Infrared Camera Measurements Reveal Diurnal Variation in
the Effect of Mechanically Induced Internal Voids on Stem
Temperatures of Small Trees Passively Heated by the Sun
Daniel C. Burcham, Eng-Choon Leong, Yok-King Fong, and Puay-Yok Tan
Abstract: The relationship between stem temperature measured by an infrared (IR) camera and a tree’s internal condition was proposed as a basis for diagnosing potentially hazardous defects in the landscape. Before practical application, this diagnostic technique needs clarification to guide expectations of its resolution and precision. In this study, cylindrical voids of varying size were created in 5 cm diameter stems of Dracaena fragrans and Syzygium grande by mechanically removing tissue from specimens in an outdoor nursery, and the surface temperature of these plants was measured twice daily at 0830h and 1830h using an IR camera. The collected IR images were analyzed using a concurrent mixed methods approach with qualitative image evaluation and quantitative temperature analysis where the temperature distributions of stems containing internal voids were compared to those without defects. For both species, there was no difference in stem temperatures, as observed in IR images, among any experimental plants at 0830h, but an anomalous temperature reduction was exclusively apparent at 1830h near the 3.8 cm void, occupying 76% stem cross-sectional area. There was also a larger decrease in the linear temperature trend (0.34°C–0.51°C) near this void margin compared with other treatments, although this was more pronounced in the monocot species than eudicot. The remaining treatments did not exhibit stem temperatures visibly different from the control. Under experimental conditions, the technique identified relatively large internal defects, but the reduced heat capacity of stems containing such defects is only apparent in the evening after being passively heated by the sun.
Keywords: Diagnostic Device; Dracaena fragrans; Infrared Camera; Internal Defect; Singapore; Syzygium grande, Temperature; Thermal.