Observations of the surface of Titan by the Radar Altimeters on the Huygens Probe

•Describes instrument operations and unique datasets in Huygens archive.•Uses terrestrial balloon tests and satellite data to aid interpretation.•Shows topography near landing site.•Identifies strong radar reflectivity with some unusual characteristics.

Results from the radar altimeters on board the Huygens probe are reported, noting the content of data archived on the NASA Planetary Data System and its ESA counterpart. These instruments provide unique high-resolution information on the topography and electrical properties of the Titan surface over a ∼15 km track across a boundary between a bright highland and the dark dissected alluvial terrain on which the probe landed. The highland appears ∼100 m higher than the dark terrain. The dark terrain has a fairly high nadir radar backscatter, consistent with terrestrial lakebeds and alluvial surfaces, and shows small (5–10 m) elevation fluctuations. Possible signatures of surface or volume scattering in the backscatter amplitude and intermediate frequency spectrum are discussed. A previously-undocumented characteristic of the Automatic Gain Control (AGC) on the flight altimeter is noted.