Characterisation of Martian dust aerosol phase function from sky radiance measurements by MSL engineering cameras. (arXiv:1905.01074v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Chen_Chen_H/0/1/0/all/0/1">H. Chen-Chen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Perez_Hoyos_S/0/1/0/all/0/1">S. Perez-Hoyos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanchez_Lavega_A/0/1/0/all/0/1">A. Sanchez-Lavega</a>
Dust is the main driver of Mars’ atmospheric variability. The determination
of Martian dust aerosol properties is of high relevance for radiative modelling
and calculating its weather forcing. In particular, the light scattering
behaviour at intermediate and large scattering angles can provide valuable
information regarding the airborne dust particle shape. The angular
distribution of sky brightness observed by the Mars Science Laboratory
engineering cameras (Navcam and Hazcam) is used here to characterise the
atmospheric dust single scattering phase function and to constrain the shape of
the particles. An iterative radiative transfer based retrieval method was
implemented in order to determine the aerosol modelling parameters which best
reproduce the observed sky radiance as a function of the scattering angle in
the solar almucantar plane. The aerosol models considered in this study for
retrieving dust radiative properties were an analytical three term Double
Henyey-Greenstein phase function, T-matrix calculations for cylindrical
particles with different diameter-to-length aspect ratios and experimental
phase functions from laboratory measurements of several Martian dust analogue
samples. Results of this study returned mean DHG phase function parameter
values in line with Wolff et al. (2009). Although differences were observed
during the low opacity aphelion season (lower forward scattering values,
presence of a peak in the backward region) compared to the rest of the year, no
clear evidences of seasonal behaviour or interannual variability were derived.
The obtained average D/L aspect ratios for T-matrix calculated cylindrical
particles were 0.70{pm}0.20 and 1.90{pm}0.20, and the best fitting Martian
dust analogue corresponded to the basalt sample.
Dust is the main driver of Mars’ atmospheric variability. The determination
of Martian dust aerosol properties is of high relevance for radiative modelling
and calculating its weather forcing. In particular, the light scattering
behaviour at intermediate and large scattering angles can provide valuable
information regarding the airborne dust particle shape. The angular
distribution of sky brightness observed by the Mars Science Laboratory
engineering cameras (Navcam and Hazcam) is used here to characterise the
atmospheric dust single scattering phase function and to constrain the shape of
the particles. An iterative radiative transfer based retrieval method was
implemented in order to determine the aerosol modelling parameters which best
reproduce the observed sky radiance as a function of the scattering angle in
the solar almucantar plane. The aerosol models considered in this study for
retrieving dust radiative properties were an analytical three term Double
Henyey-Greenstein phase function, T-matrix calculations for cylindrical
particles with different diameter-to-length aspect ratios and experimental
phase functions from laboratory measurements of several Martian dust analogue
samples. Results of this study returned mean DHG phase function parameter
values in line with Wolff et al. (2009). Although differences were observed
during the low opacity aphelion season (lower forward scattering values,
presence of a peak in the backward region) compared to the rest of the year, no
clear evidences of seasonal behaviour or interannual variability were derived.
The obtained average D/L aspect ratios for T-matrix calculated cylindrical
particles were 0.70{pm}0.20 and 1.90{pm}0.20, and the best fitting Martian
dust analogue corresponded to the basalt sample.
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