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PiCUS Sonic Tomograph
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The PiCUS Sonic Tomograph is used to investigate the internal condition of a tree using sound waves. A series of nails are installed around the tree at the measuring plane where visual inspections have identified weaknesses requiring further investigation. These nails become the measuring points and are used to send or receive sound waves. The distances between the measuring points are carefully measured and recorded by the field technician. The sound waves are generated by a hammer tapping on one of the nails. The PiCUS instrument measures the time of flight of sound waves between the sending point and the other receivers. The software calculates the apparent sonic velocities (distance/time) and draws a "velocity" or "density" map of the tree by combining the measured tree geometry with sonic data recorded during the assessment. The sonic velocity can be correlated with wood densities and therefore with the soundness of the wood. The introduction of the electronic hammer allows for full resolution tomography images to be recorded with as few as 6 to 8 sonic sensors. The PiCUS Sonic Tomograph won the Technology Award 2000 from the German Federal State of Mecklenburg-Vorpommern. |
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Advantages of using the PiCUS
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Components of the PiCUS System
The sketch below shows standard and optional components of the PiCUS Sonic Tomography system.
Recording Sonic DataThe standard method of measuring the sonic data is to attach one sensor to each measuring point (nail). The time of flight of sound waves generated by tapping each nail is recorded at each of the other sensors and used to calculate the tomoraph. The sketch below illustrates this method. Blue dots indicate the sonic sensors on each measuring point.  Advanced Recordings with the PiCUS Electronic Hammer The recently developed electronic hammer (photo on right) offers a new measuring method that employs Fewer – Sensors – Than - Measuring – Point (FSTMP) Technology. With the electronic hammer, a standard 12 sensor PiCUS test can be accomplished with as few as 4 or 6 sensors! |
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The diagrams below illustrate different measuring procedures that can be used with the FSTMP technology. In the diagrams the blue points represent sonic sensors and the black squares represent measuring points (nails). |
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In the first row of diagrams, 12 measuring points are assessed using 6 sensors. The sensors are first placed on the odd measuring points (1, 3, 5, 7, 9 and 11) and each nail is tapped in sequence. The sensors are then shifted over one position so that the even measuring points (2, 4, 6, 8, 10 and 12) now have a sensor attached to them. The technician then taps on all the nails again. The two rounds of sonic measurements are combined by the software to give one tomograph image. In the second row of diagrams, an alternate methodology is shown. This can be used when the tree is so large that the string of sensors will not reach completely around the tree. The sensors are initially set on the first 6 measuring points as can be seen in the first diagram. The technician taps all 12 measuring points regardless of whether they have a sensor attached or not. Once the first round of tapping is completed, the sensors are rotated around the tree so that the sensors are attached to measuring points 7 to 12. The tapping on all measuring points is repeated and the two rounds of sonic measurements are combined by the software to give one tomograph image. In the third row of diagrams, 10 sensors are used to assess 12 measuring points. In the first diagram, 2 of the twelve measuring points do not have a sensor attached to them. The technician taps on all the measuring points and then shifts just 2 sensors to cover the measuring points that did not have a sensor in the first round of tapping. The technician then taps on all the nails once again and the two rounds of sonic measurements are combined by the software to give one tomograph image. |
2D View of a Tree
Tomograph images are generated at the site as soon as the measurements are completed. A number of functions are available for data analysis and presentation. Measurements of residual walls and the extent of decayed areas can be taken directly from the tomograph image. The images can also be saved as digital files that can be exported into other software and used for presentations and reports.
3D View of a Tree
The 3D function can be used to combine multiple tomographs from the same tree. If the technician records the tomograph images with a similar compass orientation and aligns the measuring points, the software will combine them into a three-dimensional image. The image can then be turned and manipulated to provide unique views of the internal columns of decay. These views can help to provide further information from which risk assessment decisions can be made.
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This Eucalyptus tree was investigated at four levels. The aim of the investigation was to find out if there was a connection between the upper and lower fruiting bodies of a fungus. |
Colours of the Tomograph Image
The powerful software compares all velocities recorded at one measuring level to show where the sonic waves travel slower as compared to the “fastest” areas.
There are three main colour groups to note when analysing tomograph images:
- Brown colours (light brown to dark brown)
- Green colours
- Violet-Blue-White colours
Shades of brown indicate sound wood, green areas indicate early decay; violet is decayed wood and blue indicates a cavity, a crack or wood so decayed that it will hardly transmit any sound waves. Using the images gathered with a tomograph, the critical areas for further testing can be identified.
The violet-blue-while colour area can be shown in violet colours only. The examples below show a tomograph image in standard, violet only (no blue) and grey colours. These colour definitions are part of the PiCUS Expert Software.
Geometry is Important – There is no Circular TreeTo generate the best tomograph images, the geometry must be measured as accurately as possible. There are several different options in the software that allow the technician to choose the most appropriate method to accurately measure the geometry of the cross-section. The “free shapes” method is the most accurate way to measure tree geometry. The PiCUS software utilizes triangulation theory to calculate the correct shape of the tree. The sketch at right illustrates the measurements required to reconstruct the cross-section of a tree. While the distances can be measured with any standard calliper and entered into the PiCUS software, the PiCUS Calliper has been specifically designed to streamline and improve the efficiency of calculating tree geometry. |
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PiCUS Calliper
The PiCUS Calliper allows for quick and precise measurements of even the most complex trees and root flares. With Bluetooth connectivity and automatic integration with the expert software, the PiCUS Calliper is the fastest and most reliable tool to record tree geometry.
Using the PiCUS Calliper, the geometry of nearly any tree can be measured. The example on the left shows a challenging tree from Australia with large buttress roots and the images on the right show the calliper at work.