S18 - Session P4 - A phenotypic platform for monitoring temperature on apple surface

Authors: Nikos Tsoulias *, Sven Jörissen

Fruit surface temperature has been reported as one of the reliable indicators for sunburn occurrence in apples. When apple fruit epidermal and sub-epidermal tissues temperature exceeds the tolerance limit, it may cause sunburn symptoms, resulting in yield and quality losses. Consequently, to manage apple sunburn, monitoring fruit surface temperature is critical. This work presents a phenotype sensing system that integrates a light detection and ranging (LiDAR) sensor and a thermal camera for monitoring the distribution of fruit surface temperature in three dimensions (FT LiDAR ) on apple trees. The phenotype system was mounted on a movable linear conveyor with maximum length of 650 mm to perform intrinsic and extrinsic calibration using an active pattern with clearly defined heat sources. After calibration, the sensor system was mounted on a circular conveyor platform, established in an experimental apple orchard (TechGarden), together with a real time kinematic global navigation satellite system to geo-reference the data and an inertial measurement unit to acquire orientation data. The platform enables the automated monitoring of 109 trees ( Malus x domestica Borkh. 'Gala' and 'JonaPrince') in one row of 84 m length. In 10 trees, the temperature of apple surface (n = 293) (T Manual ) was manually measured and compared with the correspondent averaged T LiDAR . Measurements were carried out in three sections of tree heights. The intrinsic calibration of the thermal camera yielded a root mean squared error (RMSE) of 0.33 for 140 images, whereas the RMSE of the extrinsic calibration 1.30 for 22 different positions of the calibration target. These results suggest that the phenotype system is suitable for monitoring the temperature on the apple surface. A coefficient of determination of R 2 = 0.93 was obtained between T Manual and T Manual in the middle part of the tree, whereas a less pronounced relation was observed (R 2 = 0.85) at the top of the plant.