Geometry matters for sonic tomography of trees

The amount of internal decay was measured at multiple locations in 41 different trees using sonic tomography, and the percent damaged cross-sectional area, AD (%), was determined using four different software settings (A: SoT 1 - Default; B: SoT 1 - Expanded; C: SoT 2 - Default; SoT 2 - Expanded) and color interpretation strategies (GVB, VB) associated with the PiCUS 3, a commercial device commonly used by arborists for decay assessment. The measured tree parts were subsequently felled and dissected at each measurement location for comparison with tomograms. Four geometric properties of the measured tree parts were estimated from images of the destructively measured internal condition, including the cross-sectional area, A (m^2); circularity, C (dimensionless); solidity, S (dimensionless); and eccentricity, E (dimensionless). The accuracy of sonic tomograms was estimated by computing the difference between the percent damaged cross-sectional area obtained from tomograms and images of the destructively-measured internal condition, AD(error) (%).