Refinement and Validation of Empirical Techniques for the Determination of Absorption Coefficients for Marine Particulates
1992
Mitchell, B. G.
The work completed with support of N000-14-J-1071 was carried out to improve our ability to measure the light absorption by the particles contained in the boxes labeled S1, S2, and S3. The principal goal of the work in FY89 was to develop and validate a simple, practical and accurate procedure for determination of particulate absorption coefficients (ap) for samples concentrated onto glass fiber filters (Quantitative Filter Technique, QFT). Included in this effort was an analysis of the reproducibility, limitations and statistical precision of the methods and a theoretical treatment of empirical results. During FY89 a detailed study was initiated to evaluate the ability to determine ap for dilute suspensions of pigmented particles (e.g. sea water) using the QFT. The integrating sphere attachment allows direct determination of ap for suspensions. Different glass fiber filter types and particle types were analyzed and empirical algorithms were determined for correction of the pathlength application factor (Beta) which is caused by light scattering in the glass fiber medium. We have carried out a detailed evaluation of the generality, precision and accuracy of the Quantitative Filter Technique (QFT) for determination of absorption coefficients of aquatic particulates. The theoretically predicted nonlinear nature of absorption pathlength amplification for particles retained on intensely scattering filters was confirmed and a new, more direct algorithm for correction was developed.
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