In the context of a looming dramatic drop of limb sounders, there is a crying need for new missions capable of probing the atmospheric composition with good vertical resolution. This is particularly important for the continuation of the long-term time series of ozone, aerosols, and greenhouse gases that help monitoring the impacts of political decisions to protect our environment. This is also crucial for the modeling community pushing for a better inclusion of the stratospheric composition both for improving short-term (weather) and long-term (climate) numerical predictions.

As an element of answer, ALTIUS (Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere) aims at building on the great success of previous limb-scatter and occultation instruments to provide globally distributed key atmospheric species concentration profiles. A number of target species will routinely be measured: O3, NO2, aerosols, H2O, CH4, PSC, PMC, OClO, BrO, NO3, and temperature. In particular, O3 profiles will be retrieved and delivered in near real time (NRT) in order to meet the requirements of operational services such as numerical weather prediction (ECMWF) and NRT atmospheric models (CAMS, C3S). Other occasional targets are, among others, mesospheric emissions, spectro-polarimetry of the limb, northern lights, tomographic analyses.

The ALTIUS mission concept has been studied since 2006 by the Royal Belgian Institute for Space Aeronomy (BIRA-IASB), together with OIP Sensor Systems and Qinetiq Space Belgium up to phase B. The payload successfully underwent the intermediate design review (IDR) in June 2015. In December 2015, ALTIUS successfully passed two reviews which concluded that (1) ALTIUS could meet the requirements of an operational ozone mission, and (2) the mission is capable of furthering atmospheric and climate research with its additional objectives. In December 2016, ALTIUS was submitted by Belgium to ESA's ministerial council as an element of the Earth Watch program.

Within this project, the stratospheric modelling group will, using the BASCOE data assimilation system:

  • Build a reference atmosphere
  • Establish the added value of the different viewing mode of ALTIUS (limb scatter and occultation from the Sun, the Moon, stars and planets)
  • Provide operational analysis of ozone based on the assimilation of ALTIUS data