Abstract
The site displacement due to ocean tidal loading is regarded as one of the largest uncertainties in precise geodetic positioning measurements, among which the effect of minor ocean tides (MOT), except for the 11 main tidal constituents, are sometimes neglected in routine precise global positioning system (GPS) data processing. We find that MOT can cause large vertical loading displacements with peak-to-peak variations reaching more than 8 mm at coastal/island stations. The impact of MOT on the 24-hour GPS solution is slightly larger than the magnitude of MOT loading itself, with peak-to-peak displacement variation at about 10 mm for the horizontal and 30 mm for the vertical components. We also find that the vertical velocity of all the selected stations in the Southwest Pacific was reduced by more than 10% after considering the MOT effect, while stations with weighted root mean square reduced data account for 62%, 59%, and 36% for the up, east, and north components respectively, in particular for most coastal/island stations. Furthermore, MOT correction could significantly reduce the annual signal of the global stacked east component, the near fortnightly and the long-term periodic signals in the up component. The power of some anomalous harmonics of 1.04 cycle per year is also decreased to some extent. These results further proved the benefits of MOT correction in precise GPS data processing.
Highlights
Time variable deformation of the Earth caused by ocean tides could reach up to 100 mm at some special coast regions [1,2]
For coastal or island stations, such as KOKB, the peak-to-peak vertical displacement caused by minor ocean tides (MOT) reaches 8 mm
We first determine the magnitude and spatial distribution of global IGS station's loading displacement caused by MOT
Summary
Time variable deformation of the Earth caused by ocean tides could reach up to 100 mm at some special coast regions [1,2]. The 11 discrete ocean tide constituents are considered sometimes in OTL modeling during routine precise GPS data processing, including displacement induced by four semidiurnal tide waves M2, S2, N2, K2, 4 diurnal waves K1, O1, P1, Q1, together with three long-period waves Mf, Mm, and Ssa [6,7,8]. The OTL modeling method including the MOT correction is implemented in GAMIT by expanding the 11 main ocean tides into 342 constituents Based on both the original and the modified GAMIT software, the GPS data of 109 globally distributed IGS stations spanning from June, 1998 to December, 2010 has been reprocessed with state of the art models according to IERS Conventions 2010. Results of this paper may provide numerical support to the recommended data processing strategy in the IERS Conventions for crustal movement and interpretation of geophysical signal, as well as the target accuracy of ITRF to achieve 1 mm in position and 0.1 mm/a in velocity [30]
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