Hemispherical imaging of canopy light interception: A ceptometer alternative for precision irrigation in orchards and vineyards

Abstract

The amounts of solar radiation absorbed or intercepted by canopies are key parameters for determining gas exchange rates and for estimating water requirements and yield potential in precision agriculture. Measurements with portable ceptometers around midday are the most widespread field method for assessing light interception. However, in orchards and vineyards, light interception varies during the day depending on tree spacing, training system, and tree size, so a single midday measurement may not represent the daily integrated value. This study proposes a cost-effective approach based on hemispherical imaging for rapidly and reliably assessing both the diurnal pattern and the daily fraction of Intercepted Photosynthetically Active Radiation (fIPAR). The method uses hemispherical images representing the fraction of radiation reaching the ground across tree spacing, including alleys between rows. Images were processed automatically to analyse canopy occlusion along the sun’s trajectory. Application of this method, using either still camera or video recordings, was compared with concurrent ceptometer measurements in orchard and vineyard canopies, showing high agreement (R² between 0.88–0.92) and consistency across lighting conditions. The results highlight that, particularly when employing action cameras, this method offers a practical, scalable, and labour-efficient assessment of diurnal fIPAR, providing an operational alternative to traditional ceptometer measurements. Its adaptability to different orchard canopies and robustness under various lighting conditions and configurations, including anti-hail nets, make it a suitable method for precision agriculture.