Collections of straight, RADAR-bright, linear features, or BLFs, on Saturn's moon Titan are revealed in Cassini SAR (Synthetic Aperture RADAR) images. Most are widely distributed across the northern midlatitudes SAR on SAR swaths T18, T23, T30, T64, and T83 and in swath T56 in the southern midlatitudes. To understand the origin of these features, we compare them with terrestrial yardangs in Dunhuang, China, the Altiplano/Puna of Argentina, and the Lut Desert of Iran and with a similar morphological landform, linear dunes in the Namib Sand Sea, Namibia and on Titan. We apply a statistical classification model developed through random forests, a type of decision tree classification system, grown with terrestrial and titanian training data to the BLFs. To develop the classification, we measured sinuosity, width, spacing, and length for all of the BLFs and their possible terrestrial analogs. We interpret the features in T18, T64-1, and T83 as yardangs based upon morphological similarities between them and features in Iran and Argentina, such as overall SAR brightness, straightness, and lack of branching. Similarities exist between the BLFs and terrestrial yardangs in sinuosity and spacing—sinuosity values range from 1.00 to 1.04 for all the BLFs, and terrestrial yardangs in Iran range from 1.00 to 1.001. A generated statistical model classified a large number of yardangs in T18 and T64-1. In contrast, we interpret the BLFs in T23 and T30 as stabilized linear dunes due to similarities in sinuosity, spacing, and scale with linear dunes in the Namib Sand Sea and Titan swath T3. Stabilized linear dunes may be slightly brighter than the SAR-dark dunes due a change in dielectric constant from introduction of liquids and subsequent stabilization or from the formation of a crust over the top the feature. Sinuosities range from 1.00 to 1.37 in T23 and T30 whereas dunes in the Namib and in T3 range from 1.01 to 1.05. Branching behavior similar to dunes are also observed in BLFs in swaths T23 and T30. The BLF features in T56 in the southern hemisphere we interpret to be dune-related, likely SAR-bright (rough) inter-dune areas. We base this interpretation on the presence of SAR-dark lineations between the BLFs that may be linear dunes. The statistical model classifies few yardangs in T23, T30, and T56. We conclude that statistical classification of these features can be performed. We also show that yardang orientations may aid in the development of global climate and wind models as both current and paleo wind direction indicators.

Despite atmospheric and compositional differences on Titan and Earth, the similarity in the shape and spacing of linear dunes of the Belet Sand Sea of Titan and the Namib Sand Sea of Earth suggests that comparisons will yield a better understanding of the dictating factors of duneforming processes. We present a methodology for the collection of dune width and spacing measurements representative of the Namib and Belet sand seas. 94,304 locations in Belet from Cassini SAR images and 5,563 locations in the Namib from IKONOS images are used for measurements. The average width and spacing of linear dunes in Belet are 1,235 m and 2,776 m, respectively, with a standard deviation of 422 and 859 respectively. In the Namib, the average linear dune width and spacing is 736 m and 2,203 m, with a standard deviation of 204 and 592. We also analyze these morphometrics according to potential dictating factors such as elevation and distance to sand sea margins. We establish significant trends according to distance to margin, which confirms that the largest and most widely spaced dunes are generally found in the center of the sand sea. We also observe increasing dune width with increasing elevation. The strongest trend we observe is distance to the western margin in the Namib Sand Sea. In Belet, none of these trends were found to be significant. Analysis of width vs. spacing is significant in both sand seas. The disparity in results of the two sand seas suggests factors such as age, sand sea size, or proximity to source may influence linear dune morphometrics.

