Oral Session 10 | Thursday, October 6, 14:40–15:00 | Abstract 482

Significance of inelastic scattering in optical closure of CDOM-rich coastal waters

Optical closure refers to the consistency between measured Apparent Optical Properties (AOPs) and simulated AOPs using radiative transfer equations for given boundary conditions and measured Inherent Optical Properties (IOPs). Optical closure experiments are usually performed to check the consistency of in situ AOPs and IOPs in course of bio-optical characterization or inverse model development. However, achieving optical closure can be challenging in case-2 waters, especially in dark waters dominated by Coloured Dissolved Organic Matter (CDOM), due to weak radiometric signal, measurement uncertainties in AOPs and IOPs and also possibly from ignoring inelastic scattering contribution in modelling the closure. Here we investigate the contribution of inelastic scattering components (CDOM fluorescence; f_DOM and sun-induced chlorophyll fluorescence; SICF) in dark waters sampled in the nearshore zone of lower St. Lawrence Estuary in Canada, in the framework of an airborne hyperspectral data acquisition campaign. HydroLight v6.0 and a semi-analytical (Albert and Mobley, 2003) radiative transfer model were used to simulate the remote-sensing reflectance; R_rs using multiple sets of measured IOPs (Hydroscat-6, BB9, AC-S, A-sphere). We found that accounting for f_DOM and SICF improved the closure significantly (excluding inelastic: R-sqaured=0.89, slope=0.72; including inelastic: R-squared=0.93, slope=0.80), especially at green (555-590nm) and red wavelengths (667-710nm). We also quantified the inelastic scattering equivalent R_rs fraction across the affected spectral domain (At green, ~13% from f_DOM and ~17% at red from SICF). We conclude that optical closure studies should account for inelastic scattering components in R_rs for CDOM dominated dark waters in nearshore environments.

*Soham Mukherjee, Université du Québec à Rimouski, 0000-0001-9771-0778

John Hedley, Numerical Optics Ltd.

Cédric Fichot, Boston University

Julien Laliberté, Fisheries and Oceans Canada

Simon Bélanger, Université du Québec à Rimouski

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