新型高精度绝对重力仪

精密测量地球表面的重力加速度(g, 常用值9.81 m/s²) 是探测地球重力场的重要途径, 已广泛应用于计量、测绘、地质、地震与资源勘探等领域. 随着我国"2000国家重力基本网"和"中国地壳运动观测网络"的建成, 对高精度绝对重力测量的需求日益增加. 为深入研究现有绝对重力测量技术可能存在的系统误差, 并满足国内多个领域对高精度绝对重力仪的迫切需求, 自主研制T-1型可搬运式高精度绝对重力仪样机, 采用经典的真空自由落体方案, 通过激光干涉测量和数据拟合方法获得重力加速度值. T-1型绝对重力仪主要包括以下几部分: 高真空度自由落体装置、小型化激光干涉测量装置、超低频垂直隔振系统、高速信号采集系统、仪器控制与数据处理系统. 绝对重力测量的长度基准为稳频He-Ne激光器, 时间基准为铷原子钟, 这两项现有基准的测量不确定度都优于1× 10^-9. 测试结果表明, T-1型绝对重力仪在12 h内重力测值的标准差可优于1 μupGal (1 μupGal = 10^-8 m/s²), 测量结果的复现性优于3 μupGal, 可实现微伽量级不确定度的精密重力测量, 有望在我国多个关键领域发挥重要应用.

A new high precision absolute gravimeter

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 1μGal(1μGal = 10^-8 m/s²) in a typical observation within 12 h.And the reproducibility of less than 3μGal 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.