Radar Imaging for Tree Risk Management

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ECHO Journal | May 2012 15

As you are traveling home one

evening, you notice a consistent

dull pain in your lower back. As the

weeks pass the pain intensifies andyou become increasingly concerned.

You visit your family physician, and

after an examination he explains to

you your options to determine the

source of your pain. He describes

how exploratory surgery could pro-

vide him with some answers. But he

also describes other options includ-ing non-invasive ones such as ultra

sound, MRI (electromagnetic imag-

ing) or an x ray. Knowing that com-

plications can develop using

exploratory surgery, the physiciandoesnt take any chances and ordersan MRI scan on your lower back.

Trees are somewhat like people;at some time during their life theytoo will develop internal problemsthat are not always able to be seenjust by an exterior examination.


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Arborists have used all sorts of methods todetermine the internal structural conditionof a tree and its potential risk to a property.Some of these methods were very invasive,such as taking core samples, drilling or evencutting away decay within a cavity. Thosewere the standard methods used at one time,and some continue to be used today. Theres

reason to believe that the term TreeSurgeon may have been coined as a result ofthese invasive procedures.

The Value of using Non-Invasive TestingMethods for Tree Risk Management

What benefit is there in using non-invasivediagnostic procedures with trees? Trees canbe adversely affected by the methods used toevaluate their health especially using invasive

diagnostic procedures that penetrate theouter bark.

The establishment of decay1 in living treesis affected by urban environmental stressesthat range from a general weakening of a

trees natural defense system to injuries thatallows wood-rotting agents to gain entrythrough wounds. Trees have an internal pro-tection system that uses a series of four inter-nal walls, all beautifully designed to block thespread of disease causing pathogens withinthe tree. Its referred to as CODIT, an acro-nym for Compartmentalization of Decay in

Trees.However when invasive testing methods

such as drilling are used, these four protec-tive walls can be pierced by the drill bit,allowing decay pathogens that at one timemay have been localized or contained tospread throughout the tree. One concernmany people have always had with these test-ing methods is the many holes being drilled

into a tree that one is trying to save.When performing tree risk assessments,

knowing the internal structural condition ofa tree is only one part, but a very vital part, ofthe process. If this internal data could be col-

lected without drilling or using other invasivemethods, and you could just walk away withyour data as if you were never there, then itwould be a win-win situation for the treeunder evaluation.

Use of Radar Technology

Today technology has advanced to thepoint that this non-invasive type of data col-lection is possible. It is being accomplishedby using ground penetrating radar that doesnot harm the tree being evaluated. The useof radar imaging on trees creates the sametype of high- resolution, non-invasive imagethat a medical professional would utilize inhis diagnosis with his patient using MRIimagery. This is the very latest method to

16 May 2012 | ECHO Journal

1 Nicolitti, Gonthier, Guglielmo, and Garbelotto, ABiomolecular Method for the Detection of WoodDecay Fungi: A Focus on Tree StabilityAssessment. Arboriculture & Urban Forestry,Scientific Journal of the International Society of

Arboriculture. 2009.

Figure 1 Tree Trunk Inspection Procedure


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safely evaluate the internal structure of a treewithout invasion of the tree itself. Having theability to create and see an internal image ofa tree and then to identify any hidden inter-nal problems fills a critical gap in treepreservation.

How Does Radar Work?Ground-Penetrating Radar (GPR) is an

established technique that has been usedworldwide for over 40 years. Radar is anobject-detection system that uses electromag-netic wavesspecifically radio wavestoidentify the range, altitude, direction, orspeed of both moving and fixed objects. Itsuses today seem endless. When you look at

the weather report, you are looking atDoppler weather radar that tells you wherethe heaviest amounts of rain will fall in yourarea. The radar, as it passes through theclouds, measures the density of the moisturein them and the speed they are traveling soyou can know approximately when it will startraining and how much rain will fall. Radar isused in aviation, automobiles, law enforce-ment, and locating objects below ground.

When an electromagnetic wave2 emittedfrom a small surface transmit antennaencounters a boundary between objects withdifferent electromagnetic properties, it willreflect, refract and diffract from the bound-ary in a predictable manner. Radar waves orsignals are reflected especially well by materi-als of considerable electrical conductivity.The radar signals that are reflected back

towards the transmitter are the desirableones that make radar work. An air-filled treetrunk (decayed hollow) or partially air-filledincipient decay zone (early stage) inside acell wall of a tree are excellent reflectors fordetection by GPR systems. Use of GPR instru-mentation for internal tree trunk decaydetection is one of its latest uses in the fieldof tree risk assessment.

