Non-destructive testing — Infrared thermography — Vocabulary

ISO 10878:2013 defines terms used in infrared thermography for non-destructive testing and forms a common basis for standard general use.

Essais non destructifs — Thermographie infrarouge — Vocabulaire

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Non-destructive testing — Infrared
thermography — Vocabulary
Essais non destructifs — Thermographie infrarouge — Vocabulaire

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ISO 10878:2013(E)
 ISO 2013

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ISO 10878:2013(E)
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©  ISO 2013
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ISO 10878:2013(E)
Contents Page
Foreword . iv
Introduction . v
Scope . 1
1 Terms and definitions . 1
Bibliography . 26
Alphabetical index . 27
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ISO 10878:2013(E)
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The committee responsible for this document is ISO/TC 135, Non-destructive testing, Subcommittee SC 8,
Infrared thermography for non-destructive testing.
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ISO 10878:2013(E)
This International Standard is a compilation of terms and definitions to provide a precise understanding or
interpretation of infrared thermography and thermal/infrared non-destructive testing. These serve to secure the
foundation of infrared thermography technology growth within the academic and industrial communities.

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Non-destructive testing — Infrared thermography — Vocabulary

This International Standard defines terms used in infrared thermography for non-destructive testing and forms
a common basis for standard general use.
1 Terms and definitions
absorptance coefficient
proportion (as a fraction of 1) of the radiant energy impinging on a material's surface that is absorbed by the
NOTE 1 Absorptivity is dimensionless.
NOTE 2 For a blackbody, this is unity (1,0). Technically, absorptivity is the internal absorptance per path length. In
thermography, the two terms, absorptivity and absorptance, are often used interchangeably.
NOTE 3 Absorptance is the ratio between the radiation energy absorbed by a body and the total radiation incident on
the body.
NOTE 4 Absorptivity can vary with wavelength and be quoted for a specified band width or a specific wavelength. See
1.136, Spectral absorption coefficient.
active thermography
infrared thermographic examination of materials and objects which requires additional thermal stimulation
NOTE The thermal stimulation can be optical, sonic (ultrasonic), inductive, microwave or use any other form of energy.
ambient operating range
range of ambient temperatures over which an instrument is designed to operate within reported performance
ambient temperature
temperature of the air in the vicinity of a test object (target)
NOTE “Ambient temperature” is not to be confused with “reflected ambient temperature”, which is a term often used to
mean “reflected apparent temperature”.
ambient temperature compensation
correction built into infrared instruments to provide automatic compensation of temperature readings affected
by the ambient temperature
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ISO 10878:2013(E)
angular subtense
angular diameter of an optical system or subsystem
NOTE 1 Angular subtense is expressed in angular degrees or milliradians.
NOTE 2 In infrared thermography, the angle over which a sensing instrument collects radiant energy.
anomalous thermal image
observed thermal pattern of a structure that is not in accordance with the expected (reference) thermal pattern
irregularity or abnormality in a system
EXAMPLE An irregularity, such as an anomalous thermal pattern or any indication that deviates from what is normally
expected in the absence of any anomaly.
anti-reflectance coating
coating of infrared optical elements (lenses, windows) used to increase the sensitivity of a specified
wavelength range through minimization or suppression of reflections causing signal loss
apparent temperature
uncompensated reading from an infrared thermography camera containing all radiation incident on the
detector, regardless of its source
[ISO 18434-1:2008 , 3.1]
area effect
change in infrared radiometer output depending on the area of the measuring target
1 product of artificial character due to an extraneous agency
2 error caused by an uncompensated anomaly
EXAMPLE In thermography, an emissivity artefact simulates apparent variation of surface temperature.
atmospheric absorption
absorption of specific wavelengths of solar radiation, due largely to moisture, atmospheric gases and
