Abstract
The launch of the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission in February of 2024 was a significant step forward for the observation of ocean science data from low Earth orbit. PACE has a payload of two polarimeters and the Ocean Color Instrument (OCI); OCI is the next generation sensor for ocean color science, drawing heritage from sensors such as MODIS, SeaWiFS, and VIIRS, but with increased spectral coverage and improved accuracy. OCI is a grating spectrometer with hyperspectral coverage from the ultraviolet (about 315 nm) to near-infrared (about 895 nm), with additional filtered channels in the short-wave infrared (940 nm – 2260 nm). The calibration of the instrument on-orbit is vital to the maintenance of high quality science data products for the science community. This is accomplished by daily observations of the Sun reflected off a quasi-volume diffuser (a second quasi-volume diffuser is used once a month to monitor the daily diffuser reflectance). With knowledge derived prior to launch of the diffuser BRDF and the spectral acceptance of the detectors, the gain is estimated for every observation. The absolute value of the gain, as well as how the gain trends with time, are derived to allow processing of the raw data into science data products.
PACE OCI On-orbit Solar Calibration
The launch of the Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission in February of 2024 was a significant step forward for the observation of ocean science data from low Earth orbit. PACE has a payload of two polarimeters and the Ocean Color Instrument (OCI); OCI is the next generation sensor for ocean color science, drawing heritage from sensors such as MODIS, SeaWiFS, and VIIRS, but with increased spectral coverage and improved accuracy. OCI is a grating spectrometer with hyperspectral coverage from the ultraviolet (about 315 nm) to near-infrared (about 895 nm), with additional filtered channels in the short-wave infrared (940 nm – 2260 nm). The calibration of the instrument on-orbit is vital to the maintenance of high quality science data products for the science community. This is accomplished by daily observations of the Sun reflected off a quasi-volume diffuser (a second quasi-volume diffuser is used once a month to monitor the daily diffuser reflectance). With knowledge derived prior to launch of the diffuser BRDF and the spectral acceptance of the detectors, the gain is estimated for every observation. The absolute value of the gain, as well as how the gain trends with time, are derived to allow processing of the raw data into science data products.