Characterization of the Oceanic Particulate Volume Scattering Function

Radiative transfer approximations and subsequent inversions that have formed the basis of semi-analytical (SA) algorithms to derived biogeochemical parameters from ocean color remote sensing have not been rigorously assessed with respect to variability in the in-water volume scattering function (VSF), as, up until very recently, the comprehensive VSF data sets required for such an assessment have not been available. With such measurements now in hand through field work over the last decade supported by NASA and other sources, rigorous characterization of the shape, variability, and analytical representation of the VSF for ocean particle fields is now possible. VSFs were collected with a custom Multi-Angle SCattering Optical Tool (MASCOT) employing a 658 nm laser diode source with wedge depolarizer and 17 independent detectors to measure volume scattering from 10 to 170 degrees in 10 degree increments at a sampling rate of 20 Hz. For many of the MASCOT VSFs that were collected, a commercial type-B LISST diffractometer was concurrently deployed, measuring near-forward scattering from 0.1 to 13 degrees in 32 logarithmically spaced angular bins, so that the VSF, for practical purposes, was fully resolved. Shapes from over 1 million VSFs collected from approximately 18 locations around the world’s oceans, spanning turbid Case II waters to the clearest Case I environments are analyzed. Representative VSF shapes that may be used in ocean color remote sensing algorithm assessment and development are identified. This systematic characterization of VSF shapes provides a deeper understanding of light propagation in the ocean, and is expected to lead to a new family of SA algorithms for future satellite imagers and multi-angle polarimeters with better constrained errors, particularly in heterogeneous coastal regions.