atmospheric temperature
temperature of the atmosphere between the infrared camera and the object
atmospheric window
infrared any spectral interval within the infrared spectrum in which the atmosphere transmits radiant energy
well (atmospheric absorption is minimal)
EXAMPLE Atmospheric windows are roughly defined to lie in the wavelength ranges:
a)  0,78 µm to 2,0 µm in the near infrared (NIR);
b)  2,0 µm to 5,5 µm in the mid-wave infrared (MWIR);
c)  7,5 µm to 14,0 µm in the long-wave infrared (LWIR).
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ISO 10878:2013(E)
attenuating medium
material or other medium that attenuates infrared radiation emitted from a source
EXAMPLE Attenuating media include windows, filters, atmospheres, external optics.
ideal perfect emitter and absorber of thermal radiation at all wavelengths
NOTE A blackbody is described by Planck's law. In its classical form, Planck’s law describes the spectral distribution of
the radiant energy emitted by a blackbody.
blackbody equivalent temperature
apparent temperature of a test object that is equal to the temperature of a blackbody emitting the same
amount of radiant energy
blackbody radiator
radiator with the effective emissivity  close to unity (  0,98 across all relevant wavelengths)
blackbody reference
calibrated, traceable device used to check the calibration of infrared imaging radiometers or infrared
blackbody simulator
device whose radiation is close to that of a blackbody at the same temperature
EXAMPLE A cavity or a flat plate with a structured or coated surface characterized by a stable and uniform temperature
and with emissivity close to 1.
centre wavelength
wavelength in the middle of the spectral sensitivity band of an infrared detector
cooled sensor
sensor that needs cooling to improve sensitivity to infrared radiant energy by reducing thermal noise influence
detecting element
sensitive part of a detector which is directly affected by the quantity to be measured
EXAMPLE For temperature-sensing devices: a thermocouple junction; resistive element; photoelectric, pyroelectric or
quantum sensor.
differential blackbody
device for establishing two parallel isothermal planar zones of different temperatures and with effective
emissivities close to 1,0
diffraction limit
limit of geometric diffraction of optical systems
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ISO 10878:2013(E)
diffuse reflector
lambertian reflector
surface that reflects incident radiation equally in all directions
NOTE 1 A lambertian diffuser is a surface that reflects a portion of the incident radiation in such a manner that the
reflected radiation is equal in all directions, such as a gold perfect sphere.
NOTE 2 A mirror is not a diffuse reflector.
edge effect
(1) effect caused by measurement error mainly at the edge due to solid displacement or deformation by
variable loading in thermoelastic stress measurement
(2) change in thermal properties at the edge of a target object as a result of different thermal conduction and
convection properties
EXAMPLE Effect caused by measurement error at an edge due to solid displacement or deformation by variable
loading in thermoelastic stress measurement.
effective emissivity
measured emissivity value of a particular target surface under existing measurement conditions (rather than
the generic tabulated value for the same material) that can be used to correct specific temperature readings
NOTE 1 Effective emissivity is also called emittance; however, the latter term is not preferred because it has been used
to describe radiant exitance.
NOTE 2 Effective emissivity is context dependent, and is not purely a property of a material.
effective number of pixels
spatial resolution of a measured infrared image
NOTE The effective number of pixels is determined for a scanning infrared thermographic instrument according to the
scanning pitch, and for an infrared thermographic instrument with an array sensor according to the number of pixels of the
EMI/RFI noise
disturbance to electrical signals caused by electromagnetic interference (EMI) or radio frequency interference
NOTE In infrared thermography, EMI/RFI noise can cause patterns to appear on the display and is sometimes due to
poor grounding or earthing.
ratio of the radiance of a target surface to that of a blackbody at the same temperature and over the same
spectral interval
ratio of the radiant flux emitted by a real target and that emitted by a blackbody at the same temperature and
under the same conditions
NOTE 1 The total radiance, R , is obtained by an integration of the monochromatic radiance between wavelengths zero
and infinity.
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ISO 10878:2013(E)



