Earth tides observed by gravity and GPS in southeastern Alaska |
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| Institution: | 1. School of Cyber Science and Technology, Beihang University, China;2. National Computer Network Emergency Response Technical Team/Coordination Center of China, China;3. School of Information, Beijing Wuzi University, China;4. School of Computer Science and Technology, Nanjing University of Aeronautics and Astronautics, 210016, China;5. Beijing Key Laboratory of Network Technology, Beihang University, Beijing 100191, China;1. Sultan Qaboos University, Muscat, Oman;2. Institute of Geophysics, University of Tehran, Tehran, Iran |
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| Abstract: | We analyzed gravity data obtained in Juneau and global positioning system (GPS) data obtained from three PBO sites in southeastern Alaska (SE-AK), which are part of a US research facility called ‘EarthScope’, and we compared the obtained tidal amplitudes and phases with those estimated from the predicted tides including both effects of the body tide and ocean tide. Global tide models predict the ocean tides in this region of complex coastline and bathymetry. To improve the accuracy of prediction, we developed a regional ocean tide model in SE-AK.Our comparison results suggest: (1) by taking into account the ocean tide effect, the amplitude differences between the observation and the predicted body tide is remarkably reduced for both the gravity and displacement (e.g. for the M2 constituent, 8.5–0.3 μGal, and 2.4–0.1 cm at the AB50 GPS site in Juneau in terms of the vector sum of three components of the north–south, east–west and up–down), even though the ocean tide loading is large in SE-AK. (2) We have confirmed the precise point positioning (PPP) method, which was used to extract the tidal signals from the original GPS time series, works well to recover the tidal signals. Although the GPS analysis results still contain noise due to the atmosphere and multipath, we may conclude that the GPS observation surely detects the tidal signals with the sub-centimeter accuracy or better for some of the tidal constituents. (3) In order to increase the accuracy of the tidal prediction in SE-AK, it is indispensable to improve the regional ocean tide model developed in this study, especially for the phase. |
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