Top left panel: input spectra (including SW) used for the direct method to determine the bandpass curve. It also contains P^cal − P for a single spectral dump and  ⟨ P^cal − P ⟩ _t as computed using the average of 1000 spectral dumps, both scaled by a factor of five for improved visualisation. The upper right panel shows the reduced data after applying Eq. (73). Note that the standing wave contribution is included in the result. The lower panels show the final spectra after baseline subtraction for T_cal/T_sys,off ≈ 15% (left panel) and T_cal/T_sys,off ≈ 2.5% (right panel).