photometric changes on saturn s titan evidence for active cryovolcanism 1 we report infrared spectrophotometric variability on the surface of saturn s moon titan detected in images returned by the visual and infrared mapping spectrometer vims onboard the cassini saturn orbiter the changes were observed at 7 s 138 w and occurred between october 27 2005 and january 15 2006 after that date the surface was unchanged until the most recent observation march 18 2006 we previously reported spectrophotometric variability at another location 26 s 78 w cassini synthetic aperture radar sar images find that the surface morphology at both locations is consistent with surface flows possibly resulting from cryovolcanic activity wall et al companion paper this issue the vims reported time variability and sar morphology results suggest that titan currently exhibits intermittent surface changes consistent with present ongoing surface processes we suggest that these processes involve material from titan s interior being extruded or effused and deposited on the surface as might be expected from cryovolcanism

scale properties of microscale convection in the marine surface layer we analyze the scale distribution of coherent water vapor structures in the marine atmospheric boundary layer as measured by a shipboard raman lidar during the combined sensor program march 1996 using a two dimensional continuous wavelet transform coherent structures in the lidar measured water vapor concentration field correspond to locations where covariance with the wavelet is a local extremum scales of the significant structures are identified using a filtered wavelet variance detection density derived from 24 images in a horizontal plane a dominant radius of 14 m is identified using complimentary approaches to the analysis

near infrared spectral mapping of titan s mountains and channels 1 we investigate the spectral reflectance properties of channels and mountain ranges on titan using data from cassini s visual and infrared mapping spectrometer vims obtained during the t9 encounter 26 december 2005 we identify the location of channels and mountains using synthetic aperture radar maps obtained from cassini s radar instrument during the t13 30 april 2006 flyby channels are evident even in vims imaging with spatial resolution coarser than the channel size the channels share spectral characteristics with titan s dark blue terrain e g the huygens landing site that is consistent with an enhancement in water ice content relative to the rest of titan we use this fact to measure widths of 1 km for the largest channels comparison of the data sets shows that in our study area within the equatorial bright spectral unit east of xanadu mountains are darker and bluer than surrounding smooth terrain these results are consistent with the equatorial bright terrain possessing a veneer of material that is thinner in the regions where there are mountains and streambeds that have likely undergone more recent and extensive erosion we suggest a model for the geographic relationship of the dark blue dark brown and equatorial bright spectral units based on our findings

initial investigations of microscale cellular convection in an equatorial marine atmospheric boundary layer revealed by lidar during the combined sensor program csp in march of 1996 the los alamos national laboratory lanl fielded an advanced scanning raman lidar the lidar was part of a larger suite of micrometeorological sensors to quantify processes associated with the ocean atmosphere interface including intermittency and coherent atmospheric features in the open quotes warm pool close quotes of the tropical western pacific twp near manus island 2 degree s lat 147 degree e long initial inspection of the data has revealed excellent information on the microscale vertical and horizontal spatial and temporal structure of the equatorial marine atmospheric boundary layer mabl the data from this experiment have added to the increasing body of measurements on surface layer convection and intermittency including for the first time the observation of microscale cellular convective structures such as hexagonal patterns associated with rayleigh b acute e nard cells copyright 1997 american geophysical union

field experiments on the transport of rock fragments by animal trampling on scree slopes qualitative observations in an area with steep scree slopes in turkey suggested that trampling by goats and sheep may contribute significantly to the downslope movement of rock fragments in these environments therefore a series of field experiments was set up to determine the rate of rock fragment transport caused by trampling the experimental results allowed the calculation of a unit displacement distance from each trampling experiment which may then be used to extrapolate the measured transport rates over longer time periods and larger areas although such extrapolations should be interpreted with great caution the results demonstrate that trampling contributes significantly to rock fragment transport in such environments as calculated yearly displacement distances are equal to or higher than those reported in the literature for other geomorphic processes the observed travel distance distributions are not well described by a negative exponential distribution trampling causes a weak downslope sorting the coarsest clasts move farther but has a significant effect on vertical sorting and is one of the factors which can explain the layered structure of the scree slopes in the area

