| Summary: | 碩士 === 國立中山大學 === 海下科技研究所 === 107 === In the past, the suspended sediment concentration was mainly measured by optical backscattering devices and water sample filtration method. Acoustic instruments have some advantages that the optical ones do not have. For example, acoustic instruments are not affected by high turbidity, biofouling and high viscosity in the water. It will generate reflected and backscattered signals when the sound wave hit the suspended sediment. After the signal is converted to echo intensity value, we can estimate the suspended sediment grain size and concentration by using empirical formula. Therefore, in this study we explored the use of a multi-frequency acoustic instrument (AQUAscat-1000) to investigate the difference variation in the suspended sediment grain size, bulk density and concentration and compared the results measured by an optical instrument and filtered particle data.
The study sites were the coastal area south of Qinmen near Jiulong River mouth and the coastal area of the Pearl River mouth. These areas are tidal zones where river-ocean interactions are complex. Each experiment included deploying a instrumented mooring to investigate continuous river plume characteristic under the influence of tide. After measuring water temperature, salinity, chl-a and turbidity, collecting acoustic and optical data and water samples, we analyzed the suspended particle samples and compared the results. Different backscattered signals have different responses to bulk density of those three grain size groups(10-63 μm, 63-153 μm, >153 μm). Also, whether the particles are biogenic particles or not, affects the correlation of the data sets. According to the EOF analysis and linear correlation analysis, the applicability of the multi-frequency acoustic instrument to characterize and quantify suspended particles in the river plume regime needs to be investigated further.
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