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

Accurate determination of the water-leaving radiance () 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 in the field, the skylight-blocked approach (SBA) is the only scheme that can potentially measure directly. However, the apparatus associated with an SBA system will introduce self-shading effects to the measured , which is required to be corrected for an accurate determination. In this study, we experimentally evaluate several factors that could contribute to the self-shading effects of the SBA-measured , including solar zenith angle (∼18-64), 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 ∼6.0, the normalized root-mean-square difference between the SBA-measured after shade correction and the "true" is generally between ∼5 and ∼10 for wavelengths in the range of 400-750 nm. These results suggest that SBA can obtain highly accurate and precise in nearly all natural aquatic environments.