## 3 Results
### Optimal NDVI Reference Period  
Figure 9 shows the Pearson correlation coefficients between the mean FmMVC and yield for each of the 15 variable-sized periods investigated. The MVC of the period is calculated using the 66% CP threshold. The correlation coefficients are sorted in descending order by value. The best correlated month is February, with a correlation index close to unity. However, we also generally notice a better correlation during the first 3 months of the year compared to the April-May period. The correlation coefficients are, in fact, always greater than 95% when the period includes only the months from January to March and decreases sharply below 80% when the period includes only the months of April and May. The high correlation coefficients for FmMVC-yield also highlight the validity of the NDVI-CPP in optimizing cloud detection. Focusing on the winter wheat phenological phases, after sowing, the first phase encompasses germination, emergence, and tillering. This is the slowest and longest phase, depending on the weather conditions; it may either complete or be interrupted before the winter dormancy. Most of the processes that contribute to grain yield are completed during this phase [76; 77; 78]. Stem elongation (or extension), a period of rapid plant growth, typically occurs in mid-March, but its timing and intensity are highly dependent on the air temperature [79]. In Italy, winter wheat generally reaches maturity in early June, with harvesting usually completed by late June or early July. Growth stages are closely linked to weather conditions, mainly air temperature. Some indicative temperature thresholds for soft wheat phases are as follows: the minimum germination temperature is 1 \({}^{\circ}\)C, with a maximum of 37 \({}^{\circ}\)C and an optimal range of 20-25 \({}^{\circ}\)C. For stem elongation, the thermal threshold is 5-10 \({}^{\circ}\)C, with an optimal range of 15-22 \({}^{\circ}\)C, while the ideal flowering temperature is 18-24 \({}^{\circ}\)C [80]. Figure 10 shows the  
Figure 9: Pearson correlation coefficient mean for FmMVC–yield correlation for each of the 15 variable-sized periods sorted in descending order. monthly average temperatures recorded at the Conselice weather station, comparing the three seasons under investigation with the average of the previous 10 seasons. The average monthly temperatures for the three seasons under investigation were generally higher than the standard values, particularly in February 2020 and 2022, when temperatures exceeded 10 \({}^{\circ}\)C. Germination likely began shortly after sowing, supported by the November temperatures (averaging around 10 \({}^{\circ}\)C in all seasons). Tillering progressed slowly in the colder months, with possible dormancy setting in December and lasting until February. The increase in temperatures anticipated the occurrence of stem elongation in at least two of the three seasons investigated in February rather than in March. Flowering would have occurred in April across all seasons, with temperatures around 17-19 \({}^{\circ}\)C, which are slightly below the optimal range but still sufficient. By June, maturity was reached in all three seasons, supported by temperatures well above 24 \({}^{\circ}\)C.  
Therefore, in terms of phenological phases, it seems that the following is true:  
1. The best yield-NDVI correlation can be associated with the stem elongation phase;
2. The timing of this phase cannot be predicted based solely on long-term analysis (e.g., 10 years or more). Instead, field-scale analyses over shorter time periods are required to account for any more rapid interannual variations in air temperature. To further delve into the whole dynamic, we plot (in Figure 11) the FmMVC by season and how it performed after the entire input collection was cloud-masked with a 66% CP threshold. Figure 11: FmMVC by season calculated over the wheat field under investigation using the 66% CP threshold value.