Constraints on Physical and Optical Properties of Martian Dust Aerosols Using Mer, Phoenix, and Curiosity Observations

Abstract

The Martian atmosphere is dominated by the presence of irregularly shaped dust aerosols. These aerosols affect the vertical temperature profile and initiate dynamical responses on local, regional, and global scales. In order to quantify the effects of dust in dynamic and radiative transfer modeling, it is necessary to determine its physical and optical properties. This dissertation focuses on physical property retrievals of dust pertaining to particle size and shape distribution. Sky brightness observations taken at the Phoenix landing site and the Mars Exploration Rovers (MER) Opportunity and Spirit locations can be modeled using select phase functions within a Discrete Ordinate Radiative Transfer code. Each phase function is dependent on the physical properties of dust, including effective size and variance of the distribution and shape. Retrievals return values near 1.5 µm for particle size for Phoenix data sets using two different phase function models. This is consistent with previous work. Shape can be constrained using surveys with large scattering angle range. The particle sizes are consistent between models. The benefit of using an ellipsoidal shape is that the corresponding phase function model is physical, self-consistent, and available over a wider range of wavelengths. Fits to MER data return some variation in particle size, which is more evident at Opportunity sites than for Spirit sites. The methodology for retrieving particle size is unique and does not depend on the assumption of particle shape. In addition to particle size information, we present a quicklook method for retrieving optical depth from the newest rover, Mars Science Laboratory (MSL) Curiosity, in Gale crater. This method shows promise in filling in the gaps for past optical depth observation as well as providing information for operational use.