On the relationship between direct and diffuse radiation

The relationship between the direct and diffuse radiation is analyzed. It is shown that the solution of diffuse radiation is a special case of the solution for direct radiation. No extra effort is needed to find out the solution of diffuse radiation. Under the single-layer condition, the diffuse reflection/transmission/absorption are compared for the two-stream and four-stream approximations. It is found that the δ-four-stream approximation can dramatically improve the accuracy of the δ-two-stream approximation, with relative error generally less than 5%.

► The difference of direct and diffuse radiation is mainly from the boundary condition. ► The relationship between the direct and diffuse radiation is analyzed. ► No extra effort is needed to find out the solution of diffuse radiation. ► The comparisons of the single-layer diffuse reflection/transmission/absorption.