GNSS Vertical Coordinate Time Series Noise Model in Southeastern Tibet Plateau Based on Environmental Loading

Objectives: Accurately identifying the optimal noise model for global navigation satellite system (GNSS) vertical time series is vital to obtain reliable uplift or subsidence deformation velocity fields and assess the associated uncertainties. Methods: In this study, we select 9 noise models (White Noise (WN)、 Flicker Noise (FN)、 Power-Law Noise (PL)、 Random Walk Noise(RW)、 WN+FN、 WN+PL、 WN+GGM、 WN+RW、 WN+RW+FN) to analyze the noise characteristics of GNSS vertical time series before and after environmental loading correction at 94 stations spanning from January 2011 to December 2022 in the southeastern Tibet Plateau. Results: Our results showed the root mean squares reduction was - 1.3%~22%, -1.4%~17.4%, and -0.1%~ 1.3%, with a mean value of 8.7%， 6.7%， 0.6% for all stations after removing the hydrological, atmospheric, and nontidal ocean loading deformation from the GNSS vertical coordinate time series, respectively, the hydrological loading has a greater impact in the west side of Xianshuihe-Anninghe-Zemuhe fault zone, the atmospheric load has a greater impact in east side of Xianshuihe-Anninghe-Zemuhe fault zone. The optimal noise model at all stations was mainly represented by PL, a combination of WN, PL, and FN before and after environmental loading correction. The value of velocity and its uncertainty before and after environmental loading correction based on optimal noise model varied from -0.11 to 0.26 mm/a and -0.33 to 0.16 mm/a. We analyzed the stability of GNSS stations through the linear relationship between GNSS vertical velocity uncertainty and elevation、 average annual rainfall 、 longitude、 latitude, the results of correlations coefficient was 0.08, 0.07, 0.11, and 0.25, respectively, implying the average annual rainfall, elevation, longitude, and latitude have little impact on station stability in the southeastern Tibet Plateau. Conclusions: Our research suggest that the optimal noise models at most stations in the southeastern Tibet Plateau was PL. This results provides a reference for subsequent reasonable acquisition of GNSS velocity and its uncertainy in the southeastern Tibet Plateau.