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                                               A Belgian space experiment for atmospheric sounding 


ALTIUS (Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere), is a 3-channel hyperspectral imaging spectrometer to conduct a spectroscopic survey of Earth atmosphere in the UV, visible and NIR spectral ranges.
The ALTIUS payload will allow observation of the Earth’s atmospheric bright limb in an extended spectral region from the Ultraviolet to the NIR. In addition, the ALTIUS instrument will perform solar and stellar occultation observations in the dark limb.
The ALTIUS payload will be based on the use of dedicated Acousto-Optic Tuneable Filters (AOTFs) in the Visible (450-800nm) and NIR (900-1800nm) range, while in the UV (250-400nm) spectral filtering will be done by a stack of Fabry Perot interferometers. By this way, the ALTIUS payload will perform observations with a spectral resolution better than 10 nm over the complete operational spectral-range.


In the past decade, there has been a significant reduction in the number of atmospheric sounders with a high vertical resolution in space. This impacts the monitoring of long-term trends for essential atmospheric species, such as Ozone. In this frame, the ALTIUS mission was proposed by the Belgian Institute of Space Aeronomy to contribute to remote atmospheric trace gas monitoring with a high vertical resolution by the combination of limb-scatter measurements with solar, stellar, and planetary occultations. Secondary objectives focus on aerosols, NO2, H2O, CH4 and other trace gases. ALTIUS will be a component of the ESA’s Earth Watch Programme with launch expected in 2021 and a design lifetime of minimum 3 years.
The mission concept aims at bringing the limb scattering and occultation techniques a step further. First, by the introduction of hyperspectral imaging, a method that enables higher pointing calibration accuracy than scanning approaches. Second, by exploiting the synergies between different geometries: solar, stellar, and planetary occultations data not only extend the coverage of the mission beyond that of the limb scattering technique, they enable inter-comparisons across different measurement modes of a same species

OIP, as subcontractor to IASB-BIRA, participated in phases A, B0 and B1 of the ALTIUS project.
OIP will be the industrial prime for the ALTIUS mission and responsible for the development of the ALTIUS instrument during the pre-development and C/D phases.


The ALTIUS mission will consist of a 2D spectral imager, on-board a PROBA satellite, flying at an altitude of approximately 700 km Sun-Synchronous Orbit.

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 ALTIUS could meet the requirements of an operational ozone mission, and 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.
During the previous phase of instrument design, initiated by BELSPO and ESA, some critical aspects of the instrument design and performances have been investigated. In particular the following development have been undertaken.
- Elaboration of the instrument concept, focused on opto-mechanics for each channel, and preliminary integration with the platform.
- UV-channel spectral filter concept trade-off selection
- Preliminary thermal and structural analyses
- Instrument performances budgets and engineering budgets.

The ALTIUS instrument will be built by an industrial consortium on national and international partners (subcontractors) led by OIP, as industrial prime.
For the ALTIUS mission, IASB-BIRA will be the Principal investigator. OIP will be the industrial prime-contractor for the payload, while QinetiQ Space will be the supplier of the satellite and mission prime.


 old representation of the Proba-satellite

  example of AOTF crystal