Scintillation noise

As usual, we will continue in the next chapter we will now start on the derivations of formulas relating to the effects of what we have previously called scintillation noise , and which is also called flicker noise , source noise , and other labels. Basically this... 

Another characteristic of scintillation noise is that, since it represents the amount of energy in the optical beam, it can never attain a negative value. In this respect it is similar to the Poisson distribution, which also can never attain a negative value. On the other hand, since it is a continuous distribution it will behave the same way as the constant-noise case in regard to achieving an actual zero any given reading can become... 

Type of noise Constant detector Shot noise Scintillation noise... 

Here again, in the low-noise case of scintillation noise, the absorbance noise is again independent of the reference signal level, and is now independent of the sample characteristics, as well, and depends only on the magnitude of the external noise source. 

To derive the transmittance noise for the case of large scintillation noise, we begin at a somewhat earlier point than we did for the low-noise case, with equation 41-14 [2] ... 

In the case of scintillation noise, however, we cannot do either of those things. By the physical picture we set up to describe the situation, the situation can in fact occur that the obstruction would completely block the optical beam and allow zero energy through, yet since it represents a continuum of values we do not see a justification to arbitrarily reject those readings. Therefore we cannot see a clear path to trying to determine the noise performance of such a system, since it will inevitably come out as infinite in all cases. 

If the intensity of the signal varies, due either to fluctuations of the source output, the detector response, or to changes in the refractive index of the atmosphere between the source and the detector scintillation), noise will be seen over the frequency range at which these fluctuations occur. Unlike the types of noise we have considered to date, which are additive, fluctuation noise is multiplicative and is much more serious for Fourier spectrometry. 

---