Dune Height Estimation on Titan Exploiting Pairs of Synthetic Aperture Radar Images With Different Observation Angles

Widespread longitudinal dunes have been identified on Titan thanks to the 2.2-cm wavelength Cassini Synthetic Aperture Radar (SAR) instrument. Understanding the properties of these surface features, such as material composition and dune height, is very important for giving new clues about the Titan geology and climate. One of the major difficulties in the estimation of dune heights using SAR occurs when the material composition of the dunes is heterogeneous. In this paper, we propose a novel method for dune height estimation, which takes into account material heterogeneity, and in particular, the case in which the interdune exhibits different dielectric properties with respect to the remaining part of the dune. Paired data acquisitions with orthogonal observations are considered for separating the dielectric from the geometric effect on the backscattering coefficients in order to retrieve the slope and thus the height of the dunes. The results for a test area located in the Fensal region indicate that the slopes of the dune faces are generally lower than 5° and the heights range between 40 and 110 m

Dual Frequency Orbiter-Radar System for the Observation of Seas and Tides on Titan: Extraterrestrial Oceanography from Satellite

Saturn’s largest moon, Titan, is believed to have a ~100 km thick ice shell above a global ocean of liquid water. Organic materials, including liquid hydrocarbon lakes and seas in its polar terrain, cover Titan’s surface, which makes it a world of two oceans. The RADAR instrument on board Cassini, was able to probe lakes and seas during few dedicated altimetric observations, revealing its capability to work as a sounder. Herein, we describe the design of, and scientific motivation for, a dual frequency X/Ka-band radar system that is able to investigate Titan’s subsurface liquid water ocean, as well as the depth and composition of its surface liquid hydrocarbon basins. The proposed system, which could take advantage of the telecommunications dish, can operate as a sounder, as Synthetic Aperture Radar (SAR) able to map the surface at tens meters of scale resolution, and when data are acquired from close-adjacent orbits, as a repeat-pass SAR interferometer (InSAR). The instrument, which is based on the architecture of the Cassini RADAR, can also characterize Titan’s interior by using geophysical measurements of the tidal amplitude to derive high accuracy estimates of the Love number h2 from a 1500 km circular orbit

Multiple Origins of Sand-Dune Topography Interactions on Titan

The interaction between sand-dune patterns and topographic obstacles is a primary signal of sand transport direction in the equatorial region of Saturn’s moon, Titan. A streamlined, tear drop appearance emerges as dune crestlines wrap around topographic obstacles and a dune-free zone develops on the east side of many obstacles. The morphologies formed by this interaction give the impression that sand transport is from the west to east in Titan’s equatorial region. However, this transport direction is in conflict with the expected wind regime based on Titan’s rotation and many global climate models. The physical mechanism behind the interpretation of the dune-obstacle interaction is not well explained, leaving a gap in the understanding of the sand transport and equatorial wind directions on Titan. In order to better understand this interaction and evaluate wind and sand transport direction on Titan, we take a two-fold approach to studying dune-topography interactions. We use optical imagery on Earth and Cassini radar imagery on Titan in ArcGIS to map spatial variations in dune crestline orientations proximal to obstacles. We also use digital elevation models to analyze the three-dimensional geometry – height, length, width and slope of the dune-topography relationships on Earth. We identify three types of obstacles: positive topography, neutral topography and negative topography. Positive topography is defined as double or more in relief than the surrounding dune height, neutral topography is at the surrounding dune height and negative topography is lower than the surrounding dune heights. Results show that dune patterns are deflected further away from positive relief than neutral or negative relief. Furthermore, positive relief has a dune free obstacle shadow, neutral relief has a smaller dune free obstacle shadow to no obstacle shadow zone, and negative relief has an obstacle shadow zone characterized by increased dune wavelength proximal to the obstacle’s wind-shielded side. The obstacle height, width, slope and wind variability appear to play a role in determining if a lee-dune, rather than a dune-free lee-zone forms. These factors provide further geomorphic evidence that sand transport directions on Titan were from west to east during the formation of the dune-obstacle interaction morphologies