Data interpolation of SWOT/KaRIn blank for modelling marine vertical gradient of gravity anomaly

SUMMARY The Surface Water and Ocean Topography (SWOT) altimeter mission provides high-resolution sea surface heights (SSHs), which can be used to retrieve high-precision and high-resolution marine gravity fields. However, data acquisition from the SWOT satellite’s Ka-band Radar Interferometer (KaRIn) is characterized by a 20-km nadir gap and a seam gap. Interpolation methods were employed to fill the nadir and seam gaps in the SWOT/KaRIn SSHs. The 20-km nadir gaps were interpolated using SWOT/KaRIn SSHs from flanking swaths on both sides. To reduce temporal decorrelation, seam gap interpolation was performed separately for each pass using SWOT/KaRIn SSHs from adjacent passes. The vertical gradient of gravity anomaly (VGGA) model was inverted from the interpolated SWOT/KaRIn SSHs using least-squares collocation and the remove–restore methods. The study region was selected as the Philippine Sea, with SWOT/KaRIn SSHs from cycle-02 serving as the experimental data set. SWOT/KaRIn SSHs were processed using four schemes: Kriging interpolation, Cubic Spline interpolation (CSI), mean sea surface (MSS) interpolation and no interpolation. The VGGA models inverted from the respective processed SWOT/KaRIn SSHs are hereafter referred to as Kriging_SWOT_VGGA, CSI_SWOT_VGGA, MSS_SWOT_VGGA and NO_SWOT_VGGA. The results show that the NO_SWOT_VGGA model exhibits distinct strip artefacts, whereas the interpolated VGGA models eliminate these artefacts. All interpolated VGGA models exhibited superior consistency with the reference model compared to the NO_SWOT_VGGA model. Among them, the Kriging_SWOT_VGGA model achieved optimal consistency. Therefore, this study on interpolation methods for SWOT/KaRIn SSHs provides a novel methodological framework for the recovery of high-precision marine gravity fields from SWOT observations.