Figure 4. Example of ROI selections over an image of the cal-targets taken by the left eye of Mastcam-Z in the L1 filter (800 nm) on sol 69 at 48 mm focal length (Image-ID: ZL1_0069_0673052731_973IOF_N0032208ZCAM03014_048085A03, seq. ZCAM03014). All 41 regions of interest are visible in colors, including those under the gnomon’s shadow on the grayscale rings. The two ROI’s partially selected in the secondary target were edited to exclude the shadows due to the bolts of the support.
The maximum number of ROIs was 41, though not all of them were always selectable due to the position of the gnomon shadow on the grayscale rings, which depended on the incidence and azimuth angles. For these reasons, the number of ROIs on the grayscale rings within the gnomon shadow ranged from 0 to 4. On sols 3, 206, 290 and 305 some clean spots appeared shadowed by the gnomon owing to low Sun angles. More commonly, shadowing of one or both rows of the secondary target occurred due to its location on the side of the RPFA.
Once all the ROIs were selected suitably, their locations were documented along with the average and standard deviation of measured radiances over their pixels. The list of ROI groups is reported in Table 2.