Application Study Of Ocean Absolute Gravity Measurement Based On Atomic Gravimeter
Authors: Yuan Peng , Qiao Zhong-kun , Zhou Yin , Wu Bin , Lin Qiang 
Published: March 2024

The gravity field stands as an intrinsic property of the Earth, providing insights into the distribution and dynamics of substances within the planet and their evolving states. Ocean gravity is a crucial aspect of the Earth's gravity field, with significant applicative value in ocean resource development, geoscientific research, and the interpretation of geological structures. Accurate ocean gravity measurement data serves as essential foundational information for investigating the geological and tectonic features of maritime areas. It is instrumental in identifying distribution patterns and assessing the storage status of mineral resources. The conventional time-varying gravity field relies primarily on GRACE satellite gravity. However, with its spatial resolution limited to approximately 300-500 km half-wavelength, it falls short of meeting the requirements for detailed investigations into local seafloor tectonics and changes in seafloor topography. Presently, shipboard ocean gravity measurement stands out as the most effective method for acquiring high-precision ocean gravity field information. This approach is versatile, suitable for both deep-water measurements in expansive sea regions and measurements in near-shore and island-rimmed sea areas, where the accuracy of satellite altimetry inversion for the gravity field is limited. Conventional ocean gravity measurement predominantly relies on relative gravity measurement, employing a core sensor with quartz and metal spring components. However, this sensor is marred by drawbacks such as mechanical abrasion, elastic fatigue, and creep, leading to instrument zero drift and inadequate long-term stability. Periodic return to the ship is necessary for error calibration and alignment, significantly impacting the efficiency and accuracy of gravity measurement. The atomic gravimeter, leveraging cold atom interference technology, presents notable advantages such as low drift, high accuracy, and excellent long-term stability. It can be seamlessly integrated with traditional gravimeters to achieve dynamic measurements of high-precision gravity fields over extended periods and across vast ocean expanses. Advances in laser, vacuum, electronic control, and related technologies have significantly enhanced atomic gravimeters in terms of accuracy, compactness, miniaturization, and intelligence. Consequently, advancing from static measurements conducted in laboratories, atomic gravimeters are gradually transitioning to dynamic measurements aboard ships and airborne platforms.
The Quantum Precision Measurement Team at Zhejiang University of Technology has achieved successful ocean absolute gravity measurements using an independently developed atomic gravimeter (see Figure 1). The instrument consistently exhibits internal conformity accuracy within 0.6 mGal along repeated lines. Moreover, when compared with a commercial ocean relative gravity instrument on the same ship, the external conformity accuracy falls within the range of 0.5-1.5 mGal. These results meet the precision requirements for ocean gravity measurements, positioning the atomic gravimeter as a potential cornerstone in ocean gravity measurement instruments.

Figure 1 ZAG Shipboard Absolute Gravity Measurement System. (a) Dedicated inertial stabilization platform for atomic gravity. (b) Mobile laboratory for shipboard absolute gravity measurement system. (c) Composition of the atomic gravity instrument system, primarily consisting of the electronic control system and vacuum sensor head system.