1. R. Bellman, R. Kalaba andM. Prestrud,Invariant imbedding and radiative transfer in slabs of finite thickness (American Elsevier, 1963).
2. R. Bellman andG. M. Wing,An introduction to invariant imbedding (John Wiley and Sons, 1975).
3. S. Chandrasekhar,Radiative transfer (Dover Publications, 1960).
4. A. W. England (1974),Thermal microwave emission from a half space containing scatterers, Radio Science,9, 447?454.
5. A. W. England (1975),Thermal microwave emission from a scattering layer, J. Geophys. Res.,80, 4484?4496.