The signal-to-noise ratio of the simulated observations of Sect. 4.3 as a function of the source temperature. The left-hand frame corresponds to the simulated Herschel observations at 100 μm (solid line), 160 μm (dashed line), 250 μm (dash-dotted line), and 500 μm (dotted line). The right-hand frame shows the signal-to-noise ratios for the simulated IRAS 100 μm data (solid line) and the Planck 500 μm and 850 μm bands (dashed and dotted lines, respectively). The signal-to-noise ratio of the 350 μm observations is 40. The black lines correspond to the relation β = 2.2(T/20.0)^-0.3 and the red lines to β = 2.2(T/20.0)^+ 0.3.