Altius

European Space Agency (ESA)'s Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere (Altius) mission carries a high-resolution spectral imager that images in the ultraviolet, visible and near-infrared channels and uses a limb-sounding technique to deliver profiles of ozone and other trace gases in the upper atmosphere to support services such as weather forecasting, and to monitor long-term trends. Altius will not look straight down on Earth, but will observe the atmosphere along Earth’s horizon. The ‘limb-sounding’ technique allows trace gases such as ozone to be profiled so that concentrations can be seen at different altitudes with high vertical resolution. These data will be a valuable complement to that provided by nadir-looking missions such as Copernicus Sentinel-5P, Sentinel-4 and Sentinel-5. Altius is developed within ESA’s Earth Watch programme and financed mainly by Belgium with contributions from Canada, Luxembourg and Romania.