General scattering and absorbing media

IN PROGRESS

PlanarRad was designed for use with data corresponding to natural water bodies, however it can be used to model the light field or reflectance properties of homegenous slabs of any kind of media, as long as the following inputs are known at the wavelength to be modelled:

• The extinction coefficient (a.k.a. the attenuation coefficient, c, they are the same thing).
• The absorption coefficient, a.
• The refractive index inside and outside the media.
• The phase function, i.e. the angular probability of scattering when it occurs.

These concepts may be expressed in other ways that contain the required information. For example if you have a volume scattering function (VSF) and single scattering albedo. you can then calculate c, a and the phase function. Depending on the material you might be able to assume an isotropic phase function - that at each scattering event the direction of scattering is equally probable in any direction over the sphere, and that simplifies things.

The method described below assumes that the interface of the slab, what we might call the air-media interface (assuming whatever you're interested is in air) is completely flat. If it isn't the interface transmission and reflectance function needs to be modified and unfortunatly PlanarRad currently only has methods for doing that that are appropriate for wind-blown water surfaces. If you need additional functionality then it is worth contacting me.