Observed spectrum of oxygen A-band embedded on the instrumental profiles. Top: oxygen A-band observation using two dualons in the arrays. Dualonl data are displayed in black and dualon2 in blue. Middle: zoom-in on the region indicated in the top panel. The features of the chained spectrum and the absorption feature are shown on top of the instrumental profiles. The signal of the dualon2 is scaled up by a factor of 1.5. Bottom: zoom-in on the region indicated in the middle panel showing the shift between the two dualons.