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The long-term stable operation of optical atomic clocks requires precise correction for geodetic effects, particularly Earth tides. In this study, we assess the performance of conventional Earth tide models—ETGTAB, GOTIC2, and TIDE4N—in reducing gravitational uncertainties that impact clock frequency stability. Gravity data from a gPhoneX relative gravimeter at the National Institute of Information and Communications Technology (NICT) Koganei were analyzed with BAYTAP-G (Bayesian Tidal Analysis Program—Grouping Model program) to compare observed tide signals against model predictions. Among the models, TIDE4N showed the closest agreement, with residuals below 1.0 μGal, whereas ETGTAB and GOTIC2 exhibited larger deviations, potentially leading to frequency shifts that may remain significant for advanced optical clocks even after applying the models. To examine the model behavior under different geophysical conditions, we also compared tide signal differences between Koganei and three sites: National Astronomical Observatory of Japan (NAOJ) Mizusawa, Mount Fuji Research Institute (MFRI) in Yamanashi prefecture, Fujiyoshida, and Japan Meteological Agency (JMA) Ishigaki. While theoretical models provided adequate correction for Mizusawa and Fujiyoshida, significant residuals at Ishigaki indicate the need for site-specific gravity observations because of ocean tide loading. These findings primarily support strategies for maintaining long-term frequency stability in optical atomic clocks, while also offering insights into the feasibility of chronometric leveling applications.

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Impact of Earth Tide Models on Reducing Uncertainty in Continuous Operation of Optical Atomic Clocks

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  • 出版模式：

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  • 发表日期：

    2026年

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  • Ryuichi Ichikawa,
  • Yoshiyuki Tanaka,
  • Ryo Honda

摘要

The long-term stable operation of optical atomic clocks requires precise correction for geodetic effects, particularly Earth tides. In this study, we assess the performance of conventional Earth tide models—ETGTAB, GOTIC2, and TIDE4N—in reducing gravitational uncertainties that impact clock frequency stability. Gravity data from a gPhoneX relative gravimeter at the National Institute of Information and Communications Technology (NICT) Koganei were analyzed with BAYTAP-G (Bayesian Tidal Analysis Program—Grouping Model program) to compare observed tide signals against model predictions. Among the models, TIDE4N showed the closest agreement, with residuals below 1.0 μGal, whereas ETGTAB and GOTIC2 exhibited larger deviations, potentially leading to frequency shifts that may remain significant for advanced optical clocks even after applying the models. To examine the model behavior under different geophysical conditions, we also compared tide signal differences between Koganei and three sites: National Astronomical Observatory of Japan (NAOJ) Mizusawa, Mount Fuji Research Institute (MFRI) in Yamanashi prefecture, Fujiyoshida, and Japan Meteological Agency (JMA) Ishigaki. While theoretical models provided adequate correction for Mizusawa and Fujiyoshida, significant residuals at Ishigaki indicate the need for site-specific gravity observations because of ocean tide loading. These findings primarily support strategies for maintaining long-term frequency stability in optical atomic clocks, while also offering insights into the feasibility of chronometric leveling applications.