Pre-Launch Polarization Assessment of JPSS-2 VIIRS VNIR Bands

Abstract

The Visible Infrared Imaging Radiometer Suite (VIIRS) instruments on-board the Suomi National Polar-orbiting Partnership (S-NPP), National Oceanic and Atmospheric Administration 20 (NOAA-20) and Joint Polar Satellite System (JPSS-2) spacecraft, with launch dates of October 2011, November 2017 and late 2022, respectively, have polarization sensitivity that affects the at-aperture radiometric Sensor Data Record (SDR) calibration in the Visible Near InfraRed (VNIR) spectral region. These SDRs are used as inputs into the VIIRS atmospheric, land, and water Environmental Data Records (EDRs) that are integral to climate and weather applications. Pre-launch characterization of the VIIRS polarization sensitivity was performed that provides an SDR radiance correction factor to enable high fidelity EDR products for the user community. The pre-launch polarization sensitivity used an external source that consisted of a 100 cm diameter Spherical Integrating Source (SIS) in combination with several sheet polarizers. These sheet polarizers were illuminated by the SIS and viewed by the VIIRS instrument. The sheet was then rotated to measure the variation in the VIIRS response relative to the at-aperture polarization orientation. There are sensor requirements that define the maximum allowed polarization amplitude to be below 2.5–3.0% depending on the band and have an uncertainty in both amplitude and phase of less than 0.5%. The pre-launch data analysis evaluated the VIIRS response through the rotating sheet polarizer to quantify each VNIR bands polarization amplitude, phase, and uncertainty. These parameters were compared with the sensor requirements and used to create on-orbit Look-Up Tables (LUTs) for EDR ground processing. The results of the analysis showed that all bands met the uncertainty requirement of 0.5%, but band M1 failed the 3% polarization amplitude requirement. A root-cause analysis identified the optical element responsible for the non-compliance and has been modified for JPSS-3 and -4 builds. The large polarization amplitudes observed in the NOAA-20 VIIRS build, for bands M1-M4, are greatly reduced for JPSS-2 VIIRS. This improved polarization performance was due to modifications to the band M1-M4 bandpass filters between these sensor builds.