Comparison of the input spectra for the spot-crossing simulation. The figure presents the line profiles of Na I D₁ line from observed spectra obtained with FTS-QS and FTS-spot. These include a quiet Sun observation at disk center (Wallace et al. 1998), shown as solid blue lines, and a sunspot umbral region (Wallace et al. 2005), represented by dashed blue lines. For comparison, we also display PHNX spectra, including the spectrum with the properties of a solar analog for the quiet Sun (solid red) and the spectrum of a star with a temperature 663 K lower than the Sun, representing the active region (dashed red).