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Workspace Method surfaceSplitSpecularTo3beams

Description

A very simple approximation of a semi-specular surface.

This method has no direct physical basis but could be used for simpler
testing or as starting point for more advanced methods.

The method requires that the surface RT properties (e.g. surface_los)
have been set up to mimic a specular surface. This method splits the down-
welling radiation into three directions. The specular direction is given
weight w, while the other two beams each get weight (1-w)/2. The basic
polarised reflectivity from the specular calculations is maintained
for each beam. The beams are just separated in zenith angle, with a
separation of *dza*. The lowermost beam is not allowed to be closer to
the surface than 1 degree. If there is no room for the lowermost beam,
it is merged with the main beam.

Authors: Patrick Eriksson

Synopsis

surfaceSplitSpecularTo3beams(

surface_los, surface_rmatrix, atmosphere_dim, rtp_pos, rtp_los, specular_factor, dza )

Variables

OUT+IN	surface_los	(Matrix)	Downwelling radiation directions to consider in surface reflection.
OUT+IN	surface_rmatrix	(Tensor4)	The reflection coefficients for the directions given by surface_los to the direction of interest.
IN	atmosphere_dim	(Index)	The atmospheric dimensionality (1-3).
IN	rtp_pos	(Vector)	Position of a radiative transfer point.
IN	rtp_los	(Vector)	Line-of-sight at a radiative transfer point.
GIN	specular_factor	(Numeric)	The weight given to the specular direction. Denoted as w above. A value between 1/3 and 1.
GIN	dza	(Numeric)	Zenith angle seperation to each secondary direction. A between 0 and 45 degrees.