Relative system response of three KID arrays as a function of frequency. For illustration, we also show (black) the atmospheric transmission obtained with the ATM model (Pety et al. 2009; Pardo et al. 2001) for two values of precipitable water vapour (1 and 5 mm). The spectra of the model of Uranus (pink) and the model of Neptune (green), as discussed in Appendix A, are also plotted for illustration with arbitrary normalisation with respect to the NIKA2 transmission.