Impact of Light Polarization on the Measurement of Water Particulate Backscattering Coefficient
LIU Jia1,2, GONG Fang1*, HE Xian-qiang1, ZHU Qian-kun1, HUANG Hai-qing1
1. State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China 2. Laboratory of Remote Sensing and Intelligent Information System, Xi’an Institute of Optics and Precision Mechanics of Chinese Academy of Sciences, Xi’an 710119, China
Abstract：Particulate backscattering coefficient is a main inherent optical properties (IOPs) of water, which is also a determining factor of ocean color and a basic parameter for inversion of satellite ocean color remote sensing. In-situ measurement with optical instruments is currently the main method for obtaining the particulate backscattering coefficient of water. Due to reflection and refraction by the mirrors in the instrument optical path, the emergent light source from the instrument may be partly polarized, thus to impact the measurement accuracy of water backscattering coefficient. At present, the light polarization of measuring instruments and its impact on the measurement accuracy of particulate backscattering coefficient are still poorly known. For this reason, taking a widely used backscattering coefficient measuring instrument HydroScat6 (HS-6) as an example in this paper, the polarization characteristic of the emergent light from the instrument was systematically measured, and further experimental study on the impact of the light polarization on the measurement accuracy of the particulate backscattering coefficient of water was carried out. The results show that the degree of polarization(DOP) of the central wavelength of emergent light ranges from 20% to 30% for all of the six channels of the HS-6, except the 590 nm channel from which the DOP of the emergent light is slightly low (~15%). Therefore, the emergent light from the HS-6 has significant polarization. Light polarization has non-neglectable impact on the measurement of particulate backscattering coefficient, and the impact degree varies with the wave band, linear polarization angle and suspended particulate matter(SPM) concentration. At different SPM concentrations, the mean difference caused by light polarization can reach 15.49%, 11.27%, 12.79%, 14.43%, 13.76%, and 12.46% in six bands, 420, 442, 470, 510, 590, and 670 nm, respectively. Consequently, the impact of light polarization on the measurement of particulate backscattering coefficient with an optical instrument should be taken into account, and the DOP of the emergent light should be reduced as much as possible.
Key words：Polarization;Backscattering coefficient;Inherent optical properties;Ocean color remote sensing
刘 佳1,2，龚 芳1*，何贤强1，朱乾坤1，黄海清1 . 光源偏振对水体颗粒后向散射系数测量的影响 [J]. 光谱学与光谱分析, 2016, 36(01): 31-37.
LIU Jia1,2, GONG Fang1*, HE Xian-qiang1, ZHU Qian-kun1, HUANG Hai-qing1 . Impact of Light Polarization on the Measurement of Water Particulate Backscattering Coefficient . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2016, 36(01): 31-37.
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