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 2013
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©  ISO 2013
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Contents Page
Foreword . iv
Introduction . v
Scope . 1
1 Terms and definitions . 1
Bibliography . 26
Alphabetical index . 27
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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.
iv © ISO 2013 – All rights reserved

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.


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
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).
2 © ISO 2013 – All rights reserved

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
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.
4 © ISO 2013 – All rights reserved



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

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