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We present algorithms for the estimation of the vertical diffuse attenuation coefficient, K d (m −1 ), and the beam attenuation coefficient, c (m −1 ), at 490 nm from irradiance reflectance. Our aim is to retrieve as analytically as possible K d (490) + c (490) −1 , a proxy for vertical visibility. The two algorithms are based on the semianalytical retrieval of the absorption coefficient a (m −1 ) and the backscattering coefficient b b (m −1 ) from reflectance at two wavelengths, 490 and 709 nm. The use of a near‐infrared wave band allows a small number of simple assumptions to be made, (1) light absorption at 709 nm is only due to pure seawater, and (2) there exists a constant ratio between the particulate backscattering coefficients at 490 and 709 nm. To estimate c (490), we developed an empirical relationship between b and b b for particles. Algorithm development, testing, and validation are achieved using data from the literature, a synthetic data set, and a large in situ data set of inherent and apparent optical properties measured in various environments. The algorithms are found to be valid both in coastal and oceanic waters, and largely insensitive to regional peculiarities in the inherent optical properties. The values of K d (490) and c (490) are retrieved within a factor of 2.21 and 2.91 (95% confidence interval), respectively, using independent in situ data sets. This performance for K d (490) is better or comparable to that of recently published algorithms. This study opens the way to the development of simple semianalytical ocean color algorithms that make the best use of spectral information.
Doron et al. (Fri,) studied this question.