Three-parameter active in-situ optical measurements: theory, instrumentation and results from coastal waters

A submersible optical instrument has been designed and constructed which simultaneously measures chlorophyll fluorescence, beam attenuation and wide-angle light scattering in sea water. A theoretical framework is presented which shows that this instrument configuration is capable of quantitatively measuring concentrations of gelbstoff, suspended particles and phytoplankton when all three components are present in a mixture, provided the relevant set of calibration coefficients are known. The inherent variability of natural materials means that the numerical values of these calibration coefficients usually have to be determined at the site of instrument deployment. However, trials in optically complex waters indicate that the instrument can be usefully employed to interpolate between chemical measurements in order to increase the spatial and temporal coverage of survey data while minimizing the resources required for sample analysis.