What is Sonic Tomography?
Sonic tomography is an advanced tree risk assessment technique used to evaluate the internal structure and structural integrity of living trees by examining the way sound waves travel through their trunks. Developed as a non-invasive method to inspect the condition of trunks, it offers a more detailed perspective on the extent of internal decay, hollow cavities for trees, and other structural weaknesses that may not be visible through external indicators. Unlike traditional methods that rely solely on visual inspection or extraction of wood cores, sonic tomography provides an acoustic tomography-based perspective, creating a detailed sonic tomograph image of the internal structure of the tree trunk. This approach allows arborists, forest managers, and tree service professionals to detect decay in trees before it leads to tree failure, improving decision-making in arboriculture and the long-term health of a diversity of tree species—from thin-barked tree species to thick-barked trees.
How Sonic Tomography Works
Sonic tomography involves the placement of sensors—often small devices resembling nickel upholstery nails—around the circumference of a tree trunk at a standardized height aboveground. These sensors, sometimes referred to as a sensor chain, measure the flight measurement and travel time of stress waves or sonic waves generated by tapping each sensor in sequence. The velocity of sound waves in wood is recorded and processed by specialized software. By comparing the speed of these waves through solid wood to that through compromised wood or decomposed wood, the system constructs an acoustic tomogram. This tomogram provides a graphic representation displaying areas of healthy, intact wood in a blue tree outline, while identifying zones of internal decay or hollow structure in contrasting colors.
Principles of Sound Wave Transmission
Sonic tomography is rooted in Wood Science and Technology, leveraging the principle that sound waves travel faster through dense, healthy wood and slower through decayed or compromised wood. The variations in wave speed reflect differences in wood density and the presence of decomposed wood. Acoustic signals, introduced by tapping sensors or other small probes, propagate as waves in wood. When these sonic waves encounter decay cavities, fungal inoculation sites, or decomposed wood, their velocity decreases significantly. By measuring these variations, arborists can infer the degree of decomposition and occurrence of rot within the trunk. This approach works well in assessing a diversity of tree species in various environments, from urban settings to tropical rainforest trees, where challenging conditions often mask decay in tree stems.
Equipment Used in Sonic Tomography
The equipment for detection in sonic tomography typically includes a set of specialized sensors, a tapping device, and a data collection unit. Each sensor is positioned around the trunk perimeter at predetermined inter-nail distances. Sensor types can vary—some are flat head or larger steel roofing nails—and must be carefully placed to ensure consistent contact with wood, even in thicker-barked trees. Sensor magnets can improve sensor contact. In some cases, bark removal may be necessary, especially with thick-barked tree species, to ensure accurate measurements. Additional tools such as a portable drill might be employed to place sensors securely. A geometry file and software guide the sensor placement, ensuring accurate measurement of the tree diameter, trunk perimeter, and reliable tomograms. Care must be taken in selecting the measurement level, ensuring that the belt below nail locations is consistent and that the sensors are set at minimum height aboveground.
Benefits of Sonic Tomography in Arboriculture
- Non-invasive Assessment: Unlike drilling or extraction of wood cores, sonic tomography requires minimal disturbance. It reduces damage to trees and preserves their aesthetic integrity.
- Enhanced Risk Assessment: Sonic tomographs allow arborists to accurately identify factors for advanced tree risk assessment, including hidden wood decay patterns and root rot, aiding in the early detection of wood decay that might weaken structural integrity.
- Accurate Wood Decay Detection: The method’s ability to detect incipient decay ensures that even early stages of internal decay are identified before they progress, whether in thin-barked or thick-barked trees.
Applications of Sonic Tomography
- Identifying Hidden Decay: Many trees—especially tropical trees—may show no external indicators of decay. By comparing the internal structure revealed through tomograms, arborists can identify patterns of wood integrity and decay.
- Facilitating Maintenance Decisions: Armed with insights from sonic tomography, tree service professionals can determine whether to prune, brace, or remove risk trees. This supports informed interventions that prolong a tree’s life or mitigate hazards.
- Supporting Tree Health Evaluations: Sonic tomography’s measurement of patterns of wood production and density aids in understanding a tree’s overall vitality and resilience across a diversity of tree species.
