Infrared Thermography Applied to Tree Health Assessment: A Review
2. Materials and Methods
3. Tree Relevance and Risks
- Heritage: trees that are linked to history and culture; trees that are rare and/or botanically relevant (see for instance Reference ).
- Notable: trees that have reached maturity stand out from their surroundings because they are larger than the trees around them (see for instance Reference ).
- Ancient: trees that have overpassed the maturity and despite the hollow trunk they continue to be healthy. Their value is intrinsically linked to their age (see for instance Reference ).
- Veterans: trees that survived wounds and deterioration (decay); young trees that developed old trees characteristics (see for instance Reference ).
4. Methods and Techniques of Inspection
4.1. Instruments for Detecting Deterioration
- Invasive and non-invasive: invasive instruments require drilling for deep penetration in the sapwood through one or more holes; the sapwood is living wood. Non-invasive instruments do not need contact, or they penetrate superficially in the sapwood. It is noted that any type of wound is an entry for pathogens into the tree .
- Destructive and non-destructive: Unlike the destructive instruments, non-destructive ones allow the identification of damage presence or not in the trees without causing harm . Then, non-contact instruments are considered as non-destructive. Table 1 shows only non-contact instruments since they were considered non-destructive.
- Screening, diagnostic and evaluation: Screening tools allow a quick assessment to identify healthy and non-healthy trees. Diagnostic instruments allow a more accurate assessment, but require more time to identify the extent and type of damage in the tree. An intermediate method is an evaluation; it is a combination of screening speed and diagnostic accuracy methods .
4.2. Sustainable Techniques Relevance
5. Infrared Thermography Applied to Trees
5.1. Principles of IRT
|Wobj||Emission from the object|
|Wrefl||Reflected emission from ambient sources|
|Watm||Emission from the atmosphere|
5.2. Wood and Trees
5.3. Analysis of Tree Health
5.4. Advantages and Limitations of IRT Applicated to Trees
Conflicts of Interest
- Pitarma, R.; Crisóstomo, J.; Ferreira, M.E. Learning About Trees in Primary Education: Potentiality of IRT Technology in Science Teaching. In Proceedings of the EDULEARN18 Conference, Palma, Spain, 2–4 July 2018; pp. 208–213. [Google Scholar]
- Ferreira, M.; Crisóstomo, J.; Pitarma, R. Infrared thermography technology to support science teaching-meaningful learning about trees with university students. In Proceedings of the 13th International Technology, Education and Development Conference (INTED2019), Valencia, Spain, 11–13 March 2019. [Google Scholar]
- Ferreira, M.E.; André, A.C.; Pitarma, R. Potentialities of Thermography in Ecocentric Education of Children: An Experience on Training of Future Primary Teachers. Sustainability 2019, 11, 2668. [Google Scholar] [CrossRef]
- Lier, M.; Parviainen, J. Integration of Nature Protection in Forest Policy in Finland; INTEGRATE Country Report; EFICENT-OEF: Freiburg, Germany, 2013. [Google Scholar]
- Ancient Tree Forum & The Woodland Trust. Ancient Tree Guide No. 4: What Are Ancient, Veteran and Other Trees of Special Interest; The Woodland Trust: Grantham, UK, 2008. [Google Scholar]
- National Tree Safety Group. Common Sense Risk Management of Trees: Guidance on Trees and Public Safety in the UK for Owners, Managers and Advisers; Forestry Commission: Edinburgh, Scotland, 2011; ISBN 978-0-85538-840-9. [Google Scholar]
- Health and Safety Executive. Management of the Risk from Falling Trees; Health & Safety Executive/Local Authorities Enforcement Liaison Committee (HELA): Bootle, UK, 2007.
- FLIR Tools+ User´s Guide; Flir Systems, Inc.: Wilsonville, OR, USA, 2016.
