## Abstract

Accurate estimation of the diffuse attenuation coefficient is important for our understanding the availability of light to underwater communities, which provide critical information for the China seas ecosystem. However, algorithm developments and validations of the diffuse attenuation coefficient in the China seas have been seldom performed before and therefore our knowledge on the quality of retrieval of the diffuse attenuate coefficient is poor. In this paper optical data at 306 sites collected in coastal waters of the China seas between July 2000 and February 2004 are used to evaluate three typical existing *K _{d}*(490) models. The

*in situ K*(490) varied greatly among different sites from 0.029 m

_{d}^{−1}to 10.3 m

^{−1}, with a mean of 0.92 ± 1.59 m

^{−1}. Results show that the empirical model and the semi-analytical model significantly underestimate the

*K*(490) value, with estimated mean values of 0.24 m

_{d}^{−1}and 0.5 m

^{−1}, respectively. The combined model also shows significant differences when the

*in situ K*(490) range from 0.2 m

_{d}^{−1}to 1 m

^{−1}. Thus, the present study proposes that the three algorithms cannot be directly used to appropriately estimate

*K*(490) in the turbid coastal waters of the China seas without a fine tuning for regional applications. In this paper, new

_{d}*K*(490) algorithms are developed based on the semi-analytical retrieval of the absorption coefficient

_{d}*a*(m

^{−1}) and the backscattering coefficient

*b*(m

_{b}^{−1}) from the reflectance at two wavelengths, 488 and 667 nm for the Moderate Resolution Imaging Spectroradiometer (MODIS) and 490 and 705 nm for the Medium Resolution Imaging Spectrometer (MERIS) applications, respectively. With the new approaches, the mean ratio and the relative percentage difference are 1.05 and 4.6%, respectively, based on an independent

*in situ*data set. Furthermore, the estimates are reliable within a factor of 1.9 (95% confidence interval). Comparisons also show that the

*K*(490) derived with the new algorithms are well correlated with the

_{d}*in situ*measurements. Our results showed a good improvement in the estimation for

*K*(490) using the new approaches, contrasting with existing empirical, semi-analytical and combined models. Therefore, we propose the new approaches for accurate retrieval of

_{d}*K*(490) in the China seas.

_{d}©2013 Optical Society of America

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