108 / 2023-07-31 09:16:53

Evaluation of the semi-analytical algorithms for the remote sensing of inherent optical properties in the Southern Ocean

Southern Ocean,IOPs,Evaluation

Remotely sensed inherent optical properties (IOPs) are the key proxies for synoptic mapping of the primary production and carbon export in the Southern Ocean (SO), yet the inversion algorithms of IOPs are scarcely evaluated in SO due to limited field observations. In this study, we evaluated the performance of two widely used semi-analytical algorithms (SAAs) in SO, i.e., the quasi-analytical algorithm (QAA) and the generalized IOP model (GIOP), using a compiled in-situ bio-optical dataset and measurements from Visible Infrared Imaging Radiometer Suite (VIIRS). Evaluations with in-situ data show that QAA and GIOP are quite comparable in predicting the total absorption coefficients (a(λ)), as well as the absorption coefficients by phytoplankton (aph(λ)) and by detritus and gelbstoff (adg(λ)). The median absolute percentage differences (MAPD) of derived a(λ) by the two SAAs in the blue-green domain are generally between 6% and 29%, while relatively larger uncertainties are observed for derived aph(λ) (MAPD ~ 52%) and adg(λ) (MAPD ~ 54%). A match-up analysis using VIIRS measurements under low solar zenith angles (θs  < 70°) confirms the overall consistent retrievals by both SAAs, with MAPD of VIIRS-derived a(λ), aph(λ), and adg(λ) being ~35%, ~39%, and ~66%, respectively. Results of this study show that QAA and GIOP could provide acceptable estimations of a(λ), aph(λ), and adg(λ) in SO from satellite, at least for low θs conditions, but regional optimizations could be highly desired to improve the retrievals of component absorptions, particularly for adg(λ).