Objectives

2

Quantum gravimeters are an emerging gravity measurement technology with the potential to significantly change the field of gravity observation. These instruments are based on matter-wave interferometry and use cold atoms as test masses

enabling continuous absolute measurements of gravitational acceleration. Compared with traditional laser-interferometric absolute gravimeters

quantum gravimeters employ atomic matter waves with much shorter wavelengths and avoid mechanical friction by using microscopic atoms as test masses. In comparison with spring-based or superconducting gravimeters

quantum gravimeters combine continuous observation capability with absolute measurement

and are theoretically free from scale factor errors and instrumental drift. These characteristics give quantum gravimeters strong potential for acquiring high-quality gravity data.In recent years

quantum gravimeters have developed rapidly; however

most existing studies and tests have been conducted under laboratory conditions. As a result

their performance under field conditions is still not well understood. In addition

key performance indicators reported by instrument manufacturers

such as precision

accuracy

and stability

require independent verification through field experiments. Therefore

field testing of quantum gravimeters is essential for evaluating their practical observation capability

understanding the influence of environmental factors on instrument performance

and promoting their engineering development and practical application. Based on this background

this study focuses on the RAI-g quantum gravimeter and systematically analyzes its precision

accuracy

and stability under different environmental conditions through mobile observations at multiple stations

providing experimental evidence for its application in high-precision gravity measurements.

Methods

2

Field performance tests were carried out using the RAI-g quantum gravimeter developed by Huazhong University of Science and Technology. The instrument uses rubidium atoms as test masses and integrates key technologies including atomic matter-wave interferometry

real-time data acquisition and processing

and active vibration isolation. It features high measurement precision and good portability

making it suitable for mobile absolute gravity observations. The tests were conducted in a mobile observation mode in November 2020 at three sites in China: the Absolute Gravity Laboratory of the Institute of Seismology

China Earthquake Administration (Wuhansuo)

Jiufeng Seismic Station (Jiufeng)

and Xiangfan Seismic Station (Xiangfan). All three sites are equipped with stable gravity pillars

and the gravity reference at each site is maintained through repeated measurements with an FG5X absolute gravimeter

providing reliable reference gravity values.The background vibration environments at the three sites differ significantly. The Wuhansuo site is located in an urban area with frequent human activity and relatively high vibration noise. The Jiufeng station is located inside a cave

with a quiet environment and the lowest vibration level. The Xiangfan station is located in a suburban area

with vibration noise levels between those of Wuhansuo and Jiufeng. In addition

the absolute gravity values at the three sites differ by nearly 60 mGal

and the latitude and elevation conditions also vary

providing favorable conditions for a comprehensive performance evaluation of the instrument. The RAI-g quantum gravimeter completes one gravity measurement every 6 s and supports continuous observation. The observation duration at each site ranged from 3 to 15.2 h. All instrument operations during the tests were performed by manufacturer technicians

and the operators were unaware of the prior gravity values at the sites. After data processing

the RAI-g results were compared with the colocated FG5X absolute gravimeter measurements to evaluate the field performance of the instrument.

Results

2

The observation results show that the data distributions obtained by the RAI-g quantum gravimeter differ among the three sites. The data at the Jiufeng station are the most concentrated

followed by Xiangfan

while the Wuhansuo site shows the largest dispersion. This pattern is consistent with the background vibration noise levels at the sites

indicating that ground vibration is a major factor affecting the measurement quality of quantum gravimeters. During absolute gravity measurements

ground vibrations introduce errors by changing the relative position between the Raman reflection mirror and the freely falling atoms. The RAI-g quantum gravimeter uses an accelerometer to monitor vibrations in real time and applies vibration compensation

enabling stable continuous observations. Nevertheless

data quality is higher in low-noise environments.Using the FG5X absolute gravimeter measurements as reference values

a quantitative evaluation of the RAI-g results was performed. The observation precision of the RAI-g at all three sites is better than 2 μGal. In particular

the precision at Jiufeng and Xiangfan reaches 0.29 μGal and 0.44 μGal

respectively

achieving the microgal level. In terms of accuracy

defined as the difference between the mean observed value and the reference value

the results at Wuhansuo

Jiufeng

and Xiangfan are 1.70 μGal

-2.06 μGal

and 7.35 μGal

respectively

all better than 10 μGal. These results indicate that systematic errors of the instrument are well controlled.Outliers and random error distributions were further analyzed. Individual measurements differing from the mean of the observation series by more than three times the standard deviation were identified as containing outliers. The proportions of outlier observations at Wuhansuo

Jiufeng

and Xiangfan are 18‰

8‰

and 4‰

respectively

all less than 2% and comparable to those of the FG5X absolute gravimeter. This demonstrates that the RAI-g has good resistance to outliers. After removing outliers

the error histograms of the remaining data at all sites show approximately symmetric distributions with sums close to zero

consistent with the statistical characteristics of random errors and without evident systematic bias.Instrument stability was evaluated by calculating the Allan deviation of the continuous observation data. The sensitivities of the RAI-g at the Wuhansuo

the Jiufeng

and the Xiangfan are 357 μGal/Hz¹/²

72 μGal/Hz¹/²

and 89 μGal/Hz¹/²

respectively. The differences in sensitivity are mainly influenced by background vibration conditions. Quieter environments result in lower data dispersion and higher instrument sensitivity. At all sites

the Allan deviation curves continuously decrease with increasing integration time

indicating that white noise is the dominant noise type. No obvious colored noise was observed during the measurements

demonstrating good short-term stability of the instrument.In addition

the tests show that the instrument accuracy changed only slightly after short-distance transportation (from the Wuhansuo to the Jiufeng)

while a larger but still acceptable change was observed after long-distance transportation (from the Jiufeng to the Xiangfan). Even after long-distance transport

the accuracy remained better than 10 μGal

indicating that transportation may affect the instrument state to some extent

but the overall performance remains stable.

Conclusions

2

In conclusion

the RAI-g quantum gravimeter is capable of stable and continuous absolute gravity measurements under different environmental conditions. It achieves microgal-level precision

accuracy better than 10 μGal

good stability

and strong resistance to outliers. Background vibration noise at observation sites is the main factor affecting instrument sensitivity and data dispersion. However

with effective vibration monitoring and compensation

the instrument can maintain high data quality under field conditions. The RAI-g quantum gravimeter shows strong potential for applications in geodesy and geophysics. Future studies should include longer-term observations and tests under more complex environmental conditions to further evaluate its long-term stability and engineering adaptability

thereby supporting the broader application and further development of quantum gravimeters.