风浪对水体表层下行光场平均余弦影响的数值研究

Numerical research on waves of a water body affecting the mean cosine of downwelling light field just beneath the surface of water

针对不同风速造成的粗糙水面、不同入射光场,利用射线跟踪法计算了无云状况下水表下行光场的平均余弦。结果表明:对不同入射光场而言,不同风速对其几何结构的改变程度及趋势有着明显的不同,在较小直射入射的天顶角情况下,天空漫射光的比例越高,水体表层下行光场平均余弦随风速的递增而递减得越小;但当直射天顶角大到一定程度时(如:80°时),其值会随风速而增大,且直射比例越高,这种趋势越明显。太阳直射光比例越高,在风速越小时,不同太阳天顶角情况下的水体表层下行光场平均余弦的差别越大,而风速越大,其差别越小。该研究有利于水体固有光学特性的反演、提高水体初级生产力的计算精度,且该方法的计算量小,精度也较高。

The direction of incident radiance is changed by the coarse surface of water which caused by the wind. At the same time, the reflectance, the transmittance and the geometrical structure of the incident light beneath the surface of water is also changed.In this paper, the mean cosine of the downwelling incident light fields just beneath different coarse surfaces due to different wind speed in a cloud-free sky is investigated by means of the ray tracing. The results show that the geometrical structure of the downwelling light fields beneath the surface of water and their trends of changed are significantly affected by wind speed. When the zwnith angle of direct sunlight is small, the percentage of diffused light in the atmosphere is higher, and the decreasing mean cosine is smallwe with the incresing wind speed .While in a bigger zenith angle （as 80°）, the mean cosine increase with the wind speed, and this trend is more clear with the increasing of direct sunlight. In the condition of higher percentage of the direct sunlight, the difference of the mean cosine of different zenith angle is inversed with the wind speed. This research is helpful for inversion of the inherent optical property of the water, and it can improve the precision of estimating primary production. Moreover, this method acn reduce the computations and get quite precise results.