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) (%).

本研究采用声波层析成像（sonic tomography）技术，对41棵不同树木的多个测点内部腐朽程度进行了定量测定；并借助PiCUS 3——一款被树木养护专业人员广泛用于树木腐朽评估的商用设备——的四种软件设置（A：SoT 1 - 默认模式；B：SoT 1 - 扩展模式；C：SoT 2 - 默认模式；SoT 2 - 扩展模式）与两种色彩解读策略（GVB、VB），测算得到受损横截面积百分比AD（%）。随后将各测点对应的待测树段伐下并进行剖解，以与声波层析成像结果开展比对。从破坏性剖解获取的内部状态图像中，估算得到待测树段的四项几何属性，包括横截面积A（单位：平方米，m²）、圆度C（无量纲）、凸度S（无量纲）以及偏心率E（无量纲）。最后通过计算层析成像所得受损横截面积百分比与破坏性剖解内部状态图像所得结果之间的差值，评估声波层析成像的准确率，即AD(error)（%）。