# Near Real-Time Irrigation Detection at Plot Scale Using Sentinel-1 Data
## 4 Results
### Results over Montpellier
This increase in the \(\sigma^{0}_{\text{P}}\) values for three consecutive acquisitions was strongly correlated with the development of vegetation cover (NDVI values increases sharply during this period). However, among these three SAR points, two points were correctly not detected as irrigation points since they were filtered by the smoothed Gaussian filter \((S)\) that helped eliminate the effect of the vegetation development on \(\sigma^{0}_{\text{P}}\). Figure 6 explains the effect of the smoothed-Gaussian filter over P2 plot of Montpellier where the \(\sigma^{0}_{smooth}\) (red curve) is added to the results obtained by Figure 5d to demonstrate the importance of the smoothed-Gaussian filter. In Figure 6, the green dashed circle shows the three consecutive increase of \(\sigma^{0}_{\text{P}}\) between 06 and 24 June 2017. However, for two out of these three points, the \(\sigma^{0}_{smooth}\) curve is above \(\sigma^{0}_{\text{P}}\) curve thus the calculated \(S\) value is negative and these points were not detected as irrigation points. The sorghum plot (P3) encountered five irrigation episodes between 31 May 2017 and 10 August 2017 (Figure 5e,f). Using the proposed change detection method, five out of the five episodes were correctly detected as irrigation events. The first irrigation episode was detected on the evening SAR image (Figure 5f) of 01/06 due to an irrigation event occurring on the same date. Then, the 4 irrigation episodes that occurred on 26/06, 07/10, 27/10 and 10/08 were detected with both acquisition modes (ascending and descending). However, on this plot two false irrigation points were detected with medium and low power. Table 2 summarizes the results obtained on the three plots of Montpellier site. The total number of irrigation events over the three plots was 48 events. However, at each plot, several irrigation events occurring between two consecutive SAR dates are considered as only one irrigation event. We call these events the possibly detectable irrigation events. For example, three irrigation events occurring on 10/08, 11/08 and 13/08 on plot (P1) are considered as one irrigation event since the three events were  
Figure 6: Effect of smoothed-Gaussian filter on the detection of irrigation points for plot P2, Montpellier. The red dashed curve represents the \(\sigma^{0}_{smooth}\) calculated as each SAR date. followed by only one available SAR acquisition on 13 August 2017. Therefore, among the 48 irrigation events occurring on the three plots, 33 events could be possibly distinguished by the acquired SAR temporal series. This means that, 69% of the total number of irrigation events could be detected by the available SAR temporal series. Out of 33 possibly detectable irrigation events over the three plots, 28 irrigation episodes have been correctly detected. This means that among the possible detectable irrigation events 84.4% of these events are correctly detected. However, a total error of five falsely detected irrigation events has been registered over the three plots. The falsely detected irrigation points corresponds to the saturation of the radar signal caused by very well developed vegetation cover in plots P1 (maize) and P3 (Sorghum).