## Abstract

To achieve a smooth transition between algorithms for “clear” water and “turbid” water, we propose a single formula to calculate the input parameter ($ip$) used for empirical retrieval of absorption coefficients ($a$) or chlorophyll concentration ([Chl]) from remote-sensing reflectance (${R}_{rs}$). This formula for $ip$ takes the ratio of the maximum ${R}_{rs}$ in the blue-green bands to the sum of ${R}_{rs}$(green) and the scaled ${R}_{rs}$ in the red and infrared bands (termed as $i{p}_{\text{Max-Sum}}$). We found that, compared to the widely used OC4-type formula for $ip$, $i{p}_{\text{Max-Sum}}$ can improve the coefficient of determination from $\sim 0.88$ to 0.99 for absorption coefficient at 440 nm [$a(440)$] in $\sim 0.01\u201320.0\text{\hspace{0.17em}}\text{\hspace{0.17em}}{\mathrm{m}}^{\u20131}$ ([Chl] $\sim 0.01\u2013500\text{\hspace{0.17em}}\text{\hspace{0.17em}}\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{\u20133}$). Especially, the sensitivity of $i{p}_{\text{Max-Sum}}$ to the change in $a(440)$ is about five times greater than that of OC4-type for $a(440)>\sim 1.0\text{\hspace{0.17em}}\text{\hspace{0.17em}}{\mathrm{m}}^{-1}$ ($[\mathrm{Chl}]>\sim 10\text{\hspace{0.17em}}\text{\hspace{0.17em}}\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{-3}$). These results indicate an advantage of $i{p}_{\text{Max-Sum}}$ for generating robust and seamless $a(440)$ or [Chl] from clear to highly turbid waters. The inclusion of such a scheme in a quasi-analytical algorithm is also presented.

© 2019 Optical Society of America

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