modeling the sar backscatter of linear dunes on earth and titan abstract we modeled the synthetic aperture radar sar response of linear dunes of the great sand sea in egypt using a single surface scattering term based on integral equation and physical optics models using multi frequency sir c x sar radar scenes and topography obtained from the shuttle radar topography mission srtm we were able to estimate reasonable values for the parameters describing the surface roughness of the dunes as the linear dunes of the great sand sea are relevant analogs for the linear dunes observed on titan by the cassini radar instrument these results were thus used as a starting point to simulate the radar response of titan s dunes as imaged by the radar instrument onboard the cassini spacecraft during the t8 flyby in october 2005 we show that a single surface scattering term is not sufficient to simulate the radar signal backscattered by the dunes on titan one has to add a diffuse scattering term indicating that titan s dunes are likely to have somewhat inhomogeneous internal structures related to porosity and or internal layering our results also indicate that the dunes on titan should be close to perfectly smooth possibly because of the formation of smaller ripples than on earth plus smoothing resulting from precipitation events

complete pb u analysis of unspiked samples by measuring pb isotopes only abstract for the analysis of samples with a complex pb loss history during their geological evolution the measurement of single grains without chemical separation and spiking of their u and pb is desirable in such cases a 207 pb 206 pb age can only be determined if concordant 206 pb 238 u and 207 u 235 u ages are assumed because of the completely different ionisation behavior of pb and u the pb u ratio cannot be obtained in radioactive equilibrium however 238 u and 210 pb are present in a fixed ratio of 210 pb 238 u 238 210 5 10 9 so that in principle the pb u measurement can be replaced by an isotope abundance ratio 210 pb pb a sample with a concordant age of 300 ma corresponding to a 206 pb 238 u ratio of 4 76 10 2 would for example have a 210 pb 206 pb r ratio of 1 05 10 7 using a finnigan mat 262 mass spectrometer with variable multicollector arrangement masses 204 206 207 and 208 were measured simultaneously with faraday cups while mass 210 was determined with an electron multiplier sem in ion counting mode ic the system was calibrated by means of artificial mixtures with 210 pb 206 pb ratios of 10 3 10 4 10 5 10 6 and 10 7 the 208 pb abundance sensitivity to mass 210 is 1 7 10 7 the accuracy of the 210 pb 206 pb method was tested by comparison of data obtained by the conventional isotope dilution technique with those obtained by our 210 pb 206 pb method for different tobernite samples and good agreement was recorded

dune forming winds on titan and the influence of topography abstract numerous extended dunes on saturn s moon titan detected by the cassini radar constrain the long term pattern of surface winds we analyse the statistics of surface wind speed and direction and their spatial and temporal variability predicted by a general circulation model gcm in order to constrain surface wind predictions of this gcm by dune observations the model shows that modern winds are sufficient for saltation and dune formation at low latitudes in agreement with the presence of dunes there the best condition for the dune forming wind occurs with a threshold friction speed of 0 02 m s 1 or slightly less the equatorial region is conducive to longitudinal dunes because of a combined effect of a high sand drift potential and obtuse bimodal wind pattern oblique to the equator caused by the seasonal reversal of the hadley circulation the cross equatorial wind is steady and is characterised by a high weibull shape parameter k 4 the wind pattern at higher latitudes is more complex and gusty and neither longitudinal nor transversal dunes would be able to form putative large scale topography is found to have a profound influence on the near surface wind pattern generally mountains cause a convergence and speeding up on the flank while basins weaken the wind and cause a divergent flow longitudinal dunes can be deflected on the foot of mountains by up to 90 if xanadu is a hypothetical large mountain a wind pattern converging in xanadu that entirely disagrees with the dune observations is predicted if instead xanadu is a large basin the wind arcs clockwise north of xanadu and anti clockwise west and southwest of xanadu in agreement with the dune orientations in the vicinity of xanadu the albedo pattern has comparatively little influence on the wind field isolated mountain chains cause only local scale change in the wind pattern however the persistent surface easterlies in belet which are in conflict with the dune orientations do not disappear by any combination of large scale topography

