# Near Real-Time Irrigation Detection at Plot Scale Using Sentinel-1 Data
## 4 Results
### Results over Montpellier  
Figure 5 presents the results of the application of the proposed methodology (Phase 1 and 2) over the three plots P1, P2 and P3 located in Montpellier, France using the ascending (morning) and descending (evening) SAR images separately. Over Montpellier site, the morning acquisition is 36 h prior to the evening acquisition. Figure 5a,b show the morning and evening SAR acquisitions for P1 plot (maize), respectively. The first detected irrigation point was on 17/07 (morning acquisition) and 18/07 (evening acquisition) due to two irrigation episodes that took place on 16/07 and 18/07. Between 19/07 and 31/07 no irrigation occurred on the plot and no peaks where detected for two consecutive SAR acquisitions. Later, on both 05/08 (morning) and 06/08 (evening), an irrigation peak was detected due to two irrigation episode occurring on 03/08 and 04/08. In addition, two irrigation episodes that occurred on 04/09 and 05/09 appeared as an irrigation peak on the evening image of 06/09. However, the morning image acquired on 04 September 2017 did not show any detected irrigation since the episodes occurred after the SAR acquisition (SAR acquired at 06h00 while irrigation generally takes place after 09h00). Moreover, an irrigation episode occurring on 11/09 was detected on the evening image acquired on 12 September 2017. Two irrigation episodes occurring on 13/09 and 14/09 appeared on both the morning and evening acquisitions on 14/09 and 15/09, respectively. By combining the irrigation events detected from the morning and evening acquisition, 12 out of 15 possible irrigation episodes over P1 were detected including 5 points with high certainty, 5 points considered as medium certainty and 2 points with low certainty. However, it is important to mention that several irrigation episodes  
Figure 4: Temporal evolution of Synthetic Aperture Radar (SAR) backscattering coefficient \(\sigma^{\circ}\) in VV polarization at 10 km grid scale (red curve) with surface soil moisture (SSM) estimation at 10 km grid scale (green curve) and daily precipitation data from the Global Precipitation Mission (GPM) mission (blue curve) for (**a**) Montpellier, (**b**) Tarbes and (**c**) Catalonia. Black dashed circle corresponds to existing rainfall events while yellow circle shows the absence of rainfall. occurring between two consecutive SAR dates are considered as only one irrigation episode. For plot P1 only one point with low certainty was falsely detected as irrigation event. Figure 5: Irrigation detection over P1 (**a**,**b**), P2 (**c**,**d**), and P3 (**e**,**f**) using the morning SAR acquisition (**a**,**c**,**e**) and the evening SAR acquisition (**b**,**d**,**f**), in Montpellier, France. SAR VV signal at plot scale in dashed black line and VV at grid scale in dashed pink line. Points with blue, green and red are irrigation points detected on SAR signal at high, medium and low certainty respectively. The green line represents the normalized differential vegetation index (NDVI). High, medium and low correspond respectively to detected irrigation events with high, medium and low certainty. For the soya plot (P2), the results of the combined use of the morning (Figure 5c) and evening (Figure 5d) acquisitions show that 11 irrigation episodes were detected out of 13 possible irrigation episodes. Among the 11 detected irrigation points, eight points were with high certainty, two medium and one low certainty point. Moreover, among the 92 SAR acquisitions (morning and evening), only one false irrigation detection was obtained with low certainty. The first irrigation episode on 29/05 was detected in the morning SAR image of 31/05 (Figure 5c). For the morning acquisition, the radar signal then decreased between 31/05 and 06/06 due to the decrease in soil moisture but started to increase between 06/06 and 24/06 without any rainfall or irrigation events.