Opportunities and pitfalls in the use of thermal sensing for monitoring water stress and transpiration

This paper reviews recent progress in the development of thermal sensing (both in-field and remotely from unmanned aerial vehicles (UAVs), aircraft or satellites) as a tool for irrigation control, for plant phenotyping, for the study of plant water relations and for estimating stomatal conductance and transpiration from crops. Approaches to the use of thermal sensing in horticulture using both single point sensors (especially when incorporated into wireless sensor networks) and imagers are compared with discussion of the information that can be obtained. Particular challenges limiting the wider uptake of thermal sensing including the treatment of mixed pixels, the selection of appropriate reference surfaces for absolute estimates of evaporation or stomatal conductance and the critical need for improved software for extraction of information from images are discussed.