System vicarious calibration of GCOM-C/SGLI visible and near-infrared channels

Vicarious calibration coefficients (kv) of Second-generation GLobal Imager (SGLI) for ocean color processing were derived using in-situ radiometric buoy measurements from the Marine Optical BuoY (MOBY) and the BOUée pour l'acquiSition d'une Série Optique à Long termE (BOUSSOLE). Two aerosol-model look up tables (LUTs) used in the GCOM-C aerosol retrieval algorithm (LUT-A) and in the previous version of ocean color atmospheric correction algorithm (LUT-B) were tested in the procedures to calculate kv and retrieve remote sensing reflectance (Rrs) and aerosol optical thickness (AOT). Bias of the processed Rrs compared to AERONET-OC Rrs was reduced by applying the determined kv (i.e., corrected SGLI radiance = original SGLI radiance/kv). LUT-A yielded smaller AOT bias compared to AERONET-OC AOT; on the other hand, LUT-B gave smaller Rrs noise due to gentle slope of the aerosol reflectance even though it caused AOT overestimation. When kv was derived by adjusting to the AOT measurements, kv was about 1.1 by LUT-A and 1.2 by LUT-B in the near-infrared (NIR) channel. However, the kv in the NIR channel was close to 1.0 when AOT and land surface reflectance measurements of Radiometric Calibration Network (RadCalNet) were used. The LUT-A with kv from MOBY and BOUSSOLE are currently adopted for the SGLI standard ocean color processing. Improvement is needed, however, to design an optimal LUT suitable for both aerosol and ocean color purposes.