大倾斜角度下基于冷原子重力仪的绝对重力测量

冷原子重力仪的倾斜角会对绝对重力测量产生显著的影响.高精度的绝对重力测量需要对重力仪的倾斜角进行精确的测量、控制及校正.本文从理论上分析了四种不同情况下倾斜对绝对重力测量的影响规律,并在实验上对得到的理论进行了实验验证.基于此,设计了一种基于双倾斜计的绝对重力测量方案,主要是为了解决恶劣测量环境下的冷原子重力仪倾斜漂移问题.此方案利用高精度倾斜计记录放置在被动隔振平台上的拉曼反射镜的倾斜角度,并使用另外一个倾斜计监控真空系统的倾斜,以实现振动噪声的抑制和倾斜的高精度测量.基于自研的小型化冷原子重力仪,对该方案进行了实验验证,并最终实现了车间复杂环境下的高精度绝对重力测量.由于倾斜得到精确测量和补偿,冷原子重力仪的测量精度达到了12.3μGal.本文为复杂环境下的高精度绝对重力测量提供了一种可行的方案,为冷原子重力仪的实用化提供了参考数据.

Measurement of absolute gravity based on cold atom gravimeter at large tilt angle

The tilt angle of a cold atom gravimeter (CAG) could have a significant influence on the measurement of absolute gravity. The measurement, manipulation, and compensation of the tilt for CAG need to be conducted in order to obtain a high-accuracy absolute gravity measurement. In this paper, firstly, the influences of tilt on absolute gravity measurement under four different conditions are analyzed theoretically by taking into account the position of vacuum system relative to Raman retro-reflection mirror. Then, the experimental investigation is carried out and it is found that the measured results agree well with the theoretical prediction curves. According to the analysis above, we design a scheme for absolute gravity measurement based on two inclinometers, mainly to solve the problem of long-term tilt drift of CAG especially in harsh measurement environment. In this scheme, a high-resolution inclinometer is used to record the tilt angle of Raman retro-reflection mirror, which is fixed on a passive vibration isolation platform. Besides, another inclinometer is utilized to monitor the tilt angle of vacuum chamber of the CAG. By doing so, the vibration noise can be suppressed and the tilt data can be measured with a high precision. Finally, the experimental verification of this proposal is carried out based on our homemade compact cold atom gravimeter, and the high accuracy absolute gravity measurement is realized in a complex workshop environment. Since the vibration noise of Raman mirror is improved by using the vibration isolation platform, the sensitivity of our CAG can reach 319 μGal √Hz. Besides, we measure the long-term changes of gravity with time and find that the experimental results are consistent with the curves calculated by theoretical tidal model. Moreover, due to the precise measurement and compensation for the tilt drift, the accuracy of our CAG is estimated at 12.3 μGal. In order to evaluate this system accuracy, a comparison between our CAG and the FG5 at the same measured site is made. The absolute gravity values determined by both gravimeters coincide with each other. In this paper, we provide a feasible scheme for measuring the absolute gravity in the complex environment. The experimental demonstration of this measurement scheme is performed thereby acquiring some valuable reference data for the practical use of CAG.