Illustration of viewing geometries and effect of microtopography. Panel a: relations between the viewing angles. i, e, and g are the incidence angle, emission angle, and phase angle, respectively, and i′ and e′ are the incidence and emission angles after topographical correction. θ₁ and θ₂ are the slope angles along and perpendicular to the rover viewing direction, respectively. Panel b: corrected angles. φ is the relative azimuth angle between the rover and the Sun, p₁ is the length of the projection of the normal vector onto the YOZ plane, p₂ is the length of the projection of the normal vector onto the XOZ plane, and p₃ is the length of the projection of the normal vector onto the Z-axis.