Arboriculture & Urban Forestry 37(3): May 2011 Arboriculture & Urban Forestry 2011. 37(3): 93–98 93 Evaluation of an Infrared Camera Technique for Detecting Mechanically Induced Internal Voids in Syzygium grande Daniel C. Burcham, Subhadip Ghosh, Leong Eng Choon, and Fong Yok King Abstract. In order to evaluate a proposed tree diagnostic technique employing infrared cameras, research was conducted to evaluate the effect of inter- nal voids on surface temperature using a thermal photographic instrument. Three axial cylindrical voids of increasing size (Void A, 327 cm3 745 cm3 ; Void B, ; Void C, 1159 cm3 ) were introduced mechanically in 45 cm long stem sections and exposed to direct sunlight. Subsequently, infrared images were collected from two diametrically opposed sides of the stem sections at regular 30-minute intervals over 150 minutes. The collected images were evaluated visually to compare stem features with observed temperature anomalies, and temperature data was extracted from a vertical transect in the infrared images. The data extracted were compared against a control stem section without defects to determine the independent and combined effects of void size and internal position on surface temperature. Mean relative temperature revealed a significant temperature change in the stems contain- ing mechanical voids compared to the control stem. Significant increases in mean relative temperature were recorded on the stems containing Void A and Void B compared to the control. However, there was no significant change in mean relative temperature on the stem section containing Void C. Key Words. Infrared Camera; Internal Defects; Syzygium grande. Trees are indispensible elements of urban landscapes and pro- vide numerous, quantifiable environmental, economic, and social benefits (Dwyer et al. 1992; Kuo 2003; Laverne and Winson- Geideman 2003). However, an increase of harm resulting from tree failures in urban areas is becoming an essential concern worldwide. Therefore, tree hazard assessments are a viable and important tree failure risk reduction stratagem. While striving to mitigate risks, arboricultural practitioners have developed numer- ous precise diagnostic techniques for the assessment of internal structural defects in standing trees, including destructive (Bethge et al. 1996) and nondestructive (Ouis 2003) techniques. The tech- niques evaluate the condition of wood based on material proper- ties, such as density, stress wave transmission speed, and elec- trical conductivity (Nicolotti and Miglietta 1998). They provide information on the spatial extent of healthy and decayed wood within a tree stem, and the results inform decisions made on the safety of an individual tree against failure (Mattheck et al. 1993). In an attempt to advance nondestructive diagnostic testing, Catena et al. (1990) proposed the application of infrared (IR) cameras in tree hazard assessment. The cameras sense long-wave infrared electromagnetic radiation and render temperature mea- surements along a standard color gradient in a visual image. Cat- ena et al. (1990) reported that internal structural defects decrease the thermal conductive efficiency of the combined cellular ele- ments (e.g., vessel elements, fiber tracheids, parenchyma cells) constituting dicotyledonous tree stems, and this change would produce variation in the bark surface-temperature distribution. Early reports indicated that relatively cooler surface temperatures would reveal a relationship between structural defects and re- duced conductive efficiency (Catena and Catena 2008). Tree haz- ard assessment with an IR camera has several potential benefits, including general, nondestructive, and rapid diagnostic evalua- tions. The temperature measurements can be captured instanta- neously for objects within the camera’s field of view, and this permits evaluation of longitudinal wood conditions compared to point- or plane-specific diagnostic evaluation. Current IR cam- era technology accurately detects 0.05°C temperature variation between 6 mm2 surface area units from a distance of 10 m (NEC 2010). The digital images can be captured and stored in seconds. Catena and Catena (2000) reported that epiphytic vegetation, condensed bark moisture, and high solar irradiance masked un- derlying wood temperature values, and these sources of measure- ment error could impede the identification of structural defects. These conditions occur commonly in tropical environments, while existing studies of IR camera diagnostic assessments have been carried out exclusively in temperate biomes (Catena 2003). These demonstrations of the technique were limited to in-depth case study analysis on a small number of specimens, and the methodology reported relied heavily on visual interpretations of images, followed by broad comparisons with destructively har- vested physical sections of trees to confirm accuracy (Catena and Catena 2008). The potential for introduced bias and the limited transferability of these methods likely limits greater profession- al acceptance and implementation of the technique. With these points in mind, an experiment was designed to evaluate the ef- fect of mechanically introduced voids, serving as simplified ana- logues of fungal induced cavities, on stem surface temperature using the infrared camera under controlled conditions. In this way, evidence supporting the technique’s accuracy would justify further investigations applying the technique under more complex natural conditions. The objectives of the current study were to (1) identify stem morphological features associated with reduced ©2011 International Society of Arboriculture
May 2011
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