## 3 Quality Assessment
### Resolution Capability
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Experimental** & **Satellite** & **Track** & **Track Number** & **Cycle** & **Date** & **Data Quantity** &
\begin{tabular}{c} **Average Distance** \\ **between Two Cycles** \\ \end{tabular} \\ \hline
**Region** & HY-2A & ascending & 1851 & 005 & 2 April & 9285 & 1.101 km \\
**1** & HY-2B & ascending & 0095 & 033 & 24 January & 10,532 & 0.086 km \\
**1** & HY-2C & descending & 0248 & 019 & 13 March & 11,668 & 0.242 km \\
**1** & HY-2D & descending & 0108 & 026 & 3 February & 11,676 & 0.156 km \\ \hline
**2** & HY-2A & ascending & 2815 & 004 & 20 November & 9242 & 0.695 km \\
**2** & HY-2B & ascending & 0315 & 014 & 11 May & 10,504 & 0.195 km \\
**2** & HY-2C & descending & 0056 & 015 & 25 May & 10,522 & 0.195 km \\
**2** & HY-2C & descending & 0056 & 020 & 3 April & 11,644 & 0.276 km \\
**2** & HY-2D & descending & 0190 & 026 & 6 February & 11,672 & 0.025 km \\ \hline
**3** & HY-2A & ascending & 0661 & 005 & 18 February & 9254 & 0.131 km \\
**4** & HY-2B & ascending & 0283 & 017 & 21 June & 10,479 & 0.230 km \\
**4** & HY-2C & descending & 0024 & 011 & 2 January & 11,337 & 0.011 km \\
**5** & HY-2D & descending & 0076 & 028 & 22 February & 11,364 & 0.249 km \\ \hline
**4** & HY-2A & ascending & 4477 & 003 & 4 August & 9218 & 0.113 km \\
**5** & HY-2B & ascending & 0351 & 020 & 4 August & 10,518 & 0.054 km \\
**5** & HY-2C & descending & 0174 & 017 & 8 March & 11,636 & 0.159 km \\
**5** & HY-2D & descending & 0034 & 028 & 20 February & 11,633 & 0.156 km \\
**6** & HY-2A & ascending & 2171 & 007 & 15 March & 8693 & 1.369 km \\
**5** & HY-2B & ascending & 0167 & 012 & 7 April & 10,529 & 0.146 km \\
**5** & HY-2C & descending & 0167 & 013 & 21 April & 10,567 & 0.146 km \\
**6** & HY-2C & descending & 0018 & 015 & 11 February & 11,663 & 0.271 km \\
**7** & HY-2D & descending & 0152 & 028 & 24 February & 11,674 & 0.160 km \\
**8** & HY-2A & ascending & 0847 & 004 & 9 September & 9256 & 0.444 km \\
**9** & HY-2B & ascending & 0221 & 014 & 9 March & 10,524 & 0.084 km \\
**10** & HY-2C & descending & 015 & 015 & 18 March & 11,665 & 0.130 km \\
**11** & HY-2D & descending & 0042 & 027 & 11 February & 11,145 & 0.149 km \\
**12** & HY-2D & descending & 0042 & 028 & 20 February & 11,628 & 0.119 km \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of information for sample data sequences in 6 research regions: Region 1, North Pacific; Region 2, South Pacific; Region 3, Mid-Pacific; Region 4, Indian Ocean; Region 5, North Atlantic; Region 6, South Atlantic. t trends were basically consistent among the four HY-2 missions in each study region. HY-2A and HY-2B ran along the solar synchronous orbits with an inclination of \(\sim\)99\({}^{\circ}\), while orbits of \(\sim\)66\({}^{\circ}\) inclination were adopted for HY-2C and HY-2D. Hence, similar orbit inclinations led to better consistency in these two groups. We applied a Hanning window to constrain the effect of spectrum leakage caused by the limited length of the data sequence. Through the averaging effect of the Hanning window, the main lobe reduced the fluctuation in the power spectrum and then achieved a smaller estimated variance. A wider main lobe is advantageous for a more effective averaging effect and smaller variance but has decreased resolution. A stronger side-lobe effect caused more errors in signal recognition and weak signals were indistinguishable. Hence, the size of the Hanning window had to be optimally determined by considering both the main- and side-lobe effects. A 64 km Hanning window was used in this study and the power spectrum was estimated by the Welch method. The resolution capabilities were uniformly determined while the coherence dropped to 0.5, indicating a signal-to-noise ratio of 1 [31]. As shown in Figure 6, all the HY-2 missions had stable resolution capabilities in the 50+ km wavelength range. The coherence was close to 1, indicating that the signal occupied this band. While the coherence was around 0.5, different variations occurred for different missions and regions.