Proposal for the simultaneous measurement of light absorption and backscattering by aquatic particulates

Abstract

The paper presents a new experimental method that measures light absorption and backscattering by aquatic particles, combining the innovative features of the ‘modified filter–transfer–freeze’ (FTF) and ‘transmittance–reflectance’ (T-R) techniques, namely no path-length amplification and accuratecorrection for scattering loss, respectively. This method (in short: the FTF/T-R method) measures both the transmittance and the reflectance of particles deposited on a glass slide, using a double-beam spectrophotometer equipped with an integrating-sphere attachment. The data are interpreted by an algorithm that yields both the absorption and the backscattering coefficients of the particle sample. The paper includes a summary of results of validation tests, that have been performed using samples ranging from pure phytoplankton (low light scattering) to pure detrital particles (high light scattering), as well as a detailed analysis of the experimental error. The FTF/T-R measurement is somewhat more laborious than the standard transmittance measurement of particles retained on glass fibre filters. However, it has the important asset of permitting the simultaneous determination of light absorption and backscattering and it yields more accurate absorption data in situations where the magnitude of path amplification by glass fibre filters is uncertain and light scattering by the particles is high.