基于Hydrolight模拟的内陆水体光场的二向性

摘要

To promote the study on the bidirectional reflectance properties of light field above inland waters, this paper took water quality parameters and inherent optical parameters measured in Taihu Lake as input, applied the radiative transfer model of Hydrolight to bidirectional ditribution of light filed of inland waters, and obtained the variation laws of bidirectional factors of Q and f/Q changing with observational direction and wavelength affected by driven elements. Results show that the f/Q variation with wavelengths is bigger than that of the observing zenith angle and observing azimuth angle. The f/Q variation with the observing zenith angle is bigger than the observing azimuth angle. The f/Q variation at blue and near infrared wavelengths is bigger than at green and red wavelengths. Among driving factors, solar zenith, suspended matter concentration, chlorophyll-a concentration, back-scattering probability of suspended matter, and cloud amount are the leading factors, which should be carefully treated when retrieving water quality parameters in turbid waters. Meanwhile, aCDOM, back-scattering probability of chlorophyll-a, the ratio of downwelling diffuse irradiance to total downwelling irradiance, and wind speed can be ignored. In summary, when retrieving water quality parameters and only considering the influence of bi-direction properties, the remote sensing reflectance should be chosen at green and red wavelengths, with the observing zenith angle within 40 ° , observing azimuth angles of 0 °-150 ° or 210 °-360 ° , which will reduce the errors aroused by multi-angular observation, and promote the inversion accuracy of water quality parameters.%为了进一步完善内陆水体光场的二向性研究,以水体固有光学量和水质参数为输入,采用Hydrolight辐射传输模型模拟了内陆水体光场的二向性分布,获得了二向性因子Q、f/Q随观测方向、波段的变化规律以及Q、f/Q受驱动要素的影响规律.结果表明:f/Q随波段的变化大于随观测天顶角和观测方位角的变化,f/Q随观测天顶角变化大于随观测方位角的变化;观测方向对蓝光和近红波段f/Q的影响大于对绿光和红光f/Q的影响.Q、f/Q的驱动要素中太阳天顶角、悬浮物质量浓度、叶绿素a质量浓度、悬浮物后向散射概率及云量属于主导要素,在反演浑浊类水体水质参数时需要慎重对待;aCDOM、叶绿素后向散射概率、漫总比、风速等要素对光场二向性的影响可以忽略.总体而言,仅考虑二向性影响时,水质参数遥感反演时应尽量选用绿光和红光波段、观测天顶角在40°范围内、观测方位角在0°~150°和210°~360°内的遥感反射率数据,可以适当降低方向性观测引入的误差,提高水质参数反演精度.