Analysis of the Vertical Coordinate Time Series in China Taking into Account the HYDL Under the ITRF2014 Framework

The GNSS coordinate time series is affected by the hydrological loading (HYDL) in the surface elastic deformation information. This paper uses the CMONOC coordinate time series under the ITRF2014 framework and the MERRA2 hydrological loading model provided by IMLS to analyze the influence of China's regional HYDL on the GNSS coordinate time series. The results show that in the vertical component, the HYDL has a particularly significant impact on the GNSS coordinate time series. The maximum velocity can reach 3.52 mm/year, of which 37.1% of the stations are corrected by the HYDL, the velocity decreases, and 63.3% of the stations are corrected by the HYDL, the velocity value increases. The influence on the periodic term is mainly reflected in the annual amplitude and the annual phase. Among them, 82.4% of the stations are corrected by the HYDL and the annual amplitude is reduced, and the nonlinear amplitude is weakened. As for the annual phase, 22.5% of the stations is significantly reduced after the HYDL correction, and the remaining 77.5% of the stations is increased after the HYDL correction. This shows that the influence of HYDL on the annual phase of the GNSS coordinate time series cannot be ignored.