Estimating Radiation Interception in Heterogeneous Orchards Using High Spatial Resolution Airborne Imagery

This letter outlines a method for quantifying the fraction of intercepted photosynthetically active radiation (fIPAR) from high spatial resolution airborne images acquired from an unmanned aerial vehicle. Airborne campaigns provided imagery of peach and citrus orchards using a six-band multispectral camera with 15-cm resolution. At the time of the airborne flights, field measurements of fIPAR taken with a ceptometer and structural data were obtained to characterize the study sites. Measuring fIPAR can be time consuming because of the need to sample for spatial and temporal variability. In this context, remote sensing techniques are useful as they make it possible to assess large areas. There is a lack of studies exploring the use of remote sensing techniques to estimate fIPAR in structurally complex crops. In this letter, the use of high spatial resolution imagery allowed us to classify each study plot into three pure components: vegetation, shaded soil, and sunlit soil. The radiation intercepted by a canopy is determined by the architecture and optical properties of the canopy. Consequently, the fractions of each component and their pure reflectance were used to estimate fIPAR in each study area with rmse = 0.06 for orange orchards and peach orchards.