# Near Real-Time Irrigation Detection at Plot Scale Using Sentinel-1 Data
## 4 Results
### Results over Catalonia  
Over the Catalonia region, the huge database available allows us to investigate in depth the performance of the proposed method. The method was applied not only over irrigated plots but also over non-irrigated plots in order to analyze its capability to distinguish between irrigated and non-irrigated fields. First, it is important to remember that Catalonia region is a semi-arid region with a dry summer where most of the irrigation activities occur during the summer season (between May and September). Figure 7 presents the temporal profile of \(\sigma^{0}_{\text{P}}\) and \(\sigma^{0}_{\text{G}}\) over the period between September 2017 and December 2018 (evening acquisitions) along with the irrigation points detected during this period for an irrigated maize (Figure 7a) plot, irrigated alfalfa plot (Figure 7b), and non-irrigated wheat plot (Figure 7c). The daily GPM precipitation data are also presented in the three figures (blue curve). During the period between September 2017 and December 2018, 11 irrigation points were detected on the maize plot whereas 12 irrigation points were detected on the alfalfa plot. In both irrigated plots (Figure 7a,b), the irrigation points correspond to the dry summer period (between 25 April and 30 September). For example, 6 irrigation points were detected on the maize plot (Figure 7a) between 12 June 2018 and 15 August 2018. This is correlated with the existence of the maize vegetation cycle in the summer season (Increasing NDVI values). The alfalfa plot (Figure 7b) shows also frequent irrigation points detected between 12 June 2018 and 30 August 2018. For both maize and alfalfa plots, the \(\sigma^{0}_{\text{G}}\) between 01 June 2018 and 30 September 2018 shows stable low values indicating dry conditions and the absence of rainfall events. On the other hand, the frequent change of the \(\sigma^{0}_{\text{P}}\) in both plots indicates that possible irrigation events have occurred. This increase of the \(\sigma^{0}_{\text{P}}\) was detected as irrigation events based on our proposed method. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Plot**} & **Number of** & **Possibly Detectable** & **Detected** & **False** \\  & **Irigation Events** & **Irigation Events** & **Irigation Events** & **Detection** \\ \hline P1 & 30 & 15 & 12 & 2 \\ P2 & 13 & 13 & 11 & 1 \\ P3 & 5 & 5 & 5 & 2 \\ Total & 48 & 33 & 28 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Irrigation events detected over three plots in Montpellier, South-east France. Over the non-irrigated wheat plot presented in Figure 7c, no irrigation points have been detected for 82 SAR images (18 months). Such results support our criteria for detecting irrigation events and eliminating ambiguities with rainfall or vegetation effects. Following a rainfall event both \(\sigma^{0}_{\rm p}\) and \(\sigma^{0}_{\rm G}\) increase and then decrease following a dry period. The consistency between both \(\sigma^{0}_{\rm p}\) and \(\sigma^{0}_{\rm G}\) for the non-irrigated plot during the whole period indicates that the plot did not receive any water supplement other than rainfall events. Despite several frequent changes of the \(\sigma^{0}_{\rm p}\) over the complete temporal series due to several rainfall events and vegetation change, the method was able to eliminate all possible irrigation ambiguities and judge that the plot did not receive any irrigation event. Figure 7: Irrigation detection over agricultural plots in Catalonia, Spain for (**a**) irrigated maize plot, (**b**) irrigated alfalfa plot, and (**c**) non-irrigated wheat plot. The red dashed ellipse represents the period of the transition between the heading and soft dough phase of the wheat plot. An important point regarding the wheat plot in Figure 7c is the period between 19 April 2018 and 13 May 2018. During this period, the SAR backscattering signal increases gradually between each two SAR dates (red dashed circle).