Optical closure is assessed between measured and simulated remote-sensing reflectance (Rrs) using Hydrolight radiative transfer code for five data sets that included a broad range of both Case I and Case II water types. Model-input inherent optical properties (IOPs) were the absorption coefficient determined with a WET Labs ac9 and the volume scattering function (VSF) determined with a custom in situ device called MASCOT. Optimal matchups were observed using measured phase functions and reflective tube absorption measurements corrected using a scattering error independently derived from VSF measurements. Absolute bias (δ) for simulations compared to measured Rrs was 20% for the entire data set, and 17% if a relatively shallow station with optical patchiness was removed from the analysis. Approximately half of this δ is estimated to come from uncertainty in radiometric measurements of Rrs, with the other half arising from combined uncertainties in IOPs, radiative transfer modeling, and related assumptions. For exercises where such δ can be tolerated, IOPs have the potential to aid in ocean color validation. Overall, δ was roughly consistent with the sum of uncertainties derived from associated measurements, although larger deviations were observed in several cases. Applying Fournier-Forand phase functions derived from particulate backscattering ratios according to Mobley et al. [Appl. Opt. 41, 1035 (2002)] resulted in overall δ that was almost as good (23%) as simulations using measured phase functions. Possibilities for improving closure assessments in future studies are discussed.
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics