Rayleigh-Brillouin scattering profiles of air at different temperatures and pressures

Kurzfassung

Rayleigh-Brillouin (RB) scattering profiles for air have been recorded for the temperature range from 255 K to 340 K and the pressure range from 640 mbar to 3300 mbar, covering the conditions relevant for the Earth’s atmosphere and for planned atmospheric LIDAR missions. The measurements performed at a wavelength of λ = 366.8 nm detect spontaneous RB-scattering at a 90◦ scattering angle from a sensitive intra-cavity setup, delivering scattering profiles at a 1% rms noise level or better. The experimental results have been compared to a kinetic line-shape model, the acclaimed Tenti S6 model, considered to be most appropriate for such conditions, under the assumption that air can be treated as an effective single-component gas with temperature-scaled values for the relevant macroscopic transport coefficients. The elusive transport coefficient, the bulk viscosity, is effectively derived by a comparing the measurements to the model, yielding an increased trend from 1.0 to 2.5 × 10^−5 kg·m−1·s−1 for the temperature interval. The calculated (Tenti S6) line shapes are consistent with experimental data at the level of 2%, meeting the requirements for the future RB-scattering LIDAR missions in the Earth’s atmosphere. However, the systematic 2% deviation may imply that the model has a limit to describe the finest details of RB scattering in air. Finally, it is demonstrated that the RB scattering data in combination with the Tenti S6 model can be used to retrieve the actual gas temperatures.