Hourly simulation of grape bunch light microclimate using hemispherical photography

Abstract

Hemispherical photography has been widely used in forestry for the assessment of canopy structure (gap fraction and openness), estimation of biomass and leaf area index (LAI), and rate of change in canopy cover. Moreover, geographically north-oriented hemi-pictures allow the reconstruction of the percentage of direct, diffuse and global radiation from daily, weekly, monthly to annual time range. In viticulture, hemispherical pictures have been used to document canopy development, estimate the light interception efficiency, validate a three-dimensional statistical model of grapevine canopies, and to calculate the amount of direct, diffuse and total radiation during ripening of bunches. Direct radiation is one of the main driving factors affecting berry temperature and therefore quality. Continuous measurements of the light microclimate at bunch level using light sensors are demanding and expensive and cannot be widely adopted to monitor the incoming radiation and to relate this to berry temperature and the ripening status of the berry/bunch. In this study, hemispherical images were collected to develop a procedure to improve the simulation of light availability at bunch level from daily to hourly time-steps, which would also take into account the effects of row orientation or canopy management on the direct irradiance during the day. Results confirmed the validity of this approach, but some important issues have not yet been considered. Results will be used in the reconstruction of daily direct light profiles of the bunches and in energy balance models for the estimation of berry/bunch temperature.