concentric slow cooling of a low p high t terrane evidence from 1600 1300 ma mica dates in the 1780 1700 ma black hills orogen south dakota u s a the crystalline core of the southern black hills south dakota exposes an extensive low p high t aureole of garnet to second sillimanite zone schists centered on the plutonic core of the 1715 ma harney peak granite hpg this paper demonstrates regional patterns of apparent ages observed for 52 40 ar 39 ar dates of muscovite and biotite in diverse rocks from across the 1000 km 2 metamorphic aureole and its plutonic center about 20 biotite dates sampled mostly near faults are influenced by excess 40 ar and obscure the regional trends the remaining mica dates reveal radial patterns of apparent younging from outer aureole toward inner granite with previously unrecognized elliptical age zones centered on the main hpg pluton and its outliers the regional pattern of 40 ar 39 ar cooling ages indicates non uniform slow cooling of the mid crust between 1600 1250 ma this scenario of delayed slow cooling from aureole to pluton is consistent with published cooling ages for muscovite rb sr and apatite u pb which range from 1690 to 1550 ma and from 1700 to 1500 ma respectively to explain these results it is likely that ambient pre granite temperatures of the country rocks were 350 c at the 10 14 km depth of granite emplacement as previously proposed and that the entire complex resided at this depth and cooled slowly from aureole to granite for hundreds of millions of years alternatively or in addition the hpg and inner aureole were not uplifted until 1480 1330 ma whereupon they finally cooled through 300 350 c

cassini sar radiometry scatterometry and altimetry observations of titan s dune fields large expanses of linear dunes cover titan s equatorial regions as the cassini mission continues more dune fields are becoming unveiled and examined by the microwave radar in all its modes of operation sar radiometry scatterometry altimetry and with an increasing variety of observational geometries in this paper we report on cassini s radar instrument observations of the dune fields mapped through may 2009 and present our key findings in terms of titan s geology and climate we estimate that dune fields cover 12 5 of titan s surface which corresponds to an area of 10 million km 2 roughly the area of the united states if dune sand sized particles are mainly composed of solid organics as suggested by vims observations cassini visual and infrared mapping spectrometer and atmospheric modeling and supported by radiometry data dune fields are the largest known organic reservoir on titan dune regions are with the exception of the polar lakes and seas the least reflective and most emissive features on this moon interestingly we also find a latitudinal dependence in the dune field microwave properties up to a latitude of 11 dune fields tend to become less emissive and brighter as one moves northward above 11 this trend is reversed the microwave signatures of the dune regions are thought to be primarily controlled by the interdune proportion relative to that of the dune roughness and degree of sand cover in agreement with radiometry and scatterometry observations sar images suggest that the fraction of interdunes increases northward up to a latitude of 14 in general scattering from the subsurface volume scattering and surface scattering from buried interfaces makes interdunal regions brighter than the dunes the observed latitudinal trend may therefore also be partially caused by a gradual thinning of the interdunal sand cover or surrounding sand sheets to the north thus allowing wave penetration in the underlying substrate altimetry measurements over dunes have highlighted a region located in the fensal dune field 5 latitude where the icy bedrock of titan is likely exposed within smooth interdune areas the hemispherical assymetry of dune field properties may point to a general reduction in the availability of sediments and or an increase in the ground humidity toward the north which could be related to titan s asymmetric seasonal polar insolation alternatively it may indicate that either the wind pattern or the topography is less favorable for dune formation in titan s northern tropics

nature distribution and origin of titan s undifferentiated plains abstract the undifferentiated plains on titan first mapped by lopes et al lopes r m c et al 2010 icarus 205 540 588 are vast expanses of terrains that appear radar dark and fairly uniform in cassini synthetic aperture radar sar images as a result these terrains are often referred to as blandlands while the interpretation of several other geologic units on titan such as dunes lakes and well preserved impact craters has been relatively straightforward the origin of the undifferentiated plains has remained elusive sar images show that these blandlands are mostly found at mid latitudes and appear relatively featureless at radar wavelengths with no major topographic features their gradational boundaries and paucity of recognizable features in sar data make geologic interpretation particularly challenging we have mapped the distribution of these terrains using sar swaths up to flyby t92 july 2013 which cover 50 of titan s surface we compared sar images with other data sets where available including topography derived from the sartopo method and stereo dems the response from radar radiometry hyperspectral imaging data from cassini s visual and infrared mapping spectrometer vims and near infrared imaging from the imaging science subsystem iss we examined and evaluated different formation mechanisms including i cryovolcanic origin consisting of overlapping flows of low relief or ii sedimentary origins resulting from fluvial lacustrine or aeolian deposition or accumulation of photolysis products created in the atmosphere our analysis indicates that the undifferentiated plains unit is consistent with a composition predominantly containing organic rather than icy materials and formed by depositional and or sedimentary processes we conclude that aeolian processes played a major part in the formation of the undifferentiated plains however other processes fluvial deposition of photolysis products are likely to have contributed possibly in differing proportions depending on location

