Sonic Tomography (Arbotom)

Visualising internal tree structure

Tomographic assessments complement standard arboricultural techniques for assessing tree health and structure. Regular assessment of health and structure is an important component of integrated tree management.

Depending on stem shape and the location of internal decay, loading can affect a tree’s structural integrity. The Arbotom’s software accounts for these factors and displays the potential maximum loss of strength with an indication of the specific direction of loading, such as wind. Tree Dimensions provides all results and interpretation to clients as an Arboricultural Assessment (AA) report; or, as a brief summary report if requested by qualified arborists.

 


Visualising internal tree structure using sonic tomography.

Tomographic imagery:

  • reduces the level of uncertainty in a risk assessment
  • determines the location and extent of internal decay of ageing trees with known structural defects
  • assists tree managers faced with opposition to the removal of a hazardous tree, or pressure for removal of a structurally sound tree.

A decayed Poplar stump (left) and sonic tomography (Arbotom) images of this tree at the same height before felling. The centre image reveals the location of extensive, internal decay. The right-hand image indicates a maximum potential strength loss of up to 48% when the stem is loaded from the south-west.

How the Arbotom works

The Arbotom is an impulse-detecting tomographic instrument: it simultaneously records the time that impulses, or sound waves, take to travel through wood from one sensor to others placed around a tree’s stem. Sound waves travel more slowly through defective wood than through sound wood. After each sensor is tapped in turn to send sound waves to the other sensors, the differential measurements of the time each sound wave takes to travel to each sensor can be plotted as a velocity map.

A decayed Poplar stump (left) and its corresponding velocity map recorded at the same height before felling. The green lines represent sound wood: for example, the sound waves travelled at approximately 1,650 metres per second between sensors 1, 2 and 9. The magenta lines represent damaged wood, where the sound waves travelled at approximately 160 metres per second between sensors 4, 7 and 8.

These data can also be presented as a 2-D coloured cross-sectional image. Tree Dimensions’ experience is that sonic tomography is an accurate and reliable tool that complements an arborist’s knowledge and experience.

A 2-D cross-section of a Poplar overlain on a photo of the same tree after it was felled. This image shows close correlation between the Arbotom’s results and the actual decay in the tree’s stem.

When testing is done simultaneously at two heights of a tree, the Arbotom can produce 3-D images of the extent and location of decay. The images can be displayed as three cross-sectional images and two axial sections, or as animated sections on a computer.

Cross-sectional and axial images of a 3-D test, showing the extent and location of decay between the heights of 10 and
57 centimetres of an Elm.