Cassini Bistatic Radar Experiments on Titan’s Solid Surfaces: Progress Update on Flybys T14, T27, T34 and T124

Between 2006 and 2016, the Cassini mission has conducted 13 downlink bistatic radar (BSR) radio science experiments of Titan’s surface. These experiments employ the High-Gain Antenna (HGA) onboard the Cassini spacecraft as transmitter and NASA’s Deep Space Network (DSN) antennas on Earth as receivers to establish a bistatic radio link bouncing off the surface of Titan. The distinct detection of X-band (λ=3.6 cm) returns from some of the observed Titan regions across different latitudes and longitudes allows to constrain surface roughness and near-surface composition based on the investigation of waveforms’ amplitude, frequency and polarization.

Solid terrains probed by Cassini BSR experiments produce heterogeneous reflections ranging from broad and weak returns to narrower and more powerful echoes or a combination of both. This is indicative of different dominant scattering mechanisms. For purely specular returns, RMS slopes and dielectric constant values—connected to near-surface structure and composition—are retrieved using a Gaussian fit applied to echo spectra, as previously done in BSR data analysis. For weaker returns, contaminated or dominated by diffuse scattering, a full scattering-model-informed fitting approach that combines specular and diffuse reflection components is applied to decuple the two contributions and more accurately characterize surface properties.

Herein, we present a progress update on the analysis of BSR experiments from flybys T14, T27, T34 and T124, highlighting regional variations in forward scattering and providing preliminary findings on surface roughness and near-surface dielectric constant of various regions on Titan. When possible, we exploit echo recordings from different, independently calibrated DSN antennas and discuss and compare BSR results with surface properties inferred from both Earth-based and Cassini (monostatic) RADAR observations.