Syntax:

[out,data,ver] = skyline(az,el,strike,dip)

This function calculates the topographic shielding correction to the cosmic-ray flux at a site whose horizon is obstructed either by a dipping surface or by the surrounding topography.

The input arguments `strike`

and `dip`

are the strike and dip of the sampled surface in degrees.

The input arguments `az`

and `el`

are vectors containing the azimuths (degrees; 0 az 360; north = 0) and horizon angles (degrees; 0 el 360; zenith = 90) of points on the horizon.

`out`

is the shielding correction for the sample (nondimensional; the ratio of the nuclide production rate at the shielded site to the nuclide production rate at an unshielded site at the same location).

`data`

is a vector containing the interpolated horizon angle visible to the sample, in degrees, for 1-degree increments of azimuth. It can be used to plot the horizon, e.g., `plot(0:360,data)`

`ver`

is a string variable containing the version number of the function.

The calculation goes as folllows:

First, we divide the range of azimuths into 1-degree increments.

Second, we calculate the horizon angle of the dipping surface as a function of azimuth:

(73) |

where is the dip and is the strike of the surface.

Third, we interpolate the supplied horizon points to give the horizon angle of the topography as a function of azimuth.

Fourth, at each increment of azimuth, we take the higher of the horizon angle due to the dipping surface or the horizon angle due to the surrounding topography to be the horizon angle visible to the sample. This results in a vector which defines the visible horizon angle at each increment of azimuth .

Finally, the fraction of the cosmic-ray flux that lies below the horizon angle in the increment of azimuth at is:

(74) |

where is the width of the azimuth increment in radians (). The total fraction of the cosmic-ray flux that lies below the horizon is the sum of the values of for each increment of . The topographic shielding correction is then .