Near-infrared spectroscopy (NIRS) describes a physical-optical analysis method based on spectroscopy in the range of short-wave infrared light. The method originally comes from the medical sector but has also been used in agriculture for many years. For analysis, the medium (e.g. liquid manure) is irradiated with near infrared light - the human eye cannot perceive this. With the help of reflection, the NIRS sensor is able to detect the ingredients based on the difference between irradiated and reflected light.