Arbotom Sonic Tomography — Advanced Internal Tree Assessment
Urban Tree Management carries out specialist tree decay detection investigations using the Arbotom sonic tomography system with impulse sensor technology — the most advanced non-invasive diagnostic configuration available for assessing the internal condition of a tree stem.
We are completely independent from any tree surgery contractor — our findings and recommendations are based entirely on the diagnostic data, with no financial interest in the outcome.
All investigations are carried out personally by Carl Riva — we do not subcontract decay detection work. You get the consultant who operated the equipment, interpreted the findings on site, and wrote the report.
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Specialist Tree Decay Detection
What the Arbotom Actually Measures
This is something most people — and many consultants — get wrong.
The Arbotom does not show the exact condition of the wood. What it measures is the mechanical cohesion of the cross-section — how well the wood transmits sound. Reduced sound velocity can indicate decay, cracks, cavities, or ring rot. It can also in certain conditions produce readings that look like decay but are not — frozen wood, concrete-filled cavities, engulfed structures, and codominant stem geometry can all create misleading readings in the hands of an inexperienced operator.
This is why Urban Tree Management always uses the Arbotom alongside the IML Resistograph — the two instruments together provide a complete picture that neither can give alone. The Arbotom locates the zone of concern. The Resistograph physically measures the wood at that location, confirming the presence or absence of decay and the thickness of the residual structural wall.
The Impulse Sensor System — Why It Matters
Standard acoustic tomography systems are typically limited to around 24 sensors. Urban Tree Management uses the Arbotom impulse sensor system — allowing measurement at over 100 points around the stem at each assessment height.
With a standard 12 or 24 sensor configuration, small or peripherally located areas of decay can be missed or poorly resolved — particularly on large diameter stems. At over 100 measurement points the resolution improves significantly and small areas of structural concern that would be invisible on a standard survey are clearly identified and precisely located. For trees being assessed in a legal, planning, or insurance context the higher measurement density produces a demonstrably more reliable result.
How the Arbotom Works
The impulse sensor chain is placed around the stem at the assessment height. Each point is activated in turn, sending a stress wave through the wood. Dense intact wood transmits the waves rapidly. Decay or structural compromise slows them. A cavity forces the waves to travel around the void, taking significantly longer. The data is processed using species-specific wood properties to produce a two-dimensional colour cross-section of the mechanical cohesion of the stem.
The colour scale:
- Green — Dense intact wood — load bearing under wind loads
- Yellow to orange — Reduced contribution to load bearing — possible early decay, cracks, or incipient deterioration
- Red — Significant defects — cracks or advanced decay — limited load bearing contribution
- Purple — Larger defects or cavities — effectively no load bearing contribution
Important: Red does not automatically mean decayed or hollow. In ring rot, intact wood can display red because it is not contributing to bending load compensation — not because it is absent. Resistograph confirmation is essential before any management recommendation is made.
Important: Red does not automatically mean decayed or hollow. In ring rot, intact wood can display red because it is not contributing to bending load compensation — not because it is absent. Resistograph confirmation is essential before any management recommendation is made
The MECH Module — Strength Loss Analysis
- The MECH module combines the stem geometry with the tomography results to calculate the direction-dependent reduction in mechanical load-bearing capacity. It shows the percentage reduction for all wind directions and identifies the direction of maximum weakening — the most dangerous wind direction for that specific tree.
- A small area of damage at the outer edge of a cross-section can cause the same reduction as much larger damage in the interior — because the outer layers contribute most to structural strength. This is why Urban Tree Management reports the direction of maximum weakening alongside the percentage — not the percentage alone.
- Maturity matters equally. A 25% strength loss is potentially critical in a young fast-growing tree. In a 150-year-old veteran where height growth stagnated decades ago, even 50% may be structurally uncritical. Urban Tree Management uses the ArboStApp module to apply a maturity correction to every MECH percentage — giving a real-world safety assessment rather than a raw number out of context.
ArWiLo Wind Load Analysis & ArboStApp Safety Assessment
Where findings indicate structural concern Urban Tree Management carries out a wind load analysis using ArWiLo. The tree is photographed in the field, its geometry mapped in the app, and the wind load on the crown calculated. This models the effect of crown reduction on wind loading — showing what level of crown reduction would be required to bring the safety factor to an acceptable level. ArboStApp combines this with the tomography findings and a maturity correction to produce a defensible quantified safety assessment.
In some cases this analysis supports retention with managed crown reduction rather than removal — an outcome made possible only by the combination of diagnostic instruments.