hypsometry of titan cassini radar topography data are used to evaluate titan s hypsometric profile and to make comparisons with other planetary bodies titan s hypsogram is unimodal and strikingly narrow compared with the terrestrial planets to investigate topographic extremes a novel variant on the classic hypsogram is introduced with a logarithmic abscissa to highlight mountainous terrain in such a plot the top of the terrestrial hypsogram is quite distinct from those of mars and venus due to the glacial buzz saw that clips terrestrial topography above the snowline in contrast to the positive skew seen in other hypsograms with a long tail of positive relief due to mountains there is an indication weak given the limited data for titan so far that the titan hypsogram appears slightly negatively skewed suggesting a significant population of unfilled depressions limited data permit only a simplistic comparison of titan topography with other icy satellites but we find that the standard deviation of terrain height albeit at different scales is similar to those of ganymede and europa

geometric considerations of the three dimensional u pb data presentation abstract the three dimensional discordia plane is geometrically derived from basic assumptions it is shown that the projections of data which are located on a plane in xyz space onto the three coordinate planes yield different informations the projection from the common lead point yields the discordia line the yz projection the lead lead isochron plot and the xz projection the 206 pb 238 u isochron plot also discussed is the possibility to extend the wetherill discordia plot into three dimensions including the initial lead

modeling microwave backscatter and thermal emission from linear dune fields application to titan we present an electromagnetic model that relates the microwave backscatter and thermal emission from linear dune fields to their compositional physical roughness subsurface porosity heterogeneity and geometrical slope orientation properties this model shows the value of exploring these highly directional and geometrical features in light of both their backscattering cross section and emissivity compared to cassini concurrent radar and radiometry data acquired from october 2004 to june 2011 over titan s dune fields it provides clues to understand variations among dune regions on the largest saturn s moon in particular it brings a formal support to the idea first advanced in le gall et al le gall a janssen m a wye l c hayes a g radebaugh j savage c zebker h lorenz r d lunine j i kirk r l lopes r m c wall s callahan p stofan e r farr t and the cassini radar team 2011 icarus 213 608 624 that the size of the interdune valleys relative to that of the dunes varies across titan as well as the diffuse scattering properties of these interdune areas due to different thickness of sand cover i e bedrock contribution or degree of compaction heterogeneity of the sand cover the fensal and belet dune fields in particular are quite different in terms of these properties the comparison between the model and cassini data also reveals the potential presence of structures possibly small superposed dunes oriented perpendicular to the dune crests in the aztlan region

using synthetic aperture radar data of terrestrial analogs to test alluvial fan formation mechanisms on titan abstract landforms on titan include features hypothesized to be alluvial fans terrestrial alluvial fans form via two processes fluid gravity flows sheetfloods and sediment gravity flows debris flows along the panamint mountain range in death valley california usa seven fans formed primarily by debris flows are located adjacent to seven fans formed primarily by sheetfloods the causal difference between these two groupings stems from their catchment lithologies the debris flow fan catchments are clay rich and relatively sand poor and the sheetflood fan catchments are clay poor and sand rich on titan the low and mid latitudes are dominated by sand seas demonstrating that sand is available for transport at high latitudes these sand seas are absent suggesting that transportable sand is scarce based on the sedimentology of the two panamint range fan types we hypothesize that possible fans at lower latitudes on titan are formed by sheetfloods whereas those at higher latitudes formed primarily by debris flows to test these hypotheses we measured and analyzed the mean normalized radar cross sections and changes in with downfan distance for debris flow and sheetflood fans along the panamint range we then compared the results with the same measurements for possible fans on titan we find that in the panamint range debris flow fans are brighter than sheetflood fans and have greater change in with downfan distance and that on titan low latitude possible fans are likewise brighter than the fans at high latitudes with greater change in with downfan distance consequently our findings suggest that low latitude possible fans on titan are formed primarily by debris flows whereas high latitude possible fans on titan are formed primarily by sheetfloods thus our results do not support our hypotheses scenarios to explain these results include 1 high latitude possible fans are dominated by radar dark debris flow deposits 2 low and mid latitude possible fans are dominated by radar bright sheetflood deposits 3 sand sized sediments were relatively scarce at the time of low and mid latitude possible fan formation 4 bedrock composition varies as a function of latitude on titan 5 alluvial fans form differently on titan because of the lower gravity conditions and 6 fan like features may result from non alluvial processes such as form distributary fluvial systems on earth

morphometric analysis of aeolian bedforms in the namib sand sea using aster data the aster global digital elevation model gdem has made elevation data at 30 m spatial resolution freely available enabling reinvestigation of morphometric relationships derived from limited field data using much larger sample sizes these data are used to analyse a range of morphometric relationships derived for dunes between dune height spacing and equivalent sand thickness in the namib sand sea which was chosen because there are a number of extant studies that could be used for comparison with the results the relative accuracy of gdem for capturing dune height and shape was tested against multiple individual aster dem scenes and against field surveys highlighting the smoothing of the dune crest and resultant underestimation of dune height and the omission of the smallest dunes because of the 30 m sampling of aster dem products it is demonstrated that morphometric relationships derived from gdem data are broadly comparable with relationships derived by previous methods across a range of different dune types the data confirm patterns of dune height spacing and equivalent sand thickness mapped previously in the namib sand sea but add new detail to these patterns

determination of u pb ages of zircons by direct measurement of the 210pb 206pb ratio abstract precise measurements of the 210 pb 206 pb ratio in zircons permits for the first time the determination of complete u pb ages by measurement of pb isotopes only without determination of the u pb ratio by isotope dilution the 238 u daughter isotope 210 pb is generally in radioactive equilibrium with 238 u however the very short half life of 210 pb 22 3a results in extremely low 210 pb 206 pb ratios of 10 8 especially for archaean zircons these ratios have been determined using a finnigan mat 262 mass spectrometer equipped with a high abundance sensitivity lens system rpq the accuracy of the 210 pb method has been tested on nine different zircon samples with 207 pb 206 pb ages from 330 to 3365 ma corresponding to 210 pb 206 pb ratios between 1 31 10 7 and 9 09 10 9 in general the u pb ages calculated using the 210 pb 206 pb ratio are in good agreement with conventional u pb age determinations on aliquots of the same sample via isotope dilution

overview of the spaceborne imaging radar c x band synthetic aperture radar sir c x sar missions abstract the spaceborne imaging radar c x band synthetic aperture radar sir c x sar the most advanced imaging radar system to have flown in earth orbit was carried in the cargo bay of the space shuttle endeavour in april and october 1994 sir c x sar simultaneously recorded data at three wavelengths l c and x bands 23 5 cm 5 8 cm and 3 1 cm respectively in addition the full polarimetric scattering matrix was obtained at l and c band over a variety of terrain and vegetation types scientists are using multifrequency polarimetric sir c x sar data in studies of geology hydrology ecology oceanography and radar remote sensing techniques the october sir c x sar flight also included acquisition of experimental repeat pass interferometry data which have been used to generate digital elevation models and to detect surface motions in volcanic tectonic and glacial terrains results from sir c x sar clearly show the increased value of using multiparameter and interferometric capabilities to characterize earth s surface and vegetation cover and to generate geophysical products compared with optical sensors or single channel radars alone

implications of dune pattern analysis for titan s surface history abstract analysis of large scale morphological parameters can reveal the reaction of dunes to changes in atmospheric and sedimentary conditions over 7000 dune width and 7000 dune spacing measurements were obtained for linear dunes in regions across saturn s moon titan from images t21 t23 t28 t44 and t48 collected by the synthetic aperture radar sar aboard the cassini spacecraft in order to reconstruct the aeolian surface history of titan dunes in the five study areas are all linear in form with a mean width of 1 3 km and mean crest spacing of 2 7 km similar to dunes in the african saharan and namib deserts on earth at the resolution of cassini sar the dunes have the morphology of large linear dunes and they lack evidence for features of compound or complex dunes the large size spacing and uniform morphology are all indicators that titan s dunes are mature features in that they have grown toward a steady state for a long period of time dune width decreases to the north perhaps from increased sediment stabilization caused by a net transport of moisture from south to north or from increased maturity in dunes to the south cumulative probability plots of dune parameters measured at different locations across titan indicate there is a single population of intermediate to large sized dunes on titan this suggests that unlike analogous dunes in the namib and agneitir sand seas dune forming conditions that generated the current set of dunes were stable and active long enough to erase any evidence of past conditions

exploring morphology layering and formation history of linear terrestrial dunes from radar observations implications for titan abstract understanding the morphology and internal layering of large aeolian dune fields through radar observations can provide unique insights into the climatic and geophysical conditions that led to their formation in this study we perform a large scale characterization of the morphology and internal layering of linear dunes in hyper arid areas on earth through utilizing multiple complementary radar datasets sir c imaging srtm interferometry derived elevations and radar sounding or ground penetrating radar gpr linear dune fields in the egyptian desert are of special interest due to their significance as planetary analogs to dunes on mars and saturn s largest moon titan satellite radar imagery and elevation data of the region show significant variance in the geomorphology of different dune fields in egypt in addition gpr probing of the first few meters suggests different inner settings in the layering of dunes of different ages in eastern and western egypt reflecting different paleo climatic regimes that led to their formation furthermore our radiometric analysis suggests that dunes with different inner layering arrangement also exhibit different radar backscatter returns as a function of their heights for relatively younger dunes with a homogeneous inner structure like the ones in eastern egypt in the qattaniya dune field we observe that sigma0 does not change as a function of the dune height for relatively older dunes in western egypt like the great sand sea northern siwa and southern dune fields we observed a linear correlation between sigma0 and the dune height thus surface properties of dunes like morphology and backscatter variation with height are related to inner characteristics like arrangement of internal layering relative ages and can be used to infer their depositional history linear dunes discovered in the equatorial regions of titan by the cassini huygens mission are morphologically very similar to these linear dune fields in the egyptian sahara hence assessing the variability of morphology and radar backscatter properties of titan s dunes as a function of their heights can help constrain the ambiguities associated with their internal structure and formation history and provide insights into titan s paleo wind regimes

