WHAT IS sonic tomography?

Tomography is the imaging of sections of a subject using a tomograph. The result is a tomogram, an image showing a cross-sectional view, a slice. In arboriculture, a tomogram shows a slice through a tree’s stem and roots, and when this slice is mapped using ultrasound it is called a sonic tomogram.

Here you can see PiCUS sonic tomograph being used to test a mature Fraxinus excelsior (common ash) in Walker, Newcastle. PiCUS are one of the major brands in tomography equipment, sitting alongside Rinntech and Fakopp.

The results from the PiCUS sonic tomography test show the difference in travel time for sound through the wood. In general solid healthy wood is allows sound to pass easily, whilst decayed wood slows the sound waves down. Mapping the time taken for the sound to travel reveals a map of the wood inside the tree.

Late last year, working with our friend Jim from Woodsman we took three tomographs of the base of this beech tree in Cleadon using Fakopp’s Arborsonic in order to understand the impact a large cavity (on the right side there) is having on the structural integrity of the tree.

The result of the “scan” is a tomogram, as shown below. The variation in speed of sound travel is shown using different colours. Green areas are ‘good’, where the sound travelled quickly; red are ‘bad’, where the sound travelled slowly; and blue are really ‘bad’ – or really open.

We already knew there was a cavity, but with this image we can better understand the size and see the amount of good wood remaining. When decay inside a tree isn’t visible – like it is in this open cavity – we can get a great understanding of what’s going on without having to cut and physically look in the tree.

Whilst the angles of the two photos aren’t the same (this is really rough!), you can see how the interior of the tree is revealed – without having to cut the tree down.

Whilst this is a basic introduction to the work we do – it’s by no means a measured case study – there’s a lot of “noise” in the data shown. But I’m sure you get the jist of it.

Using calculations we are able to determine a safety factor which in turn informs a decision as to whether a tree can be retained, or the volume of work that needs to be carried out in order to improve it’s safety factor, such as a height reduction to reduce the wind loading.

In summary…

What is a sonic tomography?

A sonic tomography is a non-destructive testing technique used to analyze the internal structure of an object or material using sound waves. It involves sending sound waves through the object and measuring the time it takes for the waves to travel through different parts of the object. This information is then used to create a visual representation of the object’s internal structure.

How much does sonic tomography cost?

The cost of sonic tomography varies depending on several factors, including the location, the provider, and the specific requirements of the project. It is recommended to contact different service providers and request quotes to get an accurate cost estimate for your specific needs.

Does sonic tomography damage trees?

No, it does not damage trees. Well, that’s sort of true. The nails used by most devices puncture a small wound in the bark in order to get to the sapwood (the main bulk of the tree). In doing so there is a small wound, but the harm done is considered so low that this is seen as one of the least intrusive forms of decay assessment.