Characterization and video chain development of the CMOS detector applied in the multi-angle spectro-polarimeter SPEXone

This contribution presents the on-ground characterization and video chain development of the CMOS detector implemented in SPEXone, the five-angle space spectro-polarimeter for the NASA PACE observatory scheduled for launch in 2023. SPEXone is a Dutch compact payload contribution developed in a partnership between SRON and ADSN, and supported by TNO. Making use of spectral modulation, this polarimeter will enable in-depth and global characterization of the microphysical properties of fine particulate matter or aerosols in the atmosphere from low Earth orbit. In SPEXone, the spectrally modulated images are captured by means of a commercial-off-the-shelf detector module (DEM) from 3Dplus, which is equipped with a CMOS image sensor with integrated front-end-electronics. Video chain developments, including DEM firmware, read-out, flexible binning and DEM interfacing through SpaceWire have been carried out in-house. Making use of the firmware, the optimal detector parameters with associated random noise, full-well capacity, and photo response non-uniformity (PRNU) of the DEM were determined by placing the DEM in front of an integrating sphere fiber-fed with a stable white light source with accurately adjustable intensity and a highly linear reference detector, providing highly uniform illumination of the whole detector area at well-known relative light intensities. The rationale behind the measurement sequences is explained, and the full-well and read noise performance under different gain settings is described. The full-well capacity of the DEM is found to be not constant, but increasing significantly with illumination intensity.