Figure 10. Primary target imaged
by the left eye of Mastcam-Z (a) on sol 23 at 100 mm focal length (seq.
ZCAM03014) and (b) on sol 302 at 48 mm focal length (seq. ZCAM03014)
with the presence of large sand grains indicated by arrows. (c) One of
the grains in the sol 23 image is magnified for better display.
Image-IDs: (a)
ZL0_0023_0668983099_910IOF_N0030770ZCAM03003_1000LMA01, (b)
ZL0_0302_0693748246_223IOF_N0090000ZCAM03014_048085A02.
However, the regions which experienced the greatest accumulation of dust
were the magnet rings of the primary target. As anticipated in section
2, the aim of the underlying magnets was to attract magnetic dust on the
external rings of the round patches. The visible condition of these
rings was shown in Figure 7, where a small quantity of dust already
deposited during the first 23 sols and the thickness of the dust layer
was quite considerable at the end of the period under examination, in
which the color of the patches was almost completely invisible under the
dark red/brown coating (Figure 7d). We extracted the reflectance factor
values of the magnet rings from several sols, where the ROIs of the
magnet rings were selected with the template of Figure 4. Four spectra
of the magnet rings are shown in Figure 11 for sols 12, 129, 265 and 346
for the eight color and grayscale materials. Generally, the dust layers
decreased the reflectance of the brighter patches and raised that of the
darker patches, bringing their appearance to a convergence with a
reduction of the contrast and reddening. At the end of the time range
under examination (Figure 11d), the magnet rings were almost coincident
at shorter wavelengths, but showed a slight separation in the near
infrared, suggesting that in that range the dust was less optically
thick with respect to the color patches underneath.