An algorithm to retrieve absorption coefficient of chromophoric dissolved organic matter from ocean color

Abstract

We extended the quasi-analytical algorithm (QAA) architecture to analytically derive absorption coefficient of chromophoric dissolved organic matter (ag). Specifically, we used an empirical formula based on total absorption and particle backscattering coefficients to estimate and then remove detritus absorption coefficient (ad), and developed a scheme to use absorption coefficients at three wavelengths (412, 443, and 490nm) for the separation of ag and aph (absorption coefficient of phytoplankton). The algorithm was tested using an in situ data set collected in the South China Sea and the Taiwan Strait and a global in situ data set—the NASA Bio-Optical Marine Algorithm Data set (NOMAD). Our results indicated that this new analytical algorithm for retrieving ag performed reasonably well with a mean absolute percentage error of approximately 45% for ag(412), while it also presented a satisfactory performance for aph and ad in both coastal and oceanic waters. Furthermore, the applicability of this new algorithm for general oceanographic studies was briefly illustrated by applying it to MODIS measurements over the Taiwan Strait and the shelf region near the Mississippi River delta. Nevertheless, more independent tests with in situ and satellite data are needed to further validate and improve this innovative approach.