## 6 Conclusions  
To solve the problem that the accuracy of HY-2B satellite altimetry data decreases and the available data reduces in costal area, a coastal waveform retracking strategy for HY-2B altimetry is proposed. The coastal waveform of the HY-2B satellite altimeter is retracked by determining the effective trailing edge and the leading edge, which is less affected by coastal 'pollution'. The coastal waveform data of pass 323 and pass 196 are reprocessed to validate the performance of the proposed waveform retracking strategy by comparing the reprocessing results to the SGDR data and tide gauge observations, and the results are verified qualitatively and quantitatively in the study areas.  
The altimeter waveform is distorted by coastal 'pollution' in coastal areas, such as land or bright targets over the sea. Based on a certain criterion, the waveform retracker proposed in this study detects the leading edge of the waveform, which contains less noise, looks for the effective part of the trailing edge, and then corrects the waveform fitting bias due to the coastal distorted waveform. The proposed waveform retracker avoids careful waveform classification and the boundary demarcation between open sea and coastal areas. The potential application of HY-2B satellite altimeter data in coastal areas is improved under the condition that the accuracy of open sea observations is retained.  
According to the analysis of the reprocessing results against TG data and SGDR data, the data quality of the reprocessing results is basically better than that of the SGDR data, especially in the range within 15 km offshore. For the reprocessing result of the pass 323 data, the mean correlation coefficient and RMS are 0.89 and 45.1 cm within 12 km offshore, respectively, while the SGDR data are mostly invalid, with a correlation coefficient lower than 0.5 and an RMS greater than 60 cm. The reprocessing result of pass 196 data also maintains high quality, with a mean correlation coefficient and RMS of 0.92 and 36.2 cm, respectively, in the range within 5 km offshore, which is almost consistent with the quality of open sea observations. All of the above results show that the waveform retracker proposed in this study has good performance in coastal areas.  
Waveform retracking is the first step for the coastal altimetry data reprocessing, extra processes are needed, such as the recalculation of high frequency SSB, the recalculation of coastal wet tropospheric correction, the filtering of ionospheric correction, and the improvement of tide model, etc. After that, the high quality coastal altimetry data is obtained and applied into practice.  
[PERSON] and [PERSON] proposed and designed the technique route. [PERSON] gave advice about the implementation of technology. [PERSON] reprocessed the waveform data. [PERSON], [PERSON] and [PERSON] helped with analysis of reprocessed data. [PERSON], [PERSON], [PERSON] and [PERSON] reviewed the manuscript. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China under Grant No. 42106178, the Basic Scientific Fund for National Public Research Institutes of China under Grant No. 2020Q07, ESA-MOST CHINA Dragon 5 Programme under Grant No. 58900, and Science Foundation of Donghai Laboratory.  
The author would like to thank the National Satellite Ocean Application Service and University of Hawaii Sea Level Center provided the measurement data of altimeter and tide gauge, and all researchers who assisted us in studying.  
The authors declare no conflict of interest.