Using ultrasound to detect defects in trees: current knowledge and future needs

Abstract

Ultrasonic decay detectors (UDDs) have been available commercially for several years and can be used successfully to detect decay in live hardwood and conifer trees. Recently, a UDD has shown promise in detecting bacterial wetwood in red oaks in the southern United States and in a Chilean hardwood species. Two improvements to the UDD tested would make it more useful to the broader forestry community. Current UDDs only measure ultrasound signal time of flight (i.e., velocity) from the transmitter to the receiver across the diameter of a tree. This measurement is insufficient to distinguish wood decay from a void, or either of those from the cell wall degradation caused by bacterial wetwood. Further, in order to position ultrasonic transducers in contact with the wood of a live tree for good signal propagation, a "wad" punch is used to create 5-cm diameter holes in the bark. This process takes time and causes wounds that serve as entry points for pathogens and insects. An overview is presented of the current effort to develop a UDD that records time-domain and frequency-domain waveforms that can be positively linked to individual types of defects, and that uses smaller, pointed transducers to minimize tree wounds. Preliminary results support current knowledge regarding ultrasound interactions with sound and unsound wood, and suggests that further experimentation can lead to a new generation of UDDs

Citation

Leininger, Theodor D.; Schmoldt, Daniel L.; Tainter, F.H. 2001. Using ultrasound to detect defects in trees: current knowledge and future needs. Proceedings, The First International Precision Forestry Cooperative Symposium. 99-107