Feasibility Study on Using Atomic Gravimeters for Detecting Urban Underground Spaces

Microgravity measurement offers several benefits: it is highly efficient, cost-effective, resistant to interference, and nondestructive. This technique is especially valuable for exploring urban underground spaces and identifying issues such as surface collapses, underground cavities, karst formations, and other geological anomalies. The atomic gravimeter (AG), which is based on atom interferometry, provides high precision, and continuous measurement without drift. It is suitable for detecting urban underground spaces and for long-term monitoring of geological high-risk areas. This study demonstrates the potential of an independently developed AG by Zhejiang University of Technology (ZJUT) for microgravity measurements. It also examines the potential of AG as a local reference for relative gravimeters by performing cross-bridge microgravity profile measurements and validating the results with theoretical model simulations. The estimated sensitivity of the AG without the vibration isolation platform is approximately $135.1~\mu $ Gal/Hz1/2, achieving a resolution of about $3~\mu $ Gal ( $1~\mu $ Gal $=10^{-8}$ m/s2) with an integration time of 2000 s. Additionally, this study conducted cross-bridge experiments with two spring gravimeters, CG-6 and Burris, to assess their effectiveness for detecting urban underground features and to evaluate the accuracy of these conventional instruments. Due to issues like zero drift in the relative gravimeters, the comparison with AG measurements showed external coincidence accuracies of $8.5~\pm ~8.8~\mu $ Gal for the CG-6 and $7.1~\pm ~7.9~\mu $ Gal for the Burris. Overall, AGs demonstrate superior detection accuracy and offer significant potential for applications in urban underground space detection.