## 6 Conclusions  
Satellite altimetry provides the most comprehensive images of a marine gravity field, with accuracies approaching typical shipborne gravity data. Among them, the HY-2 series missions have realized networking observations and provided SSH measurements on a global scale for more than 10 years. The spatial distribution of these measurements is complementary with other altimetry missions for marine gravity recovery research. Therefore, this paper evaluated the performances of HY-2 series data in marine gravity modeling from the following four aspects: accuracy, resolution capability, vertical deflection and gravity anomaly. First, the performance of HY-2 data for four missions (HY-2A GM, HY-2B ERM, HY-2C ERM, HY-2D ERM) proved to be reliable according to the statistics of SSH discrepancies at crossover points. Second, the spectral analysis of repeated along-track data sequences showed that the geoid resolution capacity of HY-2 missions ranged from 18 to 24 km. Meanwhile, resolution capabilities were remarkably enhanced along with the increase in the number of stacking cycles. Numerical tests showed that stacking from 5, 10 and 20 cycles brought an improvement of 26.7%, 45.2% and 61.1%, respectively. Third, along-track vertical deflections and directional components of the vertical deflections at crossover points were calculated and validated with the XGM2019 model. Results showed that the along-track vertical deflections were reliable for all the HY-2 missions, but there were acceptable quality gaps between HY-2A and the others. The accuracy of the east-west component for HY-2C and HY-2D was relatively higher than for HY-2B and HY-2A. Finally, we constructed and validated the global marine gravity models based on three groups of input datasets: HY-2 missions only, multi-satellite dataset without HY-2 missions and multi-satellite dataset with HY-2 missions. To retain more short-wavelength gravity information, we incorporated high-sampled 20 Hz HY-2 waveforms instead of 1 Hz measurements and uniformly retracked them with a two-step waveform retracker. These retracked 20 Hz measurements were averaged to 5 Hz data by using a low-pass FIR filter to constrain high-frequency noise. Residual vertical deflections were then obtained through adding corrections, differentiating, eliminating outliers, low-pass filtering and removing sea surface topography and geoid height. Finally, marine gravity anomalies with 1' \(\times\) 1' resolution were inverted by a remove-restore procedure, with EGM2008 as a reference model. Two approaches were used to evaluate the accuracy of the new gravity model, altimetry-derived marine gravity models and NGDC shipborne gravity data. Verifications revealed that NSOAS22 provided reliable marine gravity anomalies but with a slightly higher noise level than DTU21 and SS V31.1. Taking into account the uncertainty in NGDC shipborne data, a gross error elimination is necessary and the validation accuracy of NSOAS22 was around 3.8-5.3 mGal. The HY-2 dataset was capable of improving marine gravity anomaly recoveries since its complementary spatial distribution may have provided detectable signals over previously unreached areas. However, the HY-2 dataset should not be the only input observation to construct a 1\({}^{\prime}\)\(\times\) 1\({}^{\prime}\) resolution marine gravity model due to its limited spatial resolution. Conceptualization, S.Z. and Y.J. ; Formal analysis, S.Z., Y.J. and T.J.; Methodology, S.Z. and R.Z. ; Validation, R.Z. and T.J.; Visualization, X.K. ; Writing--original draft, S.Z. ; Writing--review and editing, Y.J. All authors have read and agreed to the published version of the manuscript. This study was supported by the National Nature Science Foundation of China, grant number 42192531, 421932513, 41974020, 41804002. This study was also supported by the Fundamental Research Funds for the Central Universities, grant number N2201012 and by Special Fund of Hubei Luojia Laboratory.