- Barr, E.S. Historical Survey of the Early Development of the Infrared Spectral Region. Am. J. Phys. 1960, 28, 42–54. [Google Scholar] [CrossRef]
- Kylili, A.; Fokaides, P.A.; Christou, P.; Kalogirou, S.A. Infrared thermography (IRT) applications for building diagnostics: A review. Appl. Energy 2014, 134, 531–549. [Google Scholar] [CrossRef]
- Catena, A. Thermography Reveals Hidden Tree Decay. Arboric. J. 2003, 27, 27–42. [Google Scholar] [CrossRef]
- United Nations. World Urbanization Prospects: The 2018 Revision; United Nations, Department of Economic and Social Affairs, Population Division: New York, NY, USA, 2018. [Google Scholar]
- Pokorny, J.; O’Brien, J.; Hauer, R.; Johnson, G.; Albers, J.; Bedker, P.; Mielke, M. Urban Tree Risk Management: A Community Guide to Program Design and Implementation; USDA Forest Service Northeastern Area State and Private Forestr: St. Paul, MN, USA, 2003.
- Rotherham, I.D. Editorial: Trees In A Changing World. Arboric J. 2010, 33, 1–2. [Google Scholar] [CrossRef]
- Kuo, F.E.; Sullivan, W.C. Environment and Crime in the Inner City: Does Vegetation Reduce Crime? Environ. Behav. 2001, 33, 343–367. [Google Scholar] [CrossRef]
- Coder, K.D. Identified Benefits of Community Trees and Forests; University of Georgia School of Forest Resources: Athens, GA, USA, 1996. [Google Scholar]
- International Society of Arboriculture Benefits of Trees; International Society of Arboriculture: Champaign, IL, USA, 2011.
- Roy, S.; Byrne, J.; Pickering, C. A systematic quantitative review of urban tree benefits, costs, and assessment methods across cities in different climatic zones. Urban For. Urban Green. 2012, 11, 351–363. [Google Scholar] [CrossRef][Green Version]
- Song, X.P.; Tan, P.Y.; Edwards, P.; Richards, D. The economic benefits and costs of trees in urban forest stewardship: A systematic review. Urban For. Urban Green. 2018, 29, 162–170. [Google Scholar] [CrossRef]
- Johnston, M.; Hirons, A. Urban Trees. In Horticulture: Plants for People and Places; Dixon, G.R., Aldous, D.E., Eds.; Springer: Dordrecht, The Netherlands, 2014; Volume 2, ISBN 978-94-017-8580-8. [Google Scholar]
- Shigo, A.L.; Marx, H.G. Compartmentalization of Decay in Trees; U. S. Government Printing Office: Washington, DC, USA, 1977; pp. 4–15.
- Shigo, A.L. Compartmentalization: A Conceptual Framework for Understanding How Trees Grow and Defend Themselves. Annu. Rev. Phytopathol. 1984, 22, 189–214. [Google Scholar] [CrossRef]
- Shortle, W.C.; Dudzik, K.R. Wood Decay in Living and Dead Trees: A Pictorial Overview; U.S. Department of Agriculture, Forest Service, Northern Research Station: Newtown Square, PA, USA, 2012. [Google Scholar]
- Sherwood Forest. Available online: https://www.visitsherwood.co.uk/things-to-do/the-major-oak/ (accessed on 18 June 2019).
- Undiscovered Scotland. Available online: https://www.undiscoveredscotland.co.uk/blairgowrie/meikleourhedge/index.html (accessed on 18 June 2019).
- Woodland Trust. Available online: https://www.woodlandtrust.org.uk/visiting-woods/trees-woods-and-wildlife/woodland-habitats/ancient-trees/ (accessed on 18 June 2019).
- National Trust. Available online: https://www.nationaltrust.org.uk/ashridge-estate/features/looking-after-our-veteran-trees-at-ashridge-estate (accessed on 18 June 2019).
- Mattheck, C.; Breloer, H. Field guide for visual tree assessment (Vta). Arboric. J. 1994, 18, 1–23. [Google Scholar] [CrossRef]
- Goh, C.L.; Abdul Rahim, R.; Fazalul Rahiman, M.H.; Mohamad Talib, M.T.; Tee, Z.C. Sensing wood decay in standing trees: A review. Sens. Actuators A Phys. 2018, 269, 276–282. [Google Scholar] [CrossRef]
- Hellier, C. Introduction to Nondestructive Testisng. In Handbook of Nondestructive Evaluation; Hellier, C., Ed.; McGraw-Hill: New York, NY, USA, 2003; ISBN 978-0-07-139947-0. [Google Scholar]
- Leong, E.-C.; Burcham, D.C.; Fong, Y.-K. A purposeful classification of tree decay detection tools. Arboric. J. 2012, 34, 91–115. [Google Scholar] [CrossRef]
- Crisóstomo, J.; Pereira, C.; Roque, E.; Jorge, L.; Pitarma, R. Considerações na Observação do Estado de Salubridade de Árvores Através da Termografia por Infravermelhos. In Proceedings of the 1st Iberic Conference on Theoretical and Experimental Mechanics and Materials/11th National Congress on Experimental Mechanics, Porto, Portugal, 4–7 November 2018; pp. 745–748. [Google Scholar]
- Mattheck, C.; Bethge, K.; Albrecht, W. How To Read The Results Of Resistograth M. Arboric. J. 1997, 21, 331–346. [Google Scholar] [CrossRef]
- Shigo, A.L.; Shortle, W.C. Spruce Budworms Handbook: Shigometry–A Reference Guide; Agric. Handb.; U.S. Department of Agriculture, Forest Service, Cooperative State Research Service: Washington, DC, USA, 1985.
- Monk, B. Evaluation of Decay Detection Equipment in Standing Trees. Available online: https://www.fs.fed.us/t-d/programs/im/tree_decay/tree_decay_detect_equip.shtml (accessed on 17 June 2019).
- Ross, R.J.; Pellerin, R.F. Inspection of Timber Structures Using Stress Wave Timing Nondestructive Evaluation Tools. In Wood and Timber Condition Assessment Manual: Second Edition; White, R.H., Ross, R.J., Eds.; U.S. Department of Agriculture, Forest Service, Forest Products Laboratory: Madison, WI, USA, 2014. [Google Scholar]
- Oliva, J.; Romeralo, C.; Stenlid, J. Accuracy of the Rotfinder instrument in detecting decay on Norway spruce (Picea abies) trees. For. Ecol. Manag. 2011, 262, 1378–1386. [Google Scholar] [CrossRef]
- Nicolotti, G.; Socco, L.V.; Martinis, R.; Godio, A.; Sambuelli, L. Application And Comparison Of Three Tomographic Techniques For Detection Of Decay In Trees. J. Arboric. 2003, 29, 66–78. [Google Scholar]
- Bogosanovic, M.; Al Anbuky, A.; Emms, G.W. Overview and comparison of microwave noncontact wood measurement techniques. J. Wood Sci. 2010, 56, 357–365. [Google Scholar] [CrossRef]
- Wang, P.C.; Chang, S.J. Nuclear Magnetic Resonance Imaging of Wood. Wood Fiber Sci. 1986, 18, 308–314. [Google Scholar]
- Baietto, M.; Wilson, A.; Bassi, D.; Ferrini, F. Evaluation of Three Electronic Noses for Detecting Incipient Wood Decay. Sensors 2010, 10, 1062–1092. [Google Scholar] [CrossRef]
- Habermehl, A.; Ridder, H.-W. Computerised Tomographic Investigationa Of Street And Park Trees. Arboric. J. 1995, 19, 419–437. [Google Scholar] [CrossRef]
- Usamentiaga, R.; Venegas, P.; Guerediaga, J.; Vega, L.; Molleda, J.; Bulnes, F. Infrared Thermography for Temperature Measurement and Non-Destructive Testing. Sensors 2014, 14, 12305–12348. [Google Scholar] [CrossRef][Green Version]
- Maldague, X.P.V.; Streckert, H.H.; Trimm, M.W. Introduction to Infrared and Thermal Testing. In Infrared and Thermal Testing; Maldague, X.P.V., Moore, P.O., Eds.; Nondestructive Testing Handbook; American Society for Nondestructive Testing: Columbus, OH, USA, 2001; ISBN 978-1-57117-044-6. [Google Scholar]
- Snell, J.R., Jr. Thermal Infrared Testing. In Handbook of Nondestructive Evaluation; Hellier, C., Ed.; McGraw-Hill: New York, NY, USA, 2003; ISBN 978-0-07-139947-0. [Google Scholar]
- Meola, C. (Ed.) Carosena Origin and Theory of Infrared Thermography. In Infrared Thermography Recent Advances and Future Trends; Bentham Science Publishers: New York, NY, USA, 2012; pp. 3–28. ISBN 978-1-60805-143-4. [Google Scholar]
- Ibarra-Castanedo, C.; Maldague, X.P.V. Infrared Thermography. In Handbook of Technical Diagnostics; Czichos, H., Ed.; Springer: Berlin/Heidelberg, Germany, 2013; pp. 175–220. ISBN 978-3-642-25849-7. [Google Scholar]
- Holst, G.C. Common Sense Approach to Thermal Imaging; JCD Pub.; Co-Published by SPIE Optical Engineering Press: Winter Park, FL, USA; Bellingham, WA, USA, 2000; ISBN 978-0-9640000-7-0. [Google Scholar]
- Pitarma, R.; Crisóstomo, J.; Jorge, L. Analysis of Materials Emissivity Based on Image Software. In New Advances in Information Systems and Technologies; Rocha, Á., Correia, A.M., Adeli, H., Reis, L.P., Mendonça Teixeira, M., Eds.; Springer International Publishing: Cham, Switzerland, 2016; Volume 444, pp. 749–757. ISBN 978-3-319-31231-6. [Google Scholar]
- Crisóstomo, J.; Pitarma, R. The Importance of Emissivity on Monitoring and Conservation of Wooden Structures Using Infrared Thermography. In Advances in Structural Health Monitoring; Hassan, M., Ed.; IntechOpen: London, UK, 2019. [Google Scholar] [CrossRef][Green Version]
- Maldague, X.P.V. Nondestructive Evaluation of Materials by Infrared Thermography; Springer: London, UK, 1993; ISBN 978-1-4471-1997-5. [Google Scholar]
- Crisóstomo, J.; Pereira, C.; Roque, E.; Jorge, L.; Pitarma, R. Análise da Salubridade de Árvores Através da Termografia por Infravermelhos; Gomes, J.F.S., Ed.; INEGI/FEUP: Porto, Portugal, 2018; pp. 749–758. [Google Scholar]
- Meola, C.; Carlomagno, G.M. Recent advances in the use of infrared thermography. Meas. Sci. Technol. 2004, 15, R27–R58. [Google Scholar] [CrossRef]
- Wyckhuyse, A.; Maldague, X. A Study of Wood Inspection by Infrared Thermography, Part I: Wood Pole Inspection by Infrared Thermography. Res. Nondestruct. Eval. 2001, 13, 1–12. [Google Scholar] [CrossRef]
- Conde, M.J.M.; Liñán, C.R.; de Hita, P.R.; Gálvez, F.P. Infrared Thermography Applied to Wood. Res. Nondestruct. Eval. 2012, 23, 32–45. [Google Scholar] [CrossRef]
- Rodríguez-Liñán, C.; Morales-Conde, M.J.; Rubio-de Hita, P.; Pérez-Gálvez, F. Análisis sobre la influencia de la densidad en la termografía de infrarrojos y el alcance de esta técnica en la detección de defectos internos en la madera. Mater. de Construcción 2012, 62, 99–113. [Google Scholar] [CrossRef]
- Tanaka, T.; Divós, F. Wood Inspection by Thermography. In Proceedings of the 12th International Symposium on Nondestructive Testing, Sopron, Hungary, 13–15 September 2000. [Google Scholar]
- Pereira, J.C.A. Contribuição para a Análise de Manifestações Patológicas em Madeira na Construção com Recurso à Termografia; Instituto Politécnico de Castelo Branco: Castelo Branco, Portugal, 2014. [Google Scholar]
- Burcham, D.C.; Leong, E.-C.; Fong, Y.-K. Passive infrared camera measurements demonstrate modest effect of mechanically induced internal voids on Dracaena fragrans stem temperature. Urban For. Urban Green. 2012, 11, 169–178. [Google Scholar] [CrossRef]
- Catena, A.; Catena, G. Overview of Thermal Imaging For Tree Assessment. Arboric. J. 2008, 30, 259–270. [Google Scholar] [CrossRef]
- Bellett-Travers, M.; Morris, S. The Relationship Between Surface Temperature And Radial Wood Thickness Of Twelve Trees Harvested In Nottinghamshire. Arboric. J. 2010, 33, 15–26. [Google Scholar] [CrossRef]
- López, G.; Basterra, L.-A.; Ramón-Cueto, G.; Diego, A. de Detection of Singularities and Subsurface Defects in Wood by Infrared Thermography. Int. J. Archit. Herit. 2014, 8, 517–536. [Google Scholar] [CrossRef]
- Meinlschmidt, P. Thermographic Detection of Defects in Wood and Wood-based Materials. In Proceedings of the 14th International Symposium of Nondestructive Testing of Wood, Hannover, Germany, 2–4 May 2005. [Google Scholar]
- Rodríguez Liñán, C.; Morales Conde, M.J.; Rubio de Hita, P.; Pérez Gálvez, F. Inspección mediante técnicas no destructivas de un edificio histórico: Oratorio San Felipe Neri (Cádiz). Inf. de la Construcción 2011, 63, 13–22. [Google Scholar] [CrossRef]
- Kandemir-Yucel, A.; Tavukcuoglu, A.; Caner-Saltik, E.N. In situ assessment of structural timber elements of a historic building by infrared thermography and ultrasonic velocity. Infrared Phys. Technol. 2007, 49, 243–248. [Google Scholar] [CrossRef]
- Grossman, J.L. Advanced techniques in IR thermography as a tool for the pest management professional. In Proceedings of the SPIE, Orlando, FL, USA, 18 April 2006; Volume 6205. [Google Scholar]
- Grossman, J.L. Trestles anyone? A Thermographic Nightmare. In Proceedings of the SPIE, Orlando, FL, USA, 9 April 2007; Volume 6541. [Google Scholar]
- Catena, G. A new application of thermography. Atti Della Fond. Giorgio Ronchi 1990, 6, 947–952. [Google Scholar]
- Catena, A.; Catena, G.; Lugaresi, D.; Gasperoni, R. La Termografia rivela la presenza di danni anche nell’apparato radicale degli alberi. Agric. Ric. 2002, 81–100. [Google Scholar]
- Burcham, D.C.; Leong, E.-C.; Fong, Y.-K.; Tan, P.Y. An Evaluation of Internal Defects and Their Effect on Trunk Surface Temperature in Casuarina equisetifolia L. (Casuarinaceae). Arboric. Urban For. 2012, 38, 277–286. [Google Scholar]
- Catena, G. Une Appication De La Thermographie En Phytopathologie. Phytoma-La Défense Des Végétaux 1992, 439, 46–48. [Google Scholar]
- Al-doski, J.; Mansor, S.B.; Shafri, H.Z.B.M. Thermal Imaging For Pests Detecting-A Review. Int. J. Agric. For. Plant. 2016, 2, 10–30. [Google Scholar]
- Hoffmann, N.; Schröder, T.; Schlüter, F.; Meinlschmidt, P. Potenzial von Infrarotthermographie zur Detektion von Insektenstadien und -schäden in Jungbäumen. J. Für Kult. 2013, 65, 2013. [Google Scholar]
- Ballester, C.; Jiménez-Bello, M.A.; Castel, J.R.; Intrigliolo, D.S. Usefulness of thermography for plant water stress detection in citrus and persimmon trees. Agric. For. Meteorol. 2013, 168, 120–129. [Google Scholar] [CrossRef]
- Jones, H.G.; Serraj, R.; Loveys, B.R.; Xiong, L.; Wheaton, A.; Price, A.H. Thermal infrared imaging of crop canopies for the remote diagnosis and quantification of plant responses to water stress in the field. Funct. Plant Biol. 2009, 36, 978. [Google Scholar] [CrossRef]
- García-Tejero, I.; Durán-Zuazo, V.H.; Arriaga, J.; Hernández, A.; Vélez, L.M.; Muriel-Fernández, J.L. Approach to assess infrared thermal imaging of almond trees under water-stress conditions. Fruits 2012, 67, 463–474. [Google Scholar] [CrossRef]
- Giuliani, R.; Flore, J.A. Potential Use Of Infra-Red Thermometry For The Detection Of Water Stress In Apple Trees. Acta Hortic. 2000, 537, 383–392. [Google Scholar] [CrossRef]
- Ibarra-Castanedo, C.; Tarpani, J.R.; Maldague, X.P.V. Nondestructive testing with thermography. Eur. J. Phys. 2013, 34, S91–S109. [Google Scholar] [CrossRef]
- Catena, A. Thermography Shows Damaged Tissue and Cavities Present in Trees. In Nondestructive Characterization of Materials XI.; Green, R.E., Djordjevic, B.B., Hentschel, M.P., Eds.; Springer: Berlin/Heidelberg, Germany, 2002; pp. 515–522. ISBN 978-3-540-40154-4. [Google Scholar]
- Sharma, S.; Kaushik, A. Views of Irish Farmers on Smart Farming Technologies: An Observational Study. AgriEngineering 2019, 1, 164–187. [Google Scholar][Green Version]
- Bellett-Travers, M. A Risk Assessment Methodology For Trees In Parkland Based On Comparative Population Analysis. Arboric. J. 2010, 33, 3–14. [Google Scholar] [CrossRef]
Method in 
|Invasive||Increment borer, Boroscope||Resistograph||Shigometer, Fractometer|
|Non-Invasive||-||Stress wave velocity||Electrical resistance||Stress wave tomography, |
|Non-contact||Nuclear magnetic resonance (NMR)||IRT, |
|-||Gamma-ray computed Tomography|
|Technique||Principle and Brief Description||Key Highlights|
|Increment borer ||Visual inspection: a sample of tree core is extracted for visual inspection.||Measures tree growth rate, age and soundness. |
Requires experience of decay potential causes. Invasive method (it may itself be a decay factor).
|Boroscope ||Remote visual inspection: the tree trunk is drilled and it is used a small video camera to observe inside.||Enables visual confirmation from inside.|
Same disadvantages of the technique “Increment borer”.
|Resistograph ||Penetration resistance: a small drill/needle is inserted into the tree; drilling resistance is measured and registered.||Fast and easy to execute as well as interpret the graph.|
Does not detect early to intermediate decay stages; Requires comparison with known patterns (samples without decomposition).
|Shigometer [34,35]||Electrical resistivity: a pulsed direct electric current generated by electrodes is applied into a drilled hole; it goes into the wood or the tree bark; electrical resistance is measured and registered.||Detects deterioration in early stages. |
The information is limited by the probe length.
|Fractometer [28,35]||Strength and stiffness: it measures radial bending fracture strength and stiffness value.||Small device and easy to carry.|
Portable compression meter has depth limited.
|Stress wave velocity [35,36]||Single-path acoustic wave velocity: detects cavities by measuring the acoustic wave velocity as it passes through the tree stem.||Quickly performed; defines the location and extent of internal decay.|
Difficult to determine early stages of decay.
|Electrical resistance [29,37,38]||Electrical resistivity: resistivity is determined from the voltage difference between electrodes when the electricity is injected.||Effective to detect advanced stages of tree decay.|
|Stress wave tomography ||Multiple path acoustic wave velocity: |
the tomogram is obtained by measuring and registering the sound waves travel time generated by acoustic transducers positioned around the circumference of the tree stem.
|Detects internal decay; accurately locates the anomalies; sensitive to early stages of decay. |
High cost and difficult to operate.
|Electromagnetic tomography [31,38,39]||Electromagnetic wave permittivity: the tomogram is obtained by variations in the return signal. The variation is reflected by the receiving antenna when the electromagnetic wave emitted by the transmitting antenna encounters a boundary with a different dielectric constant.||Higher frequencies provide better resolution but penetration depth decreases.|
High cost and difficult to operate.
|Nuclear magnetic resonance (NMR) [29,40]||Magnetic properties: uses the magnetic properties of certain atomic nuclei (as the hydrogen nucleus). They are aligned and oscillated using a strong magnetic field in the scanner.||Non-ionising radiation; delivers very detailed images that facilitate the analysis of the structure and function of the tissues.|
High cost and difficult to operate.
|Electronic nose ||Odour: it distinguishes healthy and decayed wood through changes in the volatile organic compounds released by wood decay fungi.||Provides high levels of accuracy and reliability.|
Difficult to determine early stages of decay.
|Gamma-ray computed Tomography [31,42]||Gamma-ray transmissivity: the tomogram is obtained from radiation absorption after directing gamma rays in multiple directions on a tree trunk thin slice.||Reliable and non-invasive; evaluates fungal decay and its extension. |
Ionizing radiation; high cost and difficult to operate; difficult to carry.
|Al-doski et al. ||Pest detection.||Pest infestation detected.|
|Ballester et al. ||Water stress detection on citrus and persimmon trees.||Water stress detected.|
|Bellett-Travers & Morris ||Relationship between surface temperature and radial wood thickness.||No apparent relationship in most of the trees; strong relationship when there was a gradual change in radial wood thickness caused by a cavity.|
|Burcham et al. ||Effect of mechanically induced internal voids on Dracaena fragrans L. stem temperature.||Only able to identify reductions temperature in internal defects with at least 76% of the stem cross-sectional area.|
|Burcham et al. ||Evaluate the relationship between the internal defects and trunk surface temperature in Casuarina equisetifolia L.||Does not provide accurate results about the internal condition of trees.|
|Catena & Catena ||Review in order to assess the accuracy, reliability, and costs.||Does not automatically distinguish between different kinds of alteration; does not accurately provide the extent of the damages found; provides enough information to decide regarding the need for remedial action or a more detailed kind of assessment; non-invasive, fast, reasonable prices, in real time.|
|Catena, G. [68,71]||Internal cavities in trees detection.||Enables the detection of cavities.|
|Catena, A.  and Catena et al. ||Damages in the roots.||Enables that damages in the roots can be deduced in real time.|
|Crisóstomo et al. ||Considerations over IRT as applied to the state of the tree healthiness.||Enables healthiness evaluation.|
|Crisóstomo et al. ||Quercus pygmentosis tree Analysis.||Evaluating its healthiness status.|
|García-Tejero et al ||Water stress detection in almond trees.||Water stress detected.|
|Giuliani & Flore ||Water stress detection in apple trees.||Water stress detected.|
|Goh et al. ||Review of the current sensing methods used for decay detection in trees.||Comparing methods concerning the fundamental of measurements, hardware implementation, damage caused to the tree and the ease of use.|
|Hoffmann et al. ||Detecting the larval stage of goat moth´s larvae in young tree species.||Was not able to detect.|
|Jones et al. ||Water stress detection on grapevine.||Water stress detected.|
|Leong et al. ||Evaluating the current tree decay detection tools.||Classifying the tree decay detection tools in terms of measurement speed, resolution and accuracy.|
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Vidal, D.; Pitarma, R. Infrared Thermography Applied to Tree Health Assessment: A Review. Agriculture 2019, 9, 156. https://doi.org/10.3390/agriculture9070156
Vidal D, Pitarma R. Infrared Thermography Applied to Tree Health Assessment: A Review. Agriculture. 2019; 9(7):156. https://doi.org/10.3390/agriculture9070156Chicago/Turabian Style
Vidal, Daniele, and Rui Pitarma. 2019. "Infrared Thermography Applied to Tree Health Assessment: A Review" Agriculture 9, no. 7: 156. https://doi.org/10.3390/agriculture9070156