Nav: Home

Terahertz imaging technique reveals subsurface insect damage in wood

July 25, 2019

WASHINGTON -- Insect infestation is becoming an increasingly costly problem to the forestry industry, especially in areas experiencing increased droughts and hot spells related to climate change. A new terahertz imaging technique could help slow the spread of these infestations by detecting insect damage inside wood before it becomes visible on the outside.

"Our approach could be used to detect early-stage insect infestation on the trunks of trees, in imported wood or on wood products in an early infestation stage," said research team member Kirsti Krügener, from HAWK University of Applied Science and Arts in Germany. "This could help keep out damaging insects from other countries and stop infestation before it spreads throughout a forest."

In the Optical Society journal Applied Optics, the researchers report how they used terahertz time-of-flight tomography to noninvasively identify wood samples with otherwise invisible damage from the typographer beetle, which infects spruce and other coniferous trees in Europe. They were also able to reconstruct the internal structure of wood samples.

"Detecting the boreholes of wood-destroying insects is typically done by manually inspecting the wood, and the infected area of the forest to be removed is then estimated," said Krügener. "To our knowledge, this is the first time a technical method has been used to detect insect boreholes."

Incorporating the new approach into a portable instrument could allow assessment of individual trees in a forest so that only infested trees would need to be removed. Because it does not damage the sample being imaged, the technique might also be useful for investigating mummies, studying and restoring art or for quality control in industry.

Seeing beneath the surface

The terahertz region of the electromagnetic spectrum lies between microwave and infrared regions. It is used for applications such as the full-body scanners found in many airports because it doesn't harm people or materials being examined and can see through materials such as clothing, plastics and plant material.

Terahertz time-of-flight tomography works much like ultrasonic measurement in that each interface within the wood sample reflects a certain amount of the terahertz radiation that is detected and analyzed in respect to its time-dependent order. Each subsurface tunnel made by the insects leads to a new interface on which the radiation is reflected.

"An infested sample will reflect more terahertz radiation than one that is not infected because there will be fewer interfaces," said Krügener. "In addition, the individual reflected terahertz signals can be used to form a picture of an entire area so that the inner structure of infested wood can be visualized."

Beyond flat surfaces

Although terahertz time-of-flight tomography has been used for almost 20 years, until recently it could only be applied to flat samples. Two years ago, the researchers developed new procedures to use a robotic arm to scan an arbitrarily shaped sample point by point while keeping the emitter-receiver-head perpendicular to, and at defined distance from, the sample surface.

The researchers applied those methods to image wood samples with both known and unknown inner structures. They compared the results to conventional tomographic techniques and found that the inner structure reconstructed from terahertz signals matched well with what can be achieved with X-ray or computed tomography. They were able to distinguish between infested and non-infested samples by detecting typographer beetle burrows that were up to 1 centimeter beneath the wood's surface.

"The depth resolution of the terahertz measurements is higher than that of conventional x-ray techniques and comparable to micro-CT," said Krügener. "However, unlike micro-CT, the terahertz system can be used with any size sample."

The researchers are now working to improve the speed of the measurement and data analysis and also develop more complex data analysis to make the method more practical for detecting infested wood. They also want to develop a portable instrument that could be used in the field.
-end-
Paper: K. Krügener, E.-M. Stübling, R. Jachim, B. Kietz, M. Koch, W. Viöl, "THz tomography for detecting damages on wood caused by insects," Applied Optics, 58, 22, 6063-6066 (2019). DOI: https://doi.org/10.1364/AO.58.006063

About Applied Optics

Applied Optics publishes in-depth peer-reviewed content about applications-centered research in optics. These articles cover research in optical technology, photonics, lasers, information processing, sensing and environmental optics.

About The Optical Society

Founded in 1916, The Optical Society (OSA) is the leading professional organization for scientists, engineers, students and business leaders who fuel discoveries, shape real-life applications and accelerate achievements in the science of light. Through world-renowned publications, meetings and membership initiatives, OSA provides quality research, inspired interactions and dedicated resources for its extensive global network of optics and photonics experts. For more information, visit osa.org.

Media Contact: mediarelations@osa.org

The Optical Society

Related Climate Change Articles:

A CERN for climate change
In a Perspective article appearing in this week's Proceedings of the National Academy of Sciences, Tim Palmer (Oxford University), and Bjorn Stevens (Max Planck Society), critically reflect on the present state of Earth system modelling.
Fairy-wrens change breeding habits to cope with climate change
Warmer temperatures linked to climate change are having a big impact on the breeding habits of one of Australia's most recognisable bird species, according to researchers at The Australian National University (ANU).
Believing in climate change doesn't mean you are preparing for climate change, study finds
Notre Dame researchers found that although coastal homeowners may perceive a worsening of climate change-related hazards, these attitudes are largely unrelated to a homeowner's expectations of actual home damage.
Older forests resist change -- climate change, that is
Older forests in eastern North America are less vulnerable to climate change than younger forests, particularly for carbon storage, timber production, and biodiversity, new research finds.
Could climate change cause infertility?
A number of plant and animal species could find it increasingly difficult to reproduce if climate change worsens and global temperatures become more extreme -- a stark warning highlighted by new scientific research.
Predicting climate change
Thomas Crowther, ETH Zurich identifies long-disappeared forests available for restoration across the world.
Historical climate important for soil responses to future climate change
Researchers at Lund University in Sweden, in collaboration with colleagues from the University of Amsterdam, examined how 18 years of drought affect the billions of vital bacteria that are hidden in the soil beneath our feet.
Can forests save us from climate change?
Additional climate benefits through sustainable forest management will be modest and local rather than global.
From crystals to climate: 'Gold standard' timeline links flood basalts to climate change
Princeton geologists used tiny zircon crystals found in volcanic ash to rewrite the timeline for the eruptions of the Columbia River flood basalts, a series of massive lava flows that coincided with an ancient global warming period 16 million years ago.
Think pink for a better view of climate change
A new study says pink noise may be the key to separating out natural climate variability from climate change that is influenced by human activity.
More Climate Change News and Climate Change Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#542 Climate Doomsday
Have you heard? Climate change. We did it. And it's bad. It's going to be worse. We are already suffering the effects of it in many ways. How should we TALK about the dangers we are facing, though? Should we get people good and scared? Or give them hope? Or both? Host Bethany Brookshire talks with David Wallace-Wells and Sheril Kirschenbaum to find out. This episode is hosted by Bethany Brookshire, science writer from Science News. Related links: Why Climate Disasters Might Not Boost Public Engagement on Climate Change on The New York Times by Andrew Revkin The other kind...
Now Playing: Radiolab

An Announcement from Radiolab