Evaluation of near-blue UV remote sensing reflectance over the global ocean from SNPP VIIRS, PACE OCI, and GCOM-C SGLI

Solar radiation in the ultraviolet (UV) bands plays an important role in marine biogeochemical processes, and at the same time, measurements of a satellite sensor in the UV help the data processing of ocean color satellites. However, historically, satellite ocean color missions lack UV measurements; only in recent years have there been satellite sensors, such as PACE OCI, to provide a direct measurement of radiance in the near-blue UV (nbUV) domain. To address the limitation of earlier measurements, a deep-learning-based system (termed UVISR_dl) has been previously introduced to estimate remote-sensing reflectance (<i>R</i>_rs) of the nbUV bands at 360, 380, and 400 nm from <i>R</i>_rs(visible). In this study, as PACE OCI offers global-ocean hyperspectral <i>R</i>_rs products from UV to visible bands, we leveraged this opportunity to comprehensively evaluate the performance of this UVISR_dl system and compare the <i>R</i>_rs(nbUV) among VIIRS, OCI, and SGLI. It is found that the <i>R</i>_rs(nbUV) values from VIIRS and OCI exhibit high consistency, with mean absolute unbiased relative difference (MAURD) ranging from ~0.23-0.30 at 360 nm, ~0.21-0.22 at 380 nm, and ~0.17-0.20 at 400 nm, while the SGLI shows lower consistency compared to the former two (MAURD = ∼0.47 at 380 nm). More importantly, the consistency assessment metrics in <i>R</i>_rs(nbUV) between VIIRS and OCI are nearly the same, regardless of whether the OCI <i>R</i>_rs(nbUV) were derived from UVISR_dl or measured directly. These findings demonstrate UVISR_dl's potential for extending global-scale UV reflectance back into periods lacking direct UV observations, enabling the generation of long-term remote-sensing products, and deepening our understanding of the interactions between UV radiation and biogeochemical processes in the global ocean.