tree risk management using radar imaging

7/28/2019 Tree Risk Management Using Radar Imaging

1/5

As you are traveling home one

evening, you notice a consistentdull pain in your lower back. As theweeks pass the pain intensifies and youbecome increasingly concerned. Youvisit your family physician, and after anexamination he explains to you youroptions to determine the source of yourpain. He describes how exploratorysurgery could provide him with someanswers. But he also describes otheroptions including non-invasive onessuch as ultra sound, MRI (electromag-

netic imaging) or an X-ray. Knowingthat complications can develop usingexploratory surgery, the physician does-nt take any chances and orders an MRIscan on your lower back.

Trees are somewhat like people; atsome time during their life they too willdevelop internal problems that are notalways able to be seen just by an exteri-or examination.

Arborists have used all sorts of meth-

ods to determine the internal structuralcondition of a tree and its potential riskto a property. Some of these methodswere very invasive, such as taking coresamples, drilling or even cutting awaydecay within a cavity. Those were thestandard methods used at one time,and some continue to be used today.Theres reason to believe that the termTree Surgeon may have been coinedas a result of these invasive procedures.

May 2012

A Journal for Community Association Leaders

Reprinted from

M AY 2 0 1 2 E C H O J O U R N A L

By Robert Booty

Radar Imaging forTree Risk Management


2/5

The Value of Using Non-InvasiveTesting Methods for Tree RiskManagement

What benefit is there in using non-invasive diagnostic procedures withtrees? Trees can be adversely affectedby the methods used to evaluate theirhealth especially using invasive diagnos-tic procedures that penetrate the outerbark.

The establishment of decay1 in livingtrees is affected by urban environmen-tal stresses that range from a generalweakening of a trees natural defensesystem to injuries that allows wood-rot-ting agents to gain entry through

wounds. Trees have an internal protec-tion system that uses a series of fourinternal walls, all beautifully designedto block the spread of disease causingpathogens within the tree. Its referredto as CODIT, an acronym forCompartmentalization of Decay inTrees.

However when invasive testing meth-ods such as drilling are used, these four

protective walls can be pierced by thedrill bit, allowing decay pathogens thatat one time may have been localized orcontained to spread throughout the

tree. One concern many people havealways had with these testing methods isthe many holes being drilled into a treethat one is trying to save.

When performing tree risk assess-ments, knowing the internal structuralcondition of a tree is only one part, buta very vital part, of the process. If thisinternal data could be collected withoutdrilling or using other invasive meth-ods, and you could just walk away withyour data as if you were never there,then it would be a win-win situation for

the tree under evaluation.Use of Radar Technology

Today technology has advanced tothe point that this non-invasive type ofdata collection is possible. It is beingaccomplished by using ground pene-trating radar that does not harm thetree being evaluated. The use of radarimaging on trees creates the same typeof high- resolution, non-invasive image

that a medical professional would uti-lize in his diagnosis with his patientusing MRI imagery. This is the very lat-est method to safely evaluate the inter-

nal structure of a tree without invasionof the tree itself. Having the ability tocreate and see an internal image of atree and then to identify any hiddeninternal problems fills a critical gap intree preservation.

How Does Radar Work?

Ground-Penetrating Radar (GPR) isan established technique that has beenused worldwide for over 40 years. Radaris an object-detection system that useselectromagnetic wavesspecificallyradio wavesto identify the range, alti-

tude, direction, or speed of both mov-ing and fixed objects. Its uses todayseem endless. When you look at theweather report, you are looking atDoppler weather radar that tells youwhere the heaviest amounts of rain willfall in your area. The radar, as it passesthrough the clouds, measures thedensity of the moisture in them and thespeed they are traveling so you can


Figure 1 Tree Trunk Inspection Procedure


3/5


Figure 2 Trunk Inspection of Case Study

The figure shows the locations of cross-sectional radar images of the oak tree at dif-ferent elevations on the trunk. Decay is indicated by red (near sur face) and orange(advanced) areas on the scans.

Color Key for Radar Images

Sound Wood

Near Surface Decay

Advanced Decay

Incipient (Early-Stage) Decay

Surface Crack or Benign Reflector

Cross SectionalRadar Image

44-inch Trunk Diameter





Partial

Scan

7 foot elevation

35 inch elevation

16 inch elevation


4/5

know approximately when it will startraining and how much rain will fall.Radar is used in aviation, automobiles,law enforcement, and locating objectsbelow ground.

When an electromagnetic wave2

emitted from a small surface transmit-ter antenna encounters a boundarybetween objects with different electro-

magnetic properties, it will reflect,refract and diffract from the boundaryin a predictable manner. Radar wavesor signals are reflected especially wellby materials of considerable electricalconductivity. The radar signals that arereflected back towards the transmitterare the desirable ones that make radarwork. An air-filled tree trunk (decayedhollow) or partially air-filled incipientdecay zone (early stage) inside a cellwall of a tree are excellent reflectors fordetection by GPR systems. Use of GPR

instrumentation for internal tree trunkdecay detection is one of its latest usesin the field of tree risk assessment.

