The University of Maine Maine In-situ Sound & Color Lab
School of Marine Sciences
Optical Properties of Marine Aggregates

Current theoretical modeling of inherent optical properties (IOPs) of oceanic particles (of spherical, non-spherical and non-homogeneous particles) assumes oceanic particles are not porous. Many oceanic particles are porous aggregates comprised mostly of interstitial water. Aggregates have fractal dimensions smaller than three and nearing two meaning their surface area to mass ratio is nearly constant (unlike non-porous particles whose surface area to mass ratio scales like (diameter)-1). Large marine particles have IOPs that are proportional to the particles' cross-sectional area. It follows that for a given amount of mass, large aggregates will have significantly larger IOPs compared to non-porous particles of the same mass. In other words, in a non-porous particle material 'self-shades', while for a loose aggregate of the same mass, more of the material interacts with light. The index of refraction of aggregates is closer to that of water than the particulate material from which it is made. However, for particles such as oceanic aggregates, which are much larger than the wavelength of visible light, most IOPs are not sensitive to the index of refraction (geometric optics). Our study presents field data which supports a greater role for aggregates in IOP than currently assumed, introduces a simple model to estimate some IOPs of aggregates, and applies this model to field-based size distributions of oceanic aggregates.

Boss, E., P.S. Hill, and W.H. Slade, 2006. Optical Properties of Marine Aggregates. 2006 Spring Ocean Sciences Meeting.

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