© 2000 by Institute of Chartered Foresters
| ||||||||||||||||||||||||||||||||||||||||||||||||||||
The analytical use of stress waves for the detection of decay in standing trees
1 High Wycombe, England 2 High Wycombe, England
This paper describes the use of an innovative method to detect decay in trees. The criteria for the project required the decay detecting process to be non-invasive and to provide an estimation of the position and extent of decay. A measured impulse from a hammer blow was used to produce stress waves within the stem of a tree. The stress waves were detected by an accelerometer and the resulting amplitude-time signals were recorded on a portable oscilloscope. The time of flight and attenuation of the stress wave were determined and the signal was transformed on a computer hosting a commercial software package. Six measurements were taken between different co-ordinates positioned around the circumference of a tree stem that was suspected of containing decay. Analysis of the amplitude spectrum of the stress waves provided an indication of the presence of sound or decayed wood between each set of co-ordinates. Estimation of the position of decay in the stem was achieved by calculating a short-time Fourier transform on each temporal signal and mapping the path of the stress waves through sound wood. The information produced by the analysis of stress waves was confirmed by felling the tree.