S/N detection strength as a function of SYSREM iterations for the data of night 1. The measured signal strengths are a result of using a pure CO model (blue colour), a pure H₂O model (orange colour), and a pure CH₄ model (black colour). The top panel shows the signal strength for the real data, while the bottom panel shows the strength of an injected signal using the differential ΔCCF according to the method described in Sect. 3.3. The diamond shape indicates the SYSREM iteration with the strongest detection of the injected signal.