LAUSR

The on-orbit calibration performance of the Ocean and Land Color Instrument (OLCI) onboard the Sentinel-3A satellite, launched on February 16, 2016, is evaluated via a radiometric intersensor comparison with reference to the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) satellite. Among the 21 OLCI bands (designated as “Oa” bands), which are reflective solar bands (RSBs), seven OLCI bands match up sufficiently well with the seven shortest wavelength SNPP VIIRS bands (M1–M7)—they are Oa02 at 412.5 nm, Oa03 at 442.5 nm, Oa04 at 490 nm, Oa06 at 560 nm, Oa08 at 665 nm, Oa12 at 754 nm, and Oa17 at 865 nm. The radiometric comparison adopts a “nadir-only” refinement of the simultaneous nadir overpass (SNO) approach and uses the official SNPP VIIRS RSB data processed by the Interface Data Processing Segment (IDPS). The time-series result for bands Oa02, Oa03, Oa08, and Oa17, with spectral coverage that well represents the spectral range of OLCI, shows two-year stability at the level of 0.3% that supports nominally correct on-orbit calibration. The result for Oa08, Oa09, and Oa10, the three spectrally adjacent bands matching M5, demonstrates the effects of spectral mismatch—different radiometric ratio baselines and seasonally modulating patterns. Lastly, this result clarifies some key findings of earlier studies involving SNPP VIIRS and illustrates great potential for significantly more radiometric evaluation activities in the new era of Earth observations with many more powerful multispectral sensors coming into operation.