Raman scattering in the Earth's atmosphere, Part II: Radiative transfer modeling for remote sensing applications

Raman scattering in the Earth’s atmosphere is caused predominantly by its most abundant molecular components, N₂ and O₂. After the computation of the optical properties that govern the spectral and angular redistribution of light due to various inelastic scattering events, viz. rotational Raman scattering (RRS), vibrational Raman scattering (VRS), and rovibrational Raman scattering (RVRS), covered in Part I of this series, the next challenge in the simulation of inelastic scattering in the Earth’s atmosphere is to carry out radiative transfer (RT) computations across several wavelengths simultaneously.

In this part of our work, we provide the RT formulation for fully polarized simulations of inelastic scattering using the matrix-operator-method-based RT model vSmartMOM. The formalism is optimized for easy use with GPUs, allowing an unprecedented speedup of accurate multi-wavelength RT computations of inelastic scattering using the full Stokes-vector, thus allowing its operational use without coarse spectral binning (Rozanov and Vountas, 2014), or single scattering approximations (Sioris and Evans, 1999) at longer wavelengths.

After comparing our model against the current state-of-the-art, we demonstrate the use of vSmartMOM to simulate Raman lidar measurements, the Ring effect, the ghosting of Fraunhofer lines due to vibrational Raman scattering and spectral corrections due to inelastic scattering in the O₂ A-band in the Earth’s atmosphere. We use our model (1.) to validate the convention of neglecting the contribution of VRS and RVRS, and (2.) to quantify the speed and accuracy of the single scattering approximation in the O₂ A-band.