Research On Satellite Geodesy Inversion Theory And Method Of Surface Mass Transport

Global environmental changes such as sea level rising,glacial melting,and terrestrial water storage change are closely related to the process of surface mass transport.Researching on surface mass transport inversion to fully understand the law of spatial-temporal distribution of global surface mass transport,especially in typical regions,is of great significance to scientific issues such as prediction and mechanism research of climate and environmental changes,as well as human social activities and economic development.Since the successful launch of GRACE satellites,long-term effective monitoring of surface mass transport has become feasible,which quantitatively reveals the transport of surface mass on a large scale.The transport of surface mass will cause gravity field change of the Earth and also vertical deformation of its surface.GNSS technology provides an effective technical means for real-time continuous monitoring of vertical surface deformation.The signal of surface mass transport can be extracted by using GNSS vertical displacement.Currently,Satellite geodesy technology is developing rapidly.The successful launch of GRACE Follow-on satellites and the development of GNSS technology represented by GPS,BDS and so on provide a more powerful solution for researches on surface mass transport.Therefore,researches on satellite geodesy inversion methods for surface mass transport are not only a hotspot of current scientific researches,but also have practical significance and great application value for issues such as the monitoring of global environmental changes.This thesis focuses on satellite geodesy inversion theories and methods for surface mass transport.With the help of GRACE and GNSS observation technology,the inversion theories and methods based on GRACE data and that based on GNSS vertical displacement are studied systematically.The research work and innovation Points of this paper are as follows:1.The research progress of satellite geodesy inversion methods for surface mass transport is analyzed.The research statuses of inversion methods based on GRACE data and GNSS vertical displacement data are summarized.The progress of filtering methods of GRACE satellite time-variable gravity and its application researches of satellite time-variable gravity on terrestrial water storage variation,sea level variation,and glacier mass variation are reviewed.2.To deal with the problem of insufficiency when analyzing inter-annual variations by using linear fitting model,a quadratic term is added to the model and then it is applied to the long-term trend analysis of both global and reginal terrestrial water storage inversion.The results show that when the quadratic term is added the speed of terrestrial water storage variation can be described,which contributes to researches on areas where surface mass changes significantly.Additionally,the GRACE RL06 and RL05 time-variable gravity field model data are compared in terms of global terrestrial water storage inversion results,degree variance of time-variable gravity field model and C₂₀ time series.The RL06 model,using the new computation model and the modified calculation method,has improved greatly in data quality and accuracy.Under the same conditions,the degree variance of CSR RL06 model is minimum while that of JPL RL06 model is maximum;the signal-to-noise ratio of the inversion results by using CSR RL06 data is maximum while that of JPL RL06 data is minimum.3.To deal with the problem of south-north stripe noise,filtering methods of satellite time-variable gravity are studied.For the parameters selection of common Gaussian filtering,common filtering methods are compared and the optimal parameters selection is analyzed by using maximum signal-to-noise ratio as the criterion.And the parameters of decorrelation filtering method are determined by assessing the image of inversion result.A new filtering combination model based on the error characteristics of spherical harmonic coefficients of GRACE satellite time-variable gravity is established which requires only one step of processing so that the calculation is simpler.Based on the new filtering combination model,a new anisotropic combination filtering method is proposed which combines the characteristics of anisotropic Gaussian filtering and RMS filtering so that more low-order terms are retained and high-order noise are suppressed,and stripe noises are effectively eliminated.Compared to single filtering and traditional two-steps combined filtering method,the signal-to-noise ratio of the new anisotropic combination filtering is improved.4.The sensitivity degree of the inter-satellites distance variability observation to the regional surface mass change is analyzed.Mathematical models of Mascon method based on kinetic and energy conservation are discussed.And the results of Mascon model released by CSR,JPL and GSFC are compared on a global scale and regional scale.The results indicate that the inter-satellites distance variability observation is extremely sensitive to the regional surface mass change and the surface mass variation have a limited influence on inter-satellites distance variability observation in terms of spatial distribution.Compared with spherical harmonic coefficients inversion,Mascon inversion method does not need filtering and its results have higher signal-to-noise ratios,more retained effective signals,higher temporal-spatial resolution and stronger correlation with GLDAS model.Among the three sets of Mascon results,the JPL Mascon results have the highest signal-to-noise ratios.5.The point-mass model inversion method is improved.Additional spatial constraints that conform to reality are introduced to increase the constraint information of the parameters to be estimated and decrease the ill-condition level of norm equations.The Helmert variance component estimation method is introduced to adaptively determine the weight ratio of the virtual observation equations and the original observation equations,making the inversion results more be more in accordance with the reality and physical significance.The improved point-mass model inversion method can be effective used in regional terrestrial water storage variation inversion,which provides a new way to monitor surface mass transport by satellite gravity.6.GPS observations of stations from Gansu CORS network and the Crustal Movement Observation Network of China between September 2013 and December 2016 are processed and the vertical displacements time series of those observation stations are obtained and compared to which calculated by using GRACE data.The characteristics of the vertical displacements in the study area are analyzed and the results show a strong consistent between GPS and GRACE vertical displacement time series.More than 50 percent GPS vertical displacement annual signal amplitude can be effectively explained by GRACE vertical displacement annual signal.Average29 percent nontectonic deformation contained by GPS vertical displacement time series is rooted in load deformation by environment load change.7.The simulation verification of regional terrestrial water storage variation inversion based on GNSS vertical displacement is carried out.And terrestrial water storage variations in Shanxi-Gansu-Ningxia area are inversed by using GPS observation data of Gansu CORS network and the Crustal Movement Observation Network of China between January 2014 and December 2016.The results show that quantity and distribution of observation station in study area and outside mass variation have strong influence on inversion results.For improved accuracy inversion result,dense area should be selected and mass outside should be deducted as possible when regional terrestrial water storage is inversed.Additionally,the vertical displacement caused by the change of atmospheric mass in the seasonal periodic signal of the GPS vertical displacement of the observatory in the study area is the main component,accounting for averaged 38.4%of the GPS vertical displacement signal and terrestrial water storage variation has little effect on vertical displacement.Further,the inversion results of surface fluid mass variation show obvious seasonal periodic changes,the inversion results and GAC model calculation of atmospheric mass change results in the spatial distribution has a better overall consistency,the annual amplitude spatial distribution is basically consistent,both show the trend of reduction from east to west.The annual amplitude of atmospheric mass variation is about 10⁸0mm and the annual amplitude of the total variation of atmospheric mass and terrestrial mass is about 50²50mm.8.Characteristics of regional terrestrial water storage joint inversion based on GRACE/GRACE FO satellites and GNSS observation data is summarized.Considering the complementarity between the two methods in terms of temporal-spatial resolution and spatial coverage and aiming at the limitation of inversion method based on single observation technology,regional terrestrial water storage joint inversion based on the two methods is studied.By using GRACE/GRACE FO Level-1B data GNSS vertical displacement and GNSS vertical displacement,the observation equations of inversion are established by Mascon method and load Green function method separately and a theoretical model of regional terrestrial water storage joint inversion is established.For the problem that errors exist in coefficient matrix,weighted total least squares method for joint adjustment model with weight scaling factor is introduced,thus the theory is more rigorous.Because of the high sampling rate and high sensitivity of GNSS vertical displacement and GRACE/GRACE FO Level-1B data,the accuracy and spatial-temporal resolution of regional surface mass transport can be theoretically improved.