Publications related to the GRACE Missions (no abstracts)

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GRACE–FO gravity field recovery from integer ambiguity resolved kinematic orbits and decorrelated stochastic model

Gao, Geng, Zheng, Wei, Sun, Yongjin, Du, Jiankang, Zhao, Yongqi, and Zhao, Minxing, 2026. GRACE–FO gravity field recovery from integer ambiguity resolved kinematic orbits and decorrelated stochastic model. Advances in Space Research, 77(3):3844–3857, doi:10.1016/j.asr.2025.10.095.

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@ARTICLE{2026AdSpR..77.3844G,
       author = {{Gao}, Geng and {Zheng}, Wei and {Sun}, Yongjin and {Du}, Jiankang and {Zhao}, Yongqi and {Zhao}, Minxing},
        title = "{GRACE-FO gravity field recovery from integer ambiguity resolved kinematic orbits and decorrelated stochastic model}",
      journal = {Advances in Space Research},
     keywords = {GRACE-FO, Gravity field recovery, Integer ambiguity resolution, Kinematic orbit, Stochastic model},
         year = 2026,
        month = feb,
       volume = {77},
       number = {3},
        pages = {3844-3857},
     abstract = "{The Gravity Recovery And Climate Experiment (GRACE) series missions have
        revolutionized our understanding of Earth gravity field by
        combining Global Positioning System (GPS) tracking and inter-
        satellite K-band ranging (KBR) to monitor global mass transport
        with unprecedented resolution and continuity. Within the
        Celestial Mechanics Approach (CMA), GPS-based kinematic
        orbits{\textemdash}together with their stochastic
        characteristics{\textemdash}are treated as pseudo-observations
        to simultaneously reconstruct satellite orbits and recover Earth
        gravity field. Nevertheless, ambiguity-float kinematic orbits
        and epoch-wise covariance models, which are simplified versions
        of the fully populated covariance matrices derived from GPS
        observation noise propagation, remain widely used, thereby
        limiting further improvements in the accuracy of CMA solutions.
        This study investigates the impact of applying integer ambiguity
        resolution (IAR) to enhance kinematic orbit precision and reduce
        temporal correlations in the stochastic model. These refinements
        enable the use of simplified epoch-wise covariance matrices
        without compromising solution consistency. Using GRACE Follow-On
        (GFO) data from November 2019, we evaluate the effects of IAR-
        based orbits and decorrelated covariance structures within a
        least squares framework incorporating variance component
        estimation (VCE). Monthly gravity fields are estimated up to
        degree and order 60 using GPS-only observations, and up to 96
        when K-band range-rate (KRR) data are incorporated. The
        reconstructed IAR-based orbits exhibit three-dimensional root
        mean square (3D RMS) errors close to 1 cm, a significant
        improvement over float solutions ({\ensuremath{\sim}}2.5 cm). In
        GPS-only solutions, gravity fields based on IAR and float orbits
        remain consistent up to degree and order 45, diverging beyond
        this{\textemdash}despite the nominal resolution limit of
        {\ensuremath{\sim}}1300 km. In joint GPS and KRR solutions,
        discrepancies appear beyond degree and order 25 between IAR- and
        float-based models, as well as with the GFO Science Data System
        (SDS) RL06.1 products{\textemdash}manifested as more pronounced
        north─south striping artifacts in global mass distributions. To
        address this issue, we apply a fixed-weight strategy to
        kinematic ambiguity-fixed orbits and KRR observations, which
        substantially improves the consistency of the resulting gravity
        field with SDS models and outperforms both float and IAR
        solutions derived under VCE. This suggests that the superior
        precision of IAR-based orbits leads to relatively higher
        weighting of the kinematic positions, which in turn reduces the
        effective contribution of KBR observations to gravity field
        recovery and biases the estimates toward the polar-orbit-
        dominated sensitivity of the GFO constellation. These results
        highlight the importance of an adequate stochastic description
        of kinematic positions, which depends not only on observation
        quality but also on the underlying modeling, including ambiguity
        resolution and background force models.}",
          doi = {10.1016/j.asr.2025.10.095},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2026AdSpR..77.3844G},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}

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