The Gravity Recovery and Climate Experiment (GRACE) satellite mission has profoundly advanced our knowledge of contemporary sea level change. Owing to the coarse spatial resolution and leakage issue across the land–ocean boundary, it is challenging (even impossible) for GRACE to detect mass changes over a region smaller than its spatial resolution, especially a semi-enclosed basin (e.g., the Bohai Sea) that is adjacent to land with significant mass variation. In this contribution, the causes for the GRACE RL06 mass changes in the Bohai Sea are investigated using a reconstruction technique that is implemented with multisource data, including altimeter observations, steric estimates, and land mass changes from GRACE RL06 mascon solution. Our results by the reconstruction technique demonstrate that the GRACE annual cycles are primarily caused by water mass changes rather than sediment changes. On the other hand, the mass trends from both reconstructed signals and those observed by the GRACE RL06 spherical harmonic coefficients (SHCs) are small, ranging from − 0.38 mm/year to 0.51 mm/year (depending on different data sources). Given that our estimated accuracies are > 0.8 mm/year (the real accuracies should be larger), our reconstructed results cannot directly confirm the presence of sediment accumulation or water mass increase; however, analysis of only the altimetry data suggests the mass trends are due to water mass increase, which would amount to ~ 0.44 Gt/year. Further investigation suggests that the mass trends in the Bohai Sea suffer from a − 2.9 mm/year leakage-in effect from groundwater depletion in the North China and about 2.5 mm/year signal attenuation (resulting in a ~ 2.5 mm/year remaining trend that is roughly equivalent to the leakage-in trend, consequently leading to the small mass trend in the Bohai Sea). Our reconstruction results exemplify that elaborate data processing is necessary for specific cases. We also test whether the recently released RL06 mascon solutions that are resolved with constraints and require no further processing would improve the agreement with altimeter observations. We find that the seasonal cycles are improved relative to the RL06 SHCs; however, the rates derived from the mascon solutions cannot properly represent the altimeter-derived ocean mass estimates for the Bohai Sea, probably because the mascon solutions underestimate the rates or contain some processing artifacts. Nevertheless, the mascon solutions show enhanced signals, which offer new opportunities to investigate regional sea level change.

中文翻译：

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GRACE观测到的渤海质量变化调查

重力恢复和气候实验 (GRACE) 卫星任务极大地提高了我们对当代海平面变化的认识。由于跨海陆边界的粗略空间分辨率和泄漏问题，GRACE很难（甚至不可能）检测到小于其空间分辨率的区域的质量变化，尤其是半封闭盆地（例如渤海） ) 与质量变化显着的陆地相邻。在这篇文章中，使用重建技术研究了渤海 GRACE RL06 质量变化的原因，该技术使用多源数据实施，包括高度计观测、空间估计和来自 GRACE RL06 mascon 解的陆地质量变化。我们的重建技术结果表明 GRACE 年循环主要是由水体变化而不是沉积物变化引起的。另一方面，重建信号和 GRACE RL06 球谐系数 (SHC) 观测到的质量趋势很小，范围从 - 0.38 毫米/年到 0.51 毫米/年（取决于不同的数据源）。鉴于我们估计的精度 > 0.8 mm/年（实际精度应该更大），我们的重建结果不能直接确认是否存在沉积物堆积或水体增加；然而，仅对测高数据的分析表明，质量趋势是由于水质量增加造成的，这将达到约 0.44 Gt/年。进一步的调查表明，渤海的质量趋势受到 - 2 的影响。华北地区地下水枯竭造成 9 毫米/年的渗漏效应和约 2.5 毫米/年的信号衰减（导致约 2.5 毫米/年的剩余趋势，大致相当于渗漏趋势，因此导致较小的渤海大趋势）。我们的重建结果表明，对于特定情况，需要进行精细的数据处理。我们还测试了最近发布的 RL06 mascon 解决方案是否通过约束解决并且不需要进一步处理会提高与高度计观测的一致性。我们发现季节性周期相对于 RL06 SHC 有所改善；然而，从 mascon 解得出的速率不能正确代表渤海的高度计得出的海洋质量估计，可能是因为 mascon 解决方案低估了速率或包含一些处理工件。尽管如此，mascon 解决方案显示出增强的信号，这为调查区域海平面变化提供了新的机会。