Implication of phase-colour-ratio analysis on a typical lunar mare unit in northern Mare Imbrium. Panel a: image obtained by LROC WAC¹ with the dashed line indicating the boundary between high-Ti and low-Ti regions. Panel b: TiO₂ abundance map of panel a derived from the LROC WAC data by Sato et al. (2017). Panels c–e: images taken by the Kaguya MI² (data IDs: MV A_2B2_01_02042N443E3396, MV A_ 2B2_01_03874N443E3400, and MV A_2B2_01_04540N441E3402) at different measurement angles with their locations marked out using boxes in panel a. Panel f-h: colour-ratio images of R900/R750 corresponding to panels c–e, respectively. The incidence (i), viewing (e), and phase (g) angles are given at the bottom of panels f–h, respectively. The dashed boxes in panel c–h indicate the overlapped regions of these images.