How sonic tomography works 

Sonic tomography can detect decay and cavities in standing trees non-invasively by tracking the speed of sound waves in the trunk, roots, and larger branches.  The velocity of sound in wood depends on the modulus of elasticity (MOE) and the density of the wood itself.  Damage and disease in trees can lead to fractures, cavities, or rot, which reduces elasticity and density of the wood.  The PiCUS® Sonic Tomograph uses relative sound velocities so that the system calibrates itself automatically at each measured cross-section.  Due to the low invasiveness of the measurements, tomography can be conducted repeatedly on the same specimen and compared to earlier readings to evaluate the progress of wood decline in relation to the production of new wood.

 

Tomogram interpretation

Using the above tomogram as an example:

The fastest velocity recorded between sensors is set to 100%. Areas of high velocity are shown in dark browns, grading to light brown - 57 % of the cross section.

The slowest velocity measured was 45%, in relation to the fastest (100%).  Areas of slow velocity are shown in blues and purple and compose 31 % of the cross section.

Areas with intermediate velocities are shown in green.  These could represent wood in early stages of decay – 12% in this tomogram. 

Planes of greatest impedance to sound transmission are indicated by straight yellow lines and in some cases could indicate cracks. 

The values of solid or damaged wood are only estimations.  Please note that accuracy depends on the:

• shape of the cross section
• position of measuring points
  
• shape of the damaged area
  
• type of damage (cracks, decay, cavities).
  

Presence of defects in the trunk or branches does not automatically render the tree dangerous.  The tomogram needs to be considered together with other data and evaluated by an experienced arborist before a management plan for the individual tree can be formulated.