Estimating leaf carotenoid content in vineyards using high resolution hyperspectral imagery acquired from an unmanned aerial vehicle (UAV)

► Carotene (Cx+c) content estimation was investigated using a micro-hyperspectral imager on board a UAV. ► The index R515/R570 is highly sensitive to Cx+c content but affected by chlorophyll (Ca+b). ► Estimating Cx+c with indices R515/R570 and TCARI/OSAVI obtained RMSE below 1.3μg/cm2. ► Infinite reflectance models yielded similar results to more complex radiative transfer approximations. ► It demonstrates the carotene retrieval using micro-hyperspectral imagers on board UAVs. Chlorophyll a+b (Ca+b) and carotenoids (Cx+c) are leaf pigments associated with photosynthesis, participation in light harvesting and energy transfer, quenching and photoprotection. This manuscript makes progress on developing methods for leaf carotenoid content estimation, using high resolution hyperspectral imagery acquired from an unmanned aerial vehicle (UAV). Imagery was acquired over 3 years using two different UAV platforms, a 6-band multispectral camera and a micro-hyperspectral imager flown with 260 bands at 1.85nm/pixel and 12-bit radiometric resolution, yielding 40cm pixel size and a FWHM of 6.4nm with a 25-μm slit in the 400–885nm spectral region. Field data collections were conducted in August 2009–2011 in the western area of Ribera del Duero Appellation d’Origine, northern Spain. A total of twelve full production vineyards and two study plots per field were selected to ensure appropriate variability in leaf biochemistry and vine physiological conditions. Leaves were collected for destructive sampling and biochemical determination of chlorophyll a+b and carotenoids conducted in the laboratory. In addition to leaf sampling and biochemical determination, canopy structural parameters, such as grid size, number of vines within each plot, trunk height, plant height and width, and row orientation, were measured on each 10m×10m plot. The R515/R570 index recently proposed for carotenoid estimation in conifer forest canopies was explored for vineyards in this study. The PROSPECT-5 leaf radiative transfer model, which simulates the carotenoid and chlorophyll content effects on leaf reflectance and transmittance, was linked to the SAILH and FLIGHT canopy-level radiative transfer models, as well as to simpler approximations based on infinite reflectance R∞ formulations. The objective was to simulate the pure vine reflectance without soil and shadow effects due to the high resolution hyperspectral imagery acquired from the UAV, which enabled targeting pure vines. The simulation resul