Measurement and modeling of volume scattering functions for phytoplankton from Norwegian coastal waters

Abstract

The volume scattering function (VSF) describes the angular distribution of scattered light, and the VSF of phytoplankton is one of the most important inherent optical properties of oceanic water. Despite its importance, relatively few measurements of the VSF have been carried out in aquatic environments, and we present here data and analyses of measured VSFs at 442, 490, and 550 nm for 15 representative phytoplankton species from Norwegian coastal waters. In addition, the analytic scattering phase functions Henyey-Greenstein (HG) and Fournier-Forand, as well as Mie theory, were fitted and compared to the measured VSFs. The measured VSFs for all the species were strongly, but unequally forward peaked with HG-fitted asymmetry factors in the range 0.897-0.988. The VSF of Synechococcus sp., Phaeodactylum tricornutum, and Emiliania huxleyi (naked) had shoulders in the forward direction, whereas the VSF of the cylindrically shaped Chaetoceros calcitrans and Chaetoceros wighamii had minima in the backward direction. Results from this work indicate that internal structures influence the angular and spectral shape of the VSF more significantly than the morphology and size of the phytoplankton cells.