How does radar imaging distinguish

between decayed and healthy wood? Wooddecay fungi3 decompose lignified cell wallsin living wood tissue by using enzymatic andnon-enzymatic systems. This decay creates amicroscopically detectable hollow or voidwithin the cell walls of the wood, therebyreducing normal wood strength. Radar imag-ing can identify these small changes (voids)in the wood composition. It is the loss of the

W

COMPASSM A N A G E M E N T G R O U P

Guiding your HOA

in the rightdirection

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

3 Nicolitti et al., Ibid.

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ACE Property Management, Inc.

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Phone: 408-217-2882 Fax: 408-886-9474 Email: [email protected]

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18 May 2012 | ECHO Journal

woods mechanical strength caused by theseorganisms that is inherently linked to haz-ardous situations, often resulting in signifi-

cant damage to property or injuries.Radar imaging is one of the latest forensictechnologies used for wood decay analyses;its sensitivity to hollows, internal cracks orvoids enables it to detect and create an image

of these small internal changes in wooddensity and composition. Incipient or early-stage decay is the very beginning of the

biodegradation process of living wood tissueby decay causing pathogens; radar imagingcan detect these early changes.

Using the trunk inspection diagram inFigure 1, you can see the radar antenna is

slowly moved around the circumference ofthe tree. As it travels it sends out radar wavesevery two-tenths of an inch; with no obstruc-tions these waves penetrate to the center ofthe tree as the antenna is moved around thetrunk.

The radar waves in turn are reflected backto the antenna or receiver if decay is encoun-tered anywhere within the tree. The presenceof sometimes hundreds of these reflectedradar waves creates an internal image of thecompromised area that was found inside thetree, measuring the density of the wood andindicating the level of severity of the newlydiscovered decay.

In the process the remaining solid healthywood is identified and displayed to the tech-nician and measured in inches. The trainedarborist, knowing the diameter of the wholetree section being scanned, can use thisresulting image data to determine if theinternal decay is sufficient to warrant furtherconcern or action.

The Finished Product, A Case Study

This is a live oak tree about 100 years oldin front of a hospital. The concern was theopen cavities and the general decline in thehealth of the tree. Since this area is open tothe public, hospital management wanted toknow their liabilities without further damag-ing the tree. The radar scan provided infor-mation needed to preserve the tree, with con-

tinued monitoring of the early stage decay.

The photograph (Figure 2) shows thecompleted scan locations on the oak tree asprovided to the client. The gray areas on theradar images indicate where the radar anten-na lost contact with the bark surface; no datawas collected in these areas. The remainingouter solid wood is 7.4 inches in the lowertwo scans and 7.7 inches at the seven foot ele-

vation. All scan locations contain early-stagedecay developing through out the center ofthe tree. The orange areas on the cross sec-tional images indicate areas of advanceddecay.

Figure 2 Trunk Inspection of Case Study

The figure shows the locations of cross-sectional radar images of the oak tree at different elevations onthe trunk. Decay is indicated by red (near surface) 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


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Evaluation Without CompromisingTree Health

Today arborists have multiple optionswhen making tree risk assessments, but mostimportantly there are tools available that willnot harm the tree under inspection. While

radar imaging does not create a picture ofthe inside of a tree, it does yield an image orlikeness that allows for reasonable decisionsto be made regarding the future health ofthe tree.

What does all this mean for homeownerassociations and planned communities thatmay have hundreds of trees on their com-mon areas without knowing which ones have

the highest risk of failure? It means that treesthat are very valuable to your community andirreplaceable can be safely evaluated for therisk they may pose, without compromisingtheir health in the process. This equates totree preservation for your community andthe retention of real property values.

Trees can be safelyevaluated for the riskthey may pose withoutcompromising health.

The use of ground penetrating radar hasopened up other doors recently in the fieldof arboriculture. One that has also becomevaluable in the area of tree protection isbelow ground root mapping. How many treesare irreparably damaged every year becauseirrigation trenches are cut across their rootsunknowingly? Is that tree root causing thatdamage to an associations sidewalks or drive-way?

You didnt know in the past unless you

excavated! Now ground penetrating radar isbeing used to locate and map tree rootsbelow ground non-invasively, without remov-ing the concrete or digging up those rootsjust to see if they are the nasty ones reallydamaging the property. Watch for a futurearticle about locating and mapping belowground roots, using ground penetratingradar.

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].


Radar Imaging for Tree Risk Management

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