In the Optical Assembly the incident radiance and irradiance are collected and split according to wavelength and focussed on the detector modules of the two optical channels. The Optical Bench consists of a single aluminium structure in which all elements are mounted. Attached to this aluminium structure are the two Detector Modules. The Optical Assembly Thermal Hardware consists of a thermal radiator and heaters. The thermal radiator is thermally connected to the detector modules via cold-fingers and flex-links. The heaters are attached to the Optical Bench structure and the CCD detectors.
The OMI spectrometer is sensitive to the polarisation of the incident radiation (originating from the polarisation dependence of mirrors, dichroics and gratings). Therefore, Earth radiances with exactly the same intensity but a different polarisation state will yield different detector signals. The purpose of the polarisation scrambler is to make the instrument insensitive to the polarisation of the incident radiation.
In principle the scrambler transforms one polarisation state into a continuum of polarisation states and thus not into real totally unpolarized light. Therefore a scrambler is called a pseudo-depolariser. For OMI a spatial pseudo-polariser is applied, which transforms the polarisation state of the input into a polarisation state that varies with position over the scrambler exit aperture. Polarisation effects originating from the primary uncoated aluminium mirror are compensated for by the first scrambler surface, that is intentionally left uncoated.