WHU-IOGM: A Global Three-Dimensional Internal Oceanic Gravity Field Model Determined by Geodetic Methods

Determining the internal oceanic gravity corresponds to solving for the Earth’s internal gravitational potential, for which traditional geodetic theories (Stokes’ and Molodenskii’s theorems) are not directly applicable. To overcome this constraint, the concept of “seawater layer” is introduced. The first original global three-dimensional internal oceanic gravity field model WHU-IOGM was constructed using four key methods: (1) sliding-window Newtonian integration, (2) multi-node parallel computing on a high-performance supercomputing platform, (3) an ellipsoidal harmonic expansion algorithm with improved convergence properties, and (4) a spherical-to-ellipsoidal harmonic coefficient transformation algorithm. Compared with underwater gravity measurement continuation, the “seawater layer” method has more advantages in theoretical rigor and accuracy. The theoretical systematic error of WHU-IOGM was evaluated, with the global RMSE of about 6.28 mGal and a mean error of about 0.19 mGal. Based on the WOA18 deep stratification framework, we added a grid layer corresponding to the actual seabed depth, expanding the original 102-layer system to a total of 103 layers. The inclusion enhances the model’s conformity with actual seabed topography. This structural refinement enables a more accurate and detailed representation of the ocean’s internal gravity field, providing a theoretical basis and algorithmic models for underwater gravity measurement and underwater navigation.