unusual radar echoes from the greenland ice sheet airborne radar images of part of the greenland ice sheet reveal icy terrain whose radar properties are unique among radar studied terrestrial surfaces but resemble those of jupiter s icy galilean satellites the 5 6 and 24 centimeter wavelength echoes from the greenland percolation zone like the 3 5 and 13 centimeter wavelength echoes from the icy satellites are extremely intense and have anomalous circular and linear polarization ratios however the detailed subsurface configurations of the galilean satellite regoliths where heterogeneities are the product of prolonged meteoroid bombardment are unlikely to resemble that within the greenland percolation zone where heterogeneities are the product of seasonal melting and refreezing

mercury radar imaging evidence for polar ice the first unambiguous full disk radar mapping of mercury at 3 5 centimeter wavelength with the goldstone 70 meter antenna transmitting and 26 antennas of the very large array receiving has provided evidence for the presence of polar ice the radar experiments conducted on 8 and 23 august 1991 were designed to image the half of mercury not photographed by mariner 10 the orbital geometry allowed viewing beyond the north pole of mercury a highly reflective region was clearly visible on the north pole during both experiments this polar region has areas in which the circular polarization ratio pt was 1 0 to 1 4 values 0 1 are typical for terrestrial planets such high values of have hitherto been observed in radar observations only from icy regions of mars and icy outer planet satellites

radar backscatter from mars properties of rock strewn surfaces abstract rock strewn surfaces are apparently common on mars and radar backscatter data offer the most direct means for remotely estimating their statistical properties this paper examines the height statistics of power law and exponential rock size frequency distributions and demonstrates the dependence of root mean square rms height on horizontal scale as a function of the distribution parameters in general strewn surfaces have an inherent variation in roughness for horizontal length scales below the maximum rock diameter this leads to variations in radar echo power with wavelength even when the differential diameter function has an inverse cubed power law form size frequency data for a rock strewn test site in hawaii are consistent over a specific range of horizontal scales with a power law distribution an exponential form while better describing the rapid decline in rock abundance above a certain size threshold underestimates the population at the smaller scales most relevant to radar scattering rock sphericity statistics often cited in descriptions of rocky areas appear to be consistent with a rayleigh distribution of major and minor axis diameters about any chosen mean value depolarized backscatter data for the test site at 5 7 68 cm are proportional to the rms height at the wavelength scale mirroring a similar trend for continuous rough rocky surfaces an empirical model relating rms height to depolarized backscatter coefficient appears to well describe the behavior of strewn surfaces the polarized echoes are consistent with mie scattering from surface rocks for a reasonable choice of dielectric properties but the number of free parameters and the interaction of the scatterer and surface yields weak remote sensing roughness or dielectric constraints while depolarized backscatter data provide robust estimates of the rms height for continuous and discrete roughness populations their use in mars landing site planning is model dependent for single wavelength data we cannot uniquely determine the size frequency distribution and the maximum rock diameter dual wavelength observations in the s to p band range may better constrain the surface properties

early views of the martian surface from the mars orbiter camera of mars global surveyor high resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms dunes sandsheets and drifts are prevalent and exhibit a range of morphology composition inferred from albedo and age as seen in occurrences of different dune orientations at the same location steep walls of topographic depressions such as canyons valleys and impact craters show the martian crust to be stratified at scales of a few tens of meters the south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non volatile components low resolution regional views of the planet provide synoptic observations of polar cap retreat condensate clouds and the lifecycle of local and regional dust storms

mercury full disk radar images and the detection and stability of ice at the north pole the first full disk radar images of mercury were obtained on august 8 and 23 1991 these images were constructed using the very large array vla in socorro new mexico to receive and map radar flux at 3 5 cm x band which was continuously transmitted from the 70 m jet propulsion laboratory deep space network antenna at goldstone california approximately 77 of the surface was imaged at resolutions as good as 150 km about half of the hemisphere photographed by mariner 10 was imaged as well as most of the hemisphere which has not previously been photographed at the time of the observations the north pole was visible and the feature with the highest same sense ss circular reflectivity in the images is near the nominal polar position the peak ss reflectivity of this feature was 7 9 and the circular polarization ratio throughout much of the feature is 1 our best estimate of the size of the feature is that its diameter is 350 km we interpret the feature to be indicative of the presence of ices because of the signal strength and polarization characteristics the ices must be very clean and were thus probably deposited in a relatively short time period the most likely place to find these ices is in any permanently shadowed areas in the polar regions which would be very cold in comparison to absolute reflectivities of other icy bodies and regions in the solar system the reflectivity of the north polar feature is slightly depressed this is probably because the ices do not fill an observational resolution cell i e there is incomplete areal coverage or are covered by a layer of dust or soil which absorbs some of the incoming and outgoing radar energy or both a covering layer would also protect any ices from erosion by energetic sources other prominent features on the unphotographed hemisphere correspond to positions where atmospheric sodium enhancements have been measured from earth this may indicate that these locations are large basins similar to the caloris basin where an atmospheric potassium enhancement has been measured which may be the result of increased degassing in the disrupted surface and near surface direct comparison of the radar echoes from our features with those from the caloris basin are hard to make as caloris was not imaged by us in a favorable geometry features on the photographed hemisphere are smaller and mostly associated with craters and crater complexes most notably the kuiper crater and its environs

