Experimental evaluation of the self-shadow and its correction for on-water measurements of water-leaving radiance

摘要

Accurate determination of the water-leaving radiance (L-w) is key to correctly interpret in-water optical properties and to validate the atmospheric correction schemes in ocean color studies. Among the various approaches adopted to measure L-w in the field, the skylight-blocked approach (SBA) is the only scheme that can potentially measure L-w directly. However, the apparatus associated with an SBA system will introduce self-shading effects to the measured L-w which is required to be corrected for an accurate L-w determination. In this study, we experimentally evaluate several factors that could contribute to the self-shading effects of the SBA-measured L-w including solar zenith angle (similar to 18 degrees-64 degrees), water's optical properties, and cone size (radius of 22 mm and 45 mm). For waters with the total absorption coefficient at 440 nm as high as similar to 6.0 m(-1), the normalized root-mean-square difference between the SBA-measured L-w after shade correction and the "true" L-w is generally between similar to 5% and similar to 10% for wavelengths in the range of 400-750 nm. These results suggest that SBA can obtain highly accurate and precise L-w in nearly all natural aquatic environments. (C) 2020 Optical Society of America