Flocs are not Spheres: A new Theoretical Approach for Treating Beam Attenuation as a Proxy for Suspended Particulate Mass

L. Hachey \ Oceans First, Issue 3, 2016, pgs. 17-22

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Abstract: Visibility in water is affected by suspended particles within. One way to assess suspended particulate mass (SPM) is to measure the attenuation (Cp) of a light beam calibrated for a specific size range of particles. The relationship between SPM and Cp has consistently been linear throughout the literature, but Baker and Lavelle (1984) found disagreement between the common Mie theoretical predictions and the relationship from experiments. Here, a summary of a new theoretical understanding based on considering particles as aggregates is presented. These aggregates have a fractal dimension of non-solid gaps which constrain the Cp:SPM to particles size. This is why transmissometers have been able to produce adequate estimates of SPM throughout the literature. Experiments are presented which confirm the aggregate nature of particles, and show how size distribution co-varies with beam attenuation. This consideration does not completely explain variation between different particle types, but a validated theoretical framework allows for previous experiments to be useful for the advancement of the field of aquatic optics.