Reflection Coefficient of Omega

The data available for omega in water is interpolated and extrapolated (as a function of angle and wavelength) via a spline fit using the following assumptions:

• At glancing incidence, both reflectivities will tend to unity. ie as $\theta \longrightarrow 90^{\circ}$, $R_{s,p} \longrightarrow 1$.

• The two polarisations will have the same value at $\theta= 0^{\circ}$.

• $(R_s + R_p)/2$ has the same value at $0^{\circ}$ as it does at $20^{\circ}$.

The first two assumptions are based on the usual behaviour of Fresnel's laws, and are therefore good assumptions. The last assumption is supported by a visual inspection of the omega surface, and any error made here will be mitigated by the geometry of the reflectors; any photon hitting the omega at a small angle will almost certainly not hit the phototube. The spline fit was subsequently used to generate a look-up table, this being far faster than using the spline fit itself.

Diffuse scattering fro the Omega is implemented, albeit in a primitive form. Control of this is vested in the GEDS 400 bank. Currently, diffuse scattering is only enabled as a fixed percentage of the light, regardless of incident angle or wavelength. The exact percentage of scattering is controlled in the GEDS bank, and may be switched off.