Noise-equivalent temperature (NET) is a measure of the sensitivity of a detector of thermal radiation in the infrared, terahertz or microwave portions of the electromagnetic spectrum.
It is the amount of incident signal temperature that would be needed to match the internal noise of the detector such that the signal-to-noise ratio is equal to one.
If a relation between intensity and temperature is well defined over the passband, as in the case of a blackbody, then the NET simply scales with the NEP.
In the microwave radiation region NET values are typically several hundred millikelvins to several kelvins.
For a particular mean signal temperature there is a fundamental limit to NET given by the natural thermodynamic fluctuations of the photon flux from the source under investigation.