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Results from 44 months of observations with a superconducting gravimeter at Moxa/Germany

机译：来自德国Moxa的44个月超导重力仪观测结果

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Results for more than 42 months of observations with the superconducting gravimeter CD-034 at the Geodynamic Observatory Moxa are discussed. Moxa observatory is one of the newer stations within the 'Global Geodynamics Project' (GGP). A special feature of the gravimeter at Moxa is its dual sensor system; differences in the results obtained from the two sensor recordings are generally well within the standard deviations of the tidal analysis. One significant difference concerns the slightly different drift rates of 31 and 49.5 nm/s~2 per year for upper and lower sensor; both sensor drifts can be fitted by a linear function. We find that the noise levels are close to the 'New Low Noise Model' for the seismic-modes and are also low in the tidal bands. Due to this low noise, Moxa is a station well suited to search for small geodynamic signals. The long-period variation in the gravity residuals correlates well with the polar motion. The difference signal between the two sensor recordings has a peak-to-peak amplitude of about 6 nm/s~2 and shows systematic variations. Its spectrum is characterised by instrumental noise between 0.2 and 0.4 cph. The noise level of the difference and of the sum of the two residual datasets are clearly lower, respectively, higher than the noise contents of the gravity residuals themselves. This is a strong indication for the existence of broadband signals common to the two residual datasets, leading to the conjecture that the reduction of environmental effects is still not sufficient. Our results once more emphasize the necessity to correct the data for barometric pressure effects when analyzing the data for seismic modes. The reduction visibly increases the signal-to-noise ratio in the low frequencies of the mode band and helps to avoid misinterpreations of peaks. Besides the well known barometric pressure influence we can establish hydrological effects in the data which are probably caused by soil moisture and groundwater table variations as well as by batch-wise water movement within the weathering layer. As the major part of the observatory surroundings is above gravimeter level, an anticorrelation between hydrological and gravity changes is observed. In addition, it can be shown that global hydrological effects reach an order of magnitude that makes it necessary to consider these effects when analyzing long-period signals like polar motion. Vice versa these effects are large enough to be detectable in the gravity data. A first joint analysis of five datasets from the GGP network shows no indications for signals related to the Slichter triplet or core modes.
机译：讨论了用超导重力仪CD-034在地球动力学天文台Moxa进行的42个月以上观测的结果。 Moxa天文台是“全球地球动力学项目”（GGP）中较新的站点之一。 Moxa重力仪的一个特色是它的双传感器系统。从两个传感器记录获得的结果差异通常都在潮汐分析的标准偏差之内。一个显着的差异是上下传感器每年的漂移速率分别为31和49.5 nm / s〜2，略有不同。两个传感器漂移都可以通过线性函数进行拟合。我们发现噪声水平接近于地震模式的“新低噪声模型”，并且在潮汐带中也较低。由于噪音低，Moxa站非常适合搜索小型地球动力信号。重力残差的长期变化与极运动相关。两个传感器记录之间的差异信号的峰峰值幅度约为6 nm / s〜2，并且显示出系统的变化。其频谱的特征是仪器噪声介于0.2和0.4 cph之间。这两个残差数据集的差值和总和的噪声水平分别明显低于重力残差本身的噪声含量。这强烈表明存在两个残差数据集共有的宽带信号，这导致人们猜测减少环境影响仍然不够。我们的结果再一次强调了在分析地震模式数据时必须校正气压影响数据的必要性。降低明显增加了模式频带低频中的信噪比，并有助于避免峰值的误解。除了众所周知的大气压力影响外，我们还可以在数据中建立水文效应，这可能是由于土壤水分和地下水位变化以及风化层内的分批水分运动造成的。由于天文台环境的主要部分位于重力仪高度以上，因此可以观察到水文和重力变化之间的反相关关系。此外，可以证明，全球水文影响达到一个数量级，因此在分析极性信号等长周期信号时必须考虑这些影响。反之亦然，这些影响足够大，可以在重力数据中检测到。对来自GGP网络的五个数据集的首次联合分析没有显示与Slichter三重态或核心模式有关的信号的迹象。

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