Ultrasonic imaging of defects in standing trees: development of an automatic device for plantations

The aim of this study was to develop a specific device for ultrasonic imaging which can be used in tropical forest plantations. The imaging devices are mainly based on measuring the velocity. However, the attenuation can also be used for detecting defective areas. For this experiment, the ultrasonic emission was a pulse train of square waves at 80 kHz. A log of green poplar without bark (33 cm in diameter) was tested. Maps were computed according to the Radon theory and using a filtered back projection algorithm with fanbeam geometry. The spatial distributions of slowness and attenuation were in agreement with the visual observations (presence of decay in the middle with a crack). The analysis of quantitative assessments of these two parameters showed that error increased with slowness. The slowness values linked to the decay area were thus less accurate. This phenomenon was not observed for the attenuation parameter. Keywords Populus deltoides, imaging, ultrasound, ultrasonic slowness, ultrasonic attenuation. (Résumé d'auteur