dunes on titan observed by cassini radar thousands of longitudinal dunes have recently been discovered by the titan radar mapper on the surface of titan these are found mainly within 30 of the equator in optically near infrared and radar dark regions indicating a strong proportion of organics and cover well over 5 of titan s surface their longitudinal duneform interactions with topography and correlation with other aeolian forms indicate a single dominant wind direction aligned with the dune axis plus lesser off axis or seasonally alternating winds global compilations of dune orientations reveal the mean wind direction is dominantly eastwards with regional and local variations where winds are diverted around topographically high features such as mountain blocks or broad landforms global winds may carry sediments from high latitude regions to equatorial regions where relatively drier conditions prevail and the particles are reworked into dunes perhaps on timescales of thousands to tens of thousands of years on titan adequate sediment supply sufficient wind and the absence of sediment carriage and trapping by fluids are the dominant factors in the presence of dunes

radarclinometry of the sand seas of africa s namibia and saturn s moon titan abstract radarclinometry is a powerful technique for estimating heights of landforms in synthetic aperture radar sar images of planetary surfaces in particular it has been used to estimate heights of dunes in the sand seas of saturn s moon titan lorenz r d and 39 colleagues 2006 science 312 724 727 in this work we verify the technique by comparing dune heights derived from radarclinometry to known topography of dune fields in the namib sand sea of western africa we compared results from three different image grid spacings and found that 350 m pixel the same spacing at which the cassini radar data was processed is sufficient to determine dune height for dunes of similar morphometry to those of the namib sand sea at this grid spacing height estimates derived from radarclinometry are largely representative of though may underestimate by as much as 30 or overestimate by as much as 40 true dune height applying the technique to three regions on titan we estimate dune heights of 45 180 m and dune spacings of 2 3 3 3 km obtaining accurate heights of titan s dunes will help to constrain the total organic inventory on titan

titan s surface from cassini radar sar and high resolution radiometry data of the first five flybys abstract the first five titan flybys with cassini s synthetic aperture radar sar and radiometer are examined with emphasis on the calibration and interpretation of the high resolution radiometry data acquired during the sar mode sar radiometry maps of the 2 cm wavelength brightness temperature are obtained coincident with the sar swath imaging with spatial resolution approaching 6 km a preliminary calibration shows that brightness temperature in these maps varies from 64 to 89 k surface features and physical properties derived from the sar radiometry maps and sar imaging are strongly correlated in general we find that surface features with high radar reflectivity are associated with radiometrically cold regions while surface features with low radar reflectivity correlate with radiometrically warm regions we examined scatterplots of the normalized radar cross section 0 versus brightness temperature finding differing signatures that characterize various terrains and surface features implications for the physical and compositional properties of these features are discussed the results indicate that volume scattering is important in many areas of titan s surface particularly xanadu while other areas exhibit complex brightness temperature variations consistent with variable slopes or surface material and compositional properties

radar scattering of linear dunes and mega yardangs application to titan the ku band 13 8 ghz 2 2 cm radar instrument onboard the cassini huygens spacecraft has revealed the richness of the surface of titan as numerous seas lakes rivers cryo volcanic flows and vast dune fields have been discovered linear dunes are a major geomorphological feature present on titan covering up to 17 of its surface mainly in equatorial regions however the resolution of the radar instrument is not good enough to allow a detailed study of the morphology of these features in addition other linear wind related landforms such as mega yardangs linear wind abraded ridges formed in cohesive rocks are likely to present a comparable radar signature that could be confused with the one of dunes we conducted a comparative study of the radar radiometry of both linear dunes and mega yardangs based on representative terrestrial analogues the linear dunes located in the great sand sea in western egypt and in the namib desert in namibia and the mega yardangs observed in the lut desert in eastern iran and in the borkou desert in northern chad we analysed the radar scattering of both terrestrial linear dunes and mega yardangs using high resolution radar images acquired by the x band 9 6 ghz 3 1 cm sensor of the terrasar x satellite variations seen in the radar response of dunes are the result of a contrast between the dune and interdune scattering while for mega yardangs these variations are the result of a contrast between ridges and erosion valleys we tested a simple surface scattering model with parameters derived from the local topography and surface roughness estimates to accurately reproduce the radar signal variations for both landforms it appears that we can discriminate between two types of dunes bare interdunes as in egypt and sand covered interdunes as in namibia and between two types of mega yardangs young yardangs as in iran and older ones as in chad we applied our understanding of the radar scattering to the analysis of cassini radar t8 acquisitions over the belet sand sea on titan and show that the linear dunes encountered there are likely to be of both egyptian and namibian type we also show that the radar bright linear features observed in cassini radar t64 and t83 acquisitions are very likely to be mega yardangs possible remnants of ancient lake basins at mid latitude formed when titan s climate was different

