The Arborsonic 3D Sonic Tomograph detects defects (e.g., hollows or wood rot) in a non-invasive way by generating a two-dimensional map of the sound velocity transmitted across a tree’s section, mirroring the integrity of the inspected wood. It works on the principle that sound waves passing through decay move more slowly than sound waves traversing solid wood. The system sends sound waves from several points around a tree trunk to the same number of receiving points, the relative speed of the sound can be calculated, and a two-dimensional image is generated. Using the differences in the transit times between sensors, the analysis software constructs a two-dimensional picture, which shows zones of differing sound transmission properties within the stem. The software uses pre-set colours, for example, areas with high “sonic speed” in green whereas low sonic values are shown in magenta. Other colours of yellow & red represent various levels of rotting zones based on sonic speed measurements in the respective areas. Sonic Tomography gives valuable density information about the trees. The density strongly correlates with the soundness of the wood. This is very useful to access the stability of the tree.