Gravity changes at the Esashi Gravity Station observed by the absolute gravimeter with a rotating vacuum pipe

Abstract

We have developed an absolute gravimeter with a rotating vacuum pipe. The rotating vacuum pipe has an angular velocity high enough to keep a falling object to the end of it, where the falling object begins to drop by stopping the pipe vertical. We put a Michelson interferometer with a stabilized He-Ne laser under the vacuum pipe to measure the position of the falling object at every 1 ms synchronized with a rubidium frequency standard. This absolute gravimeter has succeeded in the measurements with a drop-to-drop scatter of 1.9 × 10−7ms−2 (19µGal) at the Esashi Gravity Station in the end of 1989 and also has succeeded in the continuous measurements for a week at the same place in December 1991. During the three-year experiments, the measured gravity values have gradually increased until the end of 1991 and then gained in the rate of increase, although we cannot deny the possibility of instrumental origin. The comparisons with other types of absolute gravimeters showed that the values obtained by the absolute gravimeter with a rotating vacuum pipe are close to those obtained by the absolute gravimeters ILOM#1 and NAOM#2 and are lower than those obtained by JILA#4, though the times of comparisons are different.