Qiuhua Zheng, Ivan Dors, James Ryan University of New Hampshire

1. Rayleigh Brillouin Scattering Spectra in atmosphere: GroundWinds Brillouin scattering investigation Qiuhua Zheng, Ivan Dors, James Ryan University of New Hampshire

2. Principle to determine the wind velocity Wind velocity is determined by the Doppler shift between unshifted Rayleigh Brillouin scattering model and measured RBS spectrum, GroundWinds lidar is the first lidar system that provides a chance to directly measure the RBS spectra in the air.

3. Three regimes of Rayleigh Brillouin scattering • –mean free path of the fluid is much larger than the incident light wavelength and the backscattering spectrum is gaussian. • –mean free path of the fluid is much smaller than the incident light wavelength and the backscattering spectrum is three lorentzians. • –mean free path of the fluid is of the order of the incident light wavelength and the backscattering spectrum is undetermined.

5. The scattering spectrum Function of index refraction n

6. Rayleigh line shape in water Benedek, G., et al(1971)

7. RBS spectrumGroundwinds NH lidar system RBS spectrum Raw fringe

8. RBS spectrum compared to Gaussian thermal broadening

9. S6 model Tenti S6 model Fitted Gaussian

10. Fit to Tenti S6 model

11. Temperature profile

12. Landau-Placzek ratio

13. Aerosol/Molecular (AM) ratio

14. Summary • GroundWinds provides opportunity to measure the RBS spectrum in air. • RBS spectrum in air has two parts: pressure and entropy (T) fluctuations. • The better the model, the better temperature profile, and the better the wind velocity we can measure. • There still is room to improve Tenti’s S6 model. Extra info can be recovered by related RBS model research. • Additional corrections are possible at low altitude when a priori Landau Placzek ratio is used

15. Acknowledgements This work was supported by NOAA Grant NA17EC1105.

17. P Molecular scattering The Krammers-Heisenberg formula

19. Hydrodynamic model