SPEXone is a compact multi-angle spectropolarimeter that measures both spectral intensity and the state of linear polarization of light scattered by aerosols in the Earth’s atmosphere at five different viewing angles simultaneously. This enables a very accurate quantification and characterization of atmospheric aerosols, helping us to better understand their effects on global climate and air quality. Building upon the success of its predecessor SPEXone, which has been launched in 2024 as part of the NASA PACE observatory, a second and improved instrument, SPEXone Second Generation, has been built within the ESA PRODEX program. Most recently, the integrated instrument underwent full on-ground characterization and calibration in ambient conditions at SRON. This contribution gives an overview of the measurements and presents preliminary results from the characterization and calibration campaign, focusing on the instrument performance. A few key performance aspects such as straylight, spatial and spectral resolution are discussed, with data from SPEXone for PACE serving as a comparison. The result of the analysis shows excellent image quality and indicates an improvement in the amount of diffuse straylight.
In this contribution, the detector-characterization results and some of the on-ground calibration plans are presented for an adjusted and improved SPEXone satellite instrument. SPEXone is a highly compact multi-angle space spectro-polarimeter developed by a Dutch consortium for the NASA PACE observatory scheduled for launch early 2024. This instrument will enable detailed characterization of the microphysical properties of fine particulate matter or aerosols in the atmosphere from low Earth orbit, which is essential for climate, ecosystem, and human-health science. A successor to the SPEXone instrument is currently being developed, with a wider swath as the main change (250 km instead of 100 km), and with several design improvements to reduce straylight. The detector firmware was adjusted to enable the required higher frame rate, and to make the readout more robust. The detector was characterized in a similar way as for PACE, though even more extensively based on lessons learned. In particular, full illumination measurements were complemented with partial illumination measurements, where parts of the detector are covered using dedicated detector masks, to investigate peculiar signal-induced offset effects that were observed only late for PACE. Additionally, direct memory measurements were performed using time-dependent illumination generated using a fast electronic shutter. Following the detector characterization, instrument-calibration preparations have started. The instrument will be fully calibrated in ambient, complemented with a highly selective set of measurements in vacuum. The approach followed will be similar to PACE, but modifications will be made to deal with the increased swath. Important improvements will be implemented to improve the data quality, such as increased number of wavelengths for straylight measurements.
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