Modelled (T_F, ε_F) and observed (T_obs, ε_obs, +) apparent temperature and emissivity as a function of Bond albedo A and thermal inertia Γ in the case of variations of regolith properties about a lens-shaped feature centred on the leading hemisphere, with maximum latitudinal width of 35° (shaded region, Fig. 6). Inside the oval, the grain size is R = 2 mm and outside of it R = 20μm. The Bond albedo is uniform, either A = 0.49 or A = 0.63. The thermal conductivity of amorphous ice is constant, either k_E0 = 0 or k_E0 = 0.001 W m⁻¹ K⁻¹ with porosity p = 0.8 (Γ = 10 MKS) for both regions. The topography of GTM (q = 64) and the spatial sensitivity of FP1 are included. The emissivity of surface elements is assumed to be isotropic (Eq. (13)).