How does radar imaging distinguishbetween decayed and healthy wood?Wood decay fungi3 decompose ligni-fied cell walls in living wood tissue byusing enzymatic and non-enzymatic sys-tems. This decay creates a microscopi-cally detectable hollow or void withinthe cell walls of the wood, therebyreducing normal wood strength. Radarimaging can identify these small

changes (voids) in the wood composi-tion. It is the loss of the woodsmechanical strength caused by theseorganisms that is inherently linked tohazardous situations, often resulting insignificant damage to property orinjuries.

Radar imaging is one of the latestforensic technologies used for wooddecay analyses; its sensitivity to hollows,internal cracks or voids enables it todetect and create an image of thesesmall internal changes in wood densityand composition. Incipient or early-stage decay is the very beginning of thebiodegradation process of living woodtissue by decay causing pathogens;radar imaging can detect these earlychanges.

Using the trunk inspection diagramin Figure 1, you can see the radarantenna is slowly moved around the cir-cumference of the tree. As it travels it

sends out radar waves every two-tenthsof an inch; with no obstructions thesewaves penetrate to the center of thetree as the antenna is moved aroundthe trunk.

The radar waves in turn are reflectedback to the antenna or receiver if decayis encountered anywhere within thetree. The presence of sometimes hun-

dreds of these reflected radar waves cre-ates an internal image of the compro-mised area that was found inside thetree, measuring the density of the woodand indicating the level of severity ofthe newly discovered decay.

In the process the remaining solidhealthy wood is identified and dis-played to the technician and measuredin inches. The trained arborist, know-ing the diameter of the whole tree sec-tion being scanned, can use this result-ing image data to determine if the

internal decay is sufficient to warrantfurther concern or action.

The Finished Product, A Case Study

This is a live oak tree about 100 yearsold in front of a hospital. The concernwas the open cavities and the generaldecline in the health of the tree. Sincethis area is open to the public, hospitalmanagement wanted to know their lia-bilities without further damaging thetree. The radar scan provided informa-tion needed to preserve the tree, with

continued monitoring of the early stagedecay.The photograph (Figure 2) shows

the completed scan locations on theoak tree as provided to the client. Thegray areas on the radar images indicatewhere the radar antenna lost contactwith the bark surface; no data was col-lected in these areas. The remainingouter solid wood is 7.4 inches in thelower two scans and 7.7 inches at theseven foot elevation. All scan locationscontain early-stage decay developing

through out the center of the tree. Theorange areas on the cross sectionalimages indicate areas of advanceddecay.

Evaluation Without CompromisingTree Health

Today arborists have multipleoptions when making tree risk assess-ments, but most importantly there aretools available that will not harm the

tree under inspection. While radarimaging does not create a picture of theinside of a tree, it does yield an imageor likeness that allows for reasonabledecisions to be made regarding thefuture health of the tree.

What does all this mean for home-owner associations and planned com-munities that may have hundreds of

trees on their common areas withoutknowing which ones have the highestrisk of failure? It means that trees thatare very valuable to your communityand irreplaceable can be safely evaluat-ed for the risk they may pose, withoutcompromising their health in theprocess. This equates to tree preserva-tion for your community and the reten-tion of real property values.

The use of ground penetrating radarhas opened up other doors recently inthe field of arboriculture. One that has

also become valuable in the area of treeprotection is below ground root map-ping. How many trees are irreparablydamaged every year because irrigationtrenches are cut across their rootsunknowingly? Is that tree root causingthat damage to an associations side-walks or driveway?

You didnt know in the past unlessyou excavated! Now ground penetrat-ing radar is being used to locate andmap tree roots below ground non-inva-sively, without removing the concrete or

digging up those roots just to see if theyare the nasty ones really damaging theproperty. Watch for a future articleabout locating and mapping belowground roots, using ground penetrat-ing radar.

Robert Booty is a consultant at Arborist

OnSite Horticultural Consulting Inc. He is

a Registered Consulting Arborist and an

ISA Certified Arborist. You can reach him at

[email protected].


1 Nicolitti, Gonthier, Guglielmo, andGarbelotto, A Biomolecular Method forthe Detection of Wood Decay Fungi: AFocus on Tree Stability Assessment.

Arboriculture & Urban Forestry, ScientificJournal of the International Society of

Arboriculture. 2009.

2 Daniels, D.J. 1996. Surface-PenetratingRadar. The Institute of Electrical Engineers,ISBN 0-85296-862-0.

3 Nicolitti et al., Ibid.


5/5


tree risk management using radar imaging

Documents