# Consolidating ICESat-2 Ocean Wave Characteristics with CryoSat-2 during the CRYO2 ICE Campaign
## 2 Data
### Satellite Altimeter Crossover Validation  
As the in situ comparison is inherently restricted in its ability to validate CryoSat-2 due to geographical limitations, we compare CryoSat-2 to several other satellite altimeters to see if there are discrepancies between the observations. The satellites used in the comparison are the Sentinel-3A and B as well as the SARAL. Together they span most of the operational time of CryoSat-2, with Sentinel-3B spanning about the same amount of time that ICESat-2 has been operational. The comparison is done at crossover points determined by the RADS radsxogen library [17]. At points in time when CryoSat-2 and one of the other satellites cross each other, the observations from each satellite are saved, and the time difference is registered. The resulting metrics from the analysis are summarized in Table 1; the un-corrected CryoSat-2 data is used.  
As can be seen in the table, the satellites have very high correlations and low errors when observations that are close together in time are compared, and the correlation decreases as the time difference between the observations increases. A comparison for each of the satellites can be seen in the scatterplots in Figure 3, which includes observations with a time lag of between two and three hours; thus, we have a slightly larger variance than we would have if we showed a scatterplot of observations with time lags of less than one hour. This time lag, as shown in Figure 3, is important, as it corresponds to the time difference between ICESat-2 and CryoSat-2 in the CRYO2 ICE campaign. The same Q-Q plot shown for the in situ stations in Figure 2 is shown in Figure 3 for each of the altimeters, and we can see that the altimeters show good agreement with each other.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Sentinel-3A**} & \multicolumn{4}{c}{**Sentinel-3B**} & \multicolumn{4}{c}{**SARAL**} \\ \cline{2-13}
**Time Sep. [H]** & **Diff.** & **RMSE** & **Diff.** & **RMSE** & **Corr** & **N** & **Diff.** & **RMSE** & **Corr** & **N** \\  & **[m]** & **[m]** & **Corr** & **N** & **[m]** & **[m]** & **Corr** & **N** & **[m]** & **[m]** & **Corr** & **N** \\ \hline
0–1 & 0.106 & 0.188 & 0.995 & 11,466 & 0.117 & 0.198 & 0.995 & 7237 & 0.003 & 0.130 & 0.996 & 16,512 \\
1–2 & 0.086 & 0.232 & 0.990 & 13,834 & 0.100 & 0.239 & 0.990 & 8664 & 0.002 & 0.178 & 0.993 & 19,259 \\
2–3 & _0.105_ & _0.292_ & _0.983_ & _11,358_ & _0.116_ & _0.294_ & _0.984_ & _6602_ & _0.003_ & _0.254_ & _0.985_ & _16,140_ \\
0–3 & 0.092 & 0.308 & 0.981 & 66,253 & 0.100 & 0.308 & 0.981 & 39,711 & 0.002 & 0.269 & 0.983 & 90,500 \\ \hline \multicolumn{13}{l}{Data interval:} & \multicolumn{1}{l}{1 March 2016 to 24 January 2022} & \multicolumn{1}{l}{8 May 2018 to 25 January 2022} & \multicolumn{1}{l}{14 March 2013 to 26 January 2022} \\ \hline \hline \end{tabular}
\end{table}
Table 1: SWH measurements from Sentinel-3A, Sentinel-3B, and SARAL compared with CryoSat-2. Here, the time separation increases by one-hour intervals up to a three-hour time separation to show the decrease in correlation and increase in root mean squared error (RMSE).  
Figure 3: Crossover analysis for three altimeters and CryoSat-2 showing the agreement between SWH observations for crossovers with a time difference of between 2 and 3 h. The correlations are also shown in Table 1; we expect correlations in this range.