A vibration correction method for free-fall absolute gravimeters

Abstract

An accurate determination of gravitational acceleration, usually approximated as 9.8 m s−2, has been playing an important role in the areas of metrology, geophysics, and geodetics. Absolute gravimetry has been experiencing rapid developments in recent years. Most absolute gravimeters today employ a free-fall method to measure gravitational acceleration. Noise from ground vibration has become one of the most serious factors limiting measurement precision. Compared to vibration isolators, the vibration correction method is a simple and feasible way to reduce the influence of ground vibrations. A modified vibration correction method is proposed and demonstrated. A two-dimensional golden section search algorithm is used to search for the best parameters of the hypothetical transfer function. Experiments using a T-1 absolute gravimeter are performed. It is verified that for an identical group of drop data, the modified method proposed in this paper can achieve better correction effects with much less computation than previous methods. Compared to vibration isolators, the correction method applies to more hostile environments and even dynamic platforms, and is expected to be used in a wider range of applications.

A coefficient searching based vibration correction method

“…该值具有简单直观的数学含义, 但物理意义不明显. 类比基于相同简化模型的振动 补偿方法在光学重力仪中的算法流程 [27] , 可以用 另一种更具有物理意义的变量作为振动补偿效果 的最终评价指标, 即干涉条纹拟合残差的变化.…”

“…他们采用的传感器为高精度地震计, 利用相关分析 法或黄金分割法搜索出当前环境下这2个系数的 具体值, 并对下落物体轨迹信号进行修正. 对同一 套振动补偿算法, 输入在中国计量科学研究院昌平 院区的安静环境中测得的重力数据和地震计数据, 算法的直接输出结果表明振动补偿后光学重力仪 的测量分辨率可以提升5倍; 输入在清华大学所处 的复杂振动环境中的数据, 结果表明振动补偿可将 重力仪的测量分辨率提升16倍, 效果更为显著 [27] .…”

Analysis of vibration correction performance of vibration sensor for absolute gravity measurement

“…拟合来得到 g 值，可实现 μGal (1 μGal = 10 −8 m/s 2 )量级的测量不确定度 [5,6] 。其 测量误差主要来自地面振动噪声 [7] ， 综合考虑噪声强度、 频率和相位因素的影响， 对于复杂振动环境下的振动补偿应用，消除或衰减 0.1 Hz ~ 100 Hz 范围的噪声 所造成的干扰是实现优于毫伽量级重力测量不确定度的关键 [8][9][10][11][12][13] 。 隔振和振动补偿是绝对重力测量处理振动噪声的两种主要方法 [14,15] 。其中， 振动补偿是通过传感器探测振动噪声来修正测量值，具备强振动环境下开展绝对 重力测量的应用潜力，但振动传感器的性能制约着振动补偿效果。目前常用于振 动补偿的振动传感器有两类：宽频带地震计和加速度计。宽频带地震计分辨率较 高，其带宽约在 0.01 Hz 至 80 Hz，相对于振动补偿应用较窄，对于高频振动存在 探测信号失真问题，而且量程较小通常不适用于较强振动噪声及移动平台环境； 加速度计测量分辨率比宽频带地震计要低，但带宽可达数百 Hz 甚至 kHz 量级， 量程一般都超过±2 g， 可以适应较强振动噪声及移动平台环境。 以卡尔加里大学、 中国计量院、清华大学、浙江大学和法国巴黎天文台等为代表的研究机构采用地 震计实现了实验室环境下的振动补偿，补偿后单次测量标准差达到百微伽量级 [15][16][17][18][19][20] 。以苏黎世联邦理工学院、法国航空航天实验室、浙江工业大学等为代表的研 究机构则应用加速度计进行了野外或移动平台的振动补偿，补偿后单次测量标准 差达到毫伽量级 [21][22][23][24] 地面振动X 0…”

“…Gs。 目前已有不少关于补偿算法的研究， 由于真实传递函数 () Gs的复杂性，现有补偿算法均将 () Gs进行了合理的简化 [15][16][17]25] 。本文采用课题组已有的振动补偿算法 [16] ，该算法将传递函数 () 量院的地基稳固性高，整体振动小于 0.1 μg (RMS 值，带宽<10 Hz) [26] ，承办过…”

An Approach of Vibration Compensation for Atomic Gravimeter under Complex Vibration Environment

“…At the end of the 20th century, vibration compensation was put forth to detect the vibration-induced noise of a reference mirror inside a gravimeter using a sensor, such as a seismometer or an accelerometer, and then correct the measured gravity accordingly. The vibration compensation with a seismometer in a laboratory had been achieved by some research teams from the Observatoire de Paris [ 16 ], the Universität Hannover [ 17 ], the National Institute of Metrology, China [ 18 ], the Tsinghua University [ 19 ], and the Zhejiang University [ 9 ]. After vibration compensation, the standard deviation of each measurement reached dozens or hundreds of µGal.…”