## 2 Materials and Methods
### Field Campaigns  
Since one of the aims of this work is to evaluate the performance of the algorithm for the ice alert code forecast, observed skin temperatures are compared with simulated and forecasted data, calculated by the same algorithm forced with observed and forecasted values, respectively, as input. As above-mentioned, in the areas of the Milano Linate airport, Chiese and Capitanata Consortium, observed LST data are measured by contactless sensors, while in the Pedemontana motorway there are contact instruments which measure an average temperature of the first centimeters of roadway asphalt. Therefore, in the case of Pedemontana, the observed data are corrected in order to obtain a more accurate value of skin temperature. This operation was performed thanks to several field campaigns at different times and weather conditions during which the comparison was carried out between observed data coming from the LUFFT sensors and measured values coming from a thermal camera (FLIR, T450 Sc, which has an accuracy of 1 \({}^{\circ}\)C or \(\pm\)1% at limited range and \(\pm\)2 \({}^{\circ}\)C or 2%, whichever is greater, at 25 \({}^{\circ}\)C nominal) sensitive to infrared radiation.  
From these comparisons it emerged that the skin temperature is lower than the one measured by LUFFT sensors, and the difference varies according to the cloud cover, the day time and the location of the station point. For this reason, the correction of the LST observed by LUFFT sensors has been calculated for time slots and for each station point. For the sake of brevity, it can be summarized that:  
- for cloudy days, the correction is approximately about 2 \({}^{\circ}\)C \(\pm\) 0.1 \({}^{\circ}\)C;
- for clear-sky days the difference between the temperatures is much more marked in the early morning hours where the correction has an average value of about 3 \({}^{\circ}\)C \(\pm\) 1.5 \({}^{\circ}\)C, while in the afternoon is of 1.4 \({}^{\circ}\)C \(\pm\) 0.7 \({}^{\circ}\)C.  
It can be observed that there is not a unique correction value for each time slot, but a range of values between a min/max. Hence, comparisons described in Section 4 show minimum and maximum values of the corrected LST.  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **Tsk\({}_{2}\)\(\leq\) -6.8 \({}^{\circ}\)C** & **-6.8 \({}^{\circ}\)C\(\leq\) Tsk\({}_{2}\)\(<\) -3.1 \({}^{\circ}\)C** & **-3.1 \({}^{\circ}\)C\(\leq\) Tsk\({}_{2}\)\(<\) 0 \({}^{\circ}\)C** & **Tsk\({}_{2}\)\(\geq\) 0 \({}^{\circ}\)C** \\ \hline
**UR \(\geq\) 95\%** & 3 & 2 & 1 & 0 \\
**95\% \(>\) UR \(\geq\) 80\%** & 2 & 2 & 1 & 0 \\
**80\% \(>\) UR \(\geq\) 40\%** & 2 & 2 & 1 & 0 \\
**40\% \(>\) UR \(\geq\) 5\%** & 1 & 1 & 0 & 0 \\ \hline \end{tabular}
\end{table}
Table 4: Ice alert code algorithm.  
\begin{table}
\begin{tabular}{c c c} \hline
**Wind\_Speed (m/s)** & **a (-)** & **b (-)** \\ \hline
0 \(\leq\) wind\_speed \(<\) 3 m/s & 1 & 0 \\
3 m/s \(\leq\) wind\_speed \(<\) 5 m/s & 0.8 & 0.2 \\
5 m/s \(\leq\) wind\_speed \(<\) 8 m/s & 0.6 & 0.4 \\
8 m/s \(\leq\) wind\_speed \(<\) 12 m/s & 0.4 & 0.6 \\
12 m/s \(\leq\) wind\_speed \(<\) 16 m/s & 0.2 & 0.8 \\
16 m/s \(\leq\) wind\_speed & 0 & 1 \\ \hline \end{tabular}
\end{table}
Table 3: Values assumed by \(a\) and \(b\) coefficients.