Finding the bulk viscosity of air from Rayleigh-Brillouin light scattering spectra.

Spectral line shape models can successfully reproduce experimental Rayleigh-Brillouin spectra, but they need knowledge about the bulk viscosity η. Light scattering involves GHz frequencies, but since η is only documented at low frequencies, η is usually left as a free parameter, which is determined by a fit of the model to an experimental spectrum. The question is whether models work so well because of this freedom.