Six-Stream Spherical Harmonic Expansion Approximation for Solar Radiative Transfer

This study presents a six-stream spherical harmonic expansion approximation scheme (δ-6SDA) for solar radiation by considering the sixth-order spherical harmonic expansion in radiative intensity. By applying δ-6SDA into two scattering mediums, it is found that δ-6SDA is more accurate than the four-stream spherical harmonic expansion approximation scheme (δ-4SDA) and Eddtington scheme (δ-2SDA), especially for thin optical depth. And another distinct advantage of δ-6SDA is that it can also calculate the bidirectional reflectance accurately after TMS correction. Computationally, δ-6SDA is more faster than the discrete ordinate method. In view of its high accuracy and computational efficiency, δ-6SDA is well suitable for resolving the solar radiative transfer in remote sensing.