Marine Gravity Field Refinement Using Iterative Frequency-Domain Combination

Summary High-accuracy marine gravity fields are essential for resolving fine-scale seafloor structures and supporting marine geophysical studies. However, the recovery of short-wavelength gravity signals from conventional satellite altimetry is limited by track spacing, measurement noise and filtering. The Surface Water and Ocean Topography (SWOT) mission provides dense wide-swath observations and improves the recovery of shorter-wavelength sea-surface slopes. Long-term multi-mission altimetry models, however, generally provide more stable gravity information at longer wavelengths. We therefore developed an iterative frequency-domain method that combines the medium- and long-wavelength component of DTU21 with the medium- and short-wavelength component of SWOT_04. A Gaussian low-pass filter and its complementary high-pass filter were used to combine the two models. Candidate cutoff wavelengths were tested at 1 km intervals. Quality-controlled National Centers for Environmental Information (NCEI) shipborne gravity observations were used only to select the cutoff wavelength. The minimum residual standard deviation (STD) of 4.25 mGal was obtained at 22 km. The final model was independently validated using Japan Agency for Marine-Earth Science and Technology (JAMSTEC) shipborne gravity data. The combined model achieved an STD of 3.83 mGal, compared with 4.11 mGal for SWOT_04 and 4.21 mGal for DTU21. This represents reductions of 6.8 per cent and 9.0 per cent, respectively. The combined model also had the lowest STD across all water-depth and distance-to-coast intervals. These results show that the proposed method combines the complementary spectral information of the two altimetry-derived gravity models and improves the accuracy of regional marine gravity fields.