The photochemical Reflectance Index (PRI) and the vegetation temperature as indicators of water stress and transpiration in Mediterranean olive grove

To increase the olive tree water use efficiency, an early tracking of water stress is crucial. Several indices based on the near-infrared (the vegetation temperature) and the visible (The photochemical reflectance index (PRI)) spectral bands have shown to be useful to remotely assess the tree eco-physiological functioning status. First, at plant scale, we analyzed the relations between close-range remote sensing measurements (PRI, vegetation temperature) and the plant water stress measurements (plant available water (PAW), the transpiration, the water stress index…). The vegetation temperature was closely associated with the transpiration and the plant water stress indicator. However, the PRI, which was promising as an indicator of the water functioning of the plant, was not able to detect water stress over complex crown of isolated tree due to its high sensitivity to the structure.