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- Tree Motion Sensors (TMS)

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The Wind-Reaction-Measurement with PiCUS TMS is used for in depth tree inspections to obtain information about a tree’s stability, defined by its root anchoring force in the ground.

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The Wind-Reaction-Measurement records the dynamic sway motion of a tree in naturally occurring wind, by measuring the root plate tilt.

Advantages:
The trees reaction is measured directly, including all environmental influences.
These include tree specific parameters (size, form of the crown, etc.), wind strength and wind exposition (buildings and other trees in the vicinity).

In contrast to this the tree pulling test (Wessolly & Erb, 1998), an established method for assessing root defects, uses an artificial wind replacement load. However, an estimate for the correlation between actually occurring natural wind and the artificial wind replacement load is rather difficult because of the previously mentioned environmental influences.



Confirmation of stability
If trees only show a small root plate tilt, even in strong wind gusts, one can assume a stable root system.

Identification of trees with root anchorage problems
After measuring tree groups comparing the results can identify trees with conspicuously large root plate tilt.

Combination with static tree pulling test (TreeQinetic) with regards to stability
If a tree with increased tilt angles has been identified, it is often meaningful to follow up with a static pulling test to measure the trees reaction to a known force.

Addition to sonic tomography (PiCUS Sonic Tomograph) and resistance tomography (TreeTronic3)
Trees with large defects in the lower stem area (with assumed root defects) should additionally have their stability tested in natural wind

Surveillance of trees near construction
Sustained changes in a tree’s tilt angle during groundworks (e.g. placing of sheet pile walls) can be detected with the PiCUS TMS.

Long term monitoring of trees
Trees suspected of having root anchorage problems can be inspected in regular intervals to check whether:

  • The root plate tilt in wind decreases (tree grows new and stronger roots)
  • The root plate tilt in wind increases (roots are dying off or get damaged otherwise)
  • The reaction remains constant

Wind causes tilting of the root plate and bending in the tree’s trunk. 
The PiCUS TMS are inclinometer which dynamically log changes in root plate tilt over hours, days or even weeks.

Precondition:

  • Wind gust speeds > 45 km/h

Implementation of measurements:

Tree Motion Sensor TMS Installation
  • Mount sensors before a wind event, end measurement after the wind calmed down (minimum measurement duration 2h)
  • 2 PiCUS TMS per tree:
    base sensor on the trunk base – direct measurement of root plate tilt
    control Sensor in 2-3m height – for filtering out ambient noise sources (e.g. road traffic) and for identifying actual wind events
  • Comfortable analysis in your office, minimized on site time

If the base sensor shows tilt while the control sensor doesn’t, it is ambient noise.
On an actual wind event the value of the control sensor has to be higher than the base sensors, because the upper sensor not only measures the root plate tilt but also the superimposed bending of the tree trunk.

The included PC software creates diagrams showing the relationship between wind speed and root plate tilt - the Wind Tipping Curve. Wind speed can be measured either on site (TMS Wind Measurement System) or it can be read and added manually from external sources (eg.windfinder.com). 

The ability to extrapolate tilt, for wind gust speeds 10 to 20 km/h above the ones measured, allows predicting the tree’s performance at said wind speeds.

Example
Below are wind tipping curves from three Douglas fir measured during hurricane Xaver (wind speeds of up to 93 km/h, measured by a weather station approx. 9 km away).

The red curve is from a Douglas fir which has both a large defect in the trunk base and strong root swellings (see PiCUS sonic tomogram). The other two curves are from neighbouring trees without defects in the trunk base. It can be seen that the Douglas fir with defect shows even less root plate tilt than the reference trees.

Conclusion:
The Douglas fir reacted to the internal defect by growing stronger roots.

An alternative method of analysis (Attention: not applicable for PiCUS TMS 3 measurement data) is calculating the measurements with an online analysis tool on the www.treesensor.comwebsite.
The charged Treesensor web service searches tilt maxima in the observation period without regards to wind data, and creates a PDF file displaying the measured data.

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