FAQ Sonic Tomography
Last Updated on Tuesday, 01 December 2009 06:53
What is the difference between Sonic Tomography and Electric Impedance Tomography?
Sonic Tomography uses sonic waves to obtain “mechanical” information about the wood of the tree. Electric impedance tomography uses electric current to gain “chemical” information about the wood. In short, two different types of information are obtained by using these two different methods.
How many sonic sensors do I need?
PiCUS technology distinguishes between sensors (the sonic sensor that receives and registers the sonic signals) and a measuring point (MP). The MP is a simple nail. By tapping on knocking on this nail, you create sonic waves. You attach the sensors to the nails and these receive the sonic signals and register them. The PiCUS system can also use MORE measuring points (nails) than sensors, which is important when you wish to inspect larger trees using only a limited number of sensors.
The distance between measuring points should be between15 and 40 cm. Very smooth and round trees will require fewer measuring points, whereas trees with buttress roots and very uneven circumferences will require more.
It is most effective to place a sensor on at least half of the number of measuring points. This table shows the correlation of tree size to MP and sensors:
| Tree circumference [meter] | Number of measuring points | Number of sensors |
| 3 | 10 to 14 | 5 to 14, optimal 8 |
| 4 - 5 | 12 to 16 | 6 to 16, optimal 10 |
| 6 | 14 to 18 | 7 to 18, optimal 12 |
Experience shows that we can inspect nearly any tree using 6 to 12 sensors, placed on anywhere from 8 to up to 30 MP, and this includes the sensors needed for 3-D measurements.
What are the limits of Sonic Tomography?
Cracks in wood are real barriers for the sonic waves. They appear in the tomogram much larger than they really are and may thus lead to incorrect conclusions about the tree. To identify “star shaped” cracks, the PiCUS software contains a CrackDect Function. We also recommended using other inspection methods, such as the Treetronic electric impedance tomography.
What is the difference between Shigometer and Treetronic?
Both Shigometer and Treetronic try to get the same information about the consistency of the wood (“what is the electric impedance?”), but the working principle is different. The Shigometer required you to drill a hole into the tree and it collected the information about the wood along the drill-line. This is a direct conductivity measurement, meaning two electrodes touch the wood in order to measure voltage and current.
The Treetronic uses a more accurate 4-electrode setup. Two electrodes are used to get the current into the tree; two other electrodes measure the drop of voltage at a different position. In doing so, the Treetronic can collect data of the entire cross section. In the strictest sense, this is data of a column of the tree).
The calculation of the Treetronic are also very different from those of the Shigometer. The results of the Treetronic measurements are recorded in an Electric Impedance Tomogramm (EIT). Interpreting an EIT requires experience and knowledge of the particular species of tree. An EIT can provide valuable additional information about the type of damage in a tree.
Example: When measuring a beech tree with Meripilus giganteus, the sonic tomograph will not be able to detect this fungus well because the wood in the stem is not affected by the fungus growth. The Treetronic would show very high conductivity which, in beech trees, is a clear indication for a fungus infection that increases moisture content. In this case, the Treetronic can also provide you with a look underneath the ground because of the 3-dimensional nature of the measurements. The sonic tomograph does not give you any information from below the ground level.
How many probes do I need to use the Treetronic?
The number of Treetronic channels or probes is 24. Electric impedance tomography requires more measuring points than sonic tomography in order to get good resolution. In many situations it is best simply to double the number of sonic measuring points in order to get a good electric impedance reading. For instance, if the sound tomogram was recorded with 10 measuring points, the electric impedance tomogram should have 20 probes. You can measure larger trees by combining up to 3 Treetronic instruments.
How important is the exact geometry?
Velocity calculations are based on the formula:
Velocity = distance / time
The more accurate the geometry of the measuring level is, the more accurate the tomograms will be. The PiCUS software offers you a number of functions to measure the geometry efficiently. The triangulation method is most accurate.
Do I need the electronic calliper?
The electronic calliper is a very efficient tool to measure the positions of the measuring points. In can help you record even complex geometries in a matter of minutes. Mechanical standard callipers can also be used.
What is the difference between the PiCUS electronic hammer (PEH) and the PiCUS Radio Hammer (PRH)?
The PEH is connected to the end of the module chain by a cable. The cable is attached to the hammer grip. The PRH is connected to the PiCUS system wirelessly. The PRH contains an accumulator battery which must be charged in order to operate the hammer. The PRH is more convenient to use because it is wireless, but the PRH radio system can pick up interference from other electronic devices in the area. If this is a problem where you are working, you can also attach the PRH to the system with a cable.
Do the instruments require annual servicing?
No. The sensors do not need to be calibrated regularly, but argus does offer check-up and maintenance services according to the regulations ISO9000 and others.
Do I need training to operate the PiCUS unit?
Yes. Training on the instruments is highly recommended and will take 1 or 2 days.
What are the recommended configurations for my PiCUS system?
With the electronic hammer, the number of sonic sensors is no longer that important. Combining sonic tomograms and electric impedance tomograms will give you much more information about most trees than simply using more measuring points.
It is more useful to work with a “smaller” PiCUS AND the Treetronic, rather than a “larger” PiCUS (12 to 16 sensors) alone.
Minimal setup
PiCUS Sonic Tomograph – 6 to 8 sensors
PiCUS Standard software
Mechanic calliper (such as Haglöf, etc.)
Standard setup
PiCUS Sonic Tomograph – 8 to 10 sensors
PiCUS Electronic Calliper
PiCUS 3-D Expert software
Scientific / Expert Setu:
PiCUS Sonic Tomograph – 8 to 12 sensors
PiCUS Electronic Calliper
PiCUS Expert software
Treetronic - Electric Impedance Tomograph
Do the tomograms show sapwood – heartwood of the trees?
Yes. Particularly the Treetronic shows you the sapwood / heartwood accurately in many situations. In trees with defects (decay or cavities), the sapwood – heartwood is more difficult to find.
Can I see growth rings in the tomograms?
No. Growth rings are much too small to detect with this technology.
Do the tomograms give me any information about the roots?
The sonic tomograms (SoT) do not give you any information about the roots. They only give information about the level of tomography.
The electric impedance tomogram (EIT) produces an integral of the resistance of a certain section of the tree. The length of this section is approximately equal to the diameter of the tree itself. Thus the EIT can give you information about the roots when you measure near ground level, particularly about the decay in roots.
Can I use the PiCUS for root mapping / detection?
Using the Sonic Tomograph instruments for root detection is limited. Under perfect conditions it could be possible to detect large roots near the tree under the surface.