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Glossary of Thermography Terms

Delta T

The temperature difference between two targets or locations. Usually of comparable targets under comparable conditions.

Detector, Infrared

A transducer element that converts incoming radiant energy impinging on its sensitive surface into an electrical signal.

Diffuse Reflector

A surface that reflects a portion of the incident radiation in such a manner that the reflected radiation is equal in all directions. Also called a Lambertian surface.

Diffusivity, Thermal,

(α) The ratio of conductivity (k) to the product of density (ρ) and specific heat (cp).

α = k/ρcp [m² secˉ¹].

The ability of a material to distribute thermal energy after a change in heat input. A body with a high diffusivity will reach a uniform temperature distribution faster than a body with lower diffusivity.

D* (Detectivity)

Sensitivity figure of merit of an infrared detector –detectivity expressed inversely so that higher D* indicate better performance; taken at specific test conditions of chopping frequency and information bandwidth and displayed as a function of spectral wavelength.

Display Resolution, Thermal

The precision with which an instrument displays its assigned measurements parameter (temperature), usually expressed in degrees, tenths of degrees, hundredths of degrees, etc.

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