Abstract Paul PetrieMark SkewesMickey WangMark WhittyStanley LamScarlett Liu

A Thermal Camera-Based Smartphone Application to Measure Vine Water Status

Paul Petrie,* Mark Skewes , Mickey Wang, Mark Whitty, Stanley Lam, and Scarlett Liu  
*Australian Wine Research Institute and the South Australian Research and Development Institute, PO Box 197, Glen Osmond, SA 5064, Australia (paul.petrie@awri.com.au)

The concept of using canopy temperature to estimate plant water status was developed during the 1970s. Unfortunately, this technique has not been widely adopted due to the high cost of equipment and the need for office-based image analysis. Smartphones have several advantages over specialist monitoring systems including ubiquity, price, user familiarity, and ease of implementing updates. They also contain sufficient computing power that analysis and support software can be contained within the handset. Thermal cameras that connect to smartphones have recently been released by several vendors. One of these (FLIR-One®) was evaluated using an irrigation trial on Chardonnay and Cabernet Sauvignon grapevines in the Riverland region of South Australia. Crop water stress index (CWSI) was calculated based on the canopy temperature relative to canopies that are well-irrigated or under severe water stress (represented by artificial reference leaves). Images were collected from the shaded side of the canopy so that the system could potentially be used under a range of environmental conditions. After 10 days of assessment over a range of irrigation levels, measurements collected with the thermal camera were correlated with stem water potential (r2 ≈ 0.6) and stomatal conductance (r2 ≈ 0.7). Under warm and clear conditions, the relationship was stronger (r2 ≈ 0.8 for stomatal conductance), but windy and humid conditions disrupted both CWSI and the reference measurements. To test the utility of this system for assessing vine water stress and making irrigation decisions, a smartphone application was developed for user acceptance testing. The application was designed to automatically select the wet and dry reference leaves and the canopy from the thermal image, making it easy to calculate the CWSI in the vineyard. User feedback has been positive and the final version of the application will be released for the 2017 to 2018 season.

Funding Support: Wine Australia