Linearity Assessment from the Plankton, Aerosol, Cloud, and Ocean Ecosystem Ocean Color Instrument Pre-Launch Testing and On-Orbit Operations

Abstract

Satellite observations have become increasingly important in scientific studies of the Earth’s climate, especially for oceanographic science. A next generation sensor known as the Ocean Color Instrument (OCI) was launched in February 2024 onboard the Plankton, Aerosol, Cloud, and ocean Ecosystem (PACE) platform, and will extend the data set of on-orbit scientific observations used for ocean and atmospheric science research. Delivering high quality data from a space-borne sensor requires the instrument to be well calibrated; while much of the calibration can be performed on-orbit, some aspects of the calibration must be measured or the mechanisms verified pre-launch. One aspect of the OCI calibration that is novel to its design (for a space-based sensor) is its ability to perform linearity measurements on orbit. When viewing the Sun reflected off a dim diffuser with ∼2–3% reflectance, the sensor is capable of recording successive pixels with increasing integration times. The result is a series of light levels measured from the same source in a given scan line. These measurements are then used to assess the linearity. During the pre-launch test campaign, this mechanism was verified using a known source in the Earth view portion of the scan. Results from these tests form a baseline that was verified once on-orbit (and the calibration may be replaced if the linearity is shown to change). The linearity measured both prior to launch and post-launch will be assessed in this work.

Keywords

• PACE
• OCI
• pre-launch
• post-launch
• linearity