DOI: 10.6076/d1630t
title: A synthetic database of hyperspectral ocean optical properties

description: Radiative transfer (RT) simulations have long been used to study
 relationships between the inherent optical properties (IOPs) of seawater
 and light fields within and leaving the ocean from which the ocean
 apparent optical properties (AOPs) can be calculated. For example, inverse
 models to estimate IOPs from ocean color radiometric measurements have
 been developed or validated using results of RT simulations. Here we
 describe the development of a new synthetic optical database based on
 hyperspectral RT simulations across the spectral range from the
 near-ultraviolet to near-infrared performed with the HydroLight radiative
 transfer code. The key component of this development was the generation of
 the synthetic dataset of seawater IOPs that served as input to RT
 simulations. Compared to similar developments of optical databases in the
 past, the present dataset of IOPs is characterized by probability
 distributions of IOPs that are consistent with global distributions
 representative of vast areas of open ocean pelagic environments and
 coastal regions covering a broad range of optical water types. The
 generation of the synthetic data of IOPs associated with particulate and
 dissolved constituents of seawater was driven largely by an extensive set
 of field measurements of the phytoplankton absorption coefficient
 collected in diverse oceanic environments. Overall, the synthetic IOP
 dataset consists of 3320 combinations of IOPs. Additionally, the pure
 seawater IOPs were assumed following recent recommendations. The RT
 simulations were performed using 3320 combinations of input IOPs assuming
 vertical homogeneity within an infinitely deep ocean. These input IOPs
 were used in three simulation scenarios associated with assumptions about
 inelastic radiative processes in the water column (not considered in
 previous synthetically-generated optical databases) and three simulation
 scenarios associated with sun zenith angle. Specifically, the simulations
 were made assuming no inelastic processes, the presence of Raman
 scattering by water molecules, and the presence of both Raman scattering
 and fluorescence of chlorophyll-a pigment. Fluorescence of colored
 dissolved organic matter was omitted from all simulations. For each of
 these three simulation scenarios, the simulations were made for three sun
 zenith angles of 0°, 30, and 60° assuming clear skies, standard
 atmosphere, and wind speed of 5 m s-1. Thus, overall 29880 RT simulations
 were performed. The output results of these simulations include the
 radiance distributions, plane and scalar irradiances, and the whole set of
 AOPs including the remote-sensing reflectance, vertical diffuse
 attenuation coefficients, and mean cosines where all optical variables are
 reported in the spectral range from 350 to 750 nm at 5 nm intervals for
 different depths between the sea surface and 50 m. The consistency of this
 new synthetic database has been assessed through comparisons with in situ
 data and previously developed empirical relationships involving the IOPs
 and AOPs.
description: The synthetic database of seawater IOPs used as input for
 performing RT simulations and the resulting output radiometric data from
 the HydroLight model runs are provided in 18 individual files. The file
 format is netCDF-4. Data for the variables contained within these files
 are in single-precision floating-point format. A detailed description of
 the data, variable names, and units is provided in the file
 Database_README.pdf.
description: # A synthetic database of hyperspectral ocean optical properties Hubert
 Loisel and Daniel Schaffer Ferreira Jorge Laboratoire d'Océanologie
 et de Géosciences, Université du Littoral-Côte-d'Opale, Université
 Lille, CNRS, IRD, UMR 8187, LOG, 32 avenue Foch, Wimereux, France Rick A.
 Reynolds and Dariusz Stramski Marine Physical Laboratory, Scripps
 Institution of Oceanography, University of California San Diego, La Jolla,
 California 92093-0238, USA Correspondence: Hubert Loisel
 ([hubert.loisel@univ-littoral.fr](mailto:hubert.loisel@univ-littoral.fr))
 This database is associated with the article: Loisel, H., D. S. F. Jorge,
 R. A. Reynolds, and D. Stramski. 2023. A synthetic optical database
 generated by radiative transfer simulations in support of studies in ocean
 optics and optical remote sensing of the global ocean. Earth Syst. Sci.
