ASTM E1149-90

Definitions of Terms Relating to NDT by Infrared Thermography (Withdrawn 1991)

General Information

• Status: Withdrawn
• ICS: 71.040.40 - Chemical analysis
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.10 - Specialized NDT Methods

Standards Content (Sample)

(IT) Designation: E 1149 - 90
Standard Terminology Relating to
NDT by Infrared Thermography'
This standard is issued under the fixed designation E 1149; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
(e) indicates an editorial change since the last revision or reapproval.
superscript epsilon
absorptance, a-the ratio of radiant flux absorbed by a viewed by the instrument. The instrumentation varies in
surface to that incident upon it. complexity from spot radiometers to two-dimensional
apparent temperature-the temperature of an object as real-time imaging systems.
determined solely from the measured radiant exitance,
infrared thermography-see thermography, infrared.
assuming an emissivity of unity.
instantaneous field of view (1FOV)-for a scanning system,
background radiation-all radiation received by the infrared
the angular dimensions in object space within which ob-
of
sensing device that was not emitted by the specified area
jects are imaged by an individual detector (unit = deg or
the surface being examined.
rad).
blackbody-an ideal thermal radiator (emissivity = 1 .O) that
NOTE-The IFOV is equivalent to the horizontal and vertical fields
emits and absorbs all of the available thermal radiation at
of view of the individual detector. For small detectors, the detector
a given temperature.
angular subtenses or projections, CY and ß, are defined by CY = a/f and
blackbody equivalent temperature-the apparent tempera-
ß = bffwhere a and b are the horizontal and vertical dimensions of
ture of an object as determined from the measured
the detector and f is the effective focal length of the optic. (IFOV may
radiance and the assumption that it is an ideal blackbody also be expressed as a solid angle in units of sr.)
with emissivity of 1.0.
irradiance, E-the radiant flux (power) per unit area incident
differential blackbody-an apparatus for establishing two
on a given surface (unit = W/m2).
parallel isothermal planar zones of different temperatures,
limiting resolution-the highest spatial frequency of a target
1.0.
and with effective emissivities of
that an imaging sensor is able to resolve.
emissivity, &-the ratio of the radiance of a body at a given
line scanner-an apparatus that scans along a single line of a
temperature to the corresponding radiance of a blackbody
scene to provide a one-dimensional thermal profile of the
at the same temperature.
scene.
extended source-a source of infrared radiation whose image
minimum detectable temperature difference (MDTD)-a
completely fills the field of view of a detector.
measure of the compound ability of an infrared imaging
NOTE-The irradiance is independent of the distance from the
system and an observer to detect a target of unknown
source to the region of observation. In practice, sources that are
location at one temperature against a large uniform
not extended sources are considered to be point sources; see point
background at another temperature when displayed on a
source.
monitor for a limited time.
field of view (F0V)-the shape and angular dimensions of
Disaission: For a given target size, the MDTD is the minimum
the cone or the pyramid which define the object space
temperature difference between the target and its background at
imaged by the system; for example, rectangular, 4" wide by
which the observer can detect the target. The standard target is a circle
3" high.
whose size is given by its angular subtense, and both target and
background are isothermal blackbodies.
Discussion-The size of the field of view is customarily expressed
in units of degrees.
minimum resolvable temperature difference (MRTD)-a
measure of the ability of an infrared imaging system and
imaging line scanner-an apparatus that scans in a single
dimension and is moved perpendicular to the scan direc- the human observer to recognize periodic bar targets on a
a two-dimensional thermogram of a display. The MRTD is the minimum temperature differ-
tion to produce
scene. ence between a standard periodic test pattern (7:l aspect
infrared imaging system-an apparatus that converts the ratio, 4 bars) and its blackbody background at which an
two-dimensional spatial variations in infrared radiance observer can resolve the pattern as a four-bar pattern (see
from any object surface into a two-dimensional thermo- Fig. 1).
gram of the same scene, in which variations in radiance
modulation transfer function (MTF)-in infrared imaging
are displayed in gradations of gray tone or in color.
systems, the modulus of a Fourier transform that describes
infrared sensing device-one of a wide class of instruments
the spatial distribution of the overall attenuation in
used to display, record or both, information related to the
amplitude of a thermal imaging system.
thermal ra
...