POSTER Session 3

AN UPDATED QUASI-ANALYTICAL ALGORITHM FOR THE INVERSION OF INHERENT OPTICAL PROPERTIES

Remote sensing of inherent optical properties (IOPs) is crucial for quantifying radiative transfer and synoptic mapping of various biogeochemical properties across global oceans. The quasi-analytical algorithm (QAA), currently at version 6 (QAA_v6), is widely adopted by the ocean color community for deriving IOPs from field- and satellite-measured remote sensing reflectance (Rrs). In this effort, QAA_v6 was upgraded to version 7 (QAA_v7) through three main modifications. Firstly, a new Rrs-IOPs relationship was introduced to account for the relative contributions of molecular and particle scattering. Secondly, the backscattering coefficient of pure seawater (bbw) was set to be temperature- and salinity-dependent. Thirdly, two empirical estimates in QAA_v6, namely the spectral slope (η) of particulate backscattering coefficient (bbp) and the total absorption coefficient (a) at reference wavelengths (i.e., 551 and 670 nm), were determined using neural network algorithms. Validation with in-situ measurements demonstrated improved retrieval of IOPs with QAA_v7, particularly in oligotrophic waters. When applied to satellite measurements, QAA_v7 yielded decreased IOPs in oligotrophic waters compared to QAA_v6, with derived a and bbp at 443 nm showing reductions of approximately 20% and 10%, respectively. Conversely, coastal and high-latitude oceans, exhibited overall increased estimations of a and bbp by 5 – 10% from QAA_v7. This study underscores the significant impact of molecular scattering on the inversion of IOPs in oligotrophic waters, and QAA_v7 is recommended for IOPs retrievals in such waters.

Xiaolong Yu, Xiamen University, China, [email protected], https://orcid.org/0000-0003-2813-0854

Zhongping Lee, Xiamen University, China, [email protected]

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