*2.2. Satellite Imagery*

Sentinel-2 is an Earth observation mission and part of the European Space Agency (ESA) Copernicus program. It includes two satellites with a payload of MSI, namely Sentinel-2A (launched 23 June 2015) and Sentinel-2B (launched 7 March 2017). Table 1 lists the spectral bands of Sentinel-2 that were used in this study. The inventory of the atmospherically and topographically corrected Level-2A Sentinel-2 images used in this study alongside the information on the LAI measurements can be found in Tables 2 and A1. Level-2A and Level-1C imagery were downloaded from the ESA Copernicus site (https: //scihub.copernicus.eu/dhus/#/home, accessed on 6 April 2021) (# means "Number"). Level-1C images were processed to Level-2A using Sen2Cor algorithm [33].

**Table 2.** Sentinel-2 imagery and LAI measurements used in the study.


\* Indicates the dates of the first and last images. \*\* A defective red edge band in a Sentinel-2 image acquired on 10 June 2019 prevented the derivation of red edge-based models for that date.

### *2.3. Model Calibration and Validation*

Linear regression models were derived to estimate LAI for specific crops based on field measurements and Sentinel-2 bands. Similarly, regression models between LAI and VIs were derived, including NDVI [34] and NDVI based on the Narrow NIR Band-8A instead of NIR Band-8. Additionally to NDVI, models were also derived for reNDVI [35], MTCI [36], WDVI [37], EVI [38], SAVI [39], MSAVI [40], DVI [34], and two new indices: WEVI (Water vapor red Edge Vegetation Index) and WNEVI (Water vapor narrow NIR red Edge Vegetation index). For every model, the R<sup>2</sup> and root mean square error (RMSE) values were calculated using the Microsoft Excel software. WEVI and WNEVI were developed based on combinations of the best performing bands for LAI estimation. The following equations and Sentinel-2 bands were used for deriving the aforementioned VIs:

$$\text{NDVI} = (\text{B8} - \text{B4}) / (\text{B8} + \text{B4}) \tag{1}$$

$$\text{NDVI8A} = (\text{B8A} - \text{B4}) / (\text{B8A} + \text{B4}) \tag{2}$$

$$\text{MTCI} = (\text{B6} - \text{B5}) / (\text{B5} - \text{B4}) \tag{3}$$

$$\text{WDVI} = \text{B8} - 0.5 \times \text{B4} \tag{4}$$

$$\text{EVI} = \left(2.5 \times (\text{B8} - \text{B4})\right) / \left(\text{B8} + 6 \times \text{B4} - 7.5 \times \text{B2} + 1\right) \tag{5}$$

$$\text{SAVI} = ((\text{B8} - \text{B4})) / (\text{B8} + \text{B4} + 0.5) \times 1.5 \tag{6}$$

$$\text{MSAVI} = ((\text{B8} - \text{B4}) \times (1 + \text{L})) / (\text{B8} + \text{B4} + \text{L}) \tag{7}$$

where: L = 1 − 2 × s × NDVI × WDVI and s is the soil line slope = 0.5

$$\text{DVI} = \text{B8} - \text{B4} \tag{8}$$

$$\text{(reNDVI)} = \text{(B8A} - \text{B6)} / \text{(B8A} + \text{B6)} \tag{9}$$

$$\text{WEVI} = \text{B}\spadesuit - \text{B}\6\tag{10}$$

$$\text{WNEVI} = (\text{BSA} - \text{B6}) / (\text{B9} + \text{B6}) \tag{11}$$
