© Measurand 2008

Background

Measurand Inc. produces arrays of MEMS (Micromachined ElectroMechanical Systems) sensors used to monitor deformations of soil and structures. Deformation is calculated from a matrix of tilts of flexibly-connected rigid segments. MEMS accelerometers, used as gravity-sensors, determine the static tilts.

Dynamic vibration and some cases of dynamic shape may also be determined from the same accelerometers. Field installations report the condition of landslides, dykes, levees and bridges using wireless cellnet communication and internet-based 3D viewers. The commercial product is called ShapeAccelArray TM , or SAA.

Objective

This SWAN sub-project is aimed at demonstrating the use of SAA in tracking:

     a) static shape of tree limbs, and

      b) movement of tree limbs and trunks.

a) is important to estimating snow and rain loads stored in the trees populating a watershed. b) can aid in understanding the effects of wind on trees in exposed or protected locations, or its effects on different species of trees.

Why?

How?

Sensor Array

The "PODs" form of SAA (triaxial MEMS accelerometers in sealed tubes separated by electrical cables) was used to instrument the trunk and two limbs of a mature white pine tree. The tree height is estimated to be over 20m. 8 PODs sense  trunk inclination in two degrees of freedom at 1.2m intervals starting ~3.7m above ground level, and 8 more PODs at 1.2m intervals sense vertical deformation of two opposed limbs attached to the trunk at approximately the same elevation,  ~7.3m from ground level.

Sensor Processing

PODs communicate with a PC installed in a nearby building using wired RS485 communication. An internet camera in a window  in the building generates near-real-time video of the tree. SAARecorder Software (see www.MeasurandGeotechnical.com) in the PC is used to generate data from the PODs showing 3D shape of the trunk and 2D shape of the limbs in a vertical plane. Data arrive at approximately 20 Hz. Temporal filtering is applied to reduce effects of rapid dynamic movements on the tilt data.

Additional Sensors

PODs include digital temperature sensing on the trunk and limbs. Additional sensors are being added for temperature, humidity, wind speed and wind direction, using wireless Mote technology.

Snow  Load

The upper right photo shows the left instrumented limb of the tree in snow-free conditions. Red lines have been added to indicate the approximate shape of the limb based on the photographic image.

The lower right photo shows the shape of the limb loaded with wet snow. The white lines show  the shape of the  loaded limb. The red lines from the above photo have been added to show  the shape of the un-loaded limb.

The inset below shows initial qualitative match between the photographic data (dotted lines) and MEMS data.

Results?

From  Poster "Precipitation and Wind Loading from tree-mounted MEMS"

2008 GEOIDE Conference, Niagara Falls, Ontario

J. Bond 1, M. Lowery-Simpson 1, B.G. Nickerson 2, J-P. Arp 2 and M. Weiler 3

1Measurand, Inc.  2University of New Brunswick  3Albert-Ludwigs-Universität Freiburg, Germany

Click Here for Live Webcam view of  tree fiitted with SAA

(Internet Explorer only)

Click here for video of tree with trunk data superimposed: