Common Sense Approach to Thermal Imaging

Holst, Gerald C.

doi:10.1117/3.2588945

Cited by 153 publications

(34 citation statements)

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“…We also describe a range of influences of angle of incidence on emissivity, with the general response as expected (Holst, 2000), with emissivity declining progressively with increasing angle of incidence;…”

Section: Angle Of Incidence and Emissivity Of Biological Surfacesmentioning

confidence: 84%

“…Thus, low resolution, wide angle lens cameras or cameras at far distance cannot properly resolve small, point heat sources present on a surface because the large spot size has averaged over a larger instantaneous field of view (IFOV) to obtain a single temperature value for a particular pixel. Indeed, Holst (2000) recommends that the chosen spot size be approximately three times smaller than the desired minimum object size to obtain accurate pixel-based temperature resolution. Additional considerations in the variability pathway are still important (Figure 1g), reflecting good laboratory practice: cameras need to be calibrated to a blackbody source at the factory and should have electronic thermal stability controls and non-uniformity correction to account for electronic drift common in microbolometer-based imagers; images should be captured to a lossless, radiometric image file for any post-capture processing or analysis (Figure 1h); finally, images should be in focus (Figure 1i)…”

Section: Losslessmentioning

confidence: 99%

“…is the same as IFOV, although Holst (2000) recommends that due to phasing effects (i.e. slight vibration during image capture) and uncertainty of spot alignment with each pixel (Figure S1), there are limits to the smallest measurable size and the target should be assumed to subtend up to 3 × 3 pixels, and thus:…”

Section: Spot Size Effectsmentioning

confidence: 99%

“…With high emissivity (i.e. >0.95) assumed of many biological surfaces (although values ranging from 0.91 to 0.97 have been reported for plant materials; Jones & Vaughan, 2010), the error in temperature estimates may be small, but certainly not trivial especially when reflected temperature differs substantially from surface temperature (Tattersall, 2016); more critical is that the angle of incidence of the object to the camera is known to alter the effect or apparent emissivity predictably and systematically (Holst, 2000). These effects might not be obvious (although see Figure 2 for an example of this effect in avian thermography), but will contribute to errors in surface temperature estimation (Jiao et al, 2016) due to the difficulty in maintaining fixed angles on moving targets and because biological surfaces are rarely perfectly flat geometric shapes.…”

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confidence: 98%

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Spot size, distance and emissivity errors in field applications of infrared thermography

Playà‐Montmany

Tattersall

2021

Methods Ecol Evol

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Infrared thermography is increasingly emerging as an analytical approach within the thermal ecology research community, providing unique and rapid temperature information crucial to understanding how plants and animals exchange heat with their environment. What is difficult to appreciate are the numerous ways in which thermography may still yield inaccurate (i.e. deviation from the ‘correct’ value) information if certain tenets are not followed. In this paper, we examine, demonstrate and discuss these tenets with an aim to provide methodological advice to ecologists interested in employing thermography. We found that spot size and distance strongly influenced the surface temperature estimates of known, calibrated temperature sources, with similar results observed in maximum eye temperature measurements in wild birds. We also report on how the angle of incidence affects the apparent emissivity of various biological surfaces (fur, feather, skin, leaves), another source of uncertainty in thermography. The variation in temperature caused by variation in distance and uncertainty in emissivity are large enough to raise flags for field applications of thermography where accuracy is necessary but control over study subjects is limited. Since accurate emissivity and distance parameters are crucial to thermography calculations, our results should serve as a framework to assist ecologists in better experimental design with respect to the use of thermography.

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Section: Angle Of Incidence and Emissivity Of Biological Surfacesmentioning

confidence: 84%

Section: Losslessmentioning

confidence: 99%

Section: Spot Size Effectsmentioning

confidence: 99%

mentioning

confidence: 98%

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Spot size, distance and emissivity errors in field applications of infrared thermography

Playà‐Montmany

Tattersall

2021

Methods Ecol Evol

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“…The infrared thermography technology allows observing peculiarities/physiological characteristics ñ temperature ñ in living beings, as in the case of the tree, not perceived by the ìnaked eyeî (Vidal & Pitarma, 2019;Pitarma et al, 2019). Based on the thermal radiation emitted by the objects, this technique allows for the evaluation of their surface temperature (Holst, 2002). In general, trees produce low metabolic heat when compared to animals (Monteith & Unsworth, 2007) and, therefore, not detectable without Infrared Thermography Technology (IRT).…”

Section: Images Vs Thermogramsmentioning

confidence: 99%

Enhancing Ecocentric Environmental Attitudes: An Experience of Science Teaching to Inspire Students to Value Trees

Ferreira

Pitarma

2021

Journal of Teacher Education for Sustainability

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Deforestation is a global issue. Education has a fundamental role to play in this context. In this regard, the direction and effectiveness of educational practices should focus on the empowerment of students in ecocentric environmental attitudes. A key point in education for environmental sustainability is pedagogical approaches focused on the development of critical and reflective thinking. In this context, objectified research was developed in the (re)conceptualization of the “living being”, with thermogram didacticization, as a way to develop egalitarian feelings of the need for similar attitudes among living beings. The study was developed in an action-research context. The pedagogical-didactic intervention was within the scope of the “Natural Sciences” curricular unit of the “Basic Education” degree at a Portuguese Institution. After a pedagogical-didactic intervention, the reconceptualization of “living being” was observed in these students, presenting, now, a reflexive argument concerning the ecocentric environmental attitudes regarding the “living being” – the tree vs. animal, highlighting the importance that the thermographic images had in the (re)significance of their “new look” regarding the tree.

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Infrared Thermography

Griffith¹,

T��rler²,

Goudey³

2002

Encyclopedia of Imaging Science and Technology

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Infrared (IR) thermographic systems, or IR imagers, provide images that represent surface temperatures, or thermograms , by measuring the magnitude of infrared radiation emanating from the surface of an object. Because IR imagers see the radiation naturally emitted by objects, imaging may be performed in the absence of any additional light source. Modern IR imagers resolve surface temperature differences of 0.1 °C or less. At this high sensitivity, they can evaluate subtle thermal phenomena that are revealed only as slight temperature gradients. Some applications that employ IR thermography include inspections for predictive maintenance, nondestructive evaluation of thermal and mechanical properties, building science, military reconnaissance and weapons guidance, and medical imaging. Infrared thermography can be used both as a qualitative and a quantitative tool. Some applications do not require exact surface temperatures. In such cases, it is sufficient to acquire thermal signatures , characteristic patterns of relative temperatures of phenomena or objects. This method of qualitative visual inspection is expedient for collecting a large number of detailed data and conveying them, so that they can be easily interpreted. In contrast, accurate quantitative thermography demands a more rigorous procedure to extract valid temperature maps from raw thermal images. However, the extra effort can produce large arrays of high‐resolution temperature data that are unrivaled by contact thermal measurement techniques, such as using thermocouple wires. A skilled operator of an IR thermographic system, or thermographer , must be conscious of the possibility that reflected or transmitted, rather than emitted, IR radiation may be emanating from an object. These additional sources manifest themselves as signals that appear to be, but are not actually, based exclusively on the temperature of the spot being imaged. To understand the challenges and possibilities of IR thermography, it is necessary to review the principles of physics on which it relies. Types of imaging systems, guidance and good practice in operation are covered.

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Common Sense Approach to Thermal Imaging

Cited by 153 publications

References 0 publications

Spot size, distance and emissivity errors in field applications of infrared thermography

Spot size, distance and emissivity errors in field applications of infrared thermography

Enhancing Ecocentric Environmental Attitudes: An Experience of Science Teaching to Inspire Students to Value Trees

Infrared Thermography

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