| The increasingly mature space science and satellite measurement technology provide a new measurement method for the development of geodesy.Since the beginning of this century,some developed countries in the United States and Europe have successively implemented multiple gravity satellite programs,providing a highprecision measurement method with high resolution,wide monitoring range,which are not affected by surface environmental factors for accurately measuring the Earth’s gravity field,describing the dynamic material flow of the Earth,and explaining the dynamic changes between various spheres of the Earth.In particular,the successful implementation of the GRACE satellite program,making it possible to obtain highprecision global time-varying gravity fields.Among the methods for retrieving the Earth’s gravity field using GRACE data,spherical harmonic coefficient inversion is the most popular one,due to its advantages of simple operation and less cost of calculation.However,owing to the construction of satellite orbit and measurement errors,the global potential field obtained by this approach has obvious stripes and serious high-frequency errors.The spherical harmonic coefficient products released by major institutions have undergone truncation,which can effectively reduce the interference of high-frequency noise in the signal.However,there are still significant stripes and residual highfrequency noise in the signal after that.In practice,filters are commonly used to remove the stripes and noise,the processed spherical harmonic coefficients can be used to invert the global time-varying gravity field,but filtering can also cause leakage of real signal.Therefore,this thesis has conducted research on the filters of spherical harmonic coefficients,signal leakage correction methods,and regional applications.The main contents and results of this Thesis are as follows:(1)The main procedures of processing the GRACE spherical harmonic coefficient are summarized,the effectiveness of different filter types is analyzed,and the optimal spatial smoothing filter and optimal decorrelation filter—Fan filter with radius of300 km and CHAMBERS decorrelation filter are determined.(2)Based on the Tikhonov regularization in traditional DDK filter and the temporal correlation between the spherical harmonic coefficients of the monthly gravity fields,a time-varying DDK i.e.,two-parameter regularization model is constructed,and a recursive algorithm of that are summarized.Besides,the theory of using the generalized cross validation to find the optimal regularization parameter combination is outlined,so that a temporal DDK filter is achieved.After analysis and verification,it is found that the signal to noise ratio of temporal DDK filter is greater than all single filters,which is 5% higher than DDK4 filter.Considering Mascon solutions as standard reference,it showed that the result of temporal DDK filter is more similar as Mascon solutions than all the others.(3)This Thesis studied the terrestrial water storage variation in the Mississippi River Basin(MRB),and compared the effects of two leakage correction methods in the basin.It was found that the results of the scale factor method and the forward modeling recovery method were highly correlated with the simulation results of GLDAS.Overall,the scale factor method outperforms the forward modeling method.In TWS variation study,the TWS variation in the MRB can be divided into three stages,with no significant change trend from 2003-04 to 2005-07,an upward trend of 1.02cm/a from2005-08 to 2011-07,and an upward trend of 0.51cm/a from 2011-08 to 2017-06.The interruption of the variation trend is caused by high temperature and reduced precipitation in 2006 and 2012.In spatial,it is found that decreased precipitation,increased temperature,and overexploitation of groundwater jointly led to a significant downward trend in TWS at the border of Kansas,Texas,and Oklahoma in the United States.The decline of TWS in the Ohio River basin is mainly caused by the reduction of runoff.(4)In the research on the application of GRACE seismic change detection,it was found that the accuracy of GRACE met the requirements for detecting the magnitude8.4 earthquake that occurred in Bengkulu,Sumatra,in September 2007,and that the coseismic gravity change of the earthquake was detected successfully.Besides,the preearthquake incubation time and the post-earthquake impact duration of the earthquake also are estimated by GRACE.Plate motion is the main reason for frequent earthquakes in this region.Gravity distribution regions with different characteristics are often distinguished by plate boundaries.Large earthquakes in this region tend to occur in the transition zone between two large bodies with significantly different gravity distribution characteristics. |
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