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Workspace Method surfaceSemiSpecularBy3beams

Description

A simplistic treatment of semi-specular surfaces.

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

This method assumes that the surface can be treated to have three facets,
all lacking surface roughness. One facet is assumed to give standard
specular reflection, while the two other facets are tilted with +dza
and -dza, respectively. The tilt is assumed to only affect the zenith
angle of the reflected direction (azimuth same as for specular direction).
The area ratio of the non-tilted facet is set by *specular_factor*.
That is, the specular beam is given weight w, while the other two beams
each get weight (1-w)/2.

If a facet tilts away from the viewing direction in such way that
the surface is observed from below, the tilt of the facet is decreased
in steps of 1 degree until a successful calculation is obtained. If this
turns out to require a tilt of zero, this facete is merged with
the specular direction.

The pure specular properties of the surface shall be described by
surface_rtprop_sub_agenda. That is, if you have specular surface
described and you want to make it semi-specular by this method, you
move the content of the existing surface_rtprop_agenda to
surface_rtprop_sub_agenda and instead fill surface_rtprop_agenda
with this method.

Authors: Patrick Eriksson

Synopsis

surfaceSemiSpecularBy3beams(

surface_skin_t, surface_los, surface_rmatrix, surface_emission, atmosphere_dim, f_grid, rtp_pos, rtp_los, surface_rtprop_sub_agenda, specular_factor, dza )

Variables

OUT	surface_skin_t	(Numeric)	Surface skin temperature.
OUT	surface_los	(Matrix)	Downwelling radiation directions to consider in surface reflection.
OUT	surface_rmatrix	(Tensor4)	The reflection coefficients for the directions given by surface_los to the direction of interest.
OUT	surface_emission	(Matrix)	The emission from the surface.
IN	atmosphere_dim	(Index)	The atmospheric dimensionality (1-3).
IN	f_grid	(Vector)	The frequency grid for monochromatic pencil beam calculations.
IN	rtp_pos	(Vector)	Position of a radiative transfer point.
IN	rtp_los	(Vector)	Line-of-sight at a radiative transfer point.
IN	surface_rtprop_sub_agenda	(Agenda)	Sub-agenda to surface_rtprop_agenda.
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.