Figure 11. Reflectance spectra of the magnet rings of the primary calibration target in four different moments of the mission: (a) sol 12, (b) 129, (c) 265, (d) 346. Each color corresponds to a different color or grayscale material. The scales of reflectance factor have been adapted to the plot size for better display.
Direct and Diffuse Sunlight on the Grayscale Rings
Suspended dust is one of the main sources of diffuse sunlight within the thin martian atmosphere. This phenomenon affects the measured radiance of the observed targets because the surfaces directly illuminated by the Sun will receive the sum of direct sunlight and diffuse light, while the shaded regions will receive only light from the diffuse component. The diffuse light and the presence of dust in the atmosphere can be evaluated using the direct fraction of sunlight \(F_{d}\) (Kinchet al. , 2007), defined as follows: