The irradiance reflectance just beneath the water surface is closely related to the absorption coefficient, scattering coefficient and solar zenith angle. However, the effect of solar zenith angle on the irradiance reflectance just beneath the water surface is not clear in Lake Taihu. The influence factors of irradiance reflectance just beneath the water surface in Lake Taihu were analyzed based on the optical parameters and numerical simulates using the data of total 27 sampling sites measured in May, 2010. The results show that while solar zenith angle is in the range of 0°-25°and 70°-89°, it has little influence on the growth of irradiance reflectance just beneath the water surface which is less than 10%. While solar zenith angle is in the range of 30°-70°, the growth of irradiance reflectance is 13.13%- 52. 19%. The correlation of theoretical results and measured data show that such numerical study is correct for Lake Taihu. Therefore, full consideration should be given to the effect of solar zenith angle when studying on the optical properties of water and the driving mechanism of the light to aquatic ecosystems.%恰在水面下辐照度比变化与吸收系数、散射系数和太阳天顶角存在着密切的关系,而太阳天顶角对太湖恰在水面下辐照度比的定量影响程度尚不明确.为此,本文基于2010年5月太湖27个样点的水体光学参数和理论数值模拟,对太湖水体的情况进行研究.理论数值模拟结果表明:当太阳天顶角分别在0°～25°和70°～89°区间内变化时,对恰在水面下辐照度比增幅影响较小,增幅相差不到10％；而当太阳天顶角在30°～70°之间时,对辐照度比增幅影响很大,增幅为13.13％～52.19％.同时,利用实测数据对理论结果进行线性相关验证表明,此数值研究整体上符合太湖的实际情况.因此,对水体光学特性以及光对水生生态系统驱动作用研究的时候,应充分考虑太阳天顶角的影响.
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