Modeling quasi-specular scattering from the surface of Titan

The Cassini spacecraft obtained several scattering observations of the surface of Titan. Four data sets, TA-Inbound, TA-Outbound, T3-Outbound, and T8-Inbound, include scatterometer data for small angles of incidence. Analysis of these data sets provides an example use of a new generalized fractal-based quasi-specular scattering law that gives the surface RMS slope as a function of horizontal scale and covers a wide range of scattering behavior using a small number of parameters. The data have a significant diffuse scattering component which is modeled with the empirical cosine law, A cosn θ. The reflectivity and RMS surface parameters are retrieved from the quasi-specular scattering model. The average RMS slope for the four data sets is about 4.2° at a horizontal scale of 5λ; λ ≈ 2.18 cm. The Fresnel power reflection coefficient ρ is approximately equal to 0.085 (corresponding to a dielectric constant ε r ≈ 3.3) for TA-Outbound and T3-Outbound and 0.034 (εr ≈ 2.1) for TA-Inbound and T8-Inbound. Inadequate modeling of diffuse scattering by the cosine law results in increased uncertainties in the inferred surface parameters, especially ρ, and, consequently, in inferences of the surface composition. Copyright 2007 by the American Geophysical Union.