# Near Real-Time Freeze Detection over Agricultural Plots Using Sentinel-1 Data
## 4 Results
### Detection of Frozen/Unfrozen Plots  
This section shows the results that correspond to only the first phase of the freezing detection algorithm over individual plots (i.e., without applying the temperature filter) in order to assess its performance. The algorithm has been tested on both study sites using all S1 images (acquired in Ascending and Descending modes, in both VH and VV polarizations). In our interpretation of the results, frozen plot detection is assumed plausible at a certain date, if the reported temperature by the nearest weather stations for each study site is below 3 \({}^{\circ}\)C. In reality, freezing only occurs when the temperatures are at, or below, 0 \({}^{\circ}\)C. However, it is possible that the nearest weather station to the studied site reports a higher temperature by a few degrees Celsius, while the temperature in a part of the study site is a few degrees Celsius below the recorded value (for reasons of distance or the morphology of the study site). Alternatively, false freeze detection corresponds to plots detected as frozen at a certain date while the reported temperature was above 3 \({}^{\circ}\)C, henceforth referred to anomalies. Finally, while we report the results of detections for both descending and ascending modes combined, the detection algorithm was run separately on each mode, and for each polarization.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Pol.**} & \multicolumn{3}{c}{**Unfrozen**} & \multicolumn{3}{c}{**Mild-to-Moderate Freezing**} & \multicolumn{3}{c}{**Severe Freezing**} \\  & \multicolumn{3}{c}{**\(\Delta\omega^{0}\)(dB)**} & \multicolumn{3}{c}{**\(\Delta\omega^{0}\)(dB)**} \\ \cline{2-10}  & **LC1** & **LC2** & **LC3** & **LC1** & **LC2** & **LC3** & **LC1** & **LC2** & **LC3** \\ \hline VH & \(\Delta\omega^{0}<3.5\) & \(\Delta\omega^{0}<2.8\) & \(\Delta\omega^{0}<2.1\) & \(3.5\leq\Delta\omega^{0}<5.3\) & \(2.8\leq\Delta\omega^{0}<3.5\) & \(2.1\leq\Delta\omega^{0}<2.9\) & \(\Delta\omega^{0}\geq 5.3\) & \(\Delta\omega^{0}\geq 3.5\) & \(\Delta\omega^{0}\geq 2.9\) \\ \hline VV & \(\Delta\omega^{0}<2.5\) & \(\Delta\omega^{0}<1.7\) & \(\Delta\omega^{0}<1.6\) & \(2.5\leq\Delta\omega^{0}<4.0\) & \(1.7\leq\Delta\omega^{0}<2.2\) & \(1.6\leq\Delta\omega^{0}<2.4\) & \(\Delta\omega^{0}\geq 4.0\) & \(\Delta\omega^{0}\geq 2.2\) & \(\Delta\omega^{0}\geq 2.4\) \\ \hline \end{tabular}
\end{table}
Table 1: Calculated thresholds for each land cover class (LC) in VV and VH polarizations.  
Figure 6: Distributions of \(\Delta\omega^{0}\) in VV polarization for the three main land cover classes: (**a**, **d**) cereals LC1, (**b**, **e**) meadows LC2, and (**c**, **f**) orchards and vineyards LC3. (**a**, **b**, and **c**) \(\Delta\omega^{0}\) over LC1, LC2, and LC3, respectively, for temperatures \(\
eg 3\)\({}^{\circ}\)C \(\leq\) t \(\leq\) 0 \({}^{\circ}\)C, (**d**, **e**, and **f**) \(\Delta\omega^{0}\) over LC1, LC2, and LC3, respectively, for t \(\leq\
eg 3\)\({}^{\circ}\)C. The Y-axis represents the frequency of different \(\Delta\omega^{0}\) ranges over the entire plots. The red curve represents the fitted normal functions, while the red vertical line represents the mean.