Fruit Water Stress Index: Case Study on Applying Jones’ Equation in Apple

In this study Jones’ equation was used for the calculation of the fruit water stress index ($\mathrm{{FWSI}_{J}}$) at the apple orchard (cv. Gala-Brookfield). Instead of the common tree’s canopy temperature, 3D fruit surface temperature (by integration of light detection and ranging (LiDAR) and thermal camera sensors) has been employed. Additionally, $\mathrm{{FWSI}_{J}}$ was monitored in the seasonal and daily courses. The results showed a moderate correlation between the index calculated by 3D fruit surface temperature and manually (reference) measured temperature during the season. Related to daily courses, $\mathrm{{FWSI}_{J}}$ showed an increase during the daytime with diurnal fluctuation. The study highlights the potential of the 3D fruit surface temperature for assessing water stress in an orchard environment. However, further investigation needs to be done to develop a well-adapted equation for computing FWSI by 3D fruit surface temperature.