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Abstract. The Picus Some Tomograph is a noninvasive tool for assessing decay in trees. It works on the principle that sound waves passing through decay move more slowly than sound waves transversing solid wood. By sending sound waves from a number of points around a tree trunk to the same number of receiving points, the relative speed of the sound can be calculated, and a two-dimensional image of the cross-section of the tree, a tomogram, can be generated. Picus tomography and visual inspection were used to evaluate 27 cross-sections from 13 trees. The tomograms correlated closely wrth the visual assessment of decay. In 10 samples where no decay was present, Picus found no decay. In the remaining 17 samples, Picus detected less decay than was observed visually. Differences in most cases were small (average of 5% of total area). In terms of predicting the location of decay, on average 3% of the total area was a false positive (where the tomogram showed that decay was present but the cross-section did not), and an average of 8% of the area was false negative (the cross-section showed decay that was not seen on the tomogram).
Key Words. Hazard trees; tree risk analysis; tree failure.
A number of products and techniques are now marketed for detecting and assessing decay in trees, reviews of which can be found in the literature (Mattheck and Breloer 1994; Nicoletti and Miglietta 1998; Harris et al. 1999; Lonsdale 1999). Equipment and techniques such as the Resistograph®, drilling, and the increment borer involve drilling through the bark into the xylem (Smiley and Fraedrich 1992; Costello and Quarles 1999). There may be some disadvantages associated with drilling (Harris et al. 1999). The Picus Sonic Tomograph (Argus Electronics GmbH, Rostock, Germany) was developed as a noninvasive method to quantify and locate wood decay.
Sonic tomography is a technique used to produce an image of the internal structure of a solid object by recording differences m the speed of sound wave transmission. The Picus Sonic Tomograph consists of a set of sensors (typically 8 to 12) that are connected to the trunk by pins (roofing nails) 0.8 to 2 mm (0.03 to 0.7 in.) in diameter (Figure 1). Sound waves are produced by tapping each...