Continuous spectral measurement of backscattering in sea water

摘要

A prototype for an active backscattering probe for continuous backscattering spectrum measurement in sea water was designed and tested in both lab and field experiments. For the laboratory experiments, at various algae concentrations, the impact of overlapping chlorophyll fluorescence was effectively eliminated by using a long pass filter on the excitation light source. In the field tests with an active light source, and under the conditions of strong algal scattering (eg bloom conditions) it was shown that the impact of ambient background day light can be accounted for by successive measurements with the lamp illumination periodically on-off. The results show that the spectral shape of backscattering of algae cells is highly structured and consistent with Mie calculations which take into account the anomalous dispersion due to the strong absorption features of chlorophyll. The backscatter ratio, however, is found to be stable (within 10%) throughout the entire spectral region outside the chlorophyll fluorescence band, even when scattering is dominated by that from algae cells.