spaceborne and airborne imaging radar observations of sand dunes seasat and aircraft radar imagery of five areas of sand dunes in the southwestern united states and northwestern mexico have been studied and compared to landsat imagery and air photos radar imaging system parameters included two wavelengths 23 5 cm and 3 0 cm and incidence angles ranging from 0 through 70 horizontal polarization was used on both transmit and receive for all radar imagery resolution ranged from 12 m for the best aircraft imagery to about 40 m for seasat sand dunes studied behave as smooth surfaces for both 23 5 cm and 3 0 cm wavelength radars and the reflection of the radar energy from the dunes is specular measured surface irregularities of sand dunes are inadequate to cause either bragg or incoherent scattering of the incident radar beam in the 3 0 to 23 5 cm wavelength region this results in dunes that appear dark when imaged at incidence angles greater than the angle of repose because none of the dune faces are oriented properly normal to the incident radar beam to give a specular return to the antenna a scattering model based on specular return from randomly oriented flat dune faces was used and experimentally verified using aircraft data imaging radar resolution must be adequate to define the changing distribution of dune faces that characterize the dune morphology linear dune features with interdune spacing of less than 3 4 resolution elements are not recognizable distributed dune types such as barchans or stars must be more than about 10 resolution elements in each direction to be defined on the imagery illumination direction of the radar beam is important directional dune features must be oriented within about 60 of perpendicular to the radar illumination direction in order to be imaged if such features have considerable topographic relief the direction of radar illumination is less important because directional trends in unexplored regions cannot be predicted availability of radar imagery from two directions greatly facilitates interpretation of dune morphology and hence conclusions about causative wind regimes

global pattern of titan s dunes radar survey from the cassini prime mission 1 we present a map of the orientation and extent of titan s sand dunes derived from the complete radar imaging dataset from the cassini prime mission the 16 000 dune segments we have mapped cover 8 of the titan s surface suggesting a total coverage of 20 are confined within 30 of the equator and show local and regional deviations of dune orientation of up to about 40 from due eastwards there is no obvious global longitudinal pattern although some divergence with latitude is apparent the most striking pattern is one of collimation by and divergence around bright and or high terrain obstacles 100 300 m high obstruct dunes when the local slope is 1 50 or steeper while slopes 1 200 or shallower cause dunes to thin out as they climb or to deviate around the obstacles

titan s inventory of organic surface materials 1 cassini radar observations now permit an initial assessment of the inventory of two classes presumed to be organic of titan surface materials polar lake liquids and equatorial dune sands several hundred lakes or seas have been observed of which dozens are each estimated to contain more hydrocarbon liquid than the entire known oil and gas reserves on earth dark dunes cover some 20 of titan s surface and comprise a volume of material several hundred times larger than earth s coal reserves overall however the identified surface inventories 3 104 km3 of liquid and 2 105 km3 of dune sands are small compared with estimated photochemical production on titan over the age of the solar system the sand volume is too large to be accounted for simply by erosion in observed river channels or ejecta from observed impact craters the lakes are adequate in extent to buffer atmospheric methane against photolysis in the short term but do not contain enough methane to sustain the atmosphere over geologic time unless frequent resupply from the interior buffers this greenhouse gas at exactly the right rate dramatic climate change on titan is likely in its past present and future

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

cryovolcanism on titan new results from cassini radar and vims 1 the existence of cryovolcanic features on titan has been the subject of some controversy here we use observations from the cassini radar including synthetic aperture radar sar imaging radiometry and topographic data as well as compositional data from the visible and infrared mapping spectrometer vims to reexamine several putative cryovolcanic features on titan in terms of likely processes of origin fluvial cryovolcanic or other we present evidence to support the cryovolcanic origin of features in the region formerly known as sotra facula which includes the deepest pit so far found on titan now known as sotra patera flow like features mohini fluctus and some of the highest mountains on titan doom and erebor montes we interpret this region to be a cryovolcanic complex of multiple cones craters and flows however we find that some other previously supposed cryovolcanic features were likely formed by other processes cryovolcanism is still a possible formation mechanism for several features including the flow like units in hotei regio we discuss implications for eruption style and composition of cryovolcanism on titan our analysis shows the great value of combining data sets when interpreting titan s geology and in particular stresses the value of radar stereogrammetry when combined with sar imaging and vims

titan dune heights retrieval by using cassini radar altimeter abstract the cassini radar is a ku band multimode instrument capable of providing topographic and mapping information during several of the 93 titan fly bys performed by cassini the radar collected a large amount of data observing many dune fields in multiple modes such as sar altimeter scatterometer and radiometer understanding dune characteristics such as shape and height will reveal important clues on titan s climatic and geological history providing a better understanding of aeolian processes on earth dunes are believed to be sculpted by the action of the wind weak at the surface but still able to activate the process of sand sized particle transport this work aims to estimate dunes height by modeling the shape of the real cassini radar altimeter echoes joint processing of sar altimeter data has been adopted to localize the altimeter footprints overlapping dune fields excluding non dune features the height of the dunes was estimated by applying maximum likelihood estimation along with a non coherent electromagnetic em echo model thus comparing the real averaged waveform with the theoretical curves such analysis has been performed over the fensal dune field observed during the t30 flyby may 2007 as a result we found that the estimated dunes peak to trough heights difference was in the order of 60 120 m estimation accuracy and robustness of the mle for different complex scenarios was assessed via radar simulations and monte carlo approach we simulated dunes interdunes different composition and roughness for a large set of values verifying that in the range of possible titan environment conditions these two surface parameters have weak effects on our estimates of standard dune heights deviation results presented here are the first part of a study that will cover all titan s sand seas

texture and composition of titan s equatorial sand seas inferred from cassini sar data implications for aeolian transport and dune morphodynamics the texture composition and morphology of dunes observed in the equatorial regions of titan may reflect present and or past climatic conditions determining the physio chemical properties and the morphodynamics of titan s dunes is therefore essential to understanding of the climatic and geological history of the largest moon of saturn we quantitatively derived average surface properties of dune and interdune areas texture composition from modeling of the microwave backscattered signal and monte carlo inversion of the despeckled cassini sar data over titan s three largest sand seas belet shangri la and fensal we present the first analysis of the backscatter functions extracted from despeckled sar images that cover such a large range in incidence angles including data from the beginning of the cassini mission up to its grand finale we show that dunes and interdunes have significantly different physical properties dunes are found to be more microwave absorbent than interdunes additionally potential secondary bedforms such as ripples and avalanches may have been detected providing potential evidence for currently active dunes and sediment transport our modelling shows that the interdunes have multi scale roughnesses with higher dielectric constants than the dunes which have a low dielectric constant consistent with organic sand the radar brightness of the interdunes can be explained by the presence of a shallow layer of significantly larger organic grains possibly non mobilized by the winds together our findings suggest that titan s sand seas evolve under the current multi directional wind regimes with dunes that elongate with their crests aligned in the residual drift direction

compositional variations of titan s impact craters indicates active surface erosion abstract titan the only moon in the solar system with a considerable atmosphere is host to a variety of exogenic processes that shape its surface these processes form features that are quite similar to features on earth including sand dunes rivers and lakes the combination of a thick atmosphere and active surface processes also leads to a scarcity of impact craters on the surface of titan the compositions of these craters vary and may relate to the type and extent of erosion occurring at their location in this work we examined the composition of 12 impact features on titan using cassini s visible and infrared mapping spectrometer vims and 2 18 cm emissivity data from the radar radiometer on board the probe comparisons were made between crater composition as inferred from vims and composition as inferred from emissivity data with corresponding crater characteristics such as latitude longitude and erosional state we see a correlation between crater subsurface composition as inferred from the emissivity data and its erosional state and location well preserved craters typically are more enriched in water ice than degraded organic rich craters suggesting that variations in composition are partially controlled by erosion and infilling moreover craters located in dune fields show more subsurface organic enrichment than craters within the plains which indicates that the efficiency of erosion and infilling varies with location and geologic context vims data provide complementary information about crater surficial composition we note that vims spectra do not change with erosional state but rather appear to depend on the crater location on the moon we suggest that there are active surface processes occurring on titan such as wind or rain which are actively clearing off its surface and filling in subsurface fractures with organic materials these processes would act to change the emissivity of the craters over time but leave the surface sensed by vims unchanged

spectroscopy morphometry and photoclinometry of titan s dunefields from cassini vims fine resolution 500 m pixel cassini visual and infrared mapping spectrometer vims t20 observations of titan resolve that moon s sand dunes the spectral variability in some dune regions shows that there are sand free interdune areas wherein vims spectra reveal the exposed dune substrate the interdunes from t20 are variously materials that correspond to the equatorial bright 5 m bright and dark blue spectral units our observations show that an enigmatic dark red spectral unit seen in t5 in fact represents a macroscopic mixture with 5 m bright material and dunes as its spectral endmembers looking more broadly similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes the presence of interdunes indicates that titan s dunefields are both mature and recently active the spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of titan various organics are consistent with the dunes measured reflectivity we measure a mean dune spacing of 2 1 km and find that the dunes are oriented on the average in an east west direction but angling up to 10 from parallel to the equator in specific cases where no interdunes are present we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m these results pave the way for future exploration and interpretation of titan s sand dunes

global mapping and characterization of titan s dune fields with cassini correlation between radar and vims observations abstract vast fields of linear dunes have been observed in the equatorial regions of titan saturn s largest moon as the cassini mission in orbit around saturn since july 2004 and extended until may 2017 carries on the high resolution coverage of titan s surface increases revealing new dune fields and allowing refinements in the examination of their properties in this paper we present the joint analysis of cassini s microwave and infrared global scale observations of titan integrating within an up to date global map of titan all the cassini radar and vims visual and infrared mapping spectrometer images the latter being empirically corrected for atmospheric scattering and surface photometry from july 2004 through july 2013 and june 2010 respectively we found very good qualitative and quantitative spatial matching between the geographic distribution of the dune fields and a specific infrared spectral unit namely the dark brown unit the high degree of spatial correlation between dunes and the dark brown unit has important implications for titan s geology and climate we found that radar mapped dunes and the dark brown unit are similarly confined within the equatorial belt 30 in latitudes with an equivalent distribution with latitude suggesting an increasing sediment availability and mobility at titan s tropics relative to higher latitudes compatible with the lower ground humidity predicted in equatorial regions by general circulation models furthermore the strong correlation between radar mapped dunes and the vims dark brown unit 72 allows us to better constrain the total surface area covered by dune material previously estimated from the extrapolation of the radar observations alone according to our calculations dune material cover 17 5 1 5 of titan s surface area equivalent to a total surface area of 14 6 1 2 million km2 1 5 times the surface area of earth s sahara desert the vims dark brown coloration of the dune material is here confirmed at large spatial scale if the sand particle composition is dominated by solid organics produced in and settling from the atmosphere as supported by our spectral modeling and by previous spectral analysis microwave radiometric data and atmospheric modeling dune fields are one of the major surface hydrocarbon reservoirs on titan assuming two possible scenarios for the sand distribution either the sand is 1 entirely trapped in dune landforms or 2 trapped in dunes at places where dune landforms are firmly observed and in sand sheets elsewhere we estimate the volume of hydrocarbons trapped in the dune sediment to be comprised between 1 7 and 4 4 105 km3 corresponding to an average total mass of 230 000 gt in comparison with 4000 30 000 gt of hydrocarbons in the polar lakes and seas this indicates a maximum age for the dune sediments of 730 myr consistent with estimations of the ages of the current titan s atmospheric methane and surface

a three dimensional upb discordia plane to evaluate samples with common lead of unknown isotopic composition abstract the concordia method introduced by g w wetherill or in a modified fashion by f tera and g j wasserburg which can only be applied to the radiogenic leead fraction of u containing minerals can be extended to the measured total pb isotope ratios by a three dimensional discordia plane the three dimensional model does not require knowledge of the isotope ratios of the common pb used for correction if the assumption of only one type of common pb with an a priori unknown isotopic composition for the investigated samples is justified the theory is derived and formulae for calculation of best fit plane parameters as well as for their errors are derived with one synthetic set of data the applicability of the method is demonstrated

fluvial erosion as a mechanism for crater modification on titan abstract there are few identifiable impact craters on titan especially in the polar regions one explanation for this observation is that the craters are being destroyed through fluvial processes such as weathering mass wasting fluvial incision and deposition in this work we use a landscape evolution model to determine whether or not this is a viable mechanism for crater destruction on titan we find that fluvial degradation can modify craters to the point where they would be unrecognizable by an orbiting spacecraft such as cassini given enough time and a large enough erosion rate a difference in the erosion rate between the equator and the poles of a factor of a few could explain the latitudinal variation in titan s crater population fluvial erosion also removes central peaks and fills in central pits possibly explaining their infrequent occurrence in titan craters although many craters on titan appear to be modified by aeolian infilling fluvial modification is necessary to explain the observed impact crater morphologies thus it is an important secondary modification process even in titan s drier equatorial regions