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Agenda ppath_step_agenda

Calculation of a propagation path step.

A propagation path step is defined as the path between some point 
to a crossing with either the pressure, latitude or longitude grid,
and this agenda performs the calculations to determine such a 
partial propagation path. The starting point is normally a grid 
crossing point, but can also be an arbitrary point inside the 
atmosphere, such as the sensor position. Only points inside the 
model atmosphere are handled.

The communication between this agenda and the calling method is 
handled by ppath_step. That variable is used both as input and 
output to ppath_step_agenda. The agenda gets back ppath_step 
as returned to the calling method and the last path point hold by 
the structure is accordingly the starting point for the new 
calculations. If a total propagation path shall be determined, this
agenda is called repeatedly until the starting point of the 
propagation path is found and ppath_step will hold all path 
steps that together make up ppath. The starting point is included
in the returned structure. 

The path is determined by starting at the end point and moving 
backwards to the starting point. The calculations are initiated by 
filling ppath_step with the practical end point of the path. 
This is either the position of the sensor (true or hypothetical), 
or some point at the top of the atmosphere (determined by
geometrical calculations starting at the sensor). This 
initialisation is not handled by ppath_step_agenda (but by 
the internal function ppath_start_stepping). 

The ppath_step_agenda put in points along the propagation path 
at all crossings with the grids, tangent points and points of 
surface reflection. It is also allowed to make agendas that put in 
additional points to fulfil some criterion, such as a maximum 
distance along the path between the points. Accordingly, the 
number of new points of each step can exceed one.

The include file 'agendas.arts' defines some agendas that can be
used here.

Group: Agenda


OUTppath_step(Ppath) A propagation path step.
INppath_step(Ppath) A propagation path step.
INppath_lmax(Numeric) Maximum length between points describing propagation paths.
INppath_lraytrace(Numeric) Maximum length of ray tracing steps when determining propagation paths.
INf_grid(Vector) The frequency grid for monochromatic pencil beam calculations.

Specific methods that can generate ppath_step_agenda

Generic and supergeneric methods that can generate ppath_step_agenda

Specific methods that require ppath_step_agenda

Generic and supergeneric methods that can use ppath_step_agenda

Agendas that can generate ppath_step_agenda

Agendas that require ppath_step_agenda