S-NPP and NOAA-20 VIIRS TEB response-versus-scan-angle assessment using an in situ ocean scene

The VIIRS sensors onboard the Suomi National Polar-orbiting Partnership (S-NPP) and NOAA-20 spacecraft have provided high-quality data to the scientific community for over a decade and four years, respectively. VIIRS has 7 Thermal Emissive Bands (TEB) whose central wavelengths cover the 3.7 mu m to 12.0 mu m spectra. These channels are calibrated on-orbit using observations from its on-board blackbody. In the past, the efficacy of the prelaunch-derived response-versus-scan-angle (RVS) of the VIIRS TEB has been assessed postlaunch using on-orbit data from a deep space pitch maneuver and was found to be reasonable. However, vicarious calibration practices involving Earth targets can also be used to track the long-term stability of the RVS for both VIIRS instruments in orbit. This manuscript focuses on evaluating the VIIRS TEB RVS stability using an in situ ocean target - moored buoy located in the Pacific Ocean that belongs to the NOAA's National Data Buoy Center - as reference. Cloud-free VIIRS TEB retrievals are used in this study. A normalization methodology is applied to standardize the VIIRS data to the in situ data. Results indicate that the S-NPP VIIRS TEB on- orbit performance appears to be quite stable with display marginal change rates (<= 0.006 K/yr), while the N20 VIIRS TEB display change rates no larger than -0.013 K/yr (except for bands M13, M14, and I5). The on-orbit RVS assessment demonstrates stable long-term trends that remain under the radiometric requirements (0.5 K) for most VIIRS TEB and angles-of-incidence with a few exceptions at the close-to- or edge-of-scan angles-of-incidence. Analogous methods can be used to assess the TEB on-orbit RVS stability of the VIIRS instruments that will be onboard the to-be-launched Joint Polar Satellite System-2 (JPSS-2), JPSS-3, and JPSS-4 satellites.