Effect of sampling resolution on the emission spectrum of our Mars-like case around the 15 μm CO₂ band. The rows show the effect for different final observing resolutions (R_fin). Left column: flux. The various colors correspond to the four sampling resolutions (i.e., the resolution used in radiative transfer calculation before binning; R_sp) shown inthe legend. The reference case is computed from our very high-resolution cross sections (Δσ ≈ 0.01 cm⁻¹). The high-resolution reference spectrum before binning is shown as the shading in the top left panel. Right column: relative error between the spectra of the left panel and the reference case. The error between the calculation with k-coefficients and the reference case is shown with the black dashed curve; the two spectra would be indistinguishable in the left panels.