中肋骨条藻和东海原甲藻的散射特性

Scattering properties of two blooming algae: Skeletonema costatum and Prorocentrum donghaiense

浮游藻类是海水中的重要组成成分,对其固有光学特性的研究有助于深入了解水体光学的辐射传输。在过去的30年中,大量的研究都集中在藻类吸收特性上,缺少对其散射特性的认识。本文利用分光光度计设计了在实验室中测量含颗粒水体散射和后向散射特性的方法,并利用标准球形颗粒对该方法的可行性进行验证,结果表明,在400～700nm范围内,散射测量结果与理论值的一致性较好,最大误差小于3%,而后向散射测量结果在蓝紫光处的一致性较好,在近红外波段处有一定误差。运用这两种测量方法对东中国海常见的赤潮藻种中肋骨条藻Skeletonema costatum和东海原甲藻Prorocentrum donghaiense进行测量,结果显示:中肋骨条藻与东海原甲藻的散射系数幅值相近但谱形差异较大,前者随波长增加散射强度递减,后者则相反;在色素吸收较强的波段,两者散射强度均出现与其它波长位置变化趋势相反的情况,这主要是受细胞物质物理性质的影响。两者的后向散射差异较小,但可以看出其谱形受色素吸收的影响很大,在幅值上,东海原甲藻略高于中肋骨条藻,在550nm处分别为0.001 74,0.001 43m2/mg(以藻类叶绿素a浓度归一化),后向散射概率分别为1.104%和0.723%。

Phytoplankton is a major component of marine water, an insight investigation of its inherent optical properties is the foundation of understanding the principle of light transferring in water. In the last 30 years, focus was mainly on the absorption measurement and comparison of different algae, very few researchers had a detailed study on their scattering properties. In this paper, a method based on spectrometer was developed to measure the total scattering and backscattering coefficient of algae containing solution. The verification procedure of the method was carried out by measuring the scattering and backscattering results of polystyrene latex micro beads with known size distribution and refractive index. The results showed a maximum deviation of 4% for scattering in the visible spectrum and around 20% higher for backscattering in the red spectrum but quite good consistency in other regions. The method was then used to measure the scattering and backscattering features of two bloom algae in East China Sea： Skeletonema costatum and Prorocentrurn donghaiense. It shows that the two algae had comparable amplitudes in both scattering and backscattering cross section, but Skeletonema costatum had a quite opposite scattering pattern to Prorocentrum donghaiense, whose scattering decreases with increasing wavelength. This could be attributed to the different cellular components which determine whether it follows normal or anomalous dispersion for the refractive index. Both algae have a regional minimum of scattering around 670 nm, which was due to the anomalous dispersion and the strong absorption of chlorophyll a. The backscattering cross section for the two algae were similar in both amplitude and spectrum pattern, Prorocentrum donghaiense had a higher but smoother backscattering spectrum. It＇d demonstrated that the backscattering spectrum is well influenced by absorption of cellular pigments. Finally, the backscattering to scattering ratio was 0. 723% for Skeletonerna costaturn and 1. 104% for Prorocentrum donghaiense, the absolute value of backscattering cross section were 0. 001 43 m2/mg and O. 001 74 m2/mg respectively.