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Your one-stop resource for defining and understanding thermal infrared terminology and related key terms for all things in the world of thermography. Be sure to browse our ever-growing library of educational white papers and our other definitions page to further your knowledge of the IR spectrum.

Absolute Zero

The temperature that is zero on the Kelvin or Rankine temperature scales, also the temperature at which a material is at its lowest energy state.

Absorptivity, a [Absorptance]

The proportion (as a fraction of 1) of the radiant energy impinging on a material’s surface that is absorbed into the material. For a blackbody, this is unity (1.0). Technically, absorptivity is the internal absorptance per unit path length. In thermography, the two terms are often used interchangeably.

Accuracy [of Measurement]

The maximum deviation, expressed in % of scale or in degrees Celsius or Fahrenheit, that the reading of an instrument will deviate from an acceptable standard reference.

Ambient Operating Range

Range of ambient temperatures at which an instrument is designed to operate within published performance specifications.

Ambient Temperature

Temperature of the air in the vicinity of the target (target ambient) or the instrument (instrument ambient).

Ambient Temperature Compensation

Correction built into an instrument to provide automatic compensation in the measurement for variations in instrument ambient temperature.

Anomaly

Any irregularity, such as a thermal anomaly on an otherwise isothermal surface. Any indication that deviates from what is expected.

Apparent Temperature

The target surface temperature indicated by an infrared point sensor, line scanner or imager before temperature corrections are made.

Artifact

A product of artificial character due to extraneous agency; an error caused by an uncompensated anomaly. In thermography, an emissivity artifact simulates a change in surface temperature but is not a real change. A hot solar reflection or a cold reflection due to narcissus would be examples of artifacts.

Atmospheric Windows [Infrared]

The spectral intervals within the infrared spectrum in which the atmosphere transmits radiant energy well (atmospheric absorption is a minimum.). These are roughly defined as 3-5 µm and 8-14 µm.