## 6 Conclusions  
In the present study, HY-2A/B altimeter L1b data over the polar regions were analyzed. The differences between the SMLE and OCOG tracking packages were analyzed using the waveform results. It was found that the different tracking packages could maintain the waveform characteristics of the diffuse and quasi-specular surfaces. Those characteristics were then utilized in this study for classification purposes.  
The echoes from the seawater areas were found to be diffuse type echoes. The echoes from the sea ice in the Arctic region were observed to be mainly quasi-specular type echoes. It was found that some \"ocean-like\" waveform data had existed in the old ice areas. In the Antarctic regions, the center surfaces of the large ice floes were determined to be diffuse surfaces. At the same time, specular reflections and diffuse reflections were found to exist on the surfaces of the shelf ice covers, and the diffuse reflections were dominant. In addition, there were differences observed between the echoes from the seawater areas, and also from the diffused echoes obtained from the old ice. These observed differences could potentially provide the basis for the future study of re-tracking algorithms for the altimeters of the HY-2A/B ALT.  
The accuracy rate of the separation results for the LIBSVM except Band Ku from HY-2B ALT was found less than 40% in Antarctic. Meanwhile, the other two methods had on average demonstrated 80% correct detections of the waveforms. The errors of LIBSVM had mainly occurred in the extractions related to the seawater areas. All of the incorrectly distinguished results of the three methods were observed to be located in the regions of the old ice. The incorrectly distinguished results were found to be related to the \"ocean-like\" waveforms. Those waveforms were similar to the seawater areas. It was also found that the AGC and PP values had displayed fewer differences between the two surfaces. An additional factor which may have impacted the results was the fact that the sea ice had been melting in November (summer season in the Antarctic region), and a large number of ice floes and leads had appeared. Therefore, a large number of non-singular ground signals in the footprint had been received by the instrument. These ground signals had resulted in increasing the difficulty in distinguishing the seawater from the sea ice.  
In conclusion, it was determined in this study that the HY-2A/B had the ability to accurately classify sea ice and seawater. Furthermore, in accordance with the statistical results of the parameters mentioned above, the data quality of the HY-2B altimeter had displayed obvious improved results when compared with those of the HY-2A altimeter.  
In the study, we just had the data of November 2018 (HY-2B has not been running for a whole year). We will analyze differences between the different seasons from a geophysical perspective after the HY-2B operates for a whole year. Meanwhile, since there were fewer data used to distinguish the 20 Hz data for validation, there were found to be some deficiencies in the analysis of the 20 Hz data in this study. In future research, more detailed analyses of the 20 Hz data will be carried out.  
All authors contributed to the conceptualization; [PERSON] performed the formal analysis and original draft writing; [PERSON] and [PERSON] contributed to the supervision; all authors contributed to the paper.  
This work was supported by National Key R&D Program of China under Project 2016 YFC1401000; and the National Natural Science Foundation of China under Grant 41876204 and 41630969.  
This work is supported by National Satellite Ocean Application Service, State Oceanic Administration. We want to thank EUMETSAT for providing the icetype product, and DTU for providing the data of Sentinel 1a/b. The authors would also like to thank [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] for the help of data processing.  
The authors declare no conflict of interest.