A new high precision absolute gravimeter

Abstract

The accurate measurement of local gravitational acceleration (g, normal value 9.81 m/s2) is a key approach to the exploration of the gravitational field of the earth, and it has been applied in metrology, geodesy, geodynamics, seismology, and mineral exploration. With the plan of '2000 national gravity network' and 'China crustal motion observation network', highly precision gravity measurement will be increasingly required in the long term. In order to further investigate the possible systematic error of current absolute gravity measurement, and satisfy various requirements for highly accurate gravity observation, the T-1 absolute gravimeter prototype is designed and built at Tsinghua University. The T-1 instrument adopts the classic free-fall scheme to measure the g value by tracking the trajectory of a free-fall motion in vacuum with a laser interferometer. The T-1 absolute gravimeter consists of several sub-systems: high vacuum free-fall chamber, compact laser interferometer, low-frequency vertical vibration isolation, high-speed signal acquisition system, instrument control and data processing system. The length and time standards used in g measurement are stabilized He-Ne laser and rubidium atomic clock respectively. It's well known that both of the two standards have an uncertainty of less than 1 10-9. The practical gravity measurement results of T-1 absolute gravimeter give a standard deviation of the mean of less than 1 upGal (1 up Gal = 10-8 m/s2) in a typical observation within 12 h. And the reproducibility of less than 3 upGal is verified by repeatedly measuring gravity. The T-1 absolute gravimeter is a promising instrument by which highly accurate gravity measurement at a microgal level can be realized, and it is hopefully to be used in many research and application areas.

The European Comparison of Absolute Gravimeters 2011 (ECAG-2011) in Walferdange, Luxembourg: results and recommendations

“…However, some non-European teams took part in the comparison to establish a link with other regional comparisons organized in other parts of the world. Twenty-two absolute gravimeters of six different types were compared: mostly FG5 (including the new model FG5X) free-fall gravimeters (Niebauer et al 2011), one atomic gravimeter (CAG-1) (Louchet-Chauvet et al 2011), one rise-and-fall gravimeter (IMGC-02) (D'Agostino et al 2008) and a new free-fall prototype from China (T1) (Hu et al 2012). Overall, only six teams come from National Metrology Institutes (NMI) or Designated Institutes (DI).…”

A vibration correction method for free-fall absolute gravimeters

“…In order to implement the modified correction algorithm, experiments are performed with a T − 1 absolute gravimeter [30,31], the combined standard uncertainty of which is around 5 μGal (1 μGal = 1 × 10 −8 m s −2 ). 75 successive…”

The development of a reference corner cube inertial suspension device

“…The falling trajectory of the free-falling corner cube relative to the reference corner cube can be reconstructed by extracting the zero-crossing information of the fringe signal. The gravity acceleration of the measuring point can then be obtained using the least-squares fitting of the trajectory(T. M. Niebauer, et al 1995;Wu Shu-qing, 2012;HU H, et al 2012). It is necessary to keep the reference 35 corner cube stationary or its motion linear during the falling process to ensure the accuracy of the obtained gravitational acceleration.…”