First observations
While the first images were captured on 15 November 2025, the steps ensuring their delivery began months earlier. On 8 September 2025, the Infrared Sounder made its first successful observation of an internal calibration target, confirming the instrument was ready for the next commissioning stages. Rather than measuring each wavelength directly, the instrument works like the interferometers many learn about in school physics – it combines incoming light waves to create a unique interference pattern known as an interferogram. Just as a prism splits white light into colours, this wavy pattern mathematically contains all 1,953 wavelength measurements at once and when processed reveal thermal emission and absorption signatures from water vapour, carbon dioxide, ozone, ammonia, carbon monoxide, and nitrous oxide – building blocks for understanding atmospheric structure and dynamics.