On-Orbit System Vicarious Calibrations for Three VIIRS Sensors Using the NIR-SWIR Ocean Color Data Processing Approach

The Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the NOAA-21 satellite was launched in November 2022 as a new VIIRS adding to the constellation of the Joint Polar Satellite System (JPSS) mission, which includes the Suomi National Polar-orbiting Partnership (SNPP) (October 2011 to present) and NOAA-20 (November 2017 to present). For satellite ocean color (OC) remote sensing, the on-orbit system vicarious calibration (SVC) for deriving sensor spectral gain factors must be carried out. In this article, we document our work to obtain SVC gains for the three VIIRS sensors covering the spectral bands of visible, near-infrared (NIR), and shortwave infrared (SWIR) using a consistent NIR-SWIR SVC approach. Specifically, we derive SVC gains using the in situ normalized water-leaving radiance nL(w)(lambda) spectra from the Marine Optical Buoy (MOBY) in the Hawaii ocean region with the updated NOAA Multi-Sensor Level-1 to Level-2 (MSL12) data processing system. For VIIRS moderate (M) resolution and imaging (I) bands of M1-M4, I1, M5-M8, M10, and M11, VIIRS SVC gain sets for SNPP, NOAA-20, and NOAA-21 are (0.9752, 0.9732, 0.9772, 0.9685, 1.0090, 0.9750, 0.9765, 1.0000, 1.0050, 0.9960, and 1.0230), (1.0044, 1.0098, 1.0051, 1.0073, 1.0301, 1.0136, 1.0052, 1.0000, 1.0435, 1.0235, and 1.0330), and (1.0284, 1.0317, 1.0165, 1.0231, 1.0236, 1.0137, 1.0051, 1.0000, 0.8982, 0.8779, and 0.8434), respectively. The SVC gains derived using the NIR and SWIR data processing approaches are highly consistent. For example, SVC gain differences at VIIRS M2 blue band between using the NIR (M6 and M7) and SWIR (M8 and M10) SVC methods are 0.021%, -0.010%, and 0.010% for SNPP, NOAA-20, and NOAA-21, respectively. With the new SVC gain sets, the three VIIRS mission-long OC data can be reprocessed. Results over the MOBY site show that reprocessed VIIRS OC products are accurate and consistent, compared to those from in situ measurements. In addition, we have used Rayleigh-corrected reflectance over the Hawaii clear ocean region in a 16-day period of November 17-December 2, 2023, to demonstrate and verify the effectiveness of the SVC gains for the three VIIRS sensors.