Simulation of the radiative flux at the martian surface between 180 and 1100 nm

Otter, Stephen (2010). Simulation of the radiative flux at the martian surface between 180 and 1100 nm. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000d3ca

Abstract

A multi-layer radiative transfer model of the atmosphere of Mars, the UVIS simulation, has been created to simulate the non-ionising radiative flux at the surface of Mars. The simulation operates over the range 180 - 1100 nm and determines the diffuse component of the surface flux using the delta-Eddington approximation. Latitude, l, and areocentric longitude, L_s, dependent abundance models of the dust and ice cloud aerosols and of the gaseous species ozone and water vapour are incorporated. Alternative aerosol distributions are also used corresponding to observations made by the Thermal Emission Spectrometer onboard Mars Global Surveyor.

Studies of the variation in surface flux in response to increasing dust optical depth predict reduced surface intensities at UV wavelengths (180 - 400 nm) but at longer wavelengths the surface flux exhibits a local increase relative to the initial incident flux at optical depths < 2.5 for VIS wavelengths (401 - 750 nm) and < 6.0 for NIR wavelengths (751 - 1100 nm). This is explained in terms of the influence of aerosol scattering parameters. Enhancement of the total surface flux by ~20% or greater is shown to occur at latitude and L_s values corresponding to the presence of the aphelion cloud belt and during the annual dust maximum.

The potential of a surface based spectrometer to be utilised as a means of detecting the trace gases, ozone, hydrogen peroxide and methane in the atmosphere is assessed. Ozone proves the only suitable candidate and the spatial and seasonal distribution of ozone is discussed in the context of potential instrument deployment sites. The effects of varying aerosol scattering parameters on the surface flux is characterised and changes in aerosol scattering parameter 'values of < 5% are shown to be theoretically detectable by a spectrometer of sensitivity 1.0x10^-2 Wm^-2nm^-1.