Measurement of stiffness of standing tress using acoustic velocity measurements made through tree stems

Standing tree stiffness measurements are commonly calculated using acoustic Time of Flight (TOF) velocity measurements. These are generally obtained by measuring the propagation time of an acoustic signal between two probes inserted into the “same face” of the tree. Studies have suggested that these TOF measurements are biased to measure the outerwood stiffness rather than that of the tree stem as a whole. However, the stiffness of tree stems increase from pith to bark. In this paper, a technique is investigated, which uses TOF measurements on the “opposite faces” of the tree stem to attempt to obtain an average stiffness through the tree stem. Unlike previous studies, this technique allows for the anisotropic nature of wave propagation in wood. The measured Modulus of Elasticity (MOE) values are compared to MOE values obtained using the “same face” TOF and acoustic resonance techniques.