In the case when we want to measure temperature in a
specific part of optical fiber z (distance from the forehead
of optical fiber), it is necessary to aim for the spectrum of
Raman scattering. IS represents the Stokes intensity part
of Raman scattering, IAS represents the anti-Stokes
intensity part of Raman scattering. The relations
describing these intensities are written below (7), (8). For
both relations it is valid the same relation for attenuation
from forehead to position z, the lasers usually used in the
optical-fiber DTS have a wavelength at 1064 nm. Peaks
of Raman spectrum are in this case shifted ± 40 nm, i. e.
1104 nm and 1024 nm. Due to the fact, that the
attenuation is a function of wavelength, this effect can
cause an error in temperature determination [4].