Radarclinometry of the sand seas of Africa’s Namibia and Saturn’s moon Titan

Cassini SAR, radiometry, scatterometry and altimetry observations of Titan’s dune fields

“…Radarclinometric heights for some of the most prominent aeolian features in the equatorial sand seas were found to be 100-150 m (Lorenz et al 2006;Neish et al, 2010), in agreement with SAR stereo results (Kirk et al, 2009). Altimetry profiles have a vertical resolution on the order of 30 m but because the altimeter echo averages the topography over an area which is usually more than 20 km wide (i.e.…”

“…This corresponds to an area of $10 million km 2 , which is roughly the area of the United States, and a volume of sand-sized sediments that approaches $2.5 Â 10 5 km 3 , assuming 100 m-high dunes, clear-of-sand interdunes and an equal areal coverage between dunes and interdunes. More accurately, accounting for the variability in dune height (30-180 m, Barnes et al, 2008;Neish et al, 2010) and dune/interdune coverage fraction (35-60% as derived from Savage and Radebaugh (2011)) and considering a maximum thickness for the interdune sand cover of 5 m, we find that the volume of sediments in the dune fields should be within the range 0.5-5 Â 10 5 km 3 which represent an equivalent layer of $0.6-6 m. The sand budget is therefore most probably higher than the volume of liquid hydrocarbons on Titan which is currently estimated to be $0.3 Â 10 5 km 3 , accounting for the up-to-date distribution of the lakes and seas, assuming a conservative depth of 20 m (as proposed by Lorenz et al (2008)) and neglecting a potential subsurface reservoir.…”

“…3c); they are very likely due to quasi-specular reflections on the radar-facing sides of the dunes. The slopes of the dunes were estimated by radarclinometry to be around 6°, with a standard deviation of 2-3° (Lorenz et al, 2006;Neish et al, 2010). However, the T8 glints were observed at incidence angles of $26°.…”

Recent developments in planetary Aeolian studies and their terrestrial analogs

“…The rather uniform spacing of $3 km of dunes on Titan seems to fit this hypothesis (Lorenz et al, 2010), and would imply also that Titan's dunes are morphologically mature. The dune height, inferred from radarclinometry (Lorenz et al, 2006;Neish et al, 2010) and photoclinometry ) appears very consistent with terrestrial dunes of the same horizontal extent (Lancaster, 2006;Radebaugh, 2009). …”

Synergy of Cassini SAR and altimeter acquisitions for the retrieval of dune field characteristics on Titan

“…Assuming a Gaussian heights distribution for the dune fields, we estimated the dunes heights from altimetry data via a Maximum Likelihood Estimation (MLE) procedure applied along with a non-coherent Cassini electromagnetic signal model [18,20]. Because of the very high percentages of superimposition area between subsequent footprints we applied this procedure after an incoherent average of 15 altimetry echoes obtaining 20 significative dunes heights (Sdh = 4 • rms height) estimations in order of 55 -110 meters (see Fig.1), these values match with previously estimated values given by radarclinometry [12,14] and SAR -stereo [13]. …”