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Picus Sonic

by editor arbor age

PiCUS Sonic Tomograph – non-invasive tree assessment.

The PiCUS Sonic Tomograph (ST) has become an established tree inspection instrument over the past two decades, providing arborists a non-invasive means of assessing the internal wood structure and strength of trees.

As advised by ENSPEC Managing Director Craig Hallam, the PiCUS ST works by passing sound waves through wood, with the speed at which sounds travels through the wood making it possible to detect areas of structurally sound timber, slightly modified wood and areas of decay or cavities in a tree.

Craig told AA that most of the PiCUS ST analysis ENSPEC undertakes is for local government authorities across Australia and internationally.

“We initially started out using the technology for the testing of high-valued trees with significance or cultural value,” he commented. “As time moved forward, and councils accepted the technology, sonic tomography is now used on all trees today.

“And as trees become more valued by more of the public, we find that municipalities complete testing for political reasons – the general public appears to accept a computer image more than a written statement arrived at from visual observations made by an arborist.”

Testing the structural integrity of trees Craig explained that, following training by a certified tomography expert, setting up the PiCUS ST is not a complicated process, with the critical component being placement of the sensor pins around the test area of the tree. He told AA that if the placement is askew, then the end test result may not look like the tree’s trunk shape when visually compared.

“Once the sensor’s pins are in place, a series of triangulation measurements are taken that allows the software to calculate the shape of the tree trunk,” Craig said. “Once the measurements are complete, the sensors are then attached and sound waves induced by tapping on each sensor with a computerised sounding hammer.

“Once each sensor point has been activated and sound waves induced, the computer then generals a 2D colour-coded digital image. Then the arborist who is trained in interpreting the image can make accurate assessments of the tree’s structural integrity at the test level.

“With the later version of the software, a series of tests on a tree can have the images collated together to provide a 3D view of the tree’s internal structure.”

Craig explained that tree preservation
and conservation are the primary benefits delivered by the PiCUS ST, with 98% of trees that had been condemned from a visual assessment, and then subsequently tested by ENSPEC, having sufficient structural wood, leading to many trees being saved.

“One of the other benefits is when decisions on tree retention become political – it is hard for an elected member to argue for the removal of a tree on behalf of a constituent when the council arborist has assessed that the tree is structural acceptable,” he commented.

A value-adding service
ENSPEC has been using the PiCUS ST for almost two decades, having initially purchased a unit in 2002, and now operates three units: a PiCUS ST series 2 with 30 sensors, another with 14 sensors, and one of the latest PiCUS ST series 3 units.

Craig believes the series 1 and 2 units take the most accurate measurements, noting that over the years as the software has improved, accuracy has improved, and said he always uses the manual tapping hammer and a series 2 unit when conducting high-level testing for CSIRO or other research institutes.

“Key to accurate measurements is the manual chrome tapping hammer, you can provide more concise and consistent taps than with the newer computerised hammers – unfortunately, you can no longer buy the manual tapping hammers,” he told AA.

Craig explained that, among ENSPEC’s suite of tools, he views the PiCUS ST as a value-adding service.

“If you were relying on a return on investment on scientific equipment like the PiCUS ST, you would be waiting for a few years, and by the time you gained the return it would be time for a rebuild or upgrade,” he commented.

“By having this equipment in the early days, it allowed ENSPEC to grow its unique range of scientific measuring tools, and these tools provide support to our arboriculture and ecology consultants and services offered.”

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