An Artificial Dry Reference Surface for Predicting Canopy Temperature Dynamics from a Moving Irrigation System

Abstract

Elevated crop canopy temperatures are a useful indicator of water stress. Single-time-of-day canopy temperatures of large field areas can be detected by infrared thermometers (IRTs) mounted on center pivots or lateral move irrigation systems. Determining canopy temperatures at other times of day from these measurements requires a method of estimating diurnal canopy temperature dynamics due to changing environmental conditions from a one time-of-day measurement. This has been shown to be possible by using canopy temperature dynamics measured with an IRT in a stationary reference location in another part of the field to scale the one time-of-day measurement. It has also been shown that the water stress condition of the reference location has little effect on the errors of the predicted canopy temperatures. It would simplify instrumentation and programming if the reference temperature dynamics could be collected from a location other than the field, such as on the moving irrigation system itself. An artificial dry reference surface was tested to determine whether it could be used as the reference surface to capture the canopy temperature dynamics. The surface consisted of a large artificial plant leaf, cut to fit and mounted in a cross-stitch hoop. This was located in a stationary position next to the field being studied. The temperatures of the artificial reference surface were measured with IRTs mounted both above and below it. Canopy temperature dynamics predicted from one time-of-day measurements using the artificial dry reference surface were compared to those predicted using living and transpiring canopy temperature measurements in a stationary location in the field. The absolute mean errors of the predicted diurnal curve from the actual measured curves were compared. The errors when using the artificial dry reference surface were significantly worse than those of the living crop. These errors were possibly due to the fact that the artificial dry reference surface was not located amongst the living canopy. Future experiments need to be done with the artificial dry reference surface located on the moving irrigation system but near or amongst the living canopy.