Analyzing dune parameters such as dune width and spacing can be useful in determining the reaction of dunes to changes in atmospheric and sedimentary conditions currently and in the recent geologic past. Dune parameters, dune width and spacing, were measured for linear dunes in regions across Saturn's moon Titan from images T21, 23, 28, 44 and 48 collected by Synthetic Aperture RADAR aboard the Cassini spacecraft in order to reconstruct the surface history of Titan. Dunes in the five study swaths are all linear in form, but lack superimposed or flanking dunes. They have a mean width of 1.3 km and mean crest spacing of 2.7 km, wider and farther apart on average than similar terrestrial dunes in the Namib and Agneitir Sand Seas though larger linear dunes exist on Earth. Because of the lack of superimposed and flanking dunes and their size, Titan's dunes are classified as very large simple linear dunes. The large size, spacing and uniform morphology are all indicators that Titan's dunes are very mature and long-lived features. The ratio of dune width to spacing for Titan's dunes is similar to that found in terrestrial dunes in that dune spacing tends to be twice dune width. In addition to being similar in size, this is further evidence that terrestrial dunes can be used as analogues for Titan's dunes and vice versa and that the essential dune-forming processes are the same on both bodies. Dune width and spacing decrease northward, which is attributed to, but not limited to, increased maturity of dune fields to the south or increased sediment stabilization to the north. Sediment stabilization may be caused by Titan's asymmetric seasons and a net transport of moisture from south to north. The majority of dunes have spacings consistent with an upper limit of 2 to 4 km established by the atmospheric boundary layer, further evidence they are mature. Dunes are more widely spaced in the south are evidence they have been growing toward a steady state for a longer period of time than those in the north. Titan's large linear dunes have long reconstitution times. This is in part due to the fact that winds sufficient for saltation are reached only near the Titan equinox every 14 Earth years. Based on rates for similar terrestrial dunes the reconstitution time for Titan's dune is 600,000 Earth years or more, and therefore substantial changes in dune form should not be observable over Cassini's lifetime. Cumulative probability plots of dune parameters measured at different locations across Titan indicate there is a single population of dunes on Titan. This suggests that, unlike analogous dunes in the Namib and Agneitir Sand Seas, dune-forming conditions that currently exist on Titan are either the only dune-friendly conditions in the moon's history, or the current conditions have been stable and active long enough to erase any evidence of past conditions.

Understanding modern features allows for their use as analogues for understanding the environments of the past and even environments on other planetary bodies. This study uses Ground-Penetrating Radar (GPR) to image the near surface sedimentary structures on a large linear dune in the northern Namib Sand Sea and image the sedimentary structure of an auxiliary dune. GPR data was collected using a 200 MHz antenna with a continuous scan method and was processed by removing direct arrival, gain balancing, migration and more which produced the highest resolution imagery from this region to date. Large dune data was analyzed to determine depositional process for different sedimentary patterns observed. Auxiliary dune data was analyzed to determine dune type and migration direction. Our results indicate five sedimentary process zones in the near surface of the large primary dune. These processes include motion of the dune crest as well as different phases of superimposed dune deposition. It is evident from our interpretation that there have been at least two phases of superimposed dune deposition separated by an erosional process boundary. These phases of deposition have produced a reversed succession of strata on opposing sides of the dune with deposits of 3D superimposed dunes beneath 2D superimposed dune deposits on the west and deposits of 2D superimposed dunes beneath 3D superimposed dune deposits on the east. This suggests a reversal of wind environment in the region in the recent past and could provide insight into the building and stability of linear dunes on Earth. Our results also indicate that the auxiliary study dune is oblique in nature with migration to the north-northeast and that it and other similar dunes in the vicinity are formed because of their proximity to Tsondab Vlei. The apparent dependence of these smaller scale features on interruptions in the dunefield like Tsondab Vlei suggest that the normal wind patterns within the dunefield are a combination of the regional wind patterns with significant influence from the large linear dunes themselves.

Linear dunes are one of the most abundant and important features on the surface of Titan. We present a model for estimating the volume of dune sediment using the area coverage of Titan's sand seas along with dune widths, spacings, and heights. This helps to reveal local sediment transport and deposition. We refine global dune area estimates from Cassini SAR (Synthetic Aperture RADAR) of 20 million km2 or 24 ± 3% of Titan's surface based on ~50% Cassini RADAR global coverage. Additionally, the global area of sand seas is estimated from a joint analysis of Cassini SAR and ISS (Imaging Science Subsystem) images of 12.8 ± 2 million km2 or 15.4 ± 2.4% of Titan's surface. Also, we provide the first area measurements by sand sea, then describe a new method for estimation of the volume of dune sands across the sand seas based on imagery and measured dune characteristics (i.e., width, spacing, profile, and height) on Titan and in Earth's Namib Sand Sea. Our volume thickness map shows sand sea volumes of 3.8--7.9 x 104 km3 in Senkyo, 6.1--12.7 x 104 km3 in Belet, 5.3--11.0 x 104 km3 in Shangri-La, and also 5.3--11.0 x 104 km3 in Fensal and Aztlan Sand Seas. Our estimate for global dune sand volume is 206,000 km3 - 427,000 km3. The volume map identifies regional changes in sediment thickness implying local variations in transport and deposition and spatial variations in wind strength and direction. We show that dunes might be isolated to equatorial regions because of wind strength, topography, sediment supply, and humidity. Our preliminary map can be used as a tool to understand sediment transport and deposition to explain spatial variations in eolian sediment volume on Titan.