Euphotic zone depth: Its derivation and implication to ocean‐color remote sensing

Abstract

[1] 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 nearanalytically 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 $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 $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.

Bio-Optical Characterization and Ocean Colour Inversion in the Eastern Lagoon of New Caledonia, South Tropical Pacific

“…The aphy(443) varied from 0.007 ± 0.0003 to 0.037 ± 0.002 m −1 , with an average of 0.018 ± 0.007 m −1 ( Figure 4A), and a positive co-variation with Chla (R 2 = 0.86). Variability in the relation between aphy(443) and Chla can be due to non-linear packaging effects associated to the phytoplankton community structure and photo-adaptation processes [27,28,31]. The specific absorption coefficient aphy*(443) (normalized by Chla) varied from 0.032 to 0.067 m 2 ·mgChla −1 , with an average of 0.049 ± 0.008 m 2 ·mgChla −1 ( Figure 4A), typical of populations mostly dominated by nanoplankton cells [28], as found in New Caledonia coastal lagoons [10,43,44].…”

Intercomparison of Ocean Color Algorithms for Picophytoplankton Carbon in the Ocean

“…The OC-CCI version 2 data had a daily sinusoidal projection (binned) and a 4 km spatial resolution. These satellite data were used as inputs for C phy algorithms: total B from OC4v6, b bp from the Quasi-Analytical Algorithm (QAA) v5 (a modification to v4 in Lee et al, 2002Lee et al, , 2007, but that does not include Raman scattering, Westberry et al, 2013;Lee and Huot, 2014). Second, the water class membership (Moore et al, 2001(Moore et al, , 2009Jackson et al, 2017).…”

“…The backscattering coefficient in this study is obtained from the OC-CCI merged dataset by applying the algorithm by the Quasi-Analytical Algorithm (QAA) v5 (a modification to v4 in Lee et al, 2002Lee et al, , 2007. In essence, the QAA first computes b bp (555), from combining remote sensing reflectance at 555 nm with an empirical relationship between remote sensing reflectance ratios and the total absorption coefficient and the backscattering of pure seawater (modeled).…”

Satellite-Derived Photic Depth on the Great Barrier Reef: Spatio-Temporal Patterns of Water Clarity

“…Recent progress in remote sensing applications includes the development of bio-optical algorithms for determining the photic depth (Z % ; units of m) from the observed satellite radiances. Z % is a measure of water clarity [4] with, for example, Z 1% reflecting the depth where only 1% of the surface irradiance (PAR, photosynthetic available radiation; units of µE· cm 2 · s −1 ) remains.…”