# Angle variable spectrum¶

An angle variable spectrum describes, as its name suggests, a spectrum that depends on an angle, generally an angle of incidence. It is used by various nodes, such as Mixed tabulated interface law or Tabulated scattering.

The data can be provided as a table with a fixed number of wavelength (in the first row) and angle. Each row corresponds to a spectrum of a given angle (indicated in the first column).

The scale and interpolation formula can be of three types:

• Angle scale : the values must be given between θ=0° (same direction as incidence) and θ=180°(opposed direction as incidence). Intermediate values are evenly spaced angle values between 0° and 180°.

• Cosine scale : the values must be given between cosθ=-1 (same as θ=180°) and cosθ=1 (same as θ=0°). Intermediate spectra correspond to values at evenly spaced cosine values between -1 and 1

• Schlicks scale : the values must be given between cosθ=-1 (same as θ=180°) and cosθ=1 (same as θ=0°). Intermediate values correspond to angles at evenly spaced (1-cos θ)5 values. This is a generalization to the Schlick’s approximation.

In each case, outrange values are dropped and missed values are filled with borders values.

Note

## Parameters¶

name

type

description

scale

list

The angular scale, must be angle, cos or schlicks

numwl

integer

The number of wavelenghts

## Ocean XML 6.1 example¶

<avspectrum name="phasefunc" scale="angle"  numwl="41">
3.80E-07    3.90E-07    4.00E-07    4.10E-07    4.20E-07    4.30E-07    4.40E-07            [...]
0.00 2.30417E-01 2.44413E-01 2.10753E-01 1.27251E-01 1.12964E-01 1.15013E-01 1.16951E-01         [...]
1.80 2.30152E-01 2.44122E-01 2.10479E-01 1.27149E-01 1.12910E-01 1.14960E-01 1.16896E-01         [...]
3.60 2.29360E-01 2.43249E-01 2.09660E-01 1.26845E-01 1.12747E-01 1.14801E-01 1.16732E-01         [...]
5.40 2.28047E-01 2.41802E-01 2.08303E-01 1.26341E-01 1.12476E-01 1.14538E-01 1.16458E-01         [...]
[...]
</avspectrum>