radar investigation of mars mercury and titan radar astronomy is the study of the surfaces and near surfaces of solar system objects using active transmission of modulated radio waves and the detection of the reflected energy the scientific goals of such experiments are surprisingly broad and include the study of surface slopes fault lines craters mountain ranges and other morphological structures electrical reflectivities contain information about surface densities and to some extent the chemical composition of the surface layers radar probes the subsurface layers to depths of the order of 10 wavelengths providing geological mapping and determinations of the object s spin state radar also allows one to study an object s atmosphere and ionic layers as well as those of the interplanetary medium precise measurements of the time delay to surface elements provide topographic maps and powerful information on planetary motions and tests of gravitational theories such as general relativity in this paper we limit our discussion to surface and near surface probing of mercury mars and titan and review the work of the past decade which includes fundamentally new techniques for earth based imaging the most primitive experiments involve just the measurement of the total echo power from the object the most sophisticated experiments would produce spatially resolved maps of the reflected power in all four stokes parameters historically the first experiments produced echoes from the moon during the period shortly after world war ii see e g evans 1962 but the subject did not really develop until the early 1960s when the radio equipment was sufficiently sensitive to detect echoes from venus and obtain the first doppler strip maps of that planet the first successful planetary radar systems were the continuous wave cw radar at the goldstone facility of the caltech s jet propulsion laboratory and the pulse radar at the mit lincoln laboratory all of the terrestrial planets were successfully studied during the following decade yielding the spin states of venus and mercury a precise value of the astronomical unit and a host of totally new discoveries concerning the surfaces of the terrestrial planets and the moon this work opened up at least a similar number of new questions although the early work was done at resolution scales on the order of the planetary radii very rapid increases in system sensitivities improved the resolution to the order of 100 km but always with map ambiguities recently unambiguous resolution of 100 m over nearly the entire surface of venus has been achieved from the magellan spacecraft using a side looking synthetic aperture radar reviews of the work up to the magellan era can be found in evans 1962 muhleman et al 1965 evans hagfors 1968 see chapters written by g pettengill t hagfors and j evans and ostro 1993 the radar study of venus from the magellan spacecraft was a tour de force and is well described in special issues of science volume 252 april 12 1991 and in the journal of geophysical research volume 97 august 25 and october 25 1992 venus will not be considered in this paper even though important polarization work on that planet continues at arecibo goldstone and the very large array vla in this paper we review the most recent work in earth based radar astronomy using new techniques of earth rotation super synthesis at the vla in new mexico operated by the national radio astronomy observatory and the recently developed long code techniques at the arecibo observatory in puerto rico operated by cornell university note it was recently brought to our attention that the vla software doubles the flux density of their primary calibrators consequently it is necessary to half the radar power and reflectivity numerical values in all of our published radar results from the vla goldstone radar the symbiotic relationship in these new developments for recent advances in our understanding of mercury and mars is remarkable vla imaging provides for the first time unambiguous images of an entire hemisphere of a planet and the long code technique makes it possible to map mars and mercury using the traditional range gated doppler strip mapping procedure which was apparently developed theoretically at the lincoln laboratory by paul green based on a citation in evans 1962 richard goldstein was the first to obtain range gated planetary maps of venus as reported in carpenter goldstein 1963 such a system was developed earlier for the moon as reported by pettengill 1960 and pettengill henry 1962 we first discuss the synthesis mapping technique

microwave thermal mapping of the stealth region on mars abstract mars was observed at 1 35 cm 22 ghz with the very large array vla on february 19 1995 we mapped the thermal emission from the martian surface in the tharsis and amazonis regions observed variations of microwave brightness temperature were compared with the results of a subsurface thermal model to derive the emissivity and dielectric constant of the soil the results revealed a region with anomalously high values of emissivity 0 99 0 01 which is approximately inversely proportional to the density of the material we interpret this region as having a low density 0 5 0 3 gm cm 3 near the surface it lies within the boundaries of stealth the echoless radar feature discovered by muhleman s radar group in 1991 science253 1508 1513 we suggest two hypotheses for the formation of stealth it may consist of ash flows from the nearby tharsis volcanoes or it might be an eolian deposit

estimation of mars radar backscatter from measured surface rock populations reanalysis of rock population data at the mars viking lander sites has yielded updated values of rock fractional surface coverage about 0 16 at both sites including outcrops and new estimates of rock burial depths and axial ratios these data are combined with a finite difference time domain fdtd numerical scattering model to estimate diffuse backscatter due to rocks at both the lander 1 vl1 and lander 2 vl2 sites we consider single scattering from both surface and subsurface objects of various shapes ranging from an ideal sphere to an accurate digitized model of a terrestrial rock the fdtd cross section calculations explicitly account for the size shape composition orientation and burial state of the scattering object the incident wave angle and polarization and the composition of the surface we calculate depolarized specific cross sections at 12 6 cm wavelength due to lossless rock like scatterers of about 0 014 at vl1 and 0 023 at vl2 which are comparable to the measured ranges of 0 019 0 032 and 0 012 0 018 respectively we also discuss the variation of the diffuse cross section as the local angle of incidence i changes numerical calculations for a limited set of rock shapes indicate a marked difference between the angular backscattering behavior of wavelength scale surface and subsurface rocks while subsurface rocks scatter approximately as a cosine power law surface rocks display a complex variation often with peak backscattering at high incidence angles i 70 75

mars radar mapping strong backscatter from the elysium basin and outflow channel abstract radar reflectivity maps of mars obtained at arecibo in 1990 using a modified delay doppler technique have revealed strong depolarized echoes coming from the elysium flood basin and outflow channel as well as from elysium mons this result is consistent with recent studies which show that much of the basin channel floor is covered with lava flows

origin and evolution of a cold based tropical mountain glacier on mars the pavonis mons fan shaped deposit 1 each of the large tharsis montes volcanoes in the equatorial region of mars has an unusual amazonian aged fan shaped deposit on its west northwestern flank on the basis of viking orbiter data the origin of these deposits has been variously ascribed to volcanic mass wasting tectonic and glacial processes using new mgs and odyssey data combined with recent developments in the study of cold based glaciers we reassess the geology and mode of origin for these deposits with particular emphasis on pavonis mons the deposits share three characteristic facies including 1 a ridged facies consisting of tens to 100 parallel concentric ridges around the margins of the deposits 2 a knobby facies composed of irregular hills and hummocks and 3 a smooth facies of broad lobate plains that superposes all other units within the deposits on the basis of morphology topography superposition relationships and close terrestrial analogs in the dry valleys of antarctica we interpret the pavonis fan shaped deposit as the depositional remains of a cold based glacier that formed on the northwestern flank in recent martian history we interpret the ridged facies as drop moraines formed around the margins of a retreating cold based glacier the knobby facies as a sublimation till derived from in situ down wasting of cold based glacial ice and the smooth facies as extant debris covered glacial ice in addition to the three main facies the fan shaped deposit at pavonis mons contains several unique features including arcuate scarps high relief flow like features and radial ridges which suggest that volcanism played a role during its formation using recent results from mars general circulation model simulations we outline a model of glacier formation involving atmospheric deposition of water ice on the northwestern flanks of the tharsis montes during periods of high mean obliquity reconstructed ice sheet profiles for each of the tharsis montes glaciers suggest that the ice sheets attained average thicknesses of 1 6 2 4 km values that are consistent with a cold based glacial origin analysis of crater size frequency distributions using new data indicates that the age of the glaciation lies within the late amazonian 10 200 ma thus our results suggest that multiple phases of tropical mountain glaciation occurred on mars within the past few hundred myr and that significant amounts of near surface equatorial ice may remain within the deposit today

the dispersal of pyroclasts from ancient explosive volcanoes on mars implications for the friable layered deposits a number of voluminous fine grained friable deposits have been mapped on mars the modes of origin for these deposits are debated the feasibility for an origin by volcanic airfall for the friable deposits is tested using a global circulation model to simulate the dispersal of pyroclasts from candidate source volcanoes near each deposit it is concluded that the medusae fossae formation and electris deposits are easily formed through volcanic processes and that the hellas deposits and south polar pitted deposits could have some contribution from volcanic sources in specific atmospheric regimes the arabia and argyre deposits are not well replicated by modeled pyroclast dispersal suggesting that these deposits were most likely emplaced by other means

mars dual polarization radar observations with extended coverage abstract thirteen centimeter wavelength radar observations of mars made in 1982 at arecibo observatory yield accurate measurements of the full backscatter spectrum in two orthogonal polarizations the data which were obtained for several widely separated subradar longitudes at 24 n latitude provide the first global view of the distribution of small scale surface roughness on mars the diffuse component of the echo exhibits strong spatial variations areas of maximum depolarization correlate well with volcanic regions tharsis and elysium while the heavily cratered upland terrain yields relatively low depolarization parts of tharsis give near complete depolarization polaziation ratio c 1 when viewed at oblique angles of incidence northern martian plains regions tharsis elysium and amazonis may comprise the most extensive area of severe decimeter scale surface roughness in the inner solar system on the average the northern martian tropics yield higher diffuse radar cross sections d 0 05 0 12 and a higher of degree disk integrated depolarization c 0 1 0 4 than is found for the moon mercury and venus comparisons between the moon and mars using radar data ground truth and simple scattering models suggest that mars possesses a relatively high average coverage by decimeter scale rocks also discussed are several of the more interesting quasispecular scattering results the most unsual of which were obtained over the olympus mons aureole region

a radar study of the chryse region mars arecibo 12 6 cm delay doppler measurements are used to study the topography and radar scattering properties of the chryse region including the viking 1 and mars pathfinder lander sites and environs the viking 1 lander lies on a gentle 0 13 east facing slope at a 6 1 mbar altitude of 1 35 km the mars pathfinder lander site lies slightly lower 1 7 km on a flat low relief plain quasi specular roughness across chryse is considerably higher than the martian average and shows some strong spatial variation not apparent from older cw observations some of the rougher regions coincide with the distal ends of the tiu and ares vallis channels while another is located just to the northeast of the viking 1 lander chryse shows asymmetric scattering skew similar to that seen in mars southern hemisphere and in recent magellan radar observations of venus comparison of 12 6 cm and 3 5 cm data indicates that chryse s quasi specular reflectivity is strongly wavelength dependent being higher at the longer wavelength suggesting a rapid density increase within the top decimeter of the regolith depolarized reflectivity images of the general chryse area show modest enhancements from decimeter scale roughness or rocks associated with maja and kasei valles and the plateau bordering simud vallis these images indicate that the rock abundance at the proposed mars pathfinder lander site is similar to that at the viking lander sites

mars mapping with delay doppler radar mars radar imaging results from arecibo 12 6 cm observations are presented the images were derived from delay doppler mapping using a coded long pulse technique to mitigate the effects of echo overspreading images of the depolarized echo are used to identify regions of high decimeter scale roughness some of the strongest echo features are located on the major shield volcanoes or on relatively young off shield flows such as the olympus and pavonis lava aprons the shields themselves have highly irregular radar signatures suggesting complex volcanic histories some mars radar features have twice the depolarized brightness of the roughest terrestrial lava flows apparently due to higher levels of multiple scattering from surfaces of spectacular roughness or from volume scattering low brightness smooth areas are associated with older surfaces such as fractured and highland terra as well as with terrain interpreted to be debris lobes ash flows and aureoles in particular a close connection was found between the 12 6 cm counterpart of the stealth feature and the medusae fossae formation postulated to be deep ignimbrite deposits marte valus is anomalous in being the only outflow channel showing strongly enhanced echoes which supports the idea that this channel and the elysium basin that it drained are filled with lava flows a weak radar feature was found for the south polar residual ice cap comparisons with goldstone 3 5 cm data show that the south polar enhancement is much weaker at 12 6 cm than at 3 5 cm indicating that the southern ice cap becomes optically thin at the longer wavelength a north polar enhancement has also been found which is comparable in strength to the 12 6 cm south polar feature

the clementine bistatic radar experiment during the clementine 1 mission a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle beta for selected lunar areas observations of the lunar south pole yield a same sense polarization enhancement around beta 0 analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole radar observations of periodically solar illuminated lunar surfaces including the north pole yielded no such enhancement a probable explanation for these differences is the presence of low loss volume scatterers such as water ice in the permanently shadowed region at the south pole

interpretation of planetary radar observations the relationship between actual and inferred slope distributions we examined the distribution of surface slopes of a variety of terrestrial surfaces by field measurement representing surfaces formed by a wide range of processes and compared the results to planetary radar data slope distributions of the measured surfaces differed considerably from the distributions assumed by accepted models of radar scattering the rms slope values for the terrestrial surfaces ranged from 0 to 16 5 compared to a range of rms slope values of 1 to about 10 for planetary surfaces as inferred from radar observations while the great majority of planetary surfaces observed by radar have rms slope estimates in the lower end of this range 5 nearly all of the terrestrial surfaces we measured have rms slope values greater than 5 we also used hagfors model of radar scattering to predict the return that would be expected from surfaces where two discrete surface types were present within the radar field of view and found that the shapes of the resulting slope distributions differed from those predicted by the hagfors model for homogeneous surfaces additionally the resulting best fit rms slope was a nonlinear combination of those of the pure surfaces emphasizing the smoother surface together these results suggest that current methods of determining surface roughness from radar may significantly underestimate the roughness of planetary surfaces and that the derived rms slope can best be used as a qualitative guide to the physical interpretation of actual surface properties

recent flood lavas in the elysium region of mars abstract a vast area of smooth plains in southeastern elysium here referred to as the cerberus formation is interpreted to be of volcanic origin surface morphology lobate edges of the unit the identification of vents low shields and the embayment relation of the unit with adjacent older units all suggest a volcanic origin the plains were formed by the eruption of low viscosity lavas that filled a topographic depression in southeast elysium and then flowed into western amazonis planitia flow into western amazonis was facilitated by a series of channels carved by an earlier fluvial episode which were exploited by lavas as they moved down slope crater frequencies and stratigraphic relations indicate that the unit is very young upper amazonian the presence of such young flood lavas indicates 1 late in martian history large scale eruptions of low viscosity lava was still possible b sufficient heat remained in the mantle to mobilize large quantities of magma and c flood volcanism either continued or resumed in elysium after activity of the large central volcanoes had ceased each of these points are important considerations in understanding the martian thermal and volcanic history

chronology eruption duration and atmospheric contribution of the martian volcano apollinaris patera geologic mapping thermal inertia measurements and an analysis of the color visual wavelengths of the martian volcano apollinaris patera indicate the existence of two different surface materials comprising an early easily eroded edifice and a more recent competent fan on the southern flank a chronology of six major events that is consistent with the present morphology of the volcano has been identified we propose that large scale explosive activity occurred during the formation of the main edifice and that the distinctive fan on the southern flank appears to have been formed by lavas of low eruptive rate similar to those that form compound pahoehoe flow fields on earth a basal escarpment typically 500 m in relief and morphologically similar to the one surrounding olympus mons was produced between the formation of the main edifice and the fan indicating multistage eruptions over a protracted period of time contact relations between the volcanic units and the adjacent chaotic material indicate that formation of the chaotic material occurred over an extended period of time and may be related to the volcanic activity that formed apollinaris patera stereophotogrammetric measurements permit the volume of the volcano to be estimated at 105 km3 from this volume measurement and an inferred eruption rate 1 5 10 2 km3 yr 1 we estimate the total eruption duration for the main edifice to be 107 yrs plausible estimates of the exsolved volatile content of the parent magma imply that greater than 1015 kg of water vapor was released into the atmosphere as a consequence of this activity this large amount of water vapor as well as other exsolved gases must have had a significant impact on local and possibly global climatic conditions

geomorphological effectiveness of floods to rework gravel bars insight from hyperscale topography and hydraulic modelling bars are key morphological units in river systems fashioning the sediment regime and bedload transport processes within a reach reworking of these features underpins channel adjustment at larger scales thereby acting as a key determinant of channel stability despite their importance to channel evolution few investigations have acquired spatially continuous data on bar morphology and sediment size to investigate bar reworking to this end four bars along a 10 km reach of a wandering gravel bed river were surveyed with terrestrial laser scanning tls capturing downstream changes in slope bed material size and channel planform detrended standard deviations z were extracted from tls point clouds and correlated to underlying physically measured median grain size d50 across a greater range of z values than have hitherto been reported the resulting linear regression model was used to create a 1 m resolution median grain size map a fusion of airborne lidar and optical empirical bathymetric mapping was used to develop reach scale digital elevation models dems for rapid two dimensional hydraulic modelling using jflow software the ratio of dimensionless shear stress over critical shear stress was calculated for each raster cell to calculate the effectiveness of a range of flood events 2 33 100 year recurrence intervals to entrain sediment and rework bar units results show that multiple bar forming discharges exist whereby frequent flood flows rework tail and back channel areas whilst much larger less frequent floods are required to mobilise the coarser sediment fraction on bar heads valley confinement is shown to exert a primary influence on patterns of bar reworking historical aerial photography hyperscale dems and hydraulic modelling are used to explain channel adjustment at the reach scale the proportion of the bar comprised of more frequently entrained units tail back channel supra platform relative to more static units bar head exerts a direct influence upon geomorphic sensitivity

radar images of mars full disk images of mars have been obtained with the use of the very large array vla to map the radar reflected flux density the transmitter system was the 70 m antenna of the deep space network at goldstone california the surface of mars was illuminated with continuous wave radiation at a wavelength of 3 5 cm the reflected energy was mapped in individual 12 minute snapshots with the vla in its largest configuration fringe spacings as small as 67 km were obtained the images reveal near surface features including a region in the tharsis volcano area over 2000 km in east west extent that displayed no echo to the very low level of the radar system noise the feature called stealth is interpreted as a deposit of dust or ash with a density less than about 0 5 gram per cubic centimeter and free of rocks larger than 1 cm across the deposit must be several meters thick and may be much deeper the strongest reflecting geological feature was the south polar ice cap which was reduced in size to the residual south polar ice cap at the season of observation the cap image is interpreted as arising from nearly pure co 2 or h 2o ice with a small amount of martian dust less than 2 percent by volume and a depth greater than 2 to 5 m only one anomalous reflecting feature was identified outside of the tharsis region although the elysium region was poorly sampled in this experiment and the north pole was not visible from earth

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

radar probing of planetary regoliths an example from the northern rim of imbrium basin 1 imaging radar measurements at long wavelengths e g 30 cm allow deep up to tens of meters probing of the physical structure and dielectric properties of planetary regoliths we illustrate a potential application for a mars orbital synthetic aperture radar sar using new earth based 70 cm wavelength radar data for the moon the terrae on the northern margin of mare imbrium the montes jura region have diffuse radar backscatter echoes that are 2 4 times weaker at 3 8 cm 70 cm and 7 5 m wavelengths than most other lunar nearside terrae possible geologic explanations are 1 a pyroclastic deposit associated with sinuous rilles in this region 2 buried mare basalt or a zone of mixed highland basaltic debris cryptomaria or 3 layers of ejecta associated with the iridum and plato impacts that have fewer meter sized rocks than typical highlands regolith while radar data at 3 8 cm to 7 5 m wavelengths suggest significant differences between the montes jura region and typical highlands the surface geochemistry and rock abundance inferred from clementine uv vis data and eclipse thermal images are consistent with other lunar terrae there is no evidence for enhanced iron abundance expected for basaltic pyroclastic deposits near the source vents of the sinuous rilles radial to plato the regions of low 70 cm radar return are consistent with overlapping concentric haloes about iridum and plato and do not occur preferentially in topographically low areas as is observed for radar mapped cryptomaria thus we suggest that the extensive radar dark area associated with the montes jura region is due to overlapping rock poor ejecta deposits from iridum and plato craters comparison of the radial extent of low radar return crater haloes with a model for ejecta thickness shows that these rock poor layers are detected by 70 cm radar where they are on the order of 10 m and thicker a sar in orbit about mars could use similar deep probing to reveal the nature of crater and basin related deposits

circular polarization ratio characteristics of impact craters from mini rf observations and implications for ice detection at the polar regions of the moon 1 in an attempt to reduce the ambiguity on radar detection of water ice at the permanently shadowed regions near the lunar poles radar echo strength and circular polarization ratio cpr of impact craters are analyzed using the miniature radio frequency mini rf radar data from the lunar reconnaissance orbiter mission eight typical craters among over 70 craters are selected and classified into four categories based on their locations and cpr characteristics polar anomalous polar fresh nonpolar anomalous and nonpolar fresh the influences on cpr caused by surface slope rocks and dielectric constant are analyzed quantitatively using high resolution topography data and optical images a two component mixed model for cpr that consists of a normal surface and a rocky surface is developed to study the effect of rocks that are perched on lunar surface and buried in regolith our analyses show that inner wall of a typical bowl shaped crater can give rise to a change of about 30 in local incidence angle of radar wave which can further result in a cpr difference of about 0 2 there is a strong correlation between mini rf cpr and rock abundance that is obtained from high resolution optical images and predictions from the two component mixed model match well with the observed cprs and the estimated rock abundances statistical results show that there is almost no apparent difference in cpr characteristics between the polar and nonpolar anomalous craters or between the polar and nonpolar fresh craters the enhanced cpr in the interior of anomalous craters is most probably caused by rocks that are perched on lunar surface or buried in regolith instead of ice deposits as suggested in previous studies

selection of the mars pathfinder landing site the mars pathfinder spacecraft will land on a depositional fan near the mouth of the catastrophic outflow channel ares vallis 19 5 n 32 8 w this site offers the prospect of analyzing a variety of rock types from the ancient cratered highlands intermediate age ridged plains and reworked channel deposits analyses of these rocks by pathfinder instruments will enable first order scientific questions to be addressed such as differentiation of the crust the development of weathering products and the nature of the early environment as well as their subsequent evolution on mars constraints imposed by 1 spacecraft and rover designs which are robust 2 entry descent and landing 3 scientific potential at various sites and 4 safety were important considerations in site selection engineering constraints require a 70 km by 200 km smooth flat low slopes area located between 10 and 20 n that is below 0 km elevation with average radar reflectivity little dust and moderate rock abundance three regions on mars are between 10 and 20 n and below 0 km elevation chryse amazonis and isidis elysium science considerations favor sites at the mouths of outflow channels grab bag sites offer an assay of rock types on mars highland sites early crustal differentiation and climate and sites covered with dark unoxidized material sites are considered safe if they are clearly below 0 km elevation appear acceptably free of hazards in high resolution 50 m pixel viking orbiter images and have acceptable reflectivity and roughness at radar wavelengths thermal inertia rock abundance red to violet ratio and albedo recent 3 5 cm wavelength radar observations were used to verify elevation reflectivity and roughness within the landing ellipses three sites meet all of these criteria ares vallis tritonis lacus and isidis although isidis appears to be safer than tritonis and ares the greater scientific potential at ares vallis resulted in its selection comparisons of the grand coulee channel and the depositional ephrata fan of the channeled scabland in eastern washington with ares vallis and its depositional fan also suggest the ares vallis landing site is safe and scientifically interesting

decline in arctic sea ice thickness from submarine and icesat records 1958 2008 1 the decline of sea ice thickness in the arctic ocean from icesat 2003 2008 is placed in the context of estimates from 42 years of submarine records 1958 2000 described by rothrock et al 1999 2008 while the earlier 1999 work provides a longer historical record of the regional changes the latter offers a more refined analysis over a sizable portion of the arctic ocean supported by a much stronger and richer data set within the data release area dra of declassified submarine sonar measurements covering 38 of the arctic ocean the overall mean winter thickness of 3 64 m in 1980 can be compared to a 1 89 m mean during the last winter of the icesat record an astonishing decrease of 1 75 m in thickness between 1975 and 2000 the steepest rate of decrease is 0 08 m yr in 1990 compared to a slightly higher winter summer rate of 0 10 0 20 m yr in the five year icesat record 2003 2008 prior to 1997 ice extent in the dra was 90 during the summer minimum this can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to 55 during the record setting minimum in 2007 this combined analysis shows a long term trend of sea ice thinning over submarine and icesat records that span five decades

aeolian dunes as evidence for explosive volcanism in the tharsis region of mars two transverse dune fields occur among late amazonian volcanic and aeolian landforms in southwestern tharsis mars the first is located 70 km northwest of biblis patera around 5 n 125 w the second is located about 500 km northwest of arsia mons at 2 s 130 w the latter is the largest dune field thus far documented to occur in the equatorial latitudes of mars unlike other dunes on the planet both dune fields in tharsis have low thermal inertias 2 7 10 3cal cm 2sec 0 5k 1 and high albedos 0 26 that are indistinct from their surrounding terrain both dune fields have superposed features such as impact craters lava flows smooth surfaced units and bright wind streaks the dune fields therefore appear to be inactive and mantled by fine grained material i e particles 60 m to form aeolian dunes require a supply of sand on earth most dune sands are supplied by fluvial and littoral processes but this is not the case in tharsis on mars because they are superposed on a late amazonian surface the climate is assumed to have been hyper arid throughout the time that the dunes have existed under these conditions the only plausible source for quantities of sediment sufficient to form transverse dune fields is explosive volcanism therefore the two dune fields in tharsis are evidence that explosive volcanism has occurred in this region in the late amazonian epoch

radar mapping of mercury full disk images and polar anomalies a random code technique has been used at arecibo to obtain delay doppler radar images of the full disk of mercury anomalously bright features were found at the north and south poles the north polar feature is oblong 4 by 8 and offset from the pole the smaller south polar feature is mostly confined to the floor of the crater chao meng fu the polar locations and radar properties of these features indicate that they may be produced by volume scattering in ice the images also reveal a variety of more subdued reflectivity features ranging in size from hundreds to thousands of kilometers some of these appear to have an impact origin

arecibo radar imagery of mars the major volcanic provinces abstract we present earth based radar images of mars obtained with the upgraded arecibo s band 12 6 cm radar during the 2005 2012 oppositions the imaging was done using the same long code delay doppler technique as for the earlier pre upgrade imaging but at a much higher resolution 3 km and for some regions a more favorable sub earth latitude this has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity a proxy for small scale surface roughness over the major volcanic provinces of tharsis elysium and amazonis we find that vast portions of these regions are covered by radar bright lava flows exhibiting circular polarization ratios close to unity a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces all of the major volcanoes have radar bright features on their shields although the brightness distribution on olympus mons is very patchy and the summit plateau of pavonis mons is entirely radar dark the older minor shields paterae and tholi are largely or entirely radar dark which is consistent with mantling by dust or pyroclastic material other prominent radar dark features include the fan shaped deposits possibly glacial associated with the three major tharsis montes shields various units of the medusae fossae formation a region south and west of biblis patera where stealth deposits appear to obscure tharsis flows and a number of dark halo craters with radar absorbing ejecta blankets deposited atop surrounding bright flows several major bright features in tharsis are associated with off shield lava flows these include the olympus mons basal plains volcanic fields east and south of pavonis mons the daedalia planum flows south of arsia mons and a broad expanse of flows extending east from the tharsis montes to echus chasma the radar bright lava plains in elysium are concentrated mainly in cerberus and include the fluvio volcanic channels of athabasca valles grjota valles and marte valles as well as an enigmatic region at the southern tip of the cerberus basin some of the cerberus bright features correspond to the distinctive platy ridged flows identified in orbiter images the radar bright terrain in amazonis planitia comprises two distinct but contiguous sections a northern section formed of lavas and sediments debouched from marte valles and a southern section whose volcanics may derive in part from local sources this south amazonis region shows perhaps the most complex radar bright structure on mars and includes features that correspond to platy ridged flows similar to those in cerberus

amazonis planitia the role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on mars 1 amazonis planitia located between the two main volcanic provinces on mars tharsis and elysium is characterized by extremely smooth topography at several scale lengths as smooth as oceanic abyssal plains topography on earth we use mars global surveyor mgs data primarily very high resolution mars orbiter laser altimeter mola topography and derivative slope maps gradient maps and detrended maps to examine the surface morphology of amazonis planitia and the stratigraphic relationships among previously mapped and newly defined units these new data reveal the presence of a 1300 km diameter noachian impact basin in northwest amazonis planitia and an extensive late hesperian lava flow unit that appears to have originated from the olympus mons source area prior to aureole formation the presence of this previously unrecognized flow unit strongly suggests that olympus mons activity dates back to at least the hesperian as did activity on the tharsis montes emplacement of this 100 meter thick flow unit formed a barrier along the northern margin of amazonis planitia which had a profound influence on the subsequent geologic history of the region formation of olympus mons aureole deposits created an eastern topographic barrier and subsequent tharsis montes lava flows entered the basin from the south flowing around the aureole these three barriers degraded noachian crater rim protoolympus mons flow unit and olympus mons aureole caused subsequent lava flows and outflow channel effluents primarily from the elysium region to the west to pond on the floor of amazonis planitia preferentially smoothing the terrain there mars orbiter camera moc images substantiate that at least two very fluid lava flows alternated with fluvial episodes from elysium planitia flowing through marte valles onto the floor of the amazonis planitia basin within amazonis planitia moc images show flow like textures heavily mantled by sediments and radar data reveal the presence of rough lava flow surfaces underlying the sedimentary debris these data thus suggest that the unique smoothness of amazonis planitia is the result of deposition of thin fluid lava flows and fluvial sediments in an enclosed basin crater counts suggest that the most recent resurfacing may have occurred in the latest amazonian period in the last 1 of the history of mars in light of its unique history it is somewhat ironic to note that amazonis planitia was originally thought to be a typical young martian surface and therefore used to name the amazonian era index terms 6225 planetology solar system objects mars 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5480 planetology solid surface planets volcanism 8450 4267 oceanography general paleoceanography keywords mars water amazonis planitia marte vallis volcanism amazonian citation fuller e r and j w head iii amazonis planitia the role of geologically recent volcanism and sedimentation in the formation of the smoothest plains on mars j geophys res 107 e10 5081 doi 10 1029 2002je001842 2002

terrestrial quadstatic interferometric radar observations of mars a new technique for resolving the ambiguity inherent in delay doppler radar observations of mars has been developed and implemented using a suite of data collected during 2001 2003 and 2005 oppositions new recording systems processing techniques and most importantly the addition of a fourth receiving telescope allow for the high resolution mapping of mars radar properties in this paper we develop a maximum likelihood method to probabilistically estimate the contributions to the received radar signal from the ambiguous resolution cells our delay doppler interferometric radar observations are designed to map the radar properties of mars surface while disregarding the historically typical goal of measuring topography instead using mars topography as a priori knowledge example data from the september 27 2003 observation over mars southern highlands including ma adim vallis and gusev crater and the june 7 2001 observation crossing terra meridiani are presented to demonstrate the effectiveness of the technique analysis of these observations predicted a root mean square rms roughness or slopes for the mars exploration rover mer spirit landing site of 1 80 0 75 similarly analysis of the gusev crater landing site of mer opportunity predicted rms slopes of 1 1 0 1 both predictions were validated by analysis of in situ rover images

