1. A synthetic optical database generated by radiative transfer simulations in support of studies in ocean optics and optical remote sensing of the global ocean
- Author
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Loisel, Hubert, Jorge, Daniel Schaffer Ferreira, Reynolds, Rick A, and Stramski, Dariusz
- Subjects
Life Below Water ,Atmospheric Sciences ,Geochemistry ,Physical Geography and Environmental Geoscience - Abstract
Abstract. Radiative transfer (RT) simulations have long been usedto study the relationships between the inherent optical properties (IOPs) ofseawater and light fields within and leaving the ocean, from which oceanapparent optical properties (AOPs) can be calculated. For example, inversemodels used to estimate IOPs from ocean color radiometric measurements have beendeveloped and validated using the results of RT simulations. Here we describe thedevelopment of a new synthetic optical database based on hyperspectral RTsimulations across the spectral range of near-ultraviolet tonear-infrared performed with the HydroLight radiative transfer code. The keycomponent of this development is the generation of a synthetic dataset ofseawater IOPs that serves as input to RT simulations. Compared to similardevelopments of optical databases in the past, the present dataset of IOPsis characterized by the probability distributions of IOPs that are consistentwith global distributions representative of vast areas of open-ocean pelagicenvironments and coastal regions, covering a broad range of optical watertypes. The generation of synthetic data of IOPs associated withparticulate and dissolved constituents of seawater was driven largely by anextensive set of field measurements of the phytoplankton absorptioncoefficient collected in diverse oceanic environments. Overall, thesynthetic IOP dataset consists of 3320 combinations of IOPs. Additionally,the pure seawater IOPs were assumed following recent recommendations. The RTsimulations were performed using 3320 combinations of input IOPs, assumingvertical homogeneity within an infinitely deep ocean. These input IOPs wereused in three simulation scenarios associated with assumptions aboutinelastic radiative processes in the water column (not considered inprevious synthetically generated optical databases) and three simulationscenarios associated with the sun zenith angle. Specifically, the simulationswere made assuming no inelastic processes, the presence of Raman scatteringby water molecules, and the presence of both Raman scattering andfluorescence of chlorophyll a pigment. Fluorescence of colored dissolvedorganic matter was omitted from all simulations. For each of these threesimulation scenarios, the simulations were made for three sun zenith anglesof 0, 30, and 60∘ assuming clear skies, standardatmosphere, and a wind speed of 5 m s−1. Thus, overall 29 880 RTsimulations were performed. The output results of these simulations includeradiance distributions, plane and scalar irradiances, and a whole setof AOPs, including remote-sensing reflectance, vertical diffuseattenuation coefficients, and mean cosines, where all optical variables arereported in the spectral range of 350 to 750 nm at 5 nm intervals fordifferent depths between the sea surface and 50 m. The consistency of thisnew synthetic database has been assessed through comparisons with in situdata and previously developed empirical relationships involving IOPs andAOPs. The database is available at the Dryad open-access repository of researchdata (https://doi.org/10.6076/D1630T, Loisel et al., 2023).
- Published
- 2023