利用SWARM卫星高低跟踪探测格陵兰岛时变重力信号

Time-variable gravity signal in Greenland revealed by SWARM high-low Satellite-to-Satellite Tracking

GRACE重力卫星任务即将结束,后续GRACE Follow-On卫星计划于2017年发射,在此期间,迫切需要一个新的卫星计划继续对全球时变重力场进行连续监测,以保证时变重力场信息时间序列的连贯性.SWARM计划包括三颗轨道高为300-500km的近极轨卫星星座,类似于三颗CHAMP卫星,具有接替时变重力场探测的潜力.本文首先分析SWARM（模拟）、CHAMP、GRACE反演至60阶时变重力场球谐系数的误差特性及不同高斯平滑半径对高频误差的抑制效果,然后分别利用SWARM、CHAMP、GRACE的时变重力场模型恢复全球质量变化,结果表明,SWARM模拟观测数据的高频误差低于CHAMP观测数据,探测时变重力场的整体精度优于CHAMP,略低于GRACE探测精度;其次,对比2003年1月—2009年12月期间CHAMP（hl-SST）和GRACE（ll-SST）时变重力场模型反演格陵兰岛冰盖质量变化趋势,结果显示,CHAMP数据得到格陵兰岛冰盖质量变化趋势为-50.2±2.0Gt/a,GRACE所得结果为-41.2±1.6Gt/a,两者相差21.8%;最后,对比2000年1月—2004年12月间SWARM模拟数据和＂真实＂模型数据反演的格陵兰岛冰盖质量变化趋势,结果表明,两者相差19.2%.本文研究表明,利用SWARM hl-SST数据探测时变重力场可以达到20%相对精度水平,有潜力用于填补GRACE和GRACE Follow-On期间探测地球时变重力场的空白.

Amid a termination of the Gravity Recovery and Climate Experiment（GRACE）mission and before the launch of GRACE Follow-On（in 2017）,There is an urgent need to have a new satellite for continuous monitoring the global time variable gravity field.SWARM mission,which has three satellites,will orbit Earth at an altitude of 300-500km on near-polar and nearcircular trajectories.This mission shares similarity to that of CHAllenging Minisatellite Payload（CHAMP）mission,and hence,capable of continuous monitoring of the global time variable gravity field.In this paper,we first analyze the error characteristics of the spherical harmoniccoefficients up to degree 60 of the variable gravity field and investigate the effect of different Gaussian smoothing radii on the higher degree frequency error for SWARM simulation,CHAMP and GRACE data,followed by inversion of the global mass change from the time variable gravity field model of SWARM,CHAMP,and GRACE data.It shows that the error in the higher degree of SWARM is lower than that CHAMP with the inversion result better than that of CHAMP,while worse than that of GRACE;Second,we get the ice mass loss during January 2003 and December 2009 over the entire of Greenland from CHAMP is-50.2±2.0Gt/a,whereas-41.2±1.6Gt/a from GRACE.Their trends differ by 21.8% whereas the trend between SWARM simulation and‘True＇model over the entire of Greenland differ by 19.2% only.Based on the above result,we conclude that SWARM hl-SST can be detected to the time-variable gravity signal in the 20%relative accuracy level and retrieve time-variable gravity information in the absence of the GRACE twin satellites,and before the launch of GRACE Follow-On.