Top: spectral retrieval of the CH₄ emission lines and the CH₃D emission lines (red line), the spectra from the observation (black solid line), the shaded grey region is the uncertainty range associated with the observed spectra, the telluric absorption (blue dot-dashedline) in this spectral range. The spectral ranges used in the retrieval are highlighted for CH₄ (green) and CH₃D (orange). Bottom: residual difference between the spectral retrieval and the spectra from the observation (black), the observation uncertainty (red solid line) is shown for each wavelength as well as the telluric absorption (blue dot-dashed line).