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.
