Figure 5 compares two MIRA and
MRTCAL-calibrated lines covered at high resolution with VESPA.
Figure 6 compares MIRA and MRTCAL-calibrated
FTS spectra for all four frequency setups. In all cases, default
calibration settings were used. Both polarizations and all consistent scans
were averaged. Spikes and a spurious signal at intermediate frequencies
5.62 and 11.240.01 GHz in the E330 setup, which stems from
interference with a network switch in the backend room, have been
blanked. No futher processing was applied. In particular, no baselines were
subtracted.
The line shape observed at high spectral resolution show variations of the order of at most a few percents (cf. Fig. 5). Systematic differences are discernable on spectral lines in Fig. 6, with either MIRA- or MRTCAL-calibrated spectra showing higher intensities depending on the frequency. For instance, the differences are exacerbated for setup E150/L170250 that is situated close to the upper edge of the atmospheric window of the 2mm band (it shows a notable increased in the baseline noise at the high frequency end). These differences will be quantified and explained in the next sections