Modeling Cassini-Titan backscatter data

The Cassini spacecraft has obtained several backscatter observations of the surface of Titan at 2.18 cm-lambda. We report the results of data reduction of the T3 dataset. Using radar equation, the received backscatter power by Cassini RADAR is converted to monostatic radar cross section (RCS) measurements. The variation of RCS with the angle of incidence is then modeled using a superposition of a quasi-specular scattering law and the diffuse cosine law. From the parameters of the quasi-specular law, we obtain estimates for the root-mean-square (RMS) slope of the surface and the dielectric constant of surface material. The latter allows us to conjecture about the composition of the surface. We use various quasi-specular models like Hagfors, Gaussian, and exponential models and a linear superposition of these. We determine the best model to fit our data according to the minimum residual. We compare the values of dielectric constant and RMS slope of the surface provided by each model. For example, the Gaussian plus exponential quasi-specular model gives a surface dielectric constant between 1.9 and 2.8. Dielectric constants between 2 and 3 are expected for a surface composed of solid simple hydrocarbons, water ice, or a mixture of both [Lorenz, R.D., 1998. Icarus 136, 344-348].