  Martian planet-encircling dust storms or global dust storms (GDS), resulting
from the combined influence of local and regional storms, are uncommon
aperiodic phenomena: with an average frequency of approximately one every 3-4
MY, they produce a substantial rise in the atmospheric dust loading that lasts
from weeks to months and have a significant impact on the atmospheric
properties, energy budget, and global circulation. During the 2018/MY34 global
dust storm, initiated at L_S = 185$^\circ$ (30-31 May 2018), an intensive
atmospheric science campaign was carried out by the Mars Science Laboratory
(MSL) rover to monitor the environmental parameters at Gale Crater. We
contribute to previous studies with independent retrievals to constrain the
dust opacity and characterise the aerosol particle properties, including: size,
shape and single scattering phase function. An iterative radiative transfer
retrieval procedure was implemented to determine the aerosol parameters that
best fit the angular distribution of sky radiance at forward and backward
scattering regions observed by MSL Navigation Cameras (Navcams) during the
2018/MY34 GDS.
