Grapevine water status estimation using thermal and digital images from proximal sensing approach

Vineyards are largely located in semi-arid areas, such as Mediterranean regions, where water deficit and high temperatures determine a drought season whose intensity largely affect the final yield and quality of production. Therefore, efficiency of water use in vineyard management, and robust techniques to accurately detect plant water stress are necessary. Infrared thermography has been used as a non-invasive methodology for assessing grapevine water status, and as a tool supporting irrigation scheduling. Moreover, proximal sensing techniques based on digital images can be a valuable tool for detecting crop canopy spectral characteristics and for evaluating crop physiological status (RGBs indices). In this study, thermal and visible images of three varieties of grapevine, under two deficit irrigation regimes, were acquired during the maturation phase using a InfRec R500Pro thermal camera (Nippon Avionics Co., Ltd.). Moreover, digital images of the same plants were acquired daily, using a Campbell CC5MPx digital camera. Thermal and complementary visible images of the crop canopy were taken in four sampling days, between 10.00 and 11.00 a.m. hours. An artificial wet surface, made of cotton cloth, was used to estimate the reference wet temperature. The reference dry temperature was estimated using a black aluminum surface. Temperature values of each pixel were calculated and then converted into average values. Crop water stress index (CWSI) values were then obtained. The preliminary results showed that the low-frequency deficit irrigation treatment resulted in higher temperatures in the vegetation compared to the high-frequency deficit irrigation regime. These results were also confirmed by the seasonal pattern of both green and red chromatic indices. Keywords: proximal sensing, infrared thermography, CWSI, image processing, grapevine.