Comparison of the line intensity ratios based on three estimators: , the integrated area W_j, or the peak intensity max(I_j) (see text for details). The four upper panels give the brightness temperature of a few o–H₂O lines. The black curve corresponds to the profile obtained with the quantum CRC set and the red curves to the QCT CRC set (see text for details). In the latter case, the profile is scaled according to the ratios of (plain curve), W_j (dashed curve), or max(I_j) (dotted curve) so that the profiles that are plotted would correspond to a ratio of unity according to the three estimators. The two bottom panels represent the variations in the ratios obtained between the various indicators and for all the lines of the model.