# Evaluation of HY-2 Series Satellites Mapping Capability on Mesoscale Eddies
## 5 Conclusions  
In this paper, we analyzed the impact of HY-2 series satellites on the detection of mesoscale eddies by combining them with Jason-3, Sentinel-3A and Sentinel-3B missions at three latitude regions. We achieved this through a series of pseudo-observation experiments based on the geographical and temporal positions of altimetry satellite along ground tracks, using the outputs from the HYCOM model. Two altimetry satellite combinations were selected, namely, the reference group in the Jason-3+Sentinel-3A/B configuration and the evaluation group in the Jason-3+Sentinel-3A/B+HY-2B/C/D configuration. After generating synthetic SSH maps by an OI procedure, we applied the eddy identification algorithm to the original model outputs and the gridded products and then compared the eddy fields characteristics. The result shows that the addition of HY-2 series satellites reduced the distance to the nearest observation by approximately 40% in all regions, with the distance to the nearest observation of 54 km at high latitudes, 102 km at middle latitudes and 116 km at low latitudes. Compared to the reference groups, the evaluation groups including HY-2 series satellites can effectively reduce synthetic product differences by 8%, 23% and 10% at high latitudes, middle latitudes, and low latitudes, which shows a great enhancement of satellite sampling capability. Moreover, the evaluation groups could alleviate eddy mis-estimation and add details to the eddy radius and amplitude. By comparing with eddies captured from model datasets, we found that the eddy recognition rate and accuracy were highest in the middle latitude regions, with values of around 50%, while the superior ability of HY-2 was demonstrated at high latitudes, with maximum improvements of 14% and 16% in eddy recognition rate and accuracy. This indicates that the enhancement of the eddy detection \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{**Eddy Recognition Rate/\%**} & \multicolumn{2}{c}{**Eddy Recognition Accuracy/\%**} \\ \hline  & **High** & **Middle** & **Low** & **High** & **Middle** & **Low** \\  & **Lattitudes** & **Lattitudes** & **Lattitudes** & **Lattitudes** & **Lattitudes** \\ \hline Reference Group & 30.97 & 55.35 & 18.80 & 31.82 & 55.87 & 42.31 \\ Evaluation Group & 35.40 & 52.56 & 21.37 & 37.04 & 55.66 & 45.45 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Eddy recognition rates and accuracy for reference groups and evaluation groups in different latitudes. Eddy recognition rate is equal to the number of real eddies captured in the gridded product divided by its total number of eddies, and eddy recognition accuracy is equal to the number of real eddies captured in the gridded product divided by the total number of eddies in its corresponding model. capability of HY-2 series satellites is not uniform. Both the level of orbital coverage and the complexity of the eddy field affect the results. Generally speaking, HY-2 series satellites can effectively improve the mapping capability of mesoscale eddies with a significant increase in orbital coverage. This study provides a comprehensive assessment of the ocean observation capability of the HY-2 series satellites and offers a basis for the future scientific use of the HY-2 satellite data. However, in this paper, the detection performance of the HY-2 series satellites is only assessed in terms of mesoscale eddy detection, and the detection capability on the ocean dynamics environment still deserves further detailed study. Conceptualization, F.Y., J.Q. and G.C. ; methodology, F.Y. and J.Q. ; software, J.Q. ; validation, F.Y., Y.J. and G.C. ; formal analysis, F.Y. ; investigation, J.Q. ; resources, Y.J. and G.C. ; data curation, J.Q. ; writing--original draft preparation, J.Q. ; writing--review and editing, F.Y. and G.C. ; visualization, J.Q. ; supervision, F.Y. ; project administration, F.Y. and G.C. ; funding acquisition, F.Y. and G.C. All authors have read and agreed to the published version of the manuscript.