| Popis: |
A thorough sensitivity analysis of the 'Transmittance-Reflectance' (T-R) method for measuring in vivo light absorption by aquatic particles retained on glass-fiber filters has been carried out. Particular attention has been devoted to the error contribution by the variability of the optical properties of the GF/F filters used. The overall error of the measurement of the filter-retained particle optical density, OD s , has been evaluated as ∼0.002 (1σr), with 0.0015 error contribution by the filter variability. The corresponding error of the optical density of the particle suspension, OD sus , has been obtained by differentiation of the equation expressing the experimental correlation (OD sus versus ODD; the error increases with the optical density value, from σ = 0.0015 for OD sus = 0.05) to σ = 0.027 at the upper limit of the optical density range tested (OD sus = 0.59). The validity range of the experimental (OD sus versus OD s ) correlation has been shown to extend to OD s = 0. 75. The importance of the accurate correction for light backscattering performed by the T-R method has been investigated by comparison with results given by the standard 'Transmittance' (T) method; it has been shown that the coarse correction for light scattering included in the T method may cause serious errors in the measured optical density spectra of mineral detritus. This evidence confirms the need to resort to the T-R method for the measurement of particle samples of detritus-rich coastal waters. The paper summarizes the latest developments of the T-R method and includes an Appendix with a synopsis of the routine now used by the authors. |