exp( )1
c is the speed of light in a vacuum;
h is the Planck constant;
k is the Boltzmann constant;
T is the thermodynamic temperature;
 is the Stefan-Boltzmann constant, in watts per square metre per kelvin to the power four, given by
 5,6710
Radiance and emittance being connected, the total emittance, M , is given by
0 0 4
M   R  σ T
NOTE 2 In thermography, the terms “radiance” and “emittance” are technically often used interchangeably.
NOTE 3 Refer to ISO 80000-7
environmental rating
rating assigned to an operating unit (typically an electrical or mechanical enclosure) to indicate the limits of the
environmental conditions under which the unit functions reliably and within reported performance
extended source
source of infrared radiation whose image fills completely or a larger part of the field of view of the infrared
field of view
field of vision
angular subtense over which an instrument integrates total incoming radiant energy
NOTE 1 Angular subtense is expressed in angular degrees or radians per side if rectangular or square and in angular
degrees or radians if circular.
NOTE 2 In infrared thermometers, field of view defines the target spot size; in a scanning/staring imager, it defines the
scan angle or picture size or a total field of view (TFOV).
NOTE 3 The field of view is the angular extent of the observable world that is seen at any given moment.
See Figure 1.
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ISO 10878:2013(E)

1 detector
A minimum detecting size
b view
l working distance
 instantaneous view angle (scanning type); spatial resolution (2D sensor type)
 vertical view angle
 horizontal view angle
Figure 1 — Field of view
fill factor
focal plane arraysratio of the total surface of sensitive detector elements to the total area of the detector
infrared thermography optical element, usually transmissive, which is used to limit spectral sensitivity of
infrared detectors
fixed pattern noise
non-temporal variations between pixels that are exposed to the same scene radiation
NOTE These variations can be caused by non-linearities in the detector, non-perfections in gain and offset maps, and
slow temporal changes that are too slow for the eye or brain to interpret as a temporal change. In uncooled detectors, the
slow temporal term is, most of the time, the dominant term of the spatial noise equivalent temperature difference.
focal plane array
type of infrared detector which involves a one- or two-dimensional array consisting of many individual sensing
elements (called “pixels”)
NOTE Detector arrays are typically placed at the focal plane of an instrument. In thermography, rectangular or square
FPAs are used in “staring” (non-scanning) infrared imagers. These are called IRFPA imagers.
focal point
infrared thermographyimage point conjugate to an infinitely distant object point on the optical axis
NOTE In infrared thermometers, this is where the spot size is the smallest. In scanning or staring imagers, this point
corresponds to the minimum instantaneous field of view (IFOV).
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ISO 10878:2013(E)
foreground temperature
temperature of the scene behind and surrounding the instrument, as viewed from the target
NOTE 1 This is often referred to as ‘Instrument background temperature’ or as ‘Observer background temperature’
NOTE 2 See ambient temperature.
frame averaging
addition of images and the division of their total for signal to noise ratio (signal level to noise level)
frame repetition rate
number of full fields of view scanned per second
frame time
time needed to obtain signal information in all field elements, or pixels)
grey body
object whose emissivity is constant (less than 1) in a particular spectral range
image display tone
grey shade or colour hue on a thermogram
image processing
converting an image to digital form and further enhancing the image to prepare it for computer or visual
NOTE For an infrared image or thermogram, image processing can include temperature scaling, spot temperature
measurements, thermal profiles, image manipulation, subtraction, and storage.
imaging line scanner
line scanner
line-scanning (one-dimensional) device which images perpendicularly to a scan direction to produce a two-
dimensional image of a scene
imaging radiometer
infrared thermal imager or point infrared sensor that can provide thermal images from which quantitative
temperature measurements are possible
infrared camera
infrared thermography camera
IRT camera
instrument that collects the infrared radiant energy from a target and produces an image in monochrome
(black and white) or colour, where the grey shades or colour hues are related to target apparent temperature
