Refining Of Quasi-geoid Based The GOCE Gravitational Model And Terrain Correction

The accuracy and resolution of the satellite gravimetric data has dramatically developed,since GOCE satellite was launched on March17,2009, which one of the goals is to determinethe global geoid within the1cm level precision. With the successful launch of GOCE satellite,studies on data processing and applications of GOCE mission will become a hot issue ingeosciences for the next several years. In this paper, the quasi-geoid height is calculated byadopting the gravity field model data in GOCE L2product and SRTM topography data.What’s more, the corresponding theories and methods are introduced.The main content of the paper is summarized as follows:(1) The conventional concepts and theories of refining of geoid, especially remove-and-restore technique are introduced.(2)The earth gravity field models based on GOCE satellite data are introduced andcompared. Firstly, the analysis of their degree variances is presented. Secondly, the geoidheight computed by the selected gravity field models is compared with GPS/leveling data inthe research area. Finally, a Least Square Fitting (LSF) is used to correct and modify themodel values. The calculation results shows that, in the three approaches of recovery of earthgravity field model using GOCE products, the precision of direct approach (DIR) is thehighest, next is time-wise approach (TIM), the space-wise approach (SPW) is the worst; Theaccuracy of the GOCE models is about0.2m lower than EGM2008gravity field model; Theerror of GOCE gravity field model in plain and mountains is about19cm and42cmrespectively.(3)The algorithm of the ultra-high degree and order normalized associated Legendrefunctions (ALFS) is introduced and analyzed. Calculation results shows that the recursivemethod between every order and degree is excellent in efficiency and numerical accuracy.(4)The indirect effect of topography on geoid is calculated and analyzed. Calculationresults show that the greater topographic relief, the greater the indirect effect; the main item ofthe formula for calculating the indirect effect has the leading role, the rest is small and can beignored on the flat areas; besides, integral radius has little effect on the calculation results ofthe indirect effect. (5)The “remove-and-restore” method which take into account the gravity field modelwith topographic correction is discussed. And, by way of example, the calculation resultsshows that this method is effective; what’s more, polynomial fitting can effectively reducesystematic errors between gravity geoid and geometry geoid.