The noise power, Noise Power(Np), is a characteristic value that plays an essential role in active and passive quadripoles, in amplifiers, mixers, filters, transponders, etc. and can affect the transmission characteristics.
The noise power indicates the relationship between noise temperature and power and depends on the spectral power density available in a certain frequency range. The noise power is specified in decibel adjusted( dBa). It is calculated by multiplying Boltzmann's constant (k), the temperature (T) in Kelvin (K) and the noise bandwidth (B) in Hertz ( Hz). Np = kTB.
At constant power density, noise power decreases at wider frequency ranges or bandwidths. Correspondingly, noise power increases at narrower frequency ranges assuming power density is constant. The noise power is the integral of the power spectral density with respect to the frequency range.
For image sensors and optical amplifiers, equivalent noise power is used instead of noise power. It is the value at which a minimum input power produces a photocurrent.