Research On Improving The Accuracy Of Gravity Inversion Of Seabed Terrain

The seabed topography plays an important role in marine monitoring,marine resource management and marine strategic development.With development of satellite altimetry and ship bathymetry,a large number of high-precision altimetry gravity data and bathymetric data have been continuously updated and published.International organizations use the gravity bathymetric inversion technology and integrate ship bathymetric data,issuing a variety of submarine topographic models,such as ETOPO1 series,GEBCO series.At present,most scholars mainly focus on the gravity seabed topography inversion in different sea areas by using different methods,but few studies focus on optimization of inversion methods,analysing the influence of ship bathymetric data density on inversion results and inversion terrain accuracy improvement.According to the distribution characteristics of actual ship bathymetric data,this paper studies the inversion methods accuracy performance under different ship bathymetric data by simulating the density distribution of ship bathymetric data,and optimizes the SAS method proposed by Smith and Sandwell.Finally,the inversion method with the best accuracy in the experiment is selected to invert the topography of the East China Sea.The main contents and work as follows:?1?The gravity admittance theory is elaborated in detail,and topographic gravity anomaly calculated process by submarine topography is given.Analysing the influence of lithosphere on the long wave term of gravity anomaly.The equilibrium state information of lithosphere is described by using the equilibrium model.Corresponding filtering is designed according to the influence of lithosphere and continuation effect on gravity anomaly.?2?The coherence between gravity anomaly and topography in the wavenumber domain is calculated by power spectral density function.The results show that the coherence between gravity anomaly and topography is strong from the 20 km to 150 km in the study area.Therefore,this band is used as the truncated band in the SAS method inversion.?3?The difference between SAS method and GGM of seabed topographic inversion is compared.Aiming at the non-linear factors between terrain and gravity anomaly,an iteration method is proposed to replace the linear regression method of coefficient solution in SAS method to optimize the SAS method.The experimental results show that optimized SAS method can improve the terrain accuracy of SAS method in the ship bathymetric data dense and sparse areas.?4?The influence of the different density ship bathymetric data in the same area on the results of SAS,GGM and optimized SAS methods is studied.The experimental results show that the accuracy of initial model?Unfused the deviation value of ship bathymetry?and final model?fused the deviation value of ship bathymetry?calculated by GGM method can reach 59.565 m and 37.326 m respectively in the ship bathymetric data dense area,which are superior to the results of the other two methods.The topographic results obtained by GGM method perform still best In the ship bathymetric data sparse area,but the accuracy of the models obtained by three methods has decreased.This paper improves the terrain inversion results in ship bathymetric data sparse area by fusing GEBCO₂014 model data.In a word,The calculation speed of SAS method is faster than that of GGM,and it is suitable for obtaining large area seabed topography quickly,while GGM method is more accurate and suitable for local high precision terrain inversion.?5?The GGM method is selected to invert the topography of local sea area.The accuracy of the initial model and the final model can reach 91.808 m and 80.780 m respectively,and the number of ship inspection points with relative error less than 5% can reach 98.37%.The model is superior to ETOPO1 model,GEBCO₂014 model and grid fusion data.