PiCUS Sonic Tomograph

The PiCUS Sonic Tomograph is used for tree risk assessments in order to measure the thickness of the residual wall of trees with internal defects such as cavities or decay non-invasively. Most often the PiCUS sonic tomograms are recorded near ground level of trees. However,  acoustic tomograms also reveal important safety information about the breaking risk near branch wounds and above ground cavities.

Operational theory of the PiCUS Sonic Tomograph

The PiCUS Tomograph measures the velocity of sound waves in wood in order to detect decay and cavities in standing trees non-invasively. The acoustic velocity depends on the modulus of elasticity and the density of the wood itself. Most damage and disease causes fractures, cavities, or rot and reduces the wood’s elasticity and density. The sketch displays the basic working principle, in that sound waves cannot take a direct path through the wood (red dotted line) if there is a cavity between the transmitter and receiver.

The acoustic waves are created manually with a little hammer, sonic sensors (receivers) record the signals. Little pins are used for coupling the sensors to the wood. Number and positions of the test points are critical to the accuracy of the scan.

By using both acoustic travel-time information and geometry data of the measuring level the software calcualtes tomograms that show the  apparent sonic velocities, thje so called sonic tomograms acoustic tomograms. The speed of sound in wood correlates with wood quality and is therefore a measure for the breakign safety of the trunk. The PiCUS sonic tomogram shows the residual wall thickness. Using this information the calculations on the web-site www.treecalc.com can show the breaking safety of the trunk.

More measuring points than sensors

The cirmcumference and outline (shape) of the tree determine the number of measuring points (test points) for a PiCUS sonic scan. The PiCUS technology differentiates between sensors and measuring points (MP). A MP is a simple nail. For a PiCUS scan a virtually unlimited number of measuring points (nails) can be used because of that technology. The photo below shows a setup of 12 sensors on 24 MP. The electronic hammer can create sonic signals on all 24 MP, regardless of whether a sensor is currently attached to the nail or not.  

The photo shows a possible sensor distribution during a scan of a 24 MP tilia tree using 12 sensors of a PiCUS 3 system.