An analysis of diffuse attenuation coefficients for downward irradiance in the KORUS-OC dataset and GOCI data

Abstract

The diffuse attenuation coefficient for downward irradiance (Kd) is an important property for estimation of clarity of ocean, and it is closely related to the in water visibility. The models for estimating the Kd from ocean color imagery can be divided into an empirical (Austin and Petzold, 1981 Mueller and Trees, 1997 Mueller, 2000 Morel, 1988 Morel and Maritorena, 2001) and semianalytic algorithm (Sathyendranath and Platt, 1997 Lee et al., 2005). In this study, the Kd models are evaluated using in situ and GOCI data and modified for accurate GOCI-derived Kd. The in situ data is analyzed firstly using the Korea-US joint field campaign for ocean color research (KORUS-OC) data. The Kd and remote sensing reflectance were measured using the profiler-II, which provides optical measurements of downward irradiances and upwelling radiances. Especially this study focuses on a highly turbid region (i.e. Total suspended matter concentration is over than 100 g/m3), where many existing algorithms tend to underestimate Kd. We also discuss the effect of the Kd accuracy on the GOCI Secchi disk depth which represents optical visibility.n be divided into an empirical (Austin and Petzold, 1981 Mueller and Trees, 1997 Mueller, 2000 Morel, 1988 Morel and Maritorena, 2001) and semianalytic algorithm (Sathyendranath and Platt, 1997 Lee et al., 2005). In this study, the Kd models are evaluated using in situ and GOCI data and modified for accurate GOCI-derived Kd. The in situ data is analyzed firstly using the Korea-US joint field campaign for ocean color research (KORUS-OC) data. The Kd and remote sensing reflectance were measured using the profiler-II, which provides optical measurements of downward irradiances and upwelling radiances. Especially this study focuses on a highly turbid region (i.e. Total suspended matter concentration is over than 100 g/m3), where many existing algorithms tend to underestimate Kd. We also discuss the effect of the Kd accuracy on the GOCI Secchi disk depth which represents optical visibility.