Performance of two semi-analytical algorithms in deriving water inherent optical properties in the Southern Ocean

Remotely sensed inherent optical properties (IOPs) are key proxies for synoptic mapping of primary production and carbon export in the global ocean. However, the IOPs inversion algorithms are scarcely evaluated in the Southern Ocean (SO) because of limited field observations. In this study, the performance of two widely used semi-analytical algorithms (SAAs), i.e., the quasi-analytical algorithm (QAA) and the generalized IOP model (GIOP), were evaluated using a compiled in situ bio-optical dataset in SO, as well as measurements from the Visible Infrared Imaging Radiometer Suite (VIIRS). Evaluations with in situ data show that QAA and GIOP have comparable performance in retrieving the total absorption coefficient (a(λ)), absorption coefficients of phytoplankton (a_ph(λ)), and that of detritus and colored dissolved organic matter (a_dg(λ)). Overall, it was found that remotely sensed a(λ) and a_ph(λ) by both SAAs agreed well with field measurements, with the mean absolute percentage difference (MAPD) of derived a(λ) and a_ph(λ) in the blue-green bands being ∼20% and ∼40%, respectively. However, derived a_dg(λ) by both SAAs were higher than the measured values at the lower end (a_dg(443) < ∼0.01 m^-1), but lower at the higher end (a_dg(443) > ∼0.02 m^-1), with MAPD of ∼60%. Results of this effort suggest confident products of a(λ) and a_ph(λ) from VIIRS in SO, but more dedicated efforts on the measurements and evaluation of a_dg(λ) in SO would be desired.