利用GRACE数据反演东海沉积物变化

GRACE卫星的成功发射为海底沉积物的监测提供了新的方法.利用2003-2014年间的GRACERL05数据,采用同期的测高数据对海面高变化进行改正,使用水文模式数据和基于均一假设的尺度因子估计方法处理泄漏误差,反演了东海地区的沉积物变化情况,并对GIA效应进行了改正.结果表明:东海入海口处沉积物的平均变化速率为5.44±0.88mm·a^-1,最大值出现在浙江沿海地区,变化速率为6~7mm·a^-1;在空间分布上,呈现河口处沉积速率大,远离河口的大洋地区沉积速率小的特征.在时空分布上均与实测数据很好的吻合.沉积物变化时间序列的周年项振为6.8cm,周年变化主要与东海泥沙扩散路径相关的海洋环流模式有关;半周年项和两周年项振幅分别为0.6cm和0.7cm,这两项变化主要与长江流域降水引起的土壤侵蚀变化有关.最后,分析讨论了本文沉积物监测方法推广到其他地区的适用性和局限性.

Inversion for sediment variation in the East China Sea using GRACE data

The Gravity Recovery and Climate Experiment (GRACE) mission provides a new tool to detect the variation of seabed sediment. We used GRACE GSM products from three data centers to determine sediment mass accumulation rates and variability in the East China Sea. Furthermore, GRACE GAD data was used to restore the atmospheric and oceanic effects in order to avoid model contaminations on gravity signals associated with sediment mass. The improved P3M9 de-correlated filter and fan filter were used to improve the quality of gravity signals from GRACE.
What's more, the monthly mean maps of sea level anomaly (MSLA) products from altimeter data were also used to correct the variation of sea level. For the leakage error, we used a hydrological model and estimate scale factor based on uniform assumption to deal with the leakage-in and leakage-out errors, respectively. Finally, we also corrected the GIA (Glacial Isostatic Adjustment) effect.
Results indicate that sediment mass accumulation rate at the estuary of the East China Sea was 5.44±0.88 mm·a^-1, with maximum about 6~7 mm·a^-1 in the coastal area of Zhejiang Province. And in terms of its spatial distribution, the rate at the estuary is larger compared to the smaller rate in the ocean areas far away from coast. Moreover, the temporal-spatial distribution between calculated results and measured data are in good agreement.
As far as is concerned to the time series, the amplitude of semi-annual oscillation is 0.6cm, which is related to the seasonal reversals of East Asian monsoon winds. The annual oscillation can be qualitatively explained by the ocean circulation pattern associated with the sediment dispersal path in the East China Sea, and sediment variation is highly influenced by the ocean circulation pattern, so the amplitude of annual oscillation is 6.8 cm, obviously higher than the semi-annual and quasi-biennial oscillation. And the amplitude of quasi-biennial oscillation is 0.7 cm, such an oscillation may be related to the atmospheric circulation that causes a precipitation.
At last, the spatial pattern of equivalent water height on the East China Sea inner shelf is revealed using records spanning different time periods, and this method is extended to other four major estuaries. It demonstrates that we can get a more reliable result using a certain period of time (~about 5 years) over the area less affected by the leakage of terrestrial signals.