Hapke model

Based on Hapke (2002). Optionally including the shadow-hiding opposition effect term.

Usage

Example:

using HapkeModel
model = ScatteringModel(HenyeyGreenstein(0.5), 0.1)
r = BRDF(model, 0.0, 0.0, 0.0)

To define a scattering model without the Shadow-Hiding Opposition Effect (SHOE) term, call model = ScatteringModel(P, w), where P is a PhaseFunction and w is the single-scattering albedo.

To use the SHOE term, define the model with:

• model = ScatteringModel(P, w, hs), where P is a PhaseFunction, w is the single-scattering albedo, and hs is the shadowing parameter (eq. 28-30 in Hapke, 2000), or
• model = ScatteringModel(P, w, E, a, phi), where P is a PhaseFunction, w is the single-scattering albedo, E is the extinction coefficient in the medium, a the mean particle radius, and phi the filling factor (eq. 30 in Hapke, 2000).

Be wary of the actual physical interpretation of the parameter values.

There are four options for PhaseFunction:

• Isotropic(), for isotropic scattering
• Rayleigh() for Rayleigh scattering
• HenyeyGreenstein(xi), for Henyey-Greenstein scattering, where xi is the asymmetry parameter.
• DoubleHenyeyGreenstein(c, xi), for Henyey-Greenstein scattering, where c is the weight parameter and xi is the asymmetry parameter.

To compute the value of the Hapke BDRF for a given scattering model, call BDRF(model, mu0, mu, g) where model is a ScatteringModel object, mu0 and mu are the cosines of incidence and emergence, and g is the phase angle.