RETRIEVAL OF AEROSOL PROPERTIES AT JEZERO CRATER USING
THE SUPERCAM INSTRUMENT ON-BOARD THE NASA MARS 2020
PERSEVERANCE ROVER
T. Bertrand, LESIA, Paris Observatory, France, M. Wolff, Space Science Institute, Boulder, USA, K.
Connour, Laboratory for Atmospheric and Space Physics, Boulder, USA, T. McConnochie, Space Science
Institute, Boulder, USA, T. Fouchet, LESIA, Paris Observatory, France, F. Montmessin, LATMOS,
Guyancourt, France, E. W. Knutsen, LATMOS, Guyancourt, France.
Introduction:
SuperCam on-board the Mars2020-Perseverance
rover is a suite of remote sensing instruments [1,2]
that includes passive visible and near-infrared
(VISIR) spectroscopy covering the following channels: 385–465 nm, 536–853 nm, and 1300–2600 nm.
At these wavelengths, the scattering of light by aerosols is strongly sensitive to the particle size. By observing the Martian sky light scattered by aerosols
(dust and water ice clouds), at two different elevation
angles with the VISIR technique, and by comparing
the measurement with the results of a multiple scattering radiative transfer model, we are able to retrieve and monitor aerosols properties such as the
particle sizes and phase functions. This “passive sky”
technique has been demonstrated in the visible range
with ChemCam on the Mars Science Laboratory
(MSL) rover [3]. With SuperCam, the atmosphere is
probed for the first time from the ground in both the
visible and near-infrared domains [4], which provides further information on the aerosol properties.
The monitoring of these properties is important because they are considered significant factors in determining the radiative effect of aerosols and therefore in controlling the climate of Mars (e.g. [5]). In
particular, the particle sizes have been observed to
change depending on location and season. Typical
values for dust sizes during non-storm events have
been reported with an effective radius (of equivalent
volume sphere) around ~1-1.5 μm (+/- 50%), and
variances around 0.2–0.5 from a broad set of spacecraft and instruments at the surface and in orbit. During major dust events, an increase in dust particle
size up to 3-4 µm is a general trend [6-8].
Our objectives are to retrieve aerosol properties
and monitor their seasonal evolution with the
VISIR passive sky technique. Here we will focus
on the characterization of dust particles using the
available dataset and the multiple scattering model
DISORT.
The effect of dust particle sizes on the climate, which
is still not well understood, will also be discussed in
light of recent modeling results, exploring multimodal dust particle size distributions [9].

Method:
SuperCam passive sky observations:
Our primary observing strategy is the same approach used for MSL ChemCam “passive sky” observations [3]: ratioing instrument signals from two
pointing positions with different elevation angles,
which eliminates solar spectrum and instrument response uncertainties (Fig. 1).

Fig. 1. Geometry of the passive sky observation.
DISORT: Multiple scattering radiative transfer
model:
We use the multiple-scattering program DISORT
(Discrete Ordinates Radiative Transfer Program for a
Multi-Layered Plane-Parallel Medium, [10,11]) to
model the Martian sky, replicate the passive sky observation by SuperCam, and fit the observed sky
radiances, taking into account the diffusion of solar
radiation by aerosols (dust and water ice clouds). We
use cylindrical dust particles and spherical ice particles. Dust refractive indices are derived from
MRO/CRISM data [12], and the library for scattering
properties are calculated for a grid of effective radius
reff=0.01,0.05,0.1,0.2,0.3,…3.0 µm assuming a variance of the distribution of veff=0.3. The input parameters of the model are gathered by a python preprocessing
tool
(https:
//github.com/
kconnour/pyRT_DISORT) and include the column
optical depth seen by the rover, the elevation and
azimuth angles of the Sun and of the instrument at

the time of observation, the surface albedo, the effective radius of the aerosol particles and their vertical
distribution.
Preliminary results:
We analyzed the passive sky observations obtained during the first 200 sols of the mission, corresponding to the northern spring and summer on Mars
(no major dust storm). Preliminary results indicate
relatively small particle sizes for dust of around 1 µm
(Fig. 2), which is broadly consistent with ChemCam
passive sky dust particle size results for the comparable season [3].
We are currently improving the model to take into account water ice clouds, spectral surface albedo,
CO2 absorption, as well as an optimization tool to
allow for better fits of the data. These improvements
will allow us to extract the maximum amount of information from the SuperCam passive sky spectra.

References:
[1] Maurice S. et al. (2021) SSR.
[2] Wiens R.C. et al. (2021) SSR 217, 4.
[3] McConnochie T.H et al. (2018), Icarus 307, 294.
[4] Fouchet T. et al. (2022), Icarus 373.
[5] Madeleine J.-B. et al. (2011), JGR Planets, 116.
[6] Dlugach et al. (2003)
[7] Kahre M. et al. (2017), The Atmosphere and
Climate of Mars, 106-171, Cambridge University
Press
[8] Chen-Chen et al. (2021)
[9] Urata et al., this meeting.
[10] Thomas and Stamnes (2002), Cambridge
Atmos. Space Sci. Ser., 546 pp., Cambridge Univ.
Press, Cambridge, U. K
[11] Wolff et al. (2006), Geophys. Res., 111,
E12S17
[12] Wolff et al., 2009, Vol. 114 Pages E00D04

Fig. 2. Mean ratio of the low elevation spectra to the high elevation spectra. Black points are observations for
sol 133 (solar longitude Ls=68°). DISORT model results are shown for different choices of dust particle sizes.
The model matches the near-infrared data relatively well using 0.8-1 µm dust particles. However, the UV-VIS
data are not well reproduced. We are currently investigating this issue.