The MERMOZ project used for its feasibility study an instrument baseline based on TreePol (Patty et al. 2017) developed at the Leiden University. In 2019, we modified the TreePol concept into FlyPol, which became the airborne version of the instrument. FlyPol includes several improvements over TreePol to improve overall stability.
The picture below shows the initial TreePol instrumental design as detailed in Patty et al. (2017).
In 2019 our team developed FlyPol+, which includes, in addition to TreePol/FlyPol, linear polarisation capability and uses a super-achromatic quarter-wave plate in lieu of the Fresnel rhomb as retarder. This instrument will be the version used for our next flight campaigns.