Precise Observation of the Secular-Gravity Changes by means of the combination of Absolute and Superconducting Gravimeters.

为了获得准确的重力变化数据集，以便与GRACE等卫星重力数据进行比较，我们研究了超导和绝对重力测量相结合的实用方法，并提高了单独测量的精度。为此，我们在日本京都、Esashi、Matsushiro和印度尼西亚万隆的观测站继续进行了超导重力观测。我们还开始在京都站和万隆站进行地下水测量，以揭示它们的重力效应：结果表明，地下水变化与重力观测之间存在明显的相关性，特别是在万隆站。我们确认，通过消除地下水的影响，重力测量的精度得到了提高。我们在2000年和2001年在Esashi和Matsusiro站以及定期进行绝对测量的京都站进行了几次绝对重力测量，同时进行了超导观测。两个台站的总观测时间都超过了一个月，这足以进行比较。此外，我们还开发了一种新的数据处理方法，最终得到了非常精确的超导重力仪定标因子。为进一步研究台站重力长期变化，我们还确定了参考重力值。为了保持准确的绝对重力测量，平差和验证是非常重要的。我们与地理勘测院合作进行了绝对重力仪的比对。除了实际测量外，我们还对卫星重力任务数据和地面测量数据进行了多次仿真研究，建立了这些数据集未来利用的基本技术。

To obtain so accurate data sets of gravity variations as to be used for the comparison with the satellite gravity data such as GRACE, we studied practical methods to combine superconducting and absolute gravity measurements as well as to improve the accuracies of the individual measurements.For this purpose, we have continued superconducting gravity observations at the observation stations of Kyoto, Esashi, Matsushiro in Japan and Bandung in Indonesia. We also started groundwater measurements to reveal their gravity effects at Kyoto and Bandung stations: The results show a clear correlation between the groundwater variations and the gravity observations, especially at the Bandung station. We confirmed that the accuracy of the gravity measurements are improved by removing the groundwater effects.We carried out several absolute gravity measurements in parallel with the superconducting observations at the Esashi and Matsusiro stations in 2000 and 2001 as well as the Kyoto stations where absolute measurements are periodically conducted. The total observation, time in both stations exceeded more than one month which is long enough for purpose of comparison. Moreover, we developed a new method for the data processing, we finally obtained very precise calibration factors for the superconducting gravimeters. We also determined reference gravity values for future studies of secular gravity changes at the stations.To maintain the accurate absolute gravity measurements, adjustments and validations are very important. We carried out the comparison between the absolute gravity meters in collaboration with Geographical Survey Institute. The comparison also contributed to accumulate the know how of the absolute gravity measurements.In addition to the actual measurements, we also conducted several simulation studies of satellite gravity mission data and ground base measurements, and we established the basic techniques of future utilization of those data sets.