Distance error for determining the acoustic velocity of standing tree using tree morphological, physical and anatomical properties

摘要

Time-of-fiight (ToF) acoustic tools is one of the most practical nondestructive methods for predicting tree stiffness. In the literature, 120 cm between probes has been adopted as the standard for the assessment of tree acoustic velocity. However, there is no empirical study supporting this assertion, hence this study is aimed at determining the effect of distance on error for a common ToF acoustic tool. Twenty-five trees each were randomly selected from four loblolly pine plantations. Seven distances from 120 to 10 cm between probes were used to measure velocity. The morphological characteristics, physical and anatomical properties of the selected trees were also determined. The results indicated, at distances below 60 cm, the waveform is dominatedby the fundamental frequency of the transmitter probe hence the velocities determined within 10-60 cm are not statistically different. Consequently, distances from 80 to 120 cm constitute the optimum range for velocity determination for this ToF acoustic tool. Furthermore, velocity determined at 40 cm is significantly higher than that determined at 120 cm suggesting velocity is dependent on the between probes distance. Using 120 cm as a standard distance, the dynamic stiffness is overestimated by 13, 50, 102, and 197 MPa respectively for 100, 80, 60, and 40 cm. Finally, microfibril angle andthe fiber wall thickness are the main anatomical properties driving the signal at the micro-level.