Estimates for the signal-to-noise ratios for the observation of the correlators along a single line of sight as a function of the source redshift z and of the length of the measured spectrum Δ z, for Planck (left panels) and ACTPOL (right panels). As long as the functions A and β can be assumed to be constant in the redshift range spanned by the Lyα spectrum, these results do not depend on the specific value taken by the latter.