Ocean reflectance spectra at the red, near‐infrared, and shortwave infrared from highly turbid waters: A study in the Bohai Sea, Yellow Sea, and East China Sea

Normalized water‐leaving radiance spectra nL w ( λ ) at the red, near‐infrared (NIR), and shortwave infrared (SWIR) are quantified and characterized in highly turbid waters of the western Pacific using 3 yr (2009–2011) observations from the Moderate Resolution Imaging Spectroradiometer on the satellite Aqua. nL w (645; red), nL w (859; NIR), and nL w (1240; SWIR) were higher in the coastal region and river estuaries, with SWIR nL w (1240) reaching up to ∼ 0.2 mW cm −2 µm −1 sr −1 in Hangzhou Bay during winter. The NIR ocean‐reflectance spectral shape represented by the ratio of the normalized water‐leaving reflectance ρ w N ( λ ) at the two NIR bands ρ w N (748) : ρ w N (869) is highly dynamic and region‐dependent. The NIR spectral feature associated with the sediment source from the Yellow River and Ancient Yellow River is noticeably different from that of the Yangtze River. There are non‐negligible SWIR nL w (1240) contributions for waters with the NIR nL w (859) > ∼ 2.5 mW cm −2 µm −1 sr −1 . Estimation of the NIR ocean reflectance with iterative approaches might only be accurate for turbid waters with nL w (859) < ∼ 1.5 mW cm −2 µm −1 sr −1 . Thus, the SWIR atmospherics correction algorithm for satellite ocean‐color data processing is indispensable to derive accurate nL w ( λ ) for highly turbid waters. Current existing satellite algorithms for chlorophyll a , diffuse attenuation coefficient at the wavelength of 490 nm ( K d (490)), total suspended matter, and inherent optical properties (IOPs) using nL w ( λ ) at the red band for coastal waters are limited and can only be applied to turbid waters with nL w (859) < ∼ 1.5 mW cm −2 µm −1 sr −1 . Thus, the NIR nL w ( λ ) measurements are required to characterize water properties for highly turbid waters. Based on the fact that pure water absorption is significantly larger than other absorption components in the NIR wavelengths, we show that it is feasible to analytically derive accurate IOP data for turbid waters with combined satellite‐measured visible‐NIR nL w ( λ ) spectra data.