# Detecting Cover Crop End-Of-Season Using VEN\(\upmu\)S and Sentinel-2 Satellite Imagery
## 4 Results
### Near-Real-Time Mapping  
Varying periods of VEN\(\mu\)S NDVI time-series in 2019 were used to test near-real-time mapping capabilities of the WIST approach. In the simulation, we used all clear VEN\(\mu\)S NDVI within the period until the ending date (the last day of available imagery). Data latency from satellite acquisition and processing was not included in the analysis. The simulations include weekly processing at the pixel level (image mode) and daily processing at the field level (text mode), using all available VEN\(\mu\)S observations from 1 January 2019, to the ending date. The pixel-level simulation used VEN\(\mu\)S time-series images. Figure 11 shows the maps of weekly termination dates starting from 1 May 2019. We demonstrate results using the six fields in the east farm since they had multiple harvests and are close in space (subset area in Figure 3). In the simulated weekly processing, the VEN\(\mu\)S time-series from 1 January to the ending day was used. The figure shows the latest termination dates before the ending date. \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & **Mean Bias** & **Mean Abs.** & **RMSE** & **Confficient of** & **Mean Uncertainty** & **Percent of** & **Percent of False** \\  & **(Day)** & **Difference (Days)** & **(Days)** & **Determination (R\({}^{2}\))** & **(Day)** & **Missing** & **Detection** \\ \hline VEN\(\mu\)S & 0.4 & 2.1 & 2.6 & 0.998 & 3.5 & 0.0\% & 3.4\% \\ Sentinel-2 & -1.4 & 4.0 & 5.1 & 0.987 & 6.1 & 6.9\% & 10.3\% \\ \hline \end{tabular}
\end{table} 
Table 1: Statistics of termination dates from VEN\(\mu\)S and Sentinel-2 over 29 harvest/termination events in 2019–2020. Figure 10: Scatter plot of the detected termination dates for fields at the BARC in 2019–2020 using the Sentinel-2 NDVI time-series and the recorded harvest operation dates. The vertical bar shows the uncertainty of the estimated termination date. For the first run on 1 May 2019 (Figure 11a), no termination was detected in any field. On 8 May 2019 (Figure 11b), termination dates on 28 April 2019, for fields #4-25, #5-2, and #5-45 were detected. The FarmLogic database recorded the harvest date on 29 April 2019, for the three fields. On 15 May 2019 (Figure 11c), termination for field #5-9 was detected on 6 May 2019. The harvest operation was recorded on 7 May 2019. In the 29 May 2019 simulation (Figure 11e), termination dates were detected on 17 May 2019, for fields #5-8 and #5-21. Both fields were moved on 20 May 2019, using a dischine machine. The estimated termination of 17 May 2019, was computed using the middle date of two observations on 10 May 2019, and 24 May 2019, as shown in Figure 12a. The lag time could be shortened if the process ran on an earlier date between 25 May and 28 May. In addition to six cover crop fields, the OPE3 (Optimizing Production inputs for Economic and Environmental Enhancement) field in the upper right of Figure 11g shows a termination date on 7 June 2019, a day before the planting date on 8 June 2019. The weeds in this field were killed by herbicide application before planting. It was regarded as a termination since the MACD momentum and NDVI amplitude were significant, as shown in Figure 12b. The simulated near-real-time process ending on 3 July 2019 (Figure 11), detected a termination date of 23 June 2019, for field #5-9, which was close to the recorded harvest date on 20 June 2019. This was the second termination date in the record for that field, which was planted to alfalfa. The simulation of 17 July 2019 (Figure 11) detected a new termination date of 14 July 2019, for four fields (#4-25, #5-8, #5-21, and #5-45). There were clear observations on 17 July 2019, and termination dates were detected just 3 days afterward. From the operation records, all four fields were moved on 13 July 2019. However, field #5-21 shows mixed terminations. Figure 12c illustrates one pixel in field #5-21 (grass) whose termination was not detected, unlike in neighboring pixels, since the downtrend momentum and the amplitude of NDVI were smaller than the specified thresholds.