Treetap9: a forestry tool for measuring standing tree stiffness

This paper describes a device for measuring the stiffness of standing trees using stress-waves created from a mechanical impactor. The device interfaces to a cellular phone for data storage, data processing, and user interface. The device has been designed to collect and record the stress-wave signals using piezoelectric accelerometers inserted into a tree. The prime motivation is to be able to record a large number of signals to help develop better stiffness estimators. An experiment is described showing the difficulty of estimating the frequency dependent stiffness using three time of arrival techniques: threshold, first peak, and second peak. All these techniques are shown to overestimate the stiffness due to the dispersive nature of the stress-wave signals.