# Angle variable spectrum¶

An angle variable spectrum describes, as its name suggests, a spectrum that
depends on an angle between 0° and 90°, generally an angle of incidence.
It is used by various nodes, such as *Mixed tabulated interface law*

The data is provided as a list of *spectra* representing the values between normal and grazing incidence.
The scale and interpolation formula can be of three types:

- Angle scale : the first spectrum is the value at θ=0° (normal incidence) and the last one is the value at θ=90° (grazing incidence). Intermediate spectra correspond to values at evenly spaced angle values between 0° and 90°.
- Cosine scale : the first spectrum is the value at cosθ=0 (grazing incidence) and the last one is the value at cosθ=1 (normal incidence). Intermediate spectra correspond to values at evenly spaced cosine values between 0 and 1
- Schlicks scale : the first spectrum is the value at θ=0° (normal incidence) and the last one is the value at θ=90° (grazing incidence).
Intermediate spectra correspond to angles at evenly spaced (1-cos θ)
^{5}values. This is a generalization to the Schlick’s approximation.

Note

Using this feature requires an Advanced Edition license

## Children Nodes¶

This node is a *Spectrum* list. It may have a variable number of spectrum children.

user-defined | First spectrum |

user-defined | Second spectrum |

user-defined | ... |

## Parameters¶

name | type | description |
---|---|---|

scale | list | The angular scale, must be angle, cos or schlicks |

## Ocean XML 3.0 example¶

```
<avspectrum type="" name="lobe" scale="angle">
<spectrum type="tabulated" name="1">4E-7 192.2 5E-7 223.4 6E-7 236.9 7E-7 245.3</spectrum>
<spectrum type="tabulated" name="2">4E-7 1.430 5E-7 1.796 6E-7 1.618 7E-7 1.434</spectrum>
<spectrum type="tabulated" name="3">4E-7 0.971 5E-7 1.330 6E-7 1.230 7E-7 1.113</spectrum>
<spectrum type="tabulated" name="4">4E-7 0.627 5E-7 0.943 6E-7 0.888 7E-7 0.824</spectrum>
</avspectrum>
```