## 5 Discussion  
To quantitatively analyze the reliability and accuracy of the reprocessed high frequency data, the absolute sea surface height (ASSH) data of the reprocessed data and the SGDR data in pass 323 and pass 196 are compared with the tide gauge data. The ASSH is calculated as follows:  
\[ \begin{array}{ll}absolute\ sea\ level\ height_{allimeter}&=altitude-retracked\ range-\\ &(dry\ tropospheric\ correction\\ &+wet\ tropospheric\ correction\\ &+ionospheric\ correction)\end{array}  \tag{9}\]  
\[absolute\ sea\ level\ height_{TG}=sea\ level \tag{10}\]  
The ASSH represents the sea surface height relative to the reference ellipsoid, which combines the effect of ocean tides and atmospheric forcing. The tide gauge data contain complete tidal information, so it is not necessary to remove the tide signal from the altimetry data. The tide gauge data do not correct the forcing of the dynamic atmosphere on the sea surface, so altimetry data do not correct the effect of atmospheric forcing. Since altimeters and tide gauges have different references, the mean difference between altimetry data and tide gauge data is removed when compared with each other. In addition, there is no sea state bias (SSB) correction in the ASSH because the SSB correction (low frequency) provided by the SGDR cannot support the high frequency data completely [33; 34; 35], and the SSB correction calculated by the inaccurate waveform retracking product in SGDR data is relatively inaccurate. By the way, once the wet tropospheric correction or the ionospheric correction provided by the instrument is lacking, the corrections provided models are adopted, which may lead an extra bias. Before the quantitative analysis, we directly compare the height of altimetry data with the tide gauge data. According to the Section 4, the data within the range where the reprocessed data and SGDR data are obviously different are selected to calculate a range average of per cycle of two passes, the result is showed in Figure 14. The systemic height difference between HY-2B altimetry ASSH data and tide gauge data is removed. From Figure 14, we can see that the changing of tide gauge observation and altimetry data are roughly same, and that the local trend is different due to the tide gauge does not completely fall into the trajectory of satellite. As stated in Section 4, the sea surface height of reprocessed data is higher than the SGDR data, and reprocessed data possesses more similar changes with the tide gauge data. In the comparison result of pass 323, the changing trend of cycle 13-17 of reprocessed data has better consistency with the tide gauge data than the SGDR data. Additionally, in the comparison result of pass 196, the SGDR data has more outliers, such as the value of cycle 15 and cycle 20, and the changing trend of cycle 40-50 of reprocessed data is more stable and coherent against tide gauge data. Then, based on the comparison method mentioned by [PERSON] [36], the different periods of the pass 323 and pass 196 data are linearly interpolated into the reference track, which consists of the normal points (NPs). Depending on the ASSH time series, the correlation coefficient and the root mean square (RMS) of reprocessing results and SGDR data against tide gauge data are calculated at each NP. The calculation results are shown in Figures 15 and 16. Figure 15 shows the correlation coefficient and RMS of the ASSH data against the tide gauge data in HY-2B pass 323. The correlation coefficient and RMS of the reprocessing results are basically better than those of the SGDR data. The correlation coefficient of reprocessing results beyond 20 km offshore is slightly higher than the SGDR data, and the RMS is maintained at approximately 30 cm. At distances between 13 km and 20 km from the shoreline, the correlation coefficient and RMS of the reprocessing results are the same as those of the SGDR data. The mean values of the correlation coefficient and RMS of the reprocessing results are 0.86 and 33.6 cm, and 0.86 and 34.0 cm for the SGDR data.