ArboRadix Root Plate Analysis
Where root failure rather than stem failure is the primary concern Urban Tree Management uses the ArboRadix module. A light tap on the ArboRadix rod generates an impulse wave through the ground. Where a structurally effective root is present it transmits the vibration to the stem base — producing a map of mechanically active root directions showing where the tree is and is not anchored in the soil.
ArboRadix cannot provide information on root depth or diameter. Results are unreliable in water-saturated or frozen soil and difficult to interpret under hard surfaces. Soil conditions are noted in every report.
When We Would NOT Use the Arbotom
- Frozen or recently frozen trunks — outer ice produces false central decay readings. Large-volume trunks lag air temperature substantially — even if today is above zero, recent freezing conditions mean the results may be unreliable.
- Trees with concrete-filled cavities — concrete carries sound at near-wood velocity and the cavity appears healthy.
- Trees with engulfed structures — steel posts, masonry, or fence rails absorbed into the stem create the same false-healthy reading.
- Codominant stems measured as a single cross-section — the included bark seam at a codominant union produces a false decay signal. Each stem must be measured separately above the union.
- Early-stage white rot — acoustic tomography detects mechanical change only. White rot fungi consume lignin but initially leave cellulose intact — so early-stage white rot can produce a clean acoustic tomogram while active colonisation is in progress. Where white rot is suspected and the acoustic result is clean but visual symptoms suggest otherwise Urban Tree Management will advise on the appropriate follow-up investigation.
What the Report Contains
Every Arbotom investigation report includes:
- Visual tree assessment findings — the context for the instrumental investigation
- Methodology — impulse sensor point count, measurement heights, stem dimensions, colour scale calibration
- 2D tomograms — colour cross-sections of mechanical cohesion at each assessment height
- MECH module outputs — direction and percentage of maximum strength loss
- Resistograph resistance profiles — confirming wood condition at tomogram zones
- ArboStApp safety assessment where structural concern warrants it
- ArWiLo wind load analysis where crown loading is a significant factor
- ArboRadix root plate map where root failure is a concern
- Discussion — whether Resistograph findings correlate with the tomogram and what this means for the recommendation
- Management recommendation — specific, proportionate, based entirely on the combined diagnostic data
- Limitations — all instrument-specific limitations relevant to the investigation
The report is suitable for planning authority submission, insurance purposes, legal proceedings, and duty of care documentation.
FAQ
What is the difference between the Arbotom and the Resistograph?
The Arbotom is non-invasive — the impulse sensor chain is placed around the outside of the stem producing a cross-sectional map of mechanical cohesion at over 100 measurement points with no drilling. The IML Resistograph is a resistance micro-drill — a very fine needle is advanced into the stem recording resistance as it passes through different wood zones. The Arbotom locates the zone of concern. The Resistograph physically confirms what is in that zone and measures the thickness of the residual structural wall.
How is the impulse sensor different from standard acoustic tomography?
Standard acoustic tomography typically uses 12 to 24 sensors. The Arbotom impulse sensor system allows measurement at over 100 points per cross-section — significantly increasing resolution and mathematical stability. Small or peripheral areas of decay that would be missed on a standard configuration are clearly identified. This is particularly important on large diameter stems and investigations that need to withstand professional scrutiny.
Does a red area on the tomogram mean the tree needs to come down?
Not necessarily. Red and purple areas represent parts of the cross-section no longer making a significant contribution to load-bearing capacity. In most cases this indicates decay or a cavity — but in ring rot, intact wood can display red. The MECH module percentage, the Resistograph findings, and the ArboStApp safety assessment together determine whether the structural condition warrants management action — and if so, what action is proportionate.
Can you carry out an Arbotom investigation on any tree?
Most trees — yes. However Urban Tree Management will not carry out acoustic tomography on frozen or recently frozen trunks, trees with concrete-filled cavities, trees with engulfed structures, or codominant stems measured as a single cross-section.
Do you subcontract Arbotom investigations to other consultancies?
Yes — Urban Tree Management is regularly subcontracted by other arboricultural practices and tree surgery contractors across the North West when specialist decay detection investigation is required. Contact us to discuss subcontract rates for regular referrals.
Arbotom Sonic Tomography — Impulse Sensor System — North West & Nationwide
Objective, independently reproducible diagnostic evidence before any management decision is made. Completely independent from any tree surgery contractor.
Get in contact with our highly experienced and personable team of arboricultural consultants today, to discuss your requirements and to obtain your zero obligation quotation.
