Characteristics of water leaving reflectance at ultraviolet wavelengths: radiative transfer simulations

Ultraviolet (UV) bands have attracted considerable attention in regard to satellite ocean color remote sensing due to their potential application in atmospheric correction, oil spill detection, and water organic matter retrieval. However, the characteristics of the water spectrum in the UV bands are still poorly understood. In this study, by extending the bio-optical model from traditional visible light wavelengths to UV light wavelengths, the water spectrum in UV bands under different water types was simulated by using the HydroLight water radiative transfer model, and influences of ocean color components on the water spectrum in UV bands were investigated. Results showed that remote sensing reflectance (Rrs) in the UV bands decreased rapidly with the increase in chlorophyll concentration (Chl) and colored dissolved organic matter (CDOM). In clean waters, Rrs in the UV bands was relatively large and sensitive to changes in Chl and CDOM, which could be of benefit for satellite retrieval of water organic matter. In eutrophic water, Rrs in the UV bands was quite low, and thence the UV bands could be used as a reference band for atmospheric correction. Compared to the monotonic decreasing effects of Chl and CDOM, concentration of non-algal particles (NAP) had a complex effect on Rrs in the UV bands, i.e., increase and decrease in Rrs in low-moderately and highly turbid waters, respectively. Thus, the traditional model for the relationship between Rrs and inherent optical properties (IOPs) could be applied to the UV bands in clean waters; in highly turbid waters, however, its deviation increases and empirical coefficients in the model should be improved.