# Consolidating ICESat-2 Ocean Wave Characteristics with CryoSat-2 during the CRYO2 ICE Campaign
## 4 Results
### Sea State Dependency Bias  
To analyze the behavior of the models for varying sea states, the RMSE and the mean deviation are determined as functions of the CryoSat-2 SWH. After sorting the observations according to their SWHs, with SWHs from 0 m (calm sea) to 10 m (rough sea), the RMSE and mean deviation of the models from CryoSat-2 are calculated; they can be seen in Figure 7. The observations above 10 m are excluded from this figure because there are too few observations above this height (only three observations above 10 m). As seen in Figure 7A, the RMSE generally increases as the SWH increases. The three models follow each other closely, especially at lower SWHs, with the RMSE being slightly higher for the histogram model until an SWH of approximately 7-8 m is reached; for higher SWHs, the RMSE of the ATL12 product is noticeably higher.  
Figure 5: Ground tracks of ICESat-2 orbit segments and the corresponding SWHs for the different models. This plot shows track pass 299 cycle 7 granule 7 (**top**) in the Atlantic Ocean, which has visible gaps for ICESat-2 (due to clouds), and pass 1019 cycle 9 granule 7 (**bottom**) in the Pacific Ocean, which has gaps for both satellites.  
the standard deviation model have stable biases for SWHs below 8 m, with that of the ATL12 product being slightly negative and that of the standard deviation model being slightly positive. The mean difference of the histogram model is similar to that of the standard deviation model until an SWH of around 4 m is reached; for higher SWHs, the mean difference becomes negative. It is clear that at higher SWHs, all models underestimate the SWH compared to CryoSat-2. The 95% confidence intervals of the mean differences are shown in Figure 7B as error bars. They are calculated using the following expression: \(\text{mean}\pm t(n-1)_{0.95}\cdot\sigma/\sqrt{n}\), where \(t()\) is the t distribution, \(\sigma\) is the standard deviation, and \(n\) is the number of samples at each indicated point. As shown in Figure 7C, the number of data points available to use for comparison drops for rougher sea states. The number of available data points drops below 100 observations above an SWH of 7 m, and there are many observations available for SWHs between 1 and 3 m.  
The model performance metrics are divided into segments of 0-1.5 m, 1.5-2.5 m, and 2.5-11 m. Approximately one-fourth of the SWH observations made by CryoSat-2 are contained in each segment, except that the middle segment has one-half of these observations; the values can be seen in Table 3. The behavior shown in Figure 7 can be seen more prominently in this table, with a positive bias of up to 0.18 m for the histogram model below SWHs of 2.5 m and a lower bias at high SWHs. Meanwhile, the standard deviation model has a better performance, with a lower difference and a lower standard deviation. While the differences between the derived models and CryoSat-2 are positive, ATL12 experiences a mean negative deviation for all segments. The scatter index (SI), which is the RMSE divided by the mean of the segment and converted to a percentage value, is largest at lower measured SWH values, and it decreases for higher SWH values.