An innovative approach to improving the accuracy of shipborne atomic gravimeters has emerged through the development of a four-coefficient transfer function model for vibration compensation. Researchers from Zhejiang University of Technology have made significant strides by utilizing particle swarm optimization (PSO) to find optimal coefficients to mitigate the detrimental effects of vibrations caused by ship movements.
The gravimetric measurements are pivotal for various reasons, including geological studies, resource exploration, and supporting military operations. The accurate measurement of gravity is particularly challenging due to environmental factors like sea breezes and ship vibrations, which can induce noise and introduce errors. This is where the new model aims to make considerable improvements.
During the mooring state tests, which took place at Qiandao Lake, Hangzhou City, China, researchers collected data showing remarkable outcomes. Following the introduction of the vibration compensation model, there was an 81.25% reduction of the standard deviation of residuals after compensation, yielding an impressive measurement standard deviation of just 0.210 mGal (milligals, where 1 mGal = 10-5 m/s2). This level of precision is fundamental for ensuring the reliability of gravity measurements from marine platforms.
Equally noteworthy were the findings from the ocean absolute gravity measurement tests conducted during the summer of 2022, which involved 50 groups of data from the North-South T5 survey line. This situation presented even harsher environments due to ship vibrations, which were more pronounced. Yet, the results still showed significant improvement, with compensation leading to a 57.97% reduction of the standard deviation, achieving external coincidence accuracy of 0.407 mGal.
The system used to collect this data included advanced instrumentation, such as the atomic gravimeter and accelerometers, both of which were strategically integrated to cope with the harsh marine conditions. A Titan accelerometer, capable of sampling at 2000 Hz, recorded vibrations and influenced how the data was processed.
Key to the success of the new compensation model was the introduction of PSO, which efficiently calculated the four coefficients needed to account for the vibrations. For the mooring test, the coefficient search area was set around specific values, and after optimizing through multiple iterations, the algorithm demonstrated significant effectiveness. The convergence of the algorithm occurred within five iterations, yielding precise coefficients for both horizontal and vertical accelerations with minimal noise interference.
The findings support the assertion made by the research team, who stated: "This research demonstrates the particle swarm organization significantly reduces computational time..." This highlights the operational advantage gained through the use of intelligent algorithms, making measuring gravity at sea both more efficient and precise.
Looking forward, the team plans to explore refinement opportunities for the transfer function model, perhaps extending their work to future setups with even more complex vibration challenges. They propose possible enhancements to their model, potentially exploring five-coefficient models or segmenting long-term measurement data for optimized accuracy.
Overall, these advancements present great potential for improving the precision of marine absolute gravity measurements. The research concludes by emphasizing the importance of accurately capturing gravity data, paving the way for their application not only in scientific exploration but also for practical, strategic operations across various fields.