Before revision: (This is to be distinguished from Temperature Noise in Thermodynamics or Principal Interferrometric Analysis Over Cross-Type Interference Between different noise types) The power spectral density of the noise is expressed in terms of the temperature (in kelvins) that would produce that level of Johnson–Nyquist noise, thus: where: is the noise power (in W, watts) is the total bandwidth (Hz, hertz) over which that noise power is measured is the Boltzmann constant (, joules per kelvin) is the noise temperature (K, kelvin) Thus the noise temperature is proportional to the power spectral density of the noise, .
After revision: The power spectral density of the noise is expressed in terms of the temperature (in kelvins) that would produce that level of Johnson–Nyquist noise, thus: where: is the noise power (in W, watts) is the total bandwidth (Hz, hertz) over which that noise power is measured is the Boltzmann constant (, joules per kelvin) is the noise temperature (K, kelvin) Thus the noise temperature is proportional to the power spectral density of the noise, .