POSTER Session 1

Characterization of uncertainties in the filter pad method for determining the spectral absorption coefficient of aquatic particles in the ultraviolet spectral region

Measurements from the NASA PACE satellite mission are extending observations of ocean optical properties to the ultraviolet (UV) portion of the spectrum. The interpretation and application of such measurements requires knowledge of the inherent optical properties of seawater and its constituents in this spectral range, including the spectral absorption coefficient of suspended particles, ap. Historically, spectrophotometric measurements of particulate matter retained on filters have been the most common method to determine ap, but these data are often restricted to the visible (VIS) spectral region because of unknown and potentially high uncertainties in the UV associated with pathlength amplification and other factors. In this study, we report on experimental measurements of the pathlength amplification factor in the spectral region 300-399 nm for diverse assemblages of aquatic particles. Importantly, absorbance measurements on both particle suspensions (ODs) and sample filters (ODf) were obtained using the inside integrating-sphere configuration as recommended by current protocols. We observe the relationship between ODs and ODf in the UV to exhibit increased scatter relative to the VIS spectral region. Analyzes of these data indicate average uncertainties of about 10-20% for ap in the UV can be achieved using UV-specific corrections for pathlength amplification. However, for the near-UV region of 350-399 nm corresponding to PACE OCI measurements the results suggest that the currently recommended pathlength amplification correction for the VIS spectral region can provide reasonable results with median uncertainty increasing to ~14% from a value of 7% observed in the VIS.

Rick Reynolds, Scripps Institution of Oceanography, University of California San Diego, USA, https://orcid.org/0000-0002-1579-3600

Dariusz Stramski, Scripps Institution of Oceanography, University of California San Diego, USA, https://orcid.org/0000-0002-8518-072X

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