NOTE Such images are sometimes called infrared thermograms.
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ISO 10878:2013(E)
infrared imaging system
infrared thermal imager
instrument that converts spatial variations of surface infrared radiation to grey tones or colours corresponding
to radiation power (temperature)
NOTE See infrared camera.
infrared thermographic instrument
instrument that converts infrared radiant energy to a temperature and displays a thermogram
indium antimonide
InSb is a narrow-gap semiconductor with an energy band gap of 0,17 eV at 300 K and spectral sensitivity in
the range of 1 m to 5 m; it is widely used as the sensor in infrared thermal imaging systems
NOTE Such detectors typically require cooling while in operation.
infrared radiation
optical radiation for which the wavelengths are longer than those for visible radiation
NOTE 1 For infrared radiation, the range between 780 nm and 1 mm is commonly subdivided into:
— IR-A: 780 nm to 1 400 nm;
— IR-B: 1,4 µm to 3 µm;
— IR-C: 3 µm to 1 mm.
[IEC 60050-845:1987 ]
NOTE 2 The range of infrared emitted by the source and which reaches the lens should be considered in the design of
an infrared-absorbing material.
infrared bolometer
sensor that provides a signal; it employs an electrical conductance
infrared thermistor bolometer
thermistor configured so as to collect radiant infrared energy
infrared thermister bolometer
type of thermal infrared detector
infrared calibration source
blackbody simulator or other target of known temperature and effective emissivity used as a calibration
infrared detector
sensor which converts absorbed infrared radiation into an electrical signal
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ISO 10878:2013(E)
infrared fibre optic
flexible fibre made of a material that transmits infrared energy, used for non-contact temperature
measurements in cases where there is no direct sight between the instrument and the target
infrared fibre optics
fibre optics which transmit infrared radiation
infrared focal plane array
one- or two-dimensional array of individual infrared sensing elements, typically used as a detector in infrared
imaging instruments
infrared image
image that shows distribution of infrared radiant energy with colour hues or grey shades
infrared-imaging line scanner
infrared (one-dimensional) line-scanning device which images perpendicularly to a scan direction to produce a
two-dimensional thermogram of a scene
infrared optical element
element that collects, transmits, restricts, refracts or reflects infrared energy as part of an infrared sensing or
imaging instrument
infrared radiant energy
energy that is radiated and propagated as infrared, an electromagnetic wave whose wavelength is longer than
visible light and shorter than 1 mm
infrared radiation thermometer
infrared non-imaging device allowing non-contact temperature measurement by sensing thermal radiation
emitted by a target (target emissivity is to be known for measuring the “true” temperature)
infrared radiometer
equipment that measures infrared radiant energy
NOTE An infrared camera is a type of infrared radiometer.
infrared reflector
material with an excellent reflectance in the infrared region, close to 1,00
EXAMPLE Polished gold is an excellent infrared reflector commonly used in first surface mirrors.
infrared sensing device
instrument intended for the analysis of objects by the capture of their infrared radiation
EXAMPLE Infrared cameras, both imaging and staring, and infrared thermometers are the most typical infrared sensing
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ISO 10878:2013(E)
infrared thermal detector
detector that absorbs infrared radiation and produces an electrical signal following changes of its temperature
EXAMPLE Measuring signals are changed to electrical resistance (bolometer), the thermal voltage (thermal element)
and electrical polarization.
infrared thermographic testing
thermographic testing
inspection of materials and products using infrared thermography
infrared thermography
thermography infrared
IR thermography
technique allowing imaging of objects by sensing their emitted infrared (thermal) radiation
instantaneous field of view
angular subtense energy or the angular projection of the detector element at the target plane
NOTE 1 The angular subtense is expressed in angular degrees or radians per side if rectangular, and angular degrees
or radians if round.
NOTE 2 In infrared thermometers, instantaneous field of view defines the target spot size; in a line scanner or imager it
represents a single resolution element in a scan line or a thermogram being a measure of spatial resolution.
NOTE 3 The instantaneous field of view is equivalent to the horizontal and vertical fields of view of an individual
detector. For small detectors, the detector angular subtenses or projections  and  are defined by   a/f and   b/f,
where a and b are horizontal and vertical dimensions of the detector, and f is the effective focal length of the optics.
NOTE 4 Instantaneous field of view can be expressed as a solid angle in units of 
NOTE 5 IFOVs may be different in the vertical (VIFOV) and horizontal (HIFOV) directions.
radiant flux (power) per area incident on a given surface
NOTE Irradiance is expressed in watts per metre squared.
zone marking an interval of equal apparent temperature in a thermogram
NOTE As an image enhancement feature, it replaces certain colours in the scale with a contrasting colour.
laser pyrometer
infrared radiation thermometer that projects a laser beam on to a target and uses the reflected laser energy to
calculate the target effective emissivity and automatically correct the target temperature (assuming that the
target is a diffuse reflector)
NOTE Laser pyrometers are not to be confused with laser-aiming infrared thermometers, where the laser is used to
indicate a measured area.
limiting resolution
highest spatial frequency of a target that an imaging sensor is able to resolve
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ISO 10878:2013(E)
line scan rate
number of target lines scanned by an infrared scanner or imager in 1 s
load frequency range
range of load frequencies used in elastic stress measurement
lock-in technique
technique allowing for the extraction of a signal of known carrier wave from an extremely noisy environment.
This signal can be, but should not be, restricted to temperature.
NOTE A common application is for non-destructive evaluation.
long-wave infrared
wavelength range 7 µm to 14 µm, in which certain infrared instruments operate
measurement spatial resolution
smallest target spot size on which an infrared camera can fulfil measurement, expressed in terms of angular
NOTE 1 The angular subtense is expressed in milliradians.
NOTE 2 The slit response function (SRF) test and the hole response function (HRF) are used to measure IFOV
mercury cadmium telluride
material sensitive to infrared radiation in the spectral range of 1,5 µm to 14 µm and widely used as a detector
in infrared imagers, especially in the 8-14 µm range.)
NOTE Such detectors typically require cooling while in operation.
mid-wave infrared
middle-wave infrared
wavelength range 3 µm to 5 µm, in which certain infrared instruments operate
minimum detectable dimension
dimension or length of the smallest object that can be measured
minimum detectable temperature difference
measure of the combined ability of an infrared imaging system and a human observer to detect a target at a
particular temperature of unknown location against a vast uniform background having another temperature,
the target being displayed on a monitor for a limited time
NOTE For a given target size, the MDTD is the minimum temperature difference between the target and its background
at which the observer can detect the target. The standard target is a circle whose size is given by its angular subtense,
and both the target and the background are isothermal black bodies.
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ISO 10878:2013(E)
minimum resolvable temperature difference
measure of the ability of an infrared imaging system and the human observer to recognize periodic bar targets
on a display
See Figure 2.
NOTE The MRTD is the minimum temperature difference between a standard periodic test pattern (7:1 aspect ratio, four
bars) and the blackbody background at which an observer can resolve the pattern as the four-bar pattern.
modulation transfer function
measure of the ability of an imaging system to reproduce an image of a target
NOTE A formalized procedure is used to measure the modulation transfer function. It assesses the spatial resolution of
a scanning or imaging system as a function of distance to the target.
motion compensation
correction of the measurement error caused by displacement or transformation of the measuring object
multi-element sensor
sensor that arranges infrared detectors in one dimension or two dimensions
near infrared
wavelength range 0,75 µm to 1,9 µm, in which certain infrared instruments operate
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ISO 10878:2013(E)

1 test target
2 infrared imaging system
3 display
4 detector
5 near plate with rectangular slot
6 far plate
b slot width
l working distance
Figure 2 — Minimum resolvable

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