Detecting defects in conifers with ground penetrating radar: Applications and challenges

An investigation of the ability of ground penetrating radar to detect decay in conifers.

"Our objective was to test ground penetrating radar (GPR) tonon-destructively estimate decay volumes in living coniferous trees.GPR is geophysical tool which uses an antenna to propagate short burstsof electromagnetic energy in solid materials and measure the two-waytravel time and amplitude of reflected signals. We compared estimatesof bole decay from data collected with a SIR 3000 GPR system equippedwith a 900 MHz antenna to measurements of decay from stem crosssections and increment cores for three conifer species (Pseudotsuga menziesii, Thuja plicata and Tsuga heterophylla).We found that near-surface decay, air-filled voids and desiccated boleshad unique electromagnetic signatures, which could be separated fromother defects. GPR successfully estimated the percent area ofair-filled cavities and was not significantly different than resultsfrom destructive sampling. However, separation of incipient to severedecay from benign reflectors (e.g. moisture gradient between sapwoodand heartwood) in conifers was much less diagnostic than withangiosperms. A limited assessment of Acer saccharum showed that GPR haspotential to detect defects in angiosperms; however, more research isneeded to outline the full range of detectable defects. Based on thetrees in this study, the potential for GPR to detect decay-relateddefects in conifers seems limited. Despite problems detecting decay,reflections originating from the sapwood: heartwood boundary may proveuseful to determine thickness of functional sapwood in conifers, butaccurate quantification will require further technical development." [Abstract]

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