Comparison of Refractive Index Estimated from Single-Cell and Bulk Optical Properties
WOODS HOLE OCEANOGRAPHIC INSTITUTION MA
Pagination or Media Count:
Particle size and refractive index distributions are important determinants of bulk optical properties in the ocean. We have compared refractive indices of phytoplankton cultures estimated from individual particle and bulk optical measurements. For individual particles, size and refractive index were estimated from flow cytometric forward and side scattering measurements combined with Mie theory. Using an inverse method, bulk refractive index was estimated from cell concentration, measured size distributions, absorption, and attenuation. For several cultures, phytoplankton refractive index estimated from the inverse method was lower than that estimated from flow cytometric scattering measurements. These differences appear to be caused by higher side scattering than predicted by Mie theory, most likely due to deviation from the assumption of homogenous spheres. Using a diameter correction factor determined for ten species of phytoplankton, we have developed a methodology that works well for determining size and refractive index of cells in the laboratory and that can be applied to natural particles. Examples of flow cytometric results for particles from New England continental shelf waters are presented.
- Physical and Dynamic Oceanography