###### Abstract
Similar to the Jason series, these altimeter measurements would have performed better obtaining the east components of vertical deflection. Consequently, the HY-2 series of measurements is extremely valuable for recovering marine gravity anomalies because of their different spatial distribution compared to other altimeter missions. [PERSON] et al. [17] verified that HY-2A provides similar marine gravity recovery to other altimeters on the basis of 1 Hz measurements. Meanwhile, HY-2A GM data were also proved to be reliable for calculating vertical deflections on regional and global scales [21; 22]. [PERSON] et al. [16] and [PERSON] et al. [23], respectively, indicated that 20 Hz waveform data records of HY-2A GM can derive a refined regional marine gravity field model. In contrast, HY-2B, HY-2C and HY-2D have a significantly lower application rate for constructing marine gravity models even though there are plans for them to be placed in drifting orbits in a future geodetic mission. In addition, the along-track analysis of the resolution capabilities of the HY-2 series missions is rare. Under this circumstance, this paper fully evaluated the performance of four HY-2 series missions (HY-2A, HY-2B, HY-2C, HY-2D) to construct a global marine gravity model. The two-step waveform retracker has proved to be effective for improving the range precision of HY-2A measurements by a factor of 1.6 [24]; thus, this two-step retracking strategy was used in this study. The performances of SSH measurements for HY-2 series missions were uniformly evaluated for accuracy and resolution; then, the vertical deflections at crossover points and along-track points were calculated and evaluated. Finally, after incorporating the data from these HY-2 missions, the derived global marine gravity models were fully evaluated by ship-borne gravity data and the latest published models. It is well known that such an analysis cannot cover all possible conditions, but we aimed to discuss this for a number of study areas. For data integrity, 30\({}^{\circ}\)\(\times\) 30\({}^{\circ}\) rectangle study regions over six open ocean areas were selected: the North, South, and Mid- Pacific; Indian; and the North and South Atlantic. The specific scopes are located, respectively, at (150-180\({}^{\circ}\)E, 10-40\({}^{\circ}\)N), (150-180\({}^{\circ}\)W, 10-40\({}^{\circ}\)S), (105-135\({}^{\circ}\)W, 15\({}^{\circ}\)S-15\({}^{\circ}\)N), (60-90\({}^{\circ}\)E, 10-40\({}^{\circ}\)S), (30-60\({}^{\circ}\)W, 10-40\({}^{\circ}\)N) and (0-30\({}^{\circ}\)W, 10-40\({}^{\circ}\)S). Hereafter, the study areas are renamed, respectively, as Region 1, Region 2, Region 3, Region 4, Region 5 and Region 6. In these regions, regional and along-track directional experiments were launched. The former contained an accuracy assessment of SSH and vertical deflection at crossover points; for the latter, groups with similar ground tracks were selected to carry out resolution analyses and directional vertical deflection calculations. The remainder of this paper is organized as follows. Section 2 provides a general description of the dataset (e.g., altimeter data and retracking), as well as other gravity models for comparison purposes. The quality assessments for both accuracy and resolution are presented in Section 3. In Section 4, the performance of the 4 HY-2 series missions in calculating vertical deflections is investigated and compared. Section 5 evaluates the HY-2 series-derived global marine gravity model using marine data, including the latest published models and shipborne measurements. The final \(1^{\prime}\times 1^{\prime}\) results will be titled with NSOAS22 and available for download. For better understanding, the methods of evaluating HY-2's performance in marine gravity research were summarized in Figure 1.