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Glossary of Thermography Terms

Measurement Spatial Resolution

The smallest target spot size on which an infrared imager can produce a measurement, expressed in terms of angular subtense (mrad per side). The slit response function (SRF) test is used to measure M.

Medium, Transmitting Medium

The composition of the measurement path between a target surface and the measuring instrument through which the radiant energy propagates. This can be vacuum, gaseous (such as air), solid, liquid or any combination of these.

Mercury Cadmium Telluride MCT (HgCdTe)

A material used for fast, sensitive infrared photo-detectors used in infrared sensors, scanners and imagers that requires cooled operation.

Micron (micrometer)

(µ or, µm) – One millionth of a meter; a unit used to express wavelength in the infrared.

Milliradian (mrad)

One thousandth of a radian (1 radian = 180/ח);a unit used to express instrument angular field of view; an angle whose tangent is equal to 0.001; 1 mrad = 0.05729578°)

Minimum Resolvable Temperature (difference),

MRT(D) – Thermal resolution; thermal sensitivity – the smallest temperature difference that an instrument can clearly distinguish out of the noise, taking into account target size and characteristics of the display and the subjective interpretation of the operator. The limit of MRTD is MDTD (minimum detectable temperature difference). MDTD is the MRTD of an extended source target, that is, a target large enough to be fully resolved by the instrument.


In general, the changes in one wave train caused by another; in thermal scanning and imaging, image luminant contract; (Lmax – Lmin)/(Lmax + Lmin).

Modulation Transfer Function (MTF)

A measure of the ability of an imaging system to reproduce the image of a target. A formalised procedure is used to measure MTF. It assesses the spatial frequency resolution of a scanning or imaging system as a function of distance to the target.

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