Chami Malik, Thirouard Alexandre, Harmel Tristan
Opt Express. 2014 Oct 20;22(21):26403-28. doi: 10.1364/OE.22.026403.
An innovative instrument dedicated to the multispectral measurements of the directional and polarized scattering properties of the hydrosols, so-called POLVSM, is described. The instrument could be used onboard a ship, as a benchtop instrument, or at laboratory. The originality of the POLVSM concept relies on the use of a double periscopic optical system whose role is (i) to separate the plane containing the light source from the scattering plane containing the sample and the receiver and (ii) to prevent from any specularly reflected light within the sample chamber. As a result, a wide range of scattering angle, namely from 1° to 179°, is covered by the detector. Another originality of the instrument is to measure the Mueller scattering matrix elements, including the degree of polarization. A relevant calibration procedure, which could be of great interest as well for other instruments, is proposed to convert the raw data into physical units. The relative uncertainty in POLVSM data was determined at ± 4.3%. The analysis of measurements of the volume scattering function and degree of polarization performed under controlled conditions for samples dominated either by inorganic hydrosols or phytoplankton monospecific species showed a good consistency with literature, thus confirming the good performance of the POLVSM device. Comparisons of POLVSM data with theoretical calculations showed that Mie theory could reproduce efficiently the measurements of the VSF and degree of polarization for the case of inorganic hydrosols sample, despite the likely non sphericity of these particles as revealed by one of the element of the Mueller matrix. Our results suggested as well that a sophisticated modeling of the heterogeneous internal structure of living cells, or at least, the use of layered sphere models, is needed to correctly predict the directional and polarized effects of phytoplankton on the oceanic radiation. The relevance of performing angularly resolved measurements of the Mueller scattering elements to gain understanding on the mechanisms processes involved in the scattering of light by marine particles, which has important implications for ocean color remote sensing studies, is demonstrated.
本文介绍了一种创新型仪器，即所谓的POLVSM，它专门用于多光谱测量水溶胶的方向和偏振散射特性。该仪器既可以安装在船上使用，也可以作为台式仪器，还能在实验室中使用。POLVSM概念的独特之处在于采用了双潜望镜光学系统，其作用是：（i）将包含光源的平面与包含样品和接收器的散射平面分开；（ii）防止样品室内出现任何镜面反射光。因此，探测器能够覆盖从1°到179°的宽散射角范围。该仪器的另一个独特之处是能够测量穆勒散射矩阵元素，包括偏振度。本文还提出了一种相关的校准程序，该程序对其他仪器也可能具有很大的参考价值，可将原始数据转换为物理单位。POLVSM数据的相对不确定度确定为±4.3%。在受控条件下，对以无机水溶胶或单一浮游植物物种为主的样品进行的体积散射函数和偏振度测量分析表明，与文献结果具有良好的一致性，从而证实了POLVSM设备的良好性能。将POLVSM数据与理论计算结果进行比较表明，尽管穆勒矩阵的一个元素显示这些颗粒可能并非球形，但米氏理论仍能有效地再现无机水溶胶样品的体积散射函数（VSF）和偏振度测量结果。我们的结果还表明，需要对活细胞的异质内部结构进行复杂建模，或者至少使用分层球体模型，才能正确预测浮游植物对海洋辐射的方向和偏振效应。本文证明了对穆勒散射元素进行角度分辨测量对于理解海洋颗粒光散射所涉及的机制过程具有重要意义，这对海洋颜色遥感研究具有重要影响。
