1. Characterization of measurement system performance

Noise Equivalent Irradiance (NEI)

This is the illuminance, usually expressed in watts per square meter, of the entrance pupil, which produces an electrical signal equivalent to the system noise. It is therefore the minimum detectable pupil illuminance.

Thermal resolution

This is the minimum discernible difference in apparent temperature between an object and its surroundings. Depending on the nature of the object, the definition of thermal resolution takes different forms.

• Noise Equivalent Temperature Difference (NETD)

  This is the apparent temperature difference between an extended object and its environment, likely to produce a peak signal equal to the system's RMS noise voltage....