Euphotic Zone Depth: Its Derivation and Implication to Ocean-Color Remote Sensing

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euphotic depth, inherent optical properties, ocean‐color remote sensing, water clarity

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Euphotic zone depth, z(1%), reflects the depth where photosynthetic available radiation ( PAR) is 1% of its surface value. The value of z(1%) is a measure of water clarity, which is an important parameter regarding ecosystems. Based on the Case-1 water assumption, z(1%) can be estimated empirically from the remotely derived concentration of chlorophyll-a ([ Chl]), commonly retrieved by employing band ratios of remote sensing reflectance ( R-rs). Recently, a model based on water's inherent optical properties ( IOPs) has been developed to describe the vertical attenuation of visible solar radiation. Since IOPs can be near-analytically calculated from R-rs, so too can z(1%). In this study, for measurements made over three different regions and at different seasons ( z(1%) were in a range of 4.3-82.0 m with [ Chl] ranging from 0.07 to 49.4 mg/m(3)), z(1%) calculated from R-rs was compared with z(1%) from in situ measured PAR profiles. It is found that the z(1%) values calculated via R-rs-derived IOPs are, on average, within similar to 14% of the measured values, and similar results were obtained for depths of 10% and 50% of surface PAR. In comparison, however, the error was similar to 33% when z(1%) is calculated via R-rs-derived [ Chl]. Further, the importance of deriving euphotic zone depth from satellite ocean-color remote sensing is discussed.

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Journal of Geophysical Research - Oceans, v. 112, no. C3, article C03009.