Geometry matters for sonic tomography of trees.

Key Message: Due to the simplifying assumptions used to analyze acoustic wave propagation in trees, the accuracy of sonic tomograms varies significantly according to the geometry of the measured tree part. For trees growing in communities, arborists routinely check for evidence of damaged wood during tree risk assessment, and sonic tomography is occasionally used to measure the amount of internal damage in trees. Existing studies investigating the accuracy of commercially available sonic tomography devices have mostly considered a limited range of measurement conditions, limiting their application in practice. Using measurements incorporating greater variability in test conditions, this study examined the accuracy of sonic tomography by comparing the percent damaged cross-sectional area in tomograms with the destructively measured internal condition of trees. Although the accuracy of tomograms differed between the examined temperate and tropical tree species, the variation was largely explained by underlying differences in the cross-sectional geometry of the measured tree parts. The amount of decay was repeatedly underestimated in measurements of small, circular cross sections, and, conversely, it was consistently overestimated in measurements of large, irregularly shaped cross sections. Using different approaches to generating and interpreting tomograms, a wide range of decay estimates was obtained for a given set of measurements. By adjusting software settings, it was possible to obtain tomograms with the least error for a given cross-sectional geometry, and the tomograms could be visually interpreted to similarly compensate for the anticipated measurement error. Although practitioners can use the identified strategies to compensate for the expected measurement error in different situations, there is also a fundamental need to develop improved measurement and analysis routines for sonic tomography relying on physically realistic assumptions about acoustic wave propagation in wood. [ABSTRACT FROM AUTHOR]