Analytic green's function for radiative transfer in plane-parallel atmospheres

Green’s function is a widely used approach for boundary value problems. In problems related to radiative transfer, Green’s function has been found to be useful in land, ocean, and atmosphere remote sensing. It is also a key element in higher order perturbation theory. This paper presents an explicit expression of the Green’s function, in terms of the source and radiation field variables, for a plane-parallel atmosphere with either vacuum boundaries or a reflecting [atmosphere–bidirectional reflectance distribution function (BRDF)] surface. A FORTRAN 95 code, Green’s function and discrete ordinate method (GDOM), has been developed to efficiently compute the Green’s function. This code also integrates with an implementation of the discrete ordinate method with several extensions and improvements. Computing complexity of the Green’s function algorithm is analyzed, and validation of the code is discussed.