Calibration of the superconducting gravimeter T011 by parallel observation with the absolute gravimeter FG5 #210 - a Bayesian approach
Calibration of the superconducting gravimeter T011 by parallel observation with the absolute gravimeter FG5 #210 - a Bayesian approach
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DOI：
10.1046/j.1365-246x.2002.01806.x
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发表时间：
2002-12-01
影响因子：
2.8
通讯作者：
Fukuda, Y
中科院分区：
文献类型：
--
作者：
Imanishi, Y;Higashi, T;Fukuda, Y
超导重力仪是一种相对重力仪，其灵敏度必须标定。可能的校准方法之一是用绝对重力仪进行平行观测。由于校准的精度大致与N-1/2成比例，其中N是数据的数量，因此由大量数据组成的长时间观测将有助于获得更好的结果。在这项工作中，进行了为期27天的实验，绝对重力测量与绝对重力仪FG 5 #210的校准SG T011在日本松代。有效测量次数约为10万次。单次测量的标准偏差在50 ~ 90 nm·s（-2）之间变化，取决于天气条件。采用常用的最小二乘法对两台重力仪的数据进行回归分析，得出SG T011的（负）比例因子为（-928.01 +/- 0.34）nm s（-2）V-1。虽然起初这一结果似乎令人满意，但仔细观察数据后发现，绝对重力数据中存在不规则的“漂移”，估计的比例因子中可能存在系统偏差。对于比例因子的无偏估计，采用了两种额外的数据分析方法。一种是基于绝对重力仪和相对重力仪重力数据潮汐分析的方法，另一种是简单最小二乘法的改进。这两种方法都是基于贝叶斯统计原理，将漂移与真实的重力变化分离开来，从而使标度因子的估计不受漂移的影响。从这些方法中获得的比例因子被发现是略大于（绝对值）比那些从简单的最小二乘法。虽然潮汐分析方法也被发现是潜在的有用的相位校准，它有最大的估计误差的比例因子的三种方法。综合考虑标定的准确度和精密度，认为修正最小二乘法的标度因子是最可靠的。因此，最终结果为（-928.79 +/- 0.36）nm s（-2）V-1。该结果的相对精度为0.039%，是单次绝对重力实验获得的SG最精确的校准结果之一。绝对重力测量值漂移的原因尚不清楚。与更换SG电子设备有关的灵敏度变化约为0.5%，这一变化已得到定量验证。
The superconducting gravimeter (SG) is a relative gravimeter and its sensitivity must be calibrated. One of the possible methods of calibration is parallel observation with an absolute gravimeter. Since the precision of the calibration is roughly proportional to N-1/2, where N is the number of data, a long time span of observation consisting of a large number of data will be helpful for a better result. In this work, a 27 day long experiment of absolute gravity measurements with the absolute gravimeter FG5 #210 was made for calibration of the SG T011 at Matsushiro, Japan. The effective number of measurements was about 100 000. The standard deviation of single measurements varied from 50 to 90 nm s(-2), depending on the weather condition. A regression analysis of the data from both gravimeters with the usual least-squares method yielded (-928.01 +/- 0.34) nm s(-2) V-1 for the (negative) scale factor of the SG T011. Although at first this result appeared satisfactory, a closer look at the data revealed existence of an irregular 'drift' in the absolute gravity data and possibly a systematic bias in the estimated scale factor. For unbiased estimation of the scale factor, two additional methods of data analysis were employed. One is the method based on tidal analysis of gravity data from both absolute and relative gravimeters, and the other is a modification of the simple least-squares method. Both of these methods separate the drift from real gravity changes based on the Bayesian statistics, so that estimation of the scale factor is free from the effect of the drift. The scalefactors obtained from these methods were found to be slightly larger (in absolute values) than those from the simple least-squares method. Although the tidal analysis method was found to also be potentially useful for phase calibration, it had the largest estimation error of the scale factor among the three methods. Considering the accuracy as well as the precision of calibration, the scale factor from the modified least-squares method was regarded as being most reliable. Thus, the final result is (-928.79 +/- 0.36) nm s(-2) V-1. The relative precision of this result is 0.039 per cent. This is one of the most precise calibration results for an SG obtained from a single absolute gravity experiment. The cause of the drift in the absolute gravity measurements is unknown. The change in the sensitivity of about 0.5 per cent associated with the replacement of the electronics for the SG has been verified quantitatively.