Trees can appear healthy on the outside while hiding severe internal decay that threatens their stability. PiCUS Sonic Tomography offers a non-invasive, highly accurate way to assess a tree’s internal condition, without cutting it down or drilling into the trunk.
In this article, we’ll explain exactly how PiCUS testing works, step by step, and show you what goes into a typical inspection.
If you’re wondering why PiCUS is often recommended over standard visual inspections, read how it compares to visual tree assessments here.
Step 1: Placing the Sensors
To begin, the arborist selects the correct height on the trunk for measurement—usually around 1.3 metres above ground (known as breast height) or near any visible defects.
Next, they attach small metal sensors (usually 10–24, depending on the trunk’s size) evenly around the tree. These sensors will detect how sound waves travel through the wood when tapped.
Step 2: Measuring the Tree
After placing the sensors, the arborist uses digital callipers to measure the diameter of the trunk at the chosen height. This measurement calibrates the tomograph and ensures the final scan reflects the actual tree structure.
Step 3: Connecting the PiCUS Sonic Tomograph
With the sensors in place, the arborist connects each one to the PiCUS control unit using wires and a strap to secure the unit to the tree. At this point, the system is ready to begin recording.
Step 4: Tapping the Sensors
Now, the arborist taps each sensor gently with a small hammer. These taps send sonic pulses through the trunk, and the PiCUS system records how long it takes the waves to travel between sensors.
Because sound moves more slowly through decayed or hollow areas, this step helps identify internal weaknesses.
Step 5: Recording and Analysing the Data
Once all the sensors have been tapped, the data is transferred to a laptop running PiCUS software. The software then generates a cross-sectional image of the tree, revealing areas of solid wood, early-stage decay, or internal cavities.
Step 6: Interpreting the Results
The software colour-codes the tomogram to help with interpretation:
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Brown/green = sound wood
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Purple = early-stage decay
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Blue = hollow or severely damaged wood
A qualified arborist analyses the scan, taking into account species, environmental conditions, and structural implications before offering any recommendations.
Step 7: Making a Recommendation
Based on the results, the arborist may recommend:
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No action (if the tree is sound)
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Crown reduction
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Remedial pruning
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Retesting after a set period
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Removal (in severe decay cases)
For a deeper look at how PiCUS fits into long-term tree care strategies, check out our article on the benefits of PiCUS testing for property and tree management.
Ready to Assess Your Trees?
Whether you’re concerned about cavities, storm damage, or just want peace of mind, PiCUS testing offers a clear view inside your tree. It’s trusted by local authorities, schools, estate managers, and private landowners across the UK.
For more information on PiCUS testing, visit directree.org