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In this paper, the admittance function between seafloor undulations and vertical gravity gradient anomalies was derived. Based on this admittance function, the bathymetry model of 1 minute resolution was predicted from vertical gravity gradient anomalies and ship soundings in the experimental area from the northwest Pacific. The accuracy of the model is evaluated using ship soundings and existing models, including ETOPOl, GEBCO, DTU10 and V15. 1 from SIO. The model's STD is 69.481m, comparable with V15. 1 which is generally believed to have the highest accuracy.

New bathymetry models in the northwestern Pacific Ocean are presented at 1 arc-minute and 15 arc-second resolution. The latest version of the altimetric vertical gravity gradient (VGG) anomalies from Scripps Institute of Oceanography, ∼7 million single-beam depths from the National Centers for Environmental Information, and ∼80 GB of multibeam grids from the Japan Agency for Marine-Earth Science and Technology are used. The ship-board depths are used to constrain bathymetry at wavelengths longer than 200 km, and calibrate the local topography to VGG ratio at 15–200 km wavelength bands. The VGG is used to predict bathymetry at 15 ∼ 200 km wavelength bands. The spectrum analysis results show that the 1 arc-minute model has more power than models predicted from gravity anomalies at wavelengths shorter than 100 km. The standard deviation of differences between the 1 arc-minute model and ship-board depths is 44.76 m, and it is 102.842 m comparing to the SIO topo_20.1.nc model. The accuracy of the new 1 arc-minute model has been improved significantly from our last bathymetry model, BAT_VGG, and has a better accuracy than that of the DTU18, GEBCO_08, and ETOPO1 models. The accuracy of the 15 arc-second model is consistent with that of SRTM + V2.1 and GEBCO_2020. [ABSTRACT FROM AUTHOR]

We design a program to calculate bathymetry model by combining vertical gravity gradients anomalies (VGG) and ship soundings. A bathymetry model in the experimental area (0 ∼ 30° N, 150 ∼ 210° E) from the North Pacific is calculated with the program. The bathymetry prediction procedure is validated by comparing the result to in situ ship depth soundings and existing models. The accuracy of the result is about 132.9 m, better than most of the existing models, such as GEBCO, DTU10, ETOPO1, and SIO V15.1. If VGG and gravity anomaly data are combined, the accuracy of recovered bathymetry model will increase by about 29.5 % to about 111.7 m, comparing to SIO V15.1. The bathymetry model constructed using VGG will be independent of gravity anomalies, and can be used to analyze the isostatic mechanism of ocean lithosphere with 3D admittance analysis technology. The accuracy of bathymetry prediction can be improved further by combining VGG and gravity anomaly data. [ABSTRACT FROM AUTHOR]

Using 3D admittance analysis technology, the state of gravity isostasy on Manihiki Plateau was studied with its gravity anomalies and bathymetry. The tectonics of the plateau was analyzed based on the isostatic results and previous research including seismic studies. The relatively low coherence observed between gravity and bathymetry at long wavelength (>100km) may indicate the existence of a low density anomaly beneath the plateau crust. According to the results from airy isostatic analysis, this anomaly is not completely caused by as isostatic adjustment of the oceanic crust to the plateau topography, there must be mass loading beneath the plateau crust causing by an underplating of magma. At short wavelengths, the topography conforms to the airy model. The crust thickness of the plateau is 22.7km, consistent with the seismic research result. A lithospheric flexural isostatic analysis showed that the effective elastic thickness of lithosphere around the Manihiki plateau is 2.5~5.5 km, with an optimal value of 3.5 km. This small elastic thickness may means the plateau is em-placed on a young lithosphere. A flexural model takes into account the mass loading beneath the plateau and the scale of the bottom load was estimated quantitatively. It demonstrates that the mean depth of the bottom load is 18km, the magnitude is about 30% of the topography, and the volume is about 9.3X105 km³. Thus the bottom load is an important part of the plateau crust, while the underplating of bottom load plays an important role in the evolution of the plateau. [ABSTRACT FROM AUTHOR]