Companies Pioneering Sonic Tomography
Several companies have spearheaded the development of advanced sonic tomography systems. Firms that produce tools such as Arbotom® and similar instruments are at the forefront. By investing in research and development, these companies expand the utility of tomography, making it more accessible, portable, and accurate for arborists. Their contributions shape how tree service professionals perform detailed examinations on trees.
Tools and Technologies in Sonic Tomography
Overview of the Arbotom® Tool: Arbotom® is one of the most renowned sonic tomography tools on the market. It utilizes a sensor chain arranged around the tree diameter, and tapping generates stress waves to produce a detailed tomogram image. The tool’s software allows for a comprehensive analysis of trunk perimeter, geometry image files, and the subtraction of geometry data to highlight compromised areas. By considering inter-nail distances, approximate distance intervals, and other factors, the Arbotom® system ensures accurate, reliable results for assessing the structural integrity and internal decay of trees.
Best Practices for Effective Use
To achieve reliable results, arborists must follow a carefully standardized field methodology. Establishing consistent sensor locations, using a practical approach for nail spacing, ensuring a chain of successive sensors, and selecting suitable sensor sizes helps maintain measurement consistency. Arborists also consider bark thickness, focusing on both thin-barked and thick-barked tree species, as bark removal might be required for effective sensor placement. Scanning of buttresses and measuring space between buttresses are critical steps, especially for tropical tree species with complex root systems and prop roots. The presence of hollow structures or decomposed sections within the trunk perimeter must be thoroughly measured, often comparing data with a healthy sample tree stump to calibrate results.
Future of Sonic Tomography in Tree Care
Innovations on the Horizon: The field of sonic tomography is continually evolving. Emerging technologies promise more sophisticated data analysis tools, faster data collection methods, and improved sensor accuracy. Software is expected to offer enhanced guides for geometry, allowing arborists to refine their tomographic images. As sensor technology improves, measurements under difficult conditions—such as scanning thick-barked tree species in tropical rainforest environments—will become more reliable. Additionally, future equipment may integrate drill testing and portable drills capable of minimal bark penetration to refine internal structure data.
Expanding Adoption in Arboriculture:
As the effectiveness of tomography becomes more widely recognized, its adoption by arborists and tree service professionals will increase. In-depth tomography studies are expanding beyond basic risk assessments to support research in wood decay patterns, wood material properties, and the structural resilience of trees across a diversity of tree species. With increased familiarity, arborists will rely more heavily on sonic tomographs as a standard component of tree examinations and advanced tree risk assessments. The popularity of sonic tomography extends to specialized contexts, such as evaluating eucalyptus trees, dead trees in urban parks, and thick-barked tree species in tropical rainforests. By offering non-invasive insights into the condition of trunks, sonic tomography enables proactive measures to prevent tree failure and maintain safety—enabling, for instance, detailed road safety examinations for trees near highways.
As tomography software continues to evolve, features like options to measure and subtract geometry data will streamline the entire process. Arborists will better understand patterns of decay, refine approaches to tomography, and harness the utility of tomography not just as a diagnostic tool but also as a predictive measure. This progress will make sonic tomography a cornerstone technology in arboriculture, guiding forest management, urban tree maintenance, and conservation efforts—especially where root rot, internal decay, and damage to trees pose challenges.
Sonic tomography stands at the intersection of Wood Science and Technology, arboriculture, and advanced data analysis. By measuring sonic waves in wood, taking into account tree diameter, trunk perimeter, sensor spacing, and sensor placement, and integrating findings into comprehensive tomography files, arborists gain unprecedented insights into the internal structure and condition of living trees, healthy trees and sick trees too. Whether applied to thin-barked trees, tropical trees, or thick-barked trees, it offers a precise method for the detection of wood decay, ensuring healthier, more resilient trees in both urban landscapes and biodiverse tropical rainforest ecosystems. As innovations continue, sonic tomography will undoubtedly become an increasingly critical tool for arborists and tree service professionals, bolstering tree health evaluations, guiding maintenance strategies, and contributing to safer, healthier environments.
