A mobile thermal-RGB imaging tool for mapping crop water stress of grapevines

This study evaluates a tablet computer-enabled miniature thermal-RGB imager to map the crop water stress index (CWSI) in grapevines. Imagery data were acquired in a commercial grapevine block irrigated at four different rates (100, 80, 60, and 40% of replacement evapotranspiration [ET]). The latter three were the subsurface irrigation treatments. A custom image analysis algorithm was developed and CWSI was estimated using empirical baseline equations. RGB imaging refined the segmentation of the target canopy from background objects. Canopy-air temperature difference had significant and strong relationships with the vapor pressure deficits as per local conditions (R2: 0.72–0.85, p < 0.05). CWSI estimates for grapevines irrigated at 40% of ET were consistently the highest and were followed by for those irrigated at 60, 80, and 100% of ET rates. Study findings highlight the potential to develop a smartphone-enabled imaging and integrated application for real-time crop water stress assessment under field conditions. Our future efforts will refine these computing algorithms and develop a smartphone application for growers to assess tree-level crop water demands for site-specific irrigation management.