The integrator of drought is the plant water status (Jones, 2007), as determined by plant water content or water potential. A direct measurement of these variables is difficult and currently not possible in a high-throughput phenotyping approach. Probably the most commonly used technique in this context is thermal infrared imaging, or infrared thermography (IRT) to measure the leaf or canopy temperature.

Plant canopy temperature is a widely measured variable because it provides insight into plant water status. Although thermal imaging does not directly measure stomatal conductance, in any given environment stomatal variation is the dominant cause of changes in canopy temperature (Jones and Mann 2004).

Thermal imaging is becoming a high-throughput tool for screening plants for differences in stomatal conductance (Merlot et al. 2002). Thermal infrared imaging for estimating conductance has potential value as it can be used at the whole plant or canopy level over time. Leaf temperature has been shown to vary when plants are subjected to water stress conditions. Recent advances in infrared thermography have increased the probability of recording drought tolerant responses more accurately.