Estimation of the light environment inside a tomato canopy in a greenhouse by using the ray tracing method

The amount of solar radiation received by leaves changes, depending on the greenhouse structure, plant species, cultivation area, and plant density. Recently, estimation of the light environment in a greenhouse by using optical simulation has become possible. Optical simulation can predict the optimal plant spacing and cultivation management options and design a greenhouse structure that maximizes the amount of solar radiation received by the leaves. In this study, 3D models of a greenhouse (144 m²) and tomato canopy were constructed using a 3D scanner. The leaf area and plant height of the 3D models for tomato could simulate those of the actual plants. A significant correlation (R²=0.99) was observed between the measured leaf area of the actual plants and that of the 3D model. The light environment in the tomato canopy was estimated using the ray tracing method, which traces rays from sunlight while considering the optical properties of objects. The date, time, latitude, longitude, and global solar radiation at the greenhouse location were used as input values to calculate the solar altitude. PPFD values at the top, middle, and lower layers of the tomato canopy were estimated every 1 min, and the hourly integrated PPFD values were calculated. The measured hourly integrated PPFD value was acquired simultaneously for comparison with the estimated value to confirm the accuracy of the simulation. The PPFD values measured on November 27-30, 2018, were used. With respect to the simulation, a significant correlation (R²=0.93) was observed between the measured and estimated values of the hourly integrated PPFD. In addition, the slope of the approximate curve between the measured and estimated values was close to 1. Thus, estimation of the hourly integrated PPFD in the tomato canopy was possible.