Observation of solar radiation in the infrared have been performed since the mid-fifties at the International Scientific Station of the Jungfraujoch (ISSJ, Swiss Alps, 46.5°N, 8.0°E, 3580 m a.s.l.), in the framework of the Network for Detection of Atmospheric Change (NDACC, www.ndacc.org). Systematic monitoring of the chemical composition of the Earth's atmosphere started in 1984 by using two state-of-the‐art Fourier Transform InfraRed (FTIR) instruments, while grating spectrometers were used previously in the early 1950s, and from the mid-1970s onwards, covering 40 years of quasi-continuous solar observations. In this framework, I will discuss optimization of retrieval strategies from infrared solar observations and methane trend analysis.