 Data, 15, 3711–3731. doi: 10.5194/essd-15-3711-2023. This dataset
 represents a new synthetic optical database based on hyperspectral RT
 simulations across the spectral range from the near-ultraviolet to
 near-infrared performed with the HydroLight radiative transfer code. The
 key component of this database was the generation of the synthetic dataset
 of seawater IOPs which served as input to RT simulations. Compared to
 similar developments of optical databases in the past, the present dataset
 of IOPs is characterized by probability distributions of IOPs that are
 consistent with global distributions representative of vast areas of open
 ocean pelagic environments and coastal regions covering a broad range of
 optical water types. The generation of the synthetic data of IOPs
 associated with particulate and dissolved constituents of seawater was
 driven largely by an extensive set of field measurements of the
 phytoplankton absorption coefficient collected in diverse oceanic
 environments. Overall, the synthetic IOP dataset consists of 3320
 combinations of IOPs. Additionally, the pure seawater IOPs were assumed
 following recent recommendations. The RT simulations were performed using
 3320 combinations of input IOPs assuming vertical homogeneity within an
 infinitely deep ocean. These input IOPs were used in three simulation
 scenarios associated with assumptions about inelastic radiative processes
 in the water column and three simulation scenarios associated with sun
 zenith angle. Specifically, the simulations were made assuming no
 inelastic processes, the presence of Raman scattering by water molecules,
 and the presence of both Raman scattering and fluorescence of
 chlorophyll-a pigment. Fluorescence of colored dissolved organic matter
 was omitted from all simulations. For each of these three simulation
 scenarios, the simulations were made for three sun zenith angles of 0°,
 30, and 60° assuming clear skies, standard atmosphere, and wind speed of 5
 m/s. Thus, overall 29880 RT simulations were performed. The output results
 of these simulations include the radiance distributions, plane and scalar
 irradiances, and the whole set of AOPs including the remote-sensing
 reflectance, vertical diffuse attenuation coefficients, and mean cosines
 where all optical variables are reported in the spectral range from 350 to
 750 nm at 5 nm intervals for different depths between the sea surface and
 50 m. The consistency of this new synthetic database has been assessed
 through comparisons with in situ data and previously developed empirical
 relationships involving the IOPs and AOPs. Users are referred to the above
 article for an in-depth description and discussion of the database.
 **Please use the latest version (currently June 2024)!** Version history:
 **2024-06-24**: All nine *_profile.nc files were updated to correct an
 error discovered in the calculation of the variable “z1_lambda”. All other
 variables in the files are unchanged. The nine files with the IOP
 scenarios (HydrolightXYY.nc) are also unchanged from the previous version.
 2023-10-18: All nine *_profile.nc files were updated. An error was
 discovered in the naming and content of these files with regards to the
 labeling of simulation scenarios for the inclusion of inelastic radiative
 transfer processes. The nine files with the IOP scenarios
 (HydrolightXYY.nc) are unchanged from the previous version. 2023-08-18:
 Readme and metadata files updated to reflect final article citation
 2023-07-19: Updated database netcdf files to repair some corrupted data
 values 2023-05-31: Revised database submitted following changes made in
 response to article peer review 2023-03-03: Initial database submission to
 Dryad during article peer review ## Description of the data and file
 structure ### Data File Organization The synthetic database of seawater
 IOPs used as input for performing RT simulations and the resulting output
 radiometric data from the HydroLight model runs are provided in 18
 individual files. The file format is netCDF-4. Data for the variables
 contained within these files are in single-precision floating-point
 format. Missing values are identified with -999, for example situations
 where z1_lambda exceeded the maximum depth of our simulations. The 18 data
 files are organized into 9 pairs of files representing different
 simulation scenarios. The file naming convention for these pairs is:
 HydrolightXYY.nc HydrolightXYY_profile.nc The first file contains the
 spectral absorption and scattering coefficients of seawater constituents
 (assumed to be vertically homogenous) used in a given simulation scenario
 as well as selected sea-surface radiometric quantities of interest to
 ocean color radiometry. The second file contains both surface and
 depth-dependent values of calculated spectral radiometric quantities and
 selected AOPs along with other ancillary information. The value of X in
 the filename refers to a specific simulation scenario with regards to the
 assumption of inelastic radiative processes occurring in the water column:
 X = 1: No inelastic processes included. X = 2: Raman scattering by water
 molecules included. X = 4: Raman scattering by water molecules and
 fluorescence of chlorophyll-a included. Note that fluorescence by colored
 dissolved organic matter was omitted from all simulations. The value of YY
 in the filename refers to the solar zenith angle used in the simulation,
 and represents a value of 00, 30, or 60 degrees. All simulations assume
 clear skies, standard atmosphere, a wind speed of 5 m/s, and an infinitely
 deep ocean. ### Data File Descriptions 1. HydrolightXYY.nc These files
 contain the spectral absorption and scattering coefficients of seawater
 constituents used as input in the simulation scenario. In addition,
 selected sea-surface radiometric quantities output from the Hydrolight
 model run are included. Most variables are stored as 81 × 3320 numerical
 arrays, representing 81 light wavelengths (350–750 nm at 5 nm increments)
 and 3320 scenarios of different IOP combinations. 2.
 HydrolightXYY_profile.nc These files contain the surface and
 depth-dependent values of selected spectral radiometric quantities and
 AOPs along with other ancillary information. Surface variables are 81 ×
 3320 as described above, but depth-dependent variables include an
 additional dimension representing values at 61 discrete depths in the
 water column from the sea surface to 50 m (variable name includes “_z”). A
 depth of –1 indicates a quantity above the sea surface (z = 0+), a depth
 of 0 indicates a quantity immediately beneath the sea surface (z = 0-),
 and the remaining depths are positive in the downward direction. Further
 details on variable names, units, and descriptions can be found in the
 file Database_README.pdf