利用GRACE、GPS和绝对重力数据监测斯堪的纳维亚陆地水储量变化

Measuring Terrestrial Water Storage Change Using GRACE,GPS and Absolute Gravity Data in Scandinavia

重力卫星GRACE(gravity recovery and climate experiment)监测斯堪的纳维亚半岛陆地水储量变化会受到冰川均衡调整(GIA)信号的严重影响。首先根据该地区绝对重力和GPS并址观测数据计算了GIA重力和垂直位移的实测线性比值,利用该比值和GPS网观测的垂直位移速度场得到了GIA重力。然后,对GRACE观测的重力变化速率进行GIA重力改正,进而可分离陆地水储量变化趋势,避免了使用GIA模型所带来的巨大不确定性,并根据观测数据完整估计了所得结果的不确定性。最后与水文模型作对比分析。结果表明,实测的GIA重力-垂直位移线性比值为0.148±0.020μGal/mm(1Gal=10-2 m/s2),该结果检验了Wahr的理论近似值且与北美实测的结果非常接近。2003年1月至2011年3月期间,斯堪的纳维亚半岛陆地水储量存在明显的增加趋势,信号的主体位于半岛南端的维纳恩湖附近,总的水量增加速率为4.6±2.1km3/a,数据观测期间的累积增加水量为38±17km3。研究结果与WGHM水文模型的结果有较好的一致性,相关系数达到0.69,而与GLDAS水文模型的相关性略小。

Gravity satellite GRACE-derived terrestrial water storage change would be seriously affected by glacial isostatic adjustment（GIA） in Scandinavia. To solve this problem, it is calculated that the measured linear ratio of GIA gravity rates and vertical displacement rates according to the data from collocation stations for absolute gravity and GPS. Using the linear ratio and uplift field derived from GPS observation network, the gravity signal of GIA is got. Gravity change rates from GRACE RL05 data can be corrected for GIA using independent gravity rates derived from GPS vertical velocities, and then it is calculated that corresponding equivalent water thickness in Scandinavia and the uncertainties are evaluated by considering the uncertainties from data. The proposed method utilizes observational data only and can avoid the enormous uncertainty from GIA models.The results are compared with that of two hydrological models. The ratio of gravity versus uplift obtained by ground-based measurements in Scandinavia is 0.148±0.020 μGal/mm（1 Gal=10-2 m/s2）, which validates Wahr＇s approximate theoretical ratio and is very close to the result from North America. From January 2003 to March 2011, terrestrial water storage shows obvious increase in Scandinavia. The main signal locates at the V？nern lake which is in the southern tip of the peninsula. The rate of total water storage is 4.6±2.1 km3/a and the corresponding cumulative quantity is 38±17 km3 for the period 2003 to 2011. Results from hydrological models are consistent with the result very well. The correlation coefficient between GRACE and WGHM hydrological model can reach 0.69, while for GLDAS model the correlation coefficient is slightly smaller.