Direction Characteristic of Radiation Energy and Transmission Characteristic of Waters at Water-air Surface

COART,a coupled ocean and atmosphere radiative transfer model,was used to simulate the water-leaving radiance of a rough surface and upward radiance just below the surface under varying observation geometric angles.Using these simulations,we analyzed the spatial distribution characteristics of the water-leaving radiance and the transmission coefficient of the upward radiance just below the surface,and discussed the effects of rough surface on these distribution characteristics.The results shows that downward and upward irradiances just below the surface decrease as solar zenith angle(SZA) increases,with a linear relations to the cosine value of solar zenith angle.The spatial distribution characteristics of the water-leaving radiance are not involved with wind-driven rough surface.A simple cubic equation was developed to fit water-leaving radiance change to viewing zenith angle.Under the conditions of the level sea surface,the transmission coefficient of the upward radiance just below the surface does not change with the viewing azimuth angle,however,it decreases with the increasing viewing zenith angle and is linear to its square tangent value.On a rough surface,the viewing zenith angle plays a more important role in determining the transmission coefficient of the upward radiance just below the surface than viewing azimuth angle.In addition,the linear relationship also exists between transmission coefficient and the square tangent value of viewing zenith angle.