Abstract
The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, recently launched in February of 2024, has a payload of two polarimeters and the Ocean Color Instrument (OCI). OCI is the next generation sensor for ocean color science from low Earth orbit, 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). In order to maintain the high levels of accuracy demanded by the science community, the sensor calibration is monitored on-orbit. The hyperspectral channels on OCI have a special operating mode in which images of varying integrations times can be measured in a single scan line. This mode in conjunction with solar observations via a dim diffuser (with ~2-3 % reflectance) allows OCI to collect images covering the dynamic range in a single scan. This data can then be used to assess the linearity of the system, comparing to measurements made prior to launch, assess the stability of the system, and possibly update the calibration algorithm. Linearity measurements are made every month and the results are trended over the mission.
Assessment of PACE OCI Linearity Prelaunch and On-orbit
The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission, recently launched in February of 2024, has a payload of two polarimeters and the Ocean Color Instrument (OCI). OCI is the next generation sensor for ocean color science from low Earth orbit, 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). In order to maintain the high levels of accuracy demanded by the science community, the sensor calibration is monitored on-orbit. The hyperspectral channels on OCI have a special operating mode in which images of varying integrations times can be measured in a single scan line. This mode in conjunction with solar observations via a dim diffuser (with ~2-3 % reflectance) allows OCI to collect images covering the dynamic range in a single scan. This data can then be used to assess the linearity of the system, comparing to measurements made prior to launch, assess the stability of the system, and possibly update the calibration algorithm. Linearity measurements are made every month and the results are trended over the mission.