Radiative Transfer Characterization of Inhomogeneous Boundary Layers

Dust aerosols are a tracer of boundary layer dynamics in the Martian atmosphere. Vertical variations in dust mixing ratios have been detected at Gale Crater and interpreted in terms of boundary layer height and local to mesoscale mixing processes (Moores et al. 2015, Moore et al. 2016). Such variations have been seen through a simplified radiative transfer analysis of images of distant features to get the near-surface dust mixing ratio, which may then be compared to column average dust amounts (e.g., Lemmon et al., this session, abstract # 182909). We have developed a 3-dimensional radiative transfer model to evaluate and validate the simplified method for measuring dust content. In this model, the radiative transfer equation (RTE) is integrated over a line of sight in an arbitrary atmosphere. For this investigation, the atmosphere is a set of spherical shells; and is horizontally homogeneous except for the existence of an idealized crater, with allowed in-crater versus out-of-crater differences. The single-scattering contribution to the RTE is calculated analytically. The multiple-scattering contribution utilizes multiple runs of DISORT (a plane parallel, discrete-ordinates radiative transfer code; Stamnes et al. 1988) to characterize the diffuse radiation field as a function of position along the line of sight. We test the limitations of the simplified method under a variety of geometries and over the range of relevant wavelengths. Moore, C.A., et al., 2016. Icarus 264, 102-108. Moores, J., et al., 2015. Icarus 249, 129-142. Stamnes, K., 1988. Appl. Opt., 27(12):2502-2509, Jun 1988.