JPSS-1VIIRS Prelaunch Polarization Testing and Performance

The Visible Infrared Imaging Radiometer Suite (VIIRS) instruments onboard both the Suomi National Polar-orbiting Partnership (S-NPP) and the first Joint Polar Satellite System (JPSS-1) spacecraft, with launch dates of October 2011 and late 2016, respectively, have polarization sensitivity, which affects the at-aperture radiometric calibration. This polarization sensitivity is caused by optics within VIIRS having different reflectance and transmission values as a function of at-aperture photon electric field orientation and is spectrally, spatially, and scan angle dependent. Characterization of the instrument's polarization sensitivity for each visible near-infrared (VNIR) band and detector was performed prelaunch at multiple cross-track scan angles. The resultant characterization parameters are VIIRS polarization amplitude and phase that enable the at-aperture radiance to be adjusted based on its polarization characteristics. The sensor requirements are that the polarization amplitude for scan angles within ±45° of nadir be below 2.5%-3% depending on the band and have an uncertainty in both amplitude and phase of less than 0.5%. The S-NPP VIIRS passed these requirements with band M1 (412 nm) having the smallest margin (~8%). Modification to the VNIR bandpass filter designs on JPSS-1 was performed to reduce out-of-band response leaks observed prelaunch on S-NPP. An unintended consequence of the spectral bandpass modification was an increase in the polarization sensitivity by roughly a factor of 2 for some VNIR bands. The degree to which JPSS-1 VIIRS polarization sensitivity characterization results exceed the sensor specifications and comparisons with S-NPP will be discussed.