全球水储量变化的GRACE卫星检测

Detection of global water storage variation using GRACE

利用GRACE月尺度变化的地球重力场反演了全球水储量变化,并与陆地水文资料、卫星测高资料及海洋模式得到的结果进行了比对.通过对SOURE台站重力变化的陆地水储量变化计算结果和GRACE重力场系数截断为15阶得到的结果比较,发现两者比较接近,且年周期变化特征明显.对于亚马逊流域,当重力场系数截断为15阶且平滑半径使用106m时,GRACE反演的区域平均水储量厚度的周年变化振幅为15.6×10-2m,小于使用平滑半径为4×105m的23.7×10-2m.在研究长江流域时,本文对水文资料做球谐系数展开,并与GRACE数据做同样的截断和平滑处理,结果发现GRACE反演的水厚度变化与水文资料结果基本上符合.对于纬度±66°之间的海洋区域,GRACE反演的海水质量变化接近于结合卫星测高和海洋模式得到的结果,但对于2°×2°网格,则在一些区域差异明显,最大超过了0.2 m,中误差为3.8×10-2m.可见,当前GRACE卫星时变重力场只能确定出上千公里及以上尺度区域的水储量变化.

Global water storage variations on the land and in the ocean are recovered by using GRACE monthly time-variable gravity fields, and these results are compared with land hydrological data, satellite altimeter data and oceanic model solutions. Comparing the gravity change at SOURE station calculated by land water storage variation with the result from GRACE gravity field coefficients truncated to degree and order 15, we find that they are close to one another with an evident annually varying term. In the Amazon drainage basin, for a 106 m smoothing radius and GRACE gravity field coefficients truncated to degree and order 15, the annual amplitude of average water storage variation thickness is about 15.6×10^-2 m, smaller than 23.7 ×10^-2 m for a 4 × 10^5 m smoothing radius. When we study the water storage variation in the Yangtse drainage basin, we expand the hydrological data in spherical harmonic coefficients, and dispose them of truncation and smoothness as same as GRACE data. The result indicates that the average thickness of water storage variation measured from GRACE agrees well with the hydrological data solution. For the range of latitudes - 66 to 66 degrees in the ocean, the seawater mass variation recovered from GRACE is in good agreement with the result from satellite altimeter combined with the oceanic model, but for the 2°× 2° grid, there exist differences in some grid regions, and the largest is over 0.2 m, the RMS is 3.8×10^-2 m. So the GRACE satellite time-variable gravity field can only determine water storage variation over thousands kilometers or more with high accuracy presently.