path_endpoint

pycraf.atm.path_endpoint(elevation, obs_alt, atm_layers_cache, max_arc_length=<Quantity 180. deg>, max_path_length=<Quantity 1000. km>)

Calculate endpoint of propagation path through atmosphere by ray-tracing.

Like raytrace_path this calculates the exact path geometry of a propagating ray through Earth’s atmosphere. The difference to raytrace_path is that only the final point is returned. This is sufficient for some applications, e.g., when an elevation angle needs to be determined with an optimization algorithm (see find_elevation).

Parameters:

elevationQuantity, scalar

(Apparent) elevation of source/target as seen from observer [deg]

obs_altQuantity, scalar

Height of observer above sea-level [km]

atm_layers_cachedict

Pre-computed physical parameters for each atmopheric layer as returned by the atm_layers function.

max_path_lengthQuantity, scalar

Maximal length of path before stopping the ray-tracing [km]

(default: 1000 km; useful for terrestrial paths)

max_arc_lengthQuantity, scalar

Maximal arc-length (true angular distance between observer and source/ target) of path before stopping ray-tracing [deg]

(default: 180 deg; useful for terrestrial paths)

Returns:

a_nQuantity, scalar

Length of path through final layer of the ray-tracing. [km]

This is not too useful (perhaps for space-paths, where it gives the fraction of the path that doesn’t go through the atmosphere.)

r_nQuantity, scalar

Distance to Earth’s center after complete ray-tracing. [km]

h_nQuantity, scalar

Height above Earth’s surface after complete ray-tracing. [km]

x_n/y_nQuantity, scalar

Cartesian coordinates of path complete ray-tracing. [km] The reference is Earth’s center. Starting point is (0, r_E + obs_alt).

alpha_nQuantity, scalar

Exit angle of path after going through the layer (relative to surface normal vector) after complete ray-tracing. [km]

delta_nQuantity, scalar

Angular distance of path position after complete ray-tracing w.r.t. starting point. [deg]

The polar coordinates (r_n, delta_n) are directly associated with the cartesian coordinates (x_n, y_n).

layer_idxint

Index of the layer, through which the path went during the last step. This is probably only useful for debugging purposes.

path_lengthQuantity, scalar

Total path length of the propagation path. [km]

nstepsint

Number of steps the algorithm performed.

refractionQuantity, scalar

Refraction angle (i.e., the total “bending” angle of the ray) [deg]

is_space_pathbool

Whether the paths ends outside of Earth’s atmosphere (in terms of the atmospheric profile function used).

Notes

Terrain heights are neglected by the atm sub-package. All heights are w.r.t. the flat (spherical) Earth (with a radius of 6371 km).

See also raytrace_path.