To monitor temporal variations of the Earth’s gravity field and mass transport in the Earth’s system, data from gravity recovery and climate experiment (GRACE) satellite mission and its successor GRACE Follow-On (GFO) are used. To fill in the temporal gap between these missions, other satellites’ kinematic orbits derived from GPS-based high-low satellite-to-satellite tracking data may be considered. However, it is well known that kinematic orbits are highly sensitive to various systematic errors. These errors are responsible for a non-stationary noise in the kinematic orbits, which is difficult to handle. As a result, the quality of the obtained gravity field solutions is reduced. In this research, we propose to apply an epoch-difference (ED) scheme in the context of the classical dynamic approach to gravity field recovery. Compared to the traditional undifferenced (UD) scheme, the ED scheme is able to mitigate constant or slowly varying systematic errors. To demonstrate the added value of the ED scheme, three sets of monthly gravity field solutions produced from 6 years of GRACE kinematic orbits are compared: two sets produced in-house (with the ED and UD scheme), and a set produced with the undifferenced scheme in the frame of the short-arc approach (Zehentner and Mayer-Gürr in J Geodesy 90(3):275–286, 2015. https://doi.org/10.1007/s00190-015-0872-7). As a reference, we use state-of-the-art ITSG-Grace2018 monthly gravity field solutions. A comparison in the spectral domain shows that the gravity field solutions suffer from a lower noise level when the ED scheme is applied, particularly at low-degree terms, with cumulative errors up to degree 20 being reduced by at least 20%. In the spatial domain, the ED scheme notably reduces noise levels in the mass anomalies recovered. In addition, the signals in terms of mean mass anomalies in selected regions become closer to those inferred from ITSG-Grace2018 solutions, while showing no evidence of any damping, when the ED scheme is used. We conclude that the proposed ED scheme is preferable for time-varying gravity field modeling, as compared to the traditional UD scheme. Our findings may facilitate, among others, bridging the gap between GRACE and GFO satellite mission.

中文翻译：

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使用历元差异方案改进从卫星运动轨道恢复地球重力场的时间变化

为了监测地球系统中地球重力场和质量传输的时间变化，使用了重力恢复和气候实验 (GRACE) 卫星任务及其后续 GRACE Follow-On (GFO) 的数据。为了填补这些任务之间的时间差距，可以考虑从基于 GPS 的高低卫星到卫星跟踪数据得出的其他卫星的运动轨道。然而，众所周知，运动轨道对各种系统误差高度敏感。这些误差是运动轨道中非平稳噪声的原因，难以处理。结果，降低了获得的重力场解的质量。在这项研究中，我们建议在重力场恢复的经典动力学方法的背景下应用历元差异 (ED) 方案。与传统的无差 (UD) 方案相比，ED 方案能够减轻恒定或缓慢变化的系统误差。为了证明 ED 方案的附加值，比较了 6 年 GRACE 运动学轨道产生的三套月重力场解：两套内部生产（使用 ED 和 UD 方案），以及一套使用无差异产生的重力场解决方案。短弧方法框架中的方案（Zehentner 和 Mayer-Gürr in J Geodesy 90(3):275–286, 2015. https://doi.org/10.1007/s00190-015-0872-7）。作为参考，我们使用最先进的 ITSG-Grace2018 月度重力场解决方案。谱域中的比较表明，当应用 ED 方案时，重力场解的噪声水平较低，特别是在低阶项下，累计误差高达 20 度至少减少 20%。在空间域中，ED 方案显着降低了恢复的质量异常中的噪声水平。此外，当使用 ED 方案时，所选区域中平均质量异常方面的信号变得更接近于从 ITSG-Grace2018 解推断的信号，同时没有显示任何阻尼的证据。我们得出的结论是，与传统的 UD 方案相比，所提出的 ED 方案更适合时变重力场建模。我们的发现可能有助于弥合 GRACE 和 GFO 卫星任务之间的差距。当使用 ED 方案时，选定区域中平均质量异常方面的信号变得更接近于从 ITSG-Grace2018 解决方案推断的信号，同时没有显示任何阻尼的证据。我们得出结论，与传统的 UD 方案相比，所提出的 ED 方案更适合时变重力场建模。我们的发现可能有助于弥合 GRACE 和 GFO 卫星任务之间的差距。当使用 ED 方案时，所选区域中平均质量异常方面的信号变得更接近于从 ITSG-Grace2018 解决方案推断的信号，同时没有显示任何阻尼的证据。我们得出的结论是，与传统的 UD 方案相比，所提出的 ED 方案更适合时变重力场建模。我们的发现可能有助于弥合 GRACE 和 GFO 卫星任务之间的差距。