the unique radar properties of silicic lava domes 1 silicic lava domes exhibit distinct morphologic characteristics at scales of centimeters to kilometers multiparameter radar observations capture the unique geometric signatures of silicic domes in a set of radar scattering properties that are unlike any other natural geologic surfaces backscatter cross section values are among the highest observed on terrestrial lava flows and show only a weak decrease with incidence angle cross polarization backscatter hv shows a unique behavior increasing with increasing wavelength circular polarization ratios are relatively high in the 0 3 0 95 range and increase with increasing wavelength field measurements of boulder size frequency distributions and microtopography indicate that silicic dome surfaces are among the roughest ever measured rms heights at a 1 m lateral scale range from 13 cm to 50 cm rms slopes at 1 m spacing range from 12 to 43 degrees modeling of the scattering behavior suggests it results from a combination of rough surface facet scattering and scattering from block edges that act as a random collection of dipoles the unusual wavelength dependence of the radar parameters appears to result from a higher component of edge scattering at large wavelengths producing for example higher cross polarized backscatter at p band 68 cm steep sided volcanic domes on venus superficially resemble terrestrial silicic domes in plan view gross morphology but few similarities remain when the radar scattering and three dimensional shapes of the features are compared the unique radar scattering properties suggest that such volcanic surfaces can be identified with multiparameter radar observations in future planetary radar missions and in active terrestrial volcanoes where dome development can represent serious hazards

secondary crater fields from 24 large primary craters on mars insights into nearby secondary crater production 1 crater statistics are used across a wide variety of applications on planetary surfaces one of the most notable being estimating relative and absolute ages of those surfaces this requires an assumed cratering rate over time and that craters be randomly distributed secondary craters craters that form from the ejecta of an impact event belie this assumption by creating greater crater density in a local area at a single time significantly affecting crater statistics there has been substantial debate over the relative importance of secondary craters and our findings in this mars study indicate that these events can be very significant and cannot be ignored when age dating surfaces we have analyzed secondary crater fields found close to 24 primary craters on mars among other findings such as terrain control over secondary crater field characteristics we conclude that a single large impact event 100 km can significantly affect crater statistics at the 1 5 km diameter level over a non trivial fraction of a planetary surface minimum secondary crater diameters examined were 0 9 km the minimum primary crater diameter was 20 km we also suggest a potential way to avoid significant contamination by the majority of secondary craters that occur close to the primary impact event without the need to manually classify every crater as primary or secondary our findings are specific to mars but further work may show the patterns are applicable to other solid bodies

the spatial distribution of rocks on mars abstract the spatial distribution of rocks exposed at the surface of mars has been mapped using viking infrared thermal mapper irtm observations overall there are no regions on the surface of mars at a scale of 1 1 in latitude and longitude that are rock free the modal value of rock abundance is 6 areal coverage with no areas having more than 30 35 rock cover the model developed to determine rock abundance relates the thermal emission in each of the four surface sensing irtm bands to temperature contrasts within the field of view non unit thermal emissivity due to absorption bands in the surface materials and the absorption and scattering of the outgoing energy by atmospheric dust and water ice each of these effects produce characteristic spectral and diurnal signatures allowing them to be separated the temperature contrasts provide a means to determine both the abundance of exposed rocks and the fine component thermal intertia rock abundance alone does not produce the observed variation in bulk thermal inertia of the surface low inertia fine bright surfaces have fewer rocks exposed than do high inertia coarse dark surfaces rock abundance does not correlate well with the rms slope nor reflectivity determined from delay doppler radar measurements there is however a possible correlation between rms slope determined from continuous wave radar observations dual polarization radar measurements which provide the best radar measure of small scale roughness indicate that the tharsis volcanic region is very rough whereas thermal measurements indicate very few rocks and a covering of dust together these observations suggest an approximately 1 m thick mantle of fines covering a very rough subsurface this fine material may be an aeolian deposit of dust storm fallout valles marineris together with several major channels and chaotic terrains have high rock abundances as does the acidalia planitia basin this observed distribution may reflect the initial deposition of coarse material associated with channel formation syrtis major is unique in having a high inertia but a very low rock abundance together with low radar roughness these observations are consistent with mantling of rocks by sand the observed distribution of rocks and fines indicates that aeolian processes both erosional and depositional play a dominant role in shaping the present martian surface

geologic analyses of shuttle imaging radar sir b data of kilauea volcano hawaii analyses of imaging radar data of volcanic terranes on earth and venus have emphasized the need for a clearer understanding of how these data can be most effectively used to accomplish important volcanological goals including the interpretation of eruptive styles and the characterization of the geologic history of volcanic centers the second shuttle imaging radar experiment sir b obtained two digital images over the summit caldera and the southwest rift zone of kilauea volcano in 1984 our geologic analyses of these images indicate that sir b data are particularly useful for delineating the distribution and surface textural variations of a9a lava flows for mapping large scale topographic features with radar facing slopes and for identifying an areally extensive pyroclastic deposit analyses of the sir b data of kilauea however do not permit unambiguous identification of landforms such as pahoehoe lava flows cinder cones and fissures although separation of low return units such as pahoehoe lava flows and adjacent pyroclastic ash is not greatly improved using standard image enhancement techniques the texture analysis technique applied here did facilitate discrimination of such smooth surfaced volcanic deposits although analyses of the sir b data permit a generally accurate interpretation of the eruptive history of kilauea the inability to distinguish low return pahoehoe flows results in misinterpretation of several aspects of kilauea volcanism suggesting that caution should be exercised in the interpretation of sar data of volcanic terranes

athabasca valles mars a lava draped channel system athabasca valles is a young outflow channel system on mars that may have been carved by catastrophic water floods however images acquired by the high resolution imaging science experiment camera onboard the mars reconnaissance orbiter spacecraft reveal that athabasca valles is now entirely draped by a thin layer of