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@ARTICLE{2025RemS...17.1509W,
       author = {{Wang}, Songyun and {Wilson}, Clark R. and {Chen}, Jianli and {Fu}, Yuning and {Kuang}, Weijia and {Seo}, Ki-Weon},
        title = "{Multi-Year Global Oscillations in GNSS Deformation and Surface Loading Contributions}",
      journal = {Remote Sensing},
     keywords = {six-year oscillation, GNSS, surface loading, satellite gravimetry, terrestrial water storage, wavelet transform},
         year = 2025,
        month = apr,
       volume = {17},
       number = {9},
          eid = {1509},
        pages = {1509},
     abstract = "{Recent studies have identified a near six-year oscillation (SYO) in
        Global Navigation Satellite Systems (GNSS) surface
        displacements, with a degree 2, order 2 spherical harmonic (SH)
        pattern and retrograde motion. The cause is uncertain, with
        proposals ranging from deep Earth to near-surface sources. This
        study investigates the SYO and possible causes from surface
        loading. Considering the irregular spatiotemporal distribution
        of GNSS data and the variety of contributors to surface
        displacements, we used synthetic experiments to identify optimal
        techniques for estimating low degree SH patterns. We confirm a
        reported retrograde SH degree 2, order 2 displacement using GNSS
        data from the same 35 stations used in a previous study for the
        1995{\textendash}2015 period. We also note that its amplitude
        diminished when the time span of observations was extended to
        2023, and the retrograde dominance became less significant using
        a larger 271-station set. Surface loading estimates showed that
        terrestrial water storage (TWS) loads contributed much more to
        the GNSS degree 2, order 2 SYO, than atmospheric and oceanic
        loads, but TWS load estimates were highly variable. Four TWS
        sources{\textemdash}European Centre for Medium-Range Weather
        Forecasts Reanalysis 5 (ERA5), Modern-Era Retrospective analysis
        for Research and Applications (MERRA), Global Land Data
        Assimilation System (GLDAS), and Gravity Recovery and Climate
        Experiment (GRACE/GRACE Follow-On){\textemdash}yielded a wide
        range (24\% to 93\%) of predicted TWS contributions with
        GRACE/GRACE Follow-On being the largest. This suggests that TWS
        may be largely responsible for SYO variations in GNSS
        observations. Variations in SYO GNSS amplitudes in the extended
        period (1995{\textendash}2023) were also consistent with near
        surface sources.}",
          doi = {10.3390/rs17091509},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2025RemS...17.1509W},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}