geology of a rift zone on venus beta regio and devana chasma beta regio is a region of rifting and volcanism on venus the nature of beta a major topographic rise and rift zone is herein characterized using pioneer venus arecibo and venera 15 16 data high resolution 1 2 km arecibo and venera radar images reveal details of faulting and volcanism and pioneer venus altimetry illustrates the density and location of faults in relation to topography faults are distributed throughout beta but are concentrated in devana chasma where they are spaced 5 20 km apart the pattern of faulting and distribution and sequence of volcanic activity in beta can be used to help understand how the rift has evolved including the origin of the high topography of beta and the origin and nature of devana chasma on the basis of geologic mapping relations and map patterns beta appears to have formed as a result of doming in response to a mantle anomaly at the same time rhea mons a major shield volcano was formed formation of devana chasma followed with extensive faulting in the rift trough geometry of the trough and fault patterns suggests that some degree of lithospheric stretching has occurred later volcanism produced a second major shield volcano theia mons which is superimposed on the western bounding fault of the rift zone both uplift and extension have been involved in forming devana chasma and beta regio and may be important in the formation of other equatorial high land regions with systems of chasmata on venus such as aphrodite terra the bifurcation of devana chasma in the vicinity of theia mons and the extension of the rift system south to phoebe regio and west toward aphrodite terra suggest that their origins may be linked

geology of the selk crater region on titan from cassini vims observations abstract observations of titan obtained by the cassini visual and infrared mapping spectrometer vims have revealed selk crater a geologically young bright rimmed impact crater located 800 km north northwest of the huygens landing site the crater rim crest diameter is 90 km its floor diameter is 60 km a central pit peak 20 30 km in diameter is seen the ratio of the size of this feature to the crater diameter is consistent with similarly sized craters on ganymede and callisto all of which are dome craters the vims data unfortunately are not of sufficient resolution to detect such a dome the inner rim of selk crater is fluted probably by eolian erosion while the outer flank and presumed ejecta blanket appear dissected by drainages particularly to the east likely the result of fluvial erosion terracing is observed on the northern and western walls of selk crater within a 10 15 km wide terrace zone identified in vims data the terrace zone is bright in sar data consistent with it being a rough surface the terrace zone is slightly wider than those observed on ganymede and callisto and may reflect differences in thermal structure and or composition of the lithosphere the polygonal appearance of the crater likely results from two preexisting planes of weakness oriented at azimuths of 21 and 122 east of north a unit of generally bright terrain that exhibits similar infrared color variation and contrast to selk crater extends east southeast from the crater several hundred kilometers we informally refer to this terrain as the selk bench both selk and the bench are surrounded by the infrared dark belet dune field hypotheses for the genesis of the optically bright terrain of the bench include wind shadowing in the lee of selk crater preventing the encroachment of dunes impact induced cryovolcanism flow of a fluidized ejecta blanket similar to the bright crater outflows observed on venus and erosion of a streamlined upland formed in the lee of selk crater by fluid flow vestigial circular outlines in this feature just east of selk s ejecta blanket suggest that this might be a remnant of an ancient cratered crust evidently the southern margin of the feature has sufficient relief to prevent the encroachment of dunes from the belet dune field we conclude that this feature either represents a relatively high viscosity fluidized ejecta flow a class intermediate to ejecta blankets and long venusian style ejecta flows or a streamlined upland remnant that formed downstream from the crater by erosive fluid flow from the west northwest

evaluation of image analysis methods used for quantification of particle angularity angularity is an important parameter in the characterization of particle morphology that is used to interpret the transport history of particles in sedimentary deposits in the past visual classification using silhouette charts was widely used to determine particle angularity but this approach is subjective and time consuming with advances in modern image analysis techniques and low cost software packages it is possible to rapidly quantify particle angularity more objectively than using visual classification methods this study re examines the performance of three existing image analysis methods and one new image analysis procedure applied to six rock and sediment samples that were visually different in angularity to facilitate comparison between the angularity results measurements were reduced to rankings for each aggregate sample these results show that the four image analysis methods rank the angularity of the samples differently and that none rank the mean angularity index in the same order as the angularity ranking using visual classification therefore further research is needed to develop an image analysis method that can quantify the angularity of sedimentary particles more precisely

titan s rotation reveals an internal ocean and changing zonal winds cassini radar observations of saturn9s moon titan over several years show that its rotational period is changing and is different from its orbital period the present day rotation period difference from synchronous spin leads to a shift of 0 36 per year in apparent longitude and is consistent with seasonal exchange of angular momentum between the surface and titan9s dense superrotating atmosphere but only if titan9s crust is decoupled from the core by an internal water ocean like that on europa

global scale surface spectral variations on titan seen from cassini vims we present global scale maps of titan from the visual and infrared mapping spectrometer vims instrument on cassini we map at 64 near infrared wavelengths simultaneously covering the atmospheric windows at 0 94 1 08 1 28 1 6 2 0 2 8 and 5 m with a typical resolution of 50 km pixel or a typical total integration time of 1 s our maps have five to ten times the resolution of ground based maps better spectral resolution across most windows coverage in multiple atmospheric windows and represent the first spatially resolved maps of titan at 5 m the vims maps provide context and surface spectral information in support of other cassini instruments we note a strong latitudinal dependence in the spectral character of titan s surface and partition the surface into 9 spectral units that we describe in terms of spectral and spatial characteristics

titan and other icy satellites dielectric properties of constituent materials and implications for radar sounding abstract a number of scientific problems concerning titan and the other icy satellites of the outer solar system could be addressed by the technique of radar sounding we consider the materials present on and within these bodies model their dielectric properties and evaluate the extent to which radar signals can penetrate through them the primary materials of interest are h2o ice h2 nh3 solution simple and polymeric organic solids and ch4 c2h6 n2 liquid plus its minor organic and inorganic solutes penetration through h2o ice is limited by multiple scattering and by the long wavelength wing of the submillimeter band deep penetration is possible at long wavelengths and strong reflections could result from pockets or layers of subsurface h2o nh3 solution the dielectric constant of a putative ch4 c2h6 n2 ocean on titan is 1 65 1 81 depending on ch4 content and optical depth 40 to 200 cm 2 for depths of 0 75 to 7 km we estimate that dissolved species especially ch3cn hcn and h2o can increase the absorption by at least a factor of 2 but the effects of these polar solutes are very difficult to predict without direct experimental investigation and could be much greater sediment is composed of simple solids 2 0 2 4 and organic hetero polymers 4 5 5 5 with negligible radar attenuation to investigate a specific case of interest we consider radar observations of titan using the sounding mode of the cassini radar experiment we use our models to calculate radar signal noise ratios for reflections from titan the surface of titan is modeled as consisting of h2o ice covered by a 100 m thick layer of organic sediments overlain in turn by an ocean of liquid ch4 c2h6 n2 only reflections from the surface of the ocean in this model would be observed at a radar wavelength of 2 2 cm but at 13 6 cm we compute signal noise exceeding 10 db from the ocean sediment and sediment ice interfaces hence such a sounding mode may offer prospects for investigating the geology of titan even if the surface of the satellite is covered locally or globally by a deep ocean

geomorphologic mapping of the menrva region of titan using cassini radar data abstract we made a detailed geomorphologic map of the menrva region of titan using cassini radar data as our map base using similar techniques and approaches that were applied to mapping magellan radar images of venus and earlier more generalized titan maps we were able to define and characterize 10 radar morphologic units along with inferred dunes and fluvial channels from the radar data structural features such as scarps ridges and lineaments were also identified using principles of superposition cross cutting and embayment relations we created a sequence of map units for this region we interpret menrva to be a 440 km wide degraded impact basin in agreement with earlier studies by elachi et al elachi c et al 2006 nature 441 709 713 and wood et al wood c a lorenz r kirk r lopes r mitchell k stofan e and the cassini radar team 2010 icarus 206 334 344 and identify it as the oldest feature in the map region exogenic processes including hydrocarbon fluid channelization forming the elivagar flumina channel network and dune fields resulting from aeolian activity are the current geologic processes dominating our map area and these processes have contributed to the erosion of the crater s ejecta field there is evidence of multiple episodes of channel formation erosion and burial by aeolian deposits as observed elsewhere on titan by e g barnes et al barnes j w et al 2005 icarus 195 400 414 channel outflow regions have morphologies suggestive of streams formed by flash floods and dune fields are small and restricted rather than forming large dune seas consistent with a desert like environment for this region with low supply of hydrocarbon particles also consistent with other studies by e g lorenz et al lorenz r d et al 2008a planet space sci 56 1132 1144 there is no evidence of cryovolcanism or non impact related tectonic activity in the menrva region although this region is too small to infer anything about the roles of these processes elsewhere on titan this work suggests detailed geomorphologic mapping can confidently be applied to cassini radar data and we suggest that more extensive mapping should be done using radar iss and vims data geographically distributed across titan to assess its usefulness for a future combined radar iss vims based global geologic map

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

retrieval of microscale flow structures from high resolution doppler lidar data using an adjoint model radial velocity data measured by high resolution doppler lidar hrdl are assimilated with a four dimensional variational data assimilation 4dvar method to retrieve microscale flow structures in an atmospheric boundary layer the control variables of 4dvar consist of initial three dimensional velocity and temperature fields as well as profiles of eddy viscosity and thermal diffusivity the effects of lateral boundary conditions and buffer zones on the retrieval quality are evaluated using identical twin experiments with synthetic observational data prior to hrdl data retrieval it is found that use of inflow outflow boundary conditions in conjunction with buffer zones yields good results hrdl field observations are then assimilated with 4dvar together with the above treatment of boundaries to recover microscale flow structures in a convective boundary layer the uncertainty of the retrieved data is assessed by conducting a grid sensitivity test a large scale flow structure resembling a dry microburst is observed in the retrieved wind field characteristics of this structure are discussed and compared with those of a typical microburst

traditional soil particle sphericity roundness and surface roughness by computational geometry definitions of soil particle sphericity roundness and roughness have existed since at least the 1930s in the 1950s charts of typical sphericity and roundness values were developed to alleviate tedious manual determination they allowed users to classify particles by visual comparison to typical particles possessing ranges of sphericity and roundness the original definitions and somewhat subjective chart methods are still widely used today this paper describes robust numerical methods based on computational geometry to determine precisely the traditional values from two dimensional images of particles statistical methods including locally weighted regression and k fold cross validation were used to discretise a mean particle surface and thereby quantify and remove roughness the paper details the algorithms for identifying particle corners and fitting circles to them for computation of roundness conclusions are also drawn regarding the most appropriate definition for particle sphericity from among f

assessing automated image analysis of sand grain shape to identify sedimentary facies gran dolina archaeological site burgos spain abstract gran dolina is a cave sierra de atapuerca spain infilled by a 25 m thick sedimentary record divided into 12 lithostratigraphic units that have been separated into 19 sedimentary facies containing early and middle pleistocene hominin remains in this paper an automated image analysis method has been used to study the shape of the sedimentary particles since particle shape is interpreted as the result of sedimentary transport and sediment source this study can provide valuable data about the sedimentological mechanism of sequence formation the shape of the sand fraction in 73 samples from gran dolina site and sierra de atapuerca was analyzed using the malvern morphologi g3 an advanced particle characterization tool in this first complete test we used this method to the published sequence of gran dolina defined previously through field work observations and geochemical and textural analysis the results indicate that this image analysis method allows differentiation of the sedimentary facies providing objective tools to identify weathered layers and measure the textural maturity of the sediments channel facies have the highest values of circularity and convexity showing the highest textural maturity of particles on the other hand terra rossa and debris flow samples show similar values with the lowest particle maturity

impact craters on titan five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22 of titan s surface imaged by cassini s high resolution radar through december 2007 the certain craters have morphologies similar to impact craters on rocky planets as well as two with radar bright jagged rims the less certain craters often appear to be eroded versions of the certain ones titan s craters are modified by a variety of processes including fluvial erosion mass wasting burial by dunes and submergence in seas but there is no compelling evidence of isostatic adjustments as on other icy moons nor draping by thick atmospheric deposits the paucity of craters implies that titan s surface is quite young but the modeled age depends on which published crater production rate is assumed using the model of artemieva and lunine 2005 suggests that craters with diameters smaller than about 35 km are younger than 200 million years old and larger craters are older craters are not distributed uniformly xanadu has a crater density 2 9 times greater than the rest of titan and the density on equatorial dune areas is much lower than average there is a small excess of craters on the leading hemisphere and craters are deficient in the north polar region compared to the rest of the world the youthful age of titan overall and the various erosional states of its likely impact craters demonstrate that dynamic processes have destroyed most of the early history of the moon and that multiple processes continue to strongly modify its surface the existence of 24 possible impact craters with diameters less than 20 km appears consistent with the ivanov basilevsky and neukum 1997 model of the effectiveness of titan s atmosphere in destroying most but not all small projectiles

working with broken agents exploring computational 2d morphometrics for studying the post depositional history of potsherds abstract the study of size and shape of ceramic fragments is a common approach used for unraveling the depositional and post depositional history of archaeological assemblages similar to sediment particles the size and shape of a potsherd are altered under conditions of abrasion breakage or weathering occurring during or after deposition which can be the product of both human and non human agents thus the analysis of dimensional and morphological changes of fragments not only points towards specific post depositional processes but can also shed light on the nature of human interaction with broken pottery by coupling a traditional sedimentological framework for shape description and a computational approach to 2d morphometrics in this paper we present a quick reproducible and accurate method for studying the alteration of shape and size of potsherds three main shape descriptors i e sphericity roundness and convexity were tested on a combination of experimental and early neolithic potsherds in northwest romania from contexts where the conditions of fragment alteration were known or could be safely inferred in addition potsherds from an early neolithic pit discovered at c linesti oas d mbul sfintei m rii satu mare county romania were analysed for determining the pit infilling process and understanding the extent of the interaction between humans and broken pots results from morphometric tests show the reliability of the computational technique and shape descriptors for identifying different conditions of alteration of potsherds the analysis of the romanian assemblages provide insight into post depositional processes showing downslope movement as the main mechanism behind the infilling of the pit at c linesti oas d mbul sfintei m rii in addition the potsherds possessed a high level of erosion and fragmentation highlighting a long span of human interaction with broken materials at this site during early neolithic times

geologic mapping of tectonic planets geological analysis of planets typically begins with the construction of a geologic map of the planets surfaces using remote data sets geologic maps provide the basis for interpretations of geologic histories which in turn provide critical relations for understanding the range of processes that contributed to the evolution because geologic mapping should ultimately lead to the discovery of the types of operative processes that have shaped a planet surface geologic mapping must be undertaken in such a way as to allow such discovery i argue for modifications in current planetary geologic mapping methodology that admit that tectonic processes may have contributed to the formation of a planet surface and i emphasize a goal of constraining geologic history rather than determining global stratigraphy to this end it is imperative that secondary tectonic structures be clearly delineated from material units each record different aspects of planet surface evolution neglecting such delineation can result in geologic maps and interpreted geohistories in which both the spatial limits and the relative ages of material units and suites of secondary structures are incorrect determination of absolute time is fundamentally difficult to constrain in planetary studies in planetary geology the only means to estimate absolute age is the density of impact craters on a surface crater density surface ages are more akin to terrestrial and average mantle model ages which reflect the average time at which all of a rock s components were extracted from the earth s mantle rocks or planetary surfaces with very different geohistories could yield the same average model age dating tectonic events or determining rates of tectonic events is even more difficult fl 2000 elsevier science b v all rights reserved

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

mapping of titan results from the first titan radar passes the first two swaths collected by cassini s titan radar mapper were obtained in october of 2004 ta and february of 2005 t3 the ta swath provides evidence for cryovolcanic processes the possible occurrence of fluvial channels and lakes and some tectonic activity the t3 swath has extensive areas of dunes and two large impact craters we interpret the brightness variations in much of the swaths to result from roughness variations caused by fracturing and erosion of titan s icy surface with additional contributions from a combination of volume scattering and compositional variations despite the small amount of titan mapped to date the significant differences between the terrains of the two swaths suggest that titan is geologically complex the overall scarcity of impact craters provides evidence that the surface imaged to date is relatively young with resurfacing by cryovolcanism fluvial erosion aeolian erosion and likely atmospheric deposition of materials future radar swaths will help to further define the nature of and extent to which internal and external processes have shaped titan s surface

titan s diverse landscapes as evidenced by cassini radar s third and fourth looks at titan abstract cassini s third and fourth radar flybys t7 and t8 covered diverse terrains in the high southern and equatorial latitudes respectively the t7 synthetic aperture radar sar swath is somewhat more straightforward to understand in terms of a progressive poleward descent from a high dissected and partly hilly terrain down to a low flat plain with embayments and deposits suggestive of the past or even current presence of hydrocarbon liquids the t8 swath is dominated by dunes likely made of organic solids but also contain somewhat enigmatic probably tectonic features that may be partly buried or degraded by erosion or relaxation in a thin crust the dark areas in t7 show no dune morphology unlike the dark areas in t8 but are radiometrically warm like the dunes the huygens landing site lies on the edge of the t8 swath correlation of the radar and huygens disr images allows accurate determination of its coordinates and indicates that to the north of the landing site sit two large longitudinal dunes indeed had the huygens probe trajectory been just 10 km north of where it actually was images of large sand dunes would have been returned in place of the fluvially dissected terrain actually seen illustrating the strong diversity of titan s landscapes even at local scales

cryovolcanic features on titan s surface as revealed by the cassini titan radar mapper abstract the cassini titan radar mapper obtained synthetic aperture radar images of titan s surface during four fly bys during the mission s first year these images show that titan s surface is very complex geologically showing evidence of major planetary geologic processes including cryovolcanism this paper discusses the variety of cryovolcanic features identified from sar images their possible origin and their geologic context the features which we identify as cryovolcanic in origin include a large 180 km diameter volcanic construct dome or shield several extensive flows and three calderas which appear to be the source of flows the composition of the cryomagma on titan is still unknown but constraints on rheological properties can be estimated using flow thickness rheological properties of one flow were estimated and appear inconsistent with ammonia water slurries and possibly more consistent with ammonia water methanol slurries the extent of cryovolcanism on titan is still not known as only a small fraction of the surface has been imaged at sufficient resolution energetic considerations suggest that cryovolcanism may have been a dominant process in the resurfacing of titan

cassini radar images at hotei arcus and western xanadu titan evidence for geologically recent cryovolcanic activity 1 images obtained by the cassini titan radar mapper radar reveal lobate flowlike features in the hotei arcus region that embay and cover surrounding terrains and channels we conclude that they are cryovolcanic lava flows younger than surrounding terrain although we cannot reject the sedimentary alternative their appearance is grossly similar to another region in western xanadu and unlike most of the other volcanic regions on titan both regions correspond to those identified by cassini s visual and infrared mapping spectrometer vims as having variable infrared brightness strengthening the case that these are recent cryovolcanoes citation wall s d et al 2009 cassini radar images at hotei arcus and western xanadu titan evidence for geologically recent cryovolcanic activity geophys res lett 36 l04203 doi 10 1029 2008gl036415

determining titan surface topography from cassini sar data a technique referred to as sartopo has been developed for obtaining surface height estimates with 10 km horizontal resolution and 75 m vertical resolution of the surface of titan along each cassini synthetic aperture radar sar swath we describe the technique and present maps of the co located data sets a global map and regional maps of xanadu and the northern hemisphere hydrocarbon lakes district are included in the results a strength of the technique is that it provides topographic information co located with sar imagery having a topographic context vastly improves the interpretability of the sar imagery and is essential for understanding titan sartopo is capable of estimating surface heights for most of the sar imaged surface of titan currently nearly 30 of the surface is within 100 km of a sartopo height profile other competing techniques provide orders of magnitude less coverage we validate the sartopo technique through comparison with known geomorphological features such as mountain ranges and craters and by comparison with co located nadir altimetry including a 3000 km strip that had been observed by sar a month earlier in this area the sartopo and nadir altimetry data sets are co located tightly within 5 10 km for one 500 km section have similar resolution and as expected agree closely in surface height furthermore the region contains prominent high spatial resolution topography so it provides an excellent test of the resolution and precision of both techniques