## 4 Results and Discussion
### Statistics of SAR-Derived Parameters
#### 4.1.2 SAR SSW Speed and Its Uncertainty  
Statistics about the SAR SSW speed (m/s) and the related maximum uncertainty (hereafter named simply uncertainty) (m/s) computed for all the ROIs, at the various dimensions and for the two GMFs, are collected in Table 2. From tabled values, it follows that:  
1. For each ROI size adopted, the two applied GMFs produce similar statistics, with an absolute difference of the mean and standard deviation of SSW speed of about 0.5 m/s and 0.3 m/s, respectively, and an absolute difference of the mean and standard deviation of the related uncertainty of about 0.1 m/s and 0.03 m/s or less, \begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline  & & \multicolumn{2}{c}{**NRCS**} & \multicolumn{4}{c}{**Incidence Angle (\({}^{\circ}\))**} & \multicolumn{4}{c}{**MS LG-Mod**} \\  & & **5 km** & **10 km** & **15 km** & **5 km** & **10 km** & **15 km** & **5 km** & **10 km** & **15 km** \\ \hline \(\min\forall_{1}\ldots N\_{\text{ROI}}\)(mA\_ROI)\({}^{\text{1}}\) & 0.0165 & 0.0182 & 0.0178 & 31.76 & 32.05 & 32.12 & 74.42 & 92.66 & 81.34 \\ \(\max\forall_{1}\ldots N\_{\text{ROI}}\)(mA\_ROI)\({}^{\text{1}}\) & 0.2887 & 0.2799 & 0.2770 & 45.03 & 44.80 & 44.68 & 282.25 & 269.86 & 267.86 \\ \(\max\forall_{1}\ldots N\_{\text{ROI}}\)(mA\_ROI)\({}^{\text{1}}\) & 0.1020 & 0.1021 & 0.1024 & 37.34 & 37.35 & 37.33 & 184.11 & 184.04 & 184.07 \\ \(\text{std}\forall_{1}\ldots N\_{\text{ROI}}\)(mA\_ROI)\({}^{\text{1}}\) & 0.0531 & 0.0525 & 0.0523 & 2.98 & 2.93 & 2.93 & 1.12 & 2.36 & 3.76 \\ \(\min\forall_{1}\ldots N\_{\text{ROI}}\)(s\_ROI)\({}^{\text{1}}\) & 0.0009 & 0.0007 & 0.0006 & 0.08 & 0.15 & 0.23 & 3.58 & 2.13 & 1.53 \\ \(\max\forall_{1}\ldots N\_{\text{ROI}}\)(s\_ROI)\({}^{\text{1}}\) & 0.0482 & 0.0318 & 0.0235 & 0.10 & 0.20 & 0.30 & 90.00 & 42.51 & 15.89 \\ \(\text{mean}\forall_{1}\ldots N\_{\text{ROI}}\)(s\_ROI)\({}^{\text{1}}\) & 0.0056 & 0.0055 & 0.0063 & 0.09 & 0.18 & 0.27 & 12.08 & 6.18 & 4.16 \\ \(\text{std}\forall_{1}\ldots N\_{\text{ROI}}\)(s\_ROI)\({}^{\text{1}}\) & 0.0029 & 0.0031 & 0.0035 & 0.01 & 0.01 & 0.02 & 5.56 & 2.40 & 1.52 \\ \hline \hline \end{tabular}  
* \({}^{\text{1}}\)mA\_ROIi and sA\_ROIi represent respectively the mean and the standard deviation of the generic input parameter A (i.e., SAR NRCS, incidence angle and MS LG-Mod SSW relative direction) within the i-th ROI.  
\end{table} 
Table 1: Statistics about the mean and standard deviation values of the input parameters SAR Normalised Radar Cross Section (NRCS), incidence angle and MS LG-Mod SSW relative direction for all Wind Vector Cells (WVCs or ROIs), at various dimensions. respectively. All statistics obtained from the CMOD7 are smaller than those from the CMOD5.N. It appears that the CMOD7 allows better precision and accuracy in the estimation of SSW speed and its uncertainty. This is in accordance with the fact that the CMOD7 represents an improvement of the CMOD5.N in general, and especially at low winds [46]. 2. For each GMF applied, the mean (about 15.24 m/s and 14.77 m/s for CMOD5.N and CMOD7, respectively) and the standard deviation (about 3.53 m/s and 3.25 m/s for CMOD5.N and CMOD7, respectively) of SSW speed are quite independent from the ROI dimension. On the contrary, the mean and the standard deviation of SSW speed uncertainty significantly depend on the ROI size. In fact, the greater the ROI dimension, the lower the estimation statistics (i.e., between 2.07 m/s and 1.35 m/s for the mean, and 1.12 m/s and 0.58 m/s for the standard deviation, in the case of CMOD5.N; between 1.97 m/s and 1.26 m/s for the mean, and 1.11 m/s and 0.56 m/s for the standard deviation, in the case of CMOD7). Therefore, once a GMF is chosen, it is crucial to pay close attention to the balance between the desired spatial resolution of the SSW speed and the overall uncertainty achievable at such resolution, the latter uncertainty depending also on the actual SAR NRCS, incidence angle and SSW relative direction values, as well as their corresponding uncertainties (see Section 4.2).