## 2 Materials and Methods
### Rosemary and Sage Harvesting Time Individuation, Collecting, and Drying  
Chlorophyll is a vital pigment in leaves, essential for photosynthesis by absorbing radiation. Total canopy chlorophyll content is determined by multiplying the leaf chlorophyll concentration by the leaf area index (LAI), a key indicator of vegetation productivity. Monitoring leaf chlorophyll content is crucial in farm management [61; 62; 63], while total canopy chlorophyll content is closely linked to primary production [64; 65; 66; 67], and crop yields [68; 69]. Vegetation indices (VIs) that strongly correlate with canopy chlorophyll content can be used to estimate gross primary production (GPP) in crops. Leaf chlorophyll content, measured in \(\mu\)g cm\({}^{-2}\), is also an important variable in agricultural remote sensing due to its close relationship with leaf nitrogen content.  
Remote sensing techniques have become an effective, non-invasive method to assess plant characteristics, using the spectral signatures of canopies, which can be influenced by environmental and agricultural factors. Vegetation indices, particularly the Normalized Difference Vegetation Index (NDVI), are widely used for this purpose because of their ease of calculation and broad applicability. NDVI is effective for estimating leaf chlorophyll content and the extent of photosynthetically active vegetation, as healthy leaves absorb visible red light and reflect near-infrared (NIR) light. NDVI can be derived from aerial imagery captured by platforms like UAVs, which offer flexibility, cost-efficiency, and high spatial resolution (Equation (6)).  
\[NDVI=\frac{(NIR-RED)}{(NIR+RED)} \tag{6}\]  
Chlorophyll content in leaves is a primary indicator of greenness, nutritional status, and carbon uptake in forests. Many studies have demonstrated a strong correlation between chlorophyll content and leaf nitrogen levels in crops. Nitrogen fertilizer applications improve chlorophyll content, leaf area index (LAI), and leaf dry weight, while a lack of nitrogen leads to premature leaf senescence and reduced chlorophyll content, as seen in safflower growth after fertilization [70].  
Leaf chlorophyll content also serves as a crucial indicator of photosynthetic activity, plant health, stress levels, and nutritional status, making it especially important for precision agriculture. Recent studies indicate that chlorophyll content can be retrieved effectively using hyperspectral vegetation indices from specific reflectance bands. This research evaluates various vegetation indices, including NDVI and modified chlorophyll absorption ratio indices (MCARI, TCARI), and their integrated forms (MCARI/OSAVI and TCARI/OSAVI). These indices have been developed to reduce the influence of atmospheric and soil interference.  
Chlorophyll has strong reflectance peaks in the red and blue regions, but the blue peak is not used for estimating chlorophyll due to interference with carotenoid absorption. Maximum absorbance occurs between 660 nm and 680 nm in the red region, but its effectiveness for predicting chlorophyll content is limited at low concentrations, prompting further exploration of other wavelengths for more accurate estimations [22].  
At the beginning of the rosmary flowering (27 April 2024) and sage before flowering (24 May 2024), measurements were carried out using a Phantom 4 UAV, equipped with a multispectral camera (DJI, Shenzhen, China). The high-resolution multispectral images were ortho-mosaicked, and thematic maps of NDVI (Normalized Difference Vegetation Index) and TCARI/OSAVI ratio indices were generated to assess the right time for rosmary and sage harvesting. The harvested rosmary and sage were then dried [52; 71].