Los Struct Reference

The line of sight (LOS). More...

#include <los.h>

List of all members.

Public Attributes

ArrayOfVector p

ArrayOfVector psi

ArrayOfVector z

Vector l_step

ArrayOfIndex ground

ArrayOfIndex start

ArrayOfIndex stop

Detailed Description

The line of sight (LOS).

The LOS structure has the fields (the type name is Los):

       ArrayOfVector  p
       ArrayOfVector  psi
       ArrayOfVector  z
       Vector         l_step
       ArrayOfIndex   ground
       ArrayOfIndex   start
       ArrayOfIndex   stop
    where 
       p        The pressure of each point of the LOS.
       psi      The angle in the observation plane between the vectors going
                from the sensor and the LOS point, respectively, to the centre
                of the earth geoid.
       z        The vertical altitude of each point of the LOS. These altitudes
                shall not be used fir the following calculations (the pressures
                shall be used), but are included as they can be handy for 
                plotting, checking the algorithms etc.
       l_step   The geometrical length along LOS between the points.
       start    start index for the iteration
       stop     stop index for the iteration
       ground   0 if no intersection with the ground. Else, GROUND
                gives the index+1 for the ground.

The LOS is defined in equal long geometrical steps along the path. This step length (L_STEP) is set to the user defined value, beside for downward observations inside the atmosphere where L_STEP is adjusted to the distance between the sensor and the tangent point, or the ground. The latter adjustment is done in such way that an integer number of steps is obtained between the two points. The highest possible value for L_STEP below the used defined value is selected.

Spectra are calculated in the following way (by RTE_ITERATE in m_los):

Iteration from START down to 0 or GROUND
If GROUND, including the effect of the ground reflection.
Iteration from 0 or GROUND-1 to STOP

The START and STOP variables make it possible to use a possible symmetry for 1D calculations. For example, for limb sounding from space, START and STOP are both set to the length of P - 1. The GROUND variable is for 1D calculations either 0 or 1. The psi angles for 1D cases are valid for the part of the LOS furthest away from the sensor.

For cases without symmetry (upward looking and 2D), STOP is always 0 and corresponds to the point closest to the sensor. Accordingly, START corresponds to the point of LOS furthest away from the sensor.

The GROUND variable is used both as a flag to indicate ground intersections of the LOS, and a variable to give the position of the ground. As mentioned, for 1D cases, the ground is always placed at index 0. For 2D cases, GROUND gives the index+1 for the ground point, that is, the point of LOS with index GROUND corresponds to the ground level.