Letter - N
National Electrical Manufactures Association. Among its activities, sets US standards for housing enclosures, similar to IEC IP.
Noise Equivalent Temperature. See NETD.
NETD (or NET)
Noise Equivalent Temperature Difference or the change in temperature of a blackbody target that fills the radiometer FOV which results in a change in the radiometer signal equal to the rms noise of the instrument.
Neutral Density Filter
An optical or infrared filter for which the transmission is constant and not a function or wavelength.
Calibration in accordance with and against standards traceable to NIST (National Institute of Standards and Technology, USA). Traceability to NIST is a means of ensuring that reference standards remain valid and their calibration remains current.