Predicting bathymetry in South China Sea using the gravity-geologic method

The gravity-geologic method (GGM) was implemented for 1' X 1' bathymetry determination in 112 degrees E-119 degrees E, 12 degrees N-20 degrees N region in the South Sea. 63179 ship-derived data (as the control points) were used in this method to divide the observed gravity anomalies into long- and short-wavelength gravity anomalies, the density contrast between the seawater and the ocean bottom topographic mass is 1. 32 g . cm(-3), which was estimated by ship data in this area. The residual 10529 ship-derived data(as the check points) were used for estimating accuracy of the predicted bathymetry model, differences between the interpolation depths of GGM model and the ship-data of check points reached approximate mean value of -1. 64 m, standard deviations of 76. 95 m and relative precision of 4. 06%. In addition, according to the differences of the quantity, distribution and ocean bottom topographic conditions of the control points, three areas were chosen for accuracy statistics, results showed that: in areas with denser and better distributed shipborne measurements,the bathymetric model predicted by GGM was more accurate than ETOPO1 model, in other areas, the accuracy of GGM model may be lower at a certain extent, but which was still more accurate than directly gridded model from dispersed ship data. In order to determine the reason of big differences, check points with worse precision were analyzed along, profile of shipborne depths from two cruises were selected for researching, what' s more, relationships between the differences, relative precisions and the bathymetry and gravity anomaly were also showed, respectively, results "showed that: In term of the GGM model' s accuracy, the influence of correlations with bathymetry and gravity anomaly was small, conversely, the influence of the complexion' s degree of ocean bottom topography was large, topography gradient varied smoother resulted in a better predicted accuracy. As a final result, the respective advantages of GGM model and ETOPO1 model were considered and then a comprehensive bathymetry model was presented by integrating all available ship data.