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

摘要

Euphotic zone depth, Z1%, reflects the depth where photosynthetic available radiation (PAR) is 1% of its surface value. The value Of Z1% is a measure of water clarity, which is an important parameter regarding ecosystems. Based on the Case-1 water assumption, Z1% can be estimated empirically from the remotely derived concentration of chlorophyll-a (Chl), commonly retrieved by employing band ratios of remote sensing reflectance (Rrs). Recently, a model based on water's inherent optical properties (IOPs) has been developed to describe the vertical attenuation of visible solar radiation. Since lOPs can be near-analytically calculated from Rrs, so too can Z1%. In this study, for measurements made over three different regions and at different seasons (Z1% were in a range of 4.3-82.0 m with (Chl) ranging from 0.07 to 49.4 mg/m3), Z1% calculated from Rrs was compared with Z1% from in situ measured PAR profiles. It is found that the Z1% values calculated via Rrs-derived lOPs are, on average, within 14% of the measured values, and similar results were obtained for depths of 10% and 50% of sufface PAR. in comparison, however, the error was 33% when Z1% is calculated via Rrs-derived (ChI). Further, the importance of deriving euphotic zone depth from satellite ocean-color remote sensing is discussed.