切机制尚不清楚。本文通过对日本两个地震局的高速重力通道的分析，在更高的频率下探测到了另一种仪器噪声。这也是一种寄生振荡，其特征是频率在1赫兹数量级，Q值非常高。详细的光谱表明，噪声实际上是由两个频率间隔很小的模式组成的。基于重力传感器中超导球体自转运动的简单理论，初步将观测到的模式识别为超导球体在水平面上绕两正交轴的转动振荡。利用地震采集的频谱研究了寄生振型之间的相互作用，得出低频寄生振型很可能是球体绕垂直轴的旋转运动。
The superconducting gravimeter (SG) has a long-period instrumental noise called the parasitic mode at periods around 100 s, whose precise mechanism has not yet been identified. In this paper, another instrumental noise is detected at much higher frequencies by analyzing the high-rate gravity channel of two SGs in Japan. This is also a parasitic oscillation, characterized by frequencies on the order of 1 Hz and very high Q values. Detailed spectra indicate that the noise actually consists of two modes with small frequency separations. Based on a simple theory on the rotational motions of the superconducting sphere in the gravity sensor, the observed modes are tentatively identified as rotational oscillations of the sphere about two orthogonal axes in the horizontal plane. Interactions between the parasitic modes are investigated using the spectra acquired on an earthquake, to conclude that the low-frequency parasitic mode is likely to be a rotational motion of the sphere about the vertical axis.