Development of an AOTF-based hyperspectral imager for atmospheric remote sensing

The evolution of atmospheric composition is a complex and living research area. Models need data on a global scale in order to follow, reproduce and forecast the spatio-temporal fields of key species and identify their contribution in the Earth radiative balance. In many aspects, the vertical distribution of these species is an important parameter. Unfortunately, the number of spaceborne sounders capable of providing such information is decreasing. Moreover, the instrumental concepts deployed so far suffer from tangent altitude registration issues. In the particular frame of ozone recovery, this causes large uncertainties compared to the small trends to be observed. IASB-BIRA has proposed a new spaceborne instrument called ALTIUS. It is a full mission concept aiming at the acquisition of spectral images in limb-scattering and occultation geometries. The spectral selection is performed by an acousto-optical tunable filter (AOTF) and the PROBA-class satellite will offer good pointing control and manoeuvrability. Altogether, the measurement modes, the hyperspectral images, and the spacecraft performance will ensure low-uncertainty and high-vertical resolution geophysical products. This work addresses important aspects in the development of ALTIUS. The imaging capability is first applied to the inversion of atmospheric pressure profiles from the analysis of the apparent flattening of a setting Sun. Then the spectral feature is added such that the simulation of limb-scattering measurements yield the final error budget of O3 and NO2 profiles. A complete description of the AOTF is also provided and the performance of two units operating in the UV and VIS ranges is examined in laboratory experiments. Finally, a prototype is used to demonstrate remote sensing capabilities with the detection of NO2 in industrial smokes.