## 1 Introduction  
In the Mediterranean basin, the olive tree (_Olea europaea_ L., 1753) is one of the most important crops [1, 2]. It has been grown to produce oil and table olives, basic components of the Mediterranean diet, since the Roman and Greek eras [3]. In Italy, olive oil production is around 0.33 million tons, accounting for 14.48% of the total production in the European Union [4]. It is well known that this evergreen crop has a high resistance to water stress [5; 6]. Indeed, it has been cultivated for centuries in regions characterized by a Mediterranean climate, where summers are hot and dry while winters are mild and humid [7]. In response to these environmental traits, olive trees developed different adaptation systems from an anatomical, morphological, physiological, and biochemical point of view [8]. However, the increase in extreme or continuous drought events due to climate change could represent a significant risk to olive tree cultivation [1; 9]. Remote sensing is an increasingly adopted technology in modern agriculture; it enables the acquisition of crop information without direct contact, reducing fieldwork [10; 11]. This approach makes it possible to assess crop status, identify stress factors, and estimate yield losses before they become permanent, supporting informed decision-making in agricultural management. The impact of water shortage on olive yields depends on the timing of its occurrence, as well as its intensity and duration [12]. Drought stress negatively impacts photosynthesis processes with stomatal and metabolic limitations [13]. Different parameters could be measured to investigate plant stresses, including chlorophyll fluorescence, since it is closely linked to the photosynthetic efficiency of plants [14; 15]. The influence of abiotic stress (e.g., heat and drought conditions) on chlorophyll fluorescence is well-documented [16; 17; 18]. It has been demonstrated that drought conditions have negative effects on chlorophyll fluorescence. Drought stress increases the likelihood of overexcitation of photosystem II (PSII), causing dissipation of the absorbed energy through nonradiative processes [18]. Many parameters are measured to investigate chlorophyll fluorescence, such as \(\mathrm{Fv}^{\prime}/\mathrm{Fm}^{\prime}\), which is widely adopted in agronomic research. Given the vulnerability of olive trees to drought stress, measuring \(\mathrm{Fv}^{\prime}/\mathrm{Fm}^{\prime}\) can serve as a powerful tool for early water stress detection. \(\mathrm{Fv}^{\prime}/\mathrm{Fm}^{\prime}\) measures the maximum quantum efficiency of PSII under light conditions, representing the ability of PSII's open reaction centers to capture and utilize light energy for photosynthetic processes [19]. Conversely, the \(\mathrm{Fv}/\mathrm{Fm}\) ratio represents the initial maximal efficiency of photons captured by open photosystem II reaction centers (PSII) under dark-adaptation conditions [20]. \(\mathrm{Fv}^{\prime}/\mathrm{Fm}^{\prime}\) is calculated as the ratio of variable fluorescence (\(\mathrm{Fv}^{\prime}\)) to maximum fluorescence (\(\mathrm{Fm}^{\prime}\)), where \(\mathrm{Fv}^{\prime}\) is the difference between \(\mathrm{Fm}^{\prime}\) and the minimum fluorescence (\(\mathrm{Fv}^{\prime}\)) under the presence of Non-Photochemical Quenching (NPQ) [20]. Values of \(\mathrm{Fv}^{\prime}/\mathrm{Fm}^{\prime}\) range between 0.75 and 0.85 in optimal conditions [21]. Lower values may indicate plant stress (e.g., occurrence of photoinhibition or photosynthesis downregulation) [22]. Therefore, it would be a useful tool for monitoring the physiological state of plants and their ability to adapt to environmental changes. For instance, [PERSON] et al. used \(\mathrm{Fv}^{\prime}/\mathrm{Fm}^{\prime}\) to monitor the physiological activities of olive trees under different irrigation conditions [23]. Using sensors mounted on satellites, aircraft, or unmanned aerial vehicles, it is possible to acquire data in various spectral bands, facilitating comprehensive crop monitoring.