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Noise Equivalent Temperature [Difference], NET[D] - The temperature difference that is just equal to the rms noise signal; a measure of thermal resolution; (thermal sensitivity), but not taking into account target size, characteristics of the display and the subjective interpretation of the operator.

NIST, NIST Traceability - The National Institute of Standards and Technology (formerly NBS). Traceability to NIST is a means of ensuring that reference standards remain valid and their calibration remains current.

Non-Gray body - An object whose emissivity varies with wavelength over the wavelength interval of interest. A radiating object that does not have a spectral radiation distribution similar to a blackbody; also called a “colored body” or “realbody”. Glass and plastic films are examples of non-graybodies. An object can be a graybody over one wavelength interval and a non-gray body over another.