**2. Materials and Methods**

### *2.1. Test Sites and Field Measurements*

The field data used in this study were collected during one cotton, two wheat, and three processing tomatoes experiments conducted in five locations in Israel (Figure 1).

**Figure 1.** Locations and analysis polygons of the experiments conducted in Israel in 2018–2020.

The Sentinel-2 image inventory used for this study is presented in Table 1. Overall, 56 Sentinel-2 images were used in the study (14—wheat, 33—processing tomatoes, 9—cotton). During these experiments, LAI was measured by a SunScan Canopy Analysis System—SS1 developed by Delta-T Company (Cambridge, United Kingdom). The SunScan is a widely used, accurate, nondestructive LAI measurement system successfully employed in many previous studies [5,30,32]. The SunScan system measures LAI by calculating the difference in solar radiance received by the dome sensor installed under unobscured Sun view and the hand-held probe placed below vegetation canopy on the ground level (Figure 2).


**Table 1.** The Sentinel-2 bands used in the present study.

**Figure 2.** Main components of the SunScan system: (**A**) Dome sensor; (**B**) Probe; (**C**) Field computer.

Each LAI value used for model calibration was an average value of at least 30 field measurements. LAI was measured in the center of the fields and was correlated to average values of Sentinel-2 bands and VIs of homogenous areas in the fields' centers. In the Megido 2020 experiment, LAI was measured in two areas of the field (in the center of the field (six LAI measurements) and on the northwest corner (four LAI measurements)) where the crop developed at different rates and, thus, LAI was different. Accordingly, both time series of the field measurements were correlated with the average values of bands and VIs within defined polygons. In-field paths and their surrounding area were masked out from analysis polygons of the tomato experiments to remove bare soil areas and avoid border effects. These excluded areas consisted of approximately 20% of the overall polygon areas in the tomato fields. Therefore, each tomato polygon consisted of either two or four vegetated regions separated by the paths.

Overall, 11 averaged LAI values taken during two growing seasons were used for deriving the wheat models, nine for cotton (one season), and 23 for tomato (three seasons). The linear regression models in this study utilised the average values derived from satellite imagery within the analysis polygons and same-date field measurements or linearly interpolated LAI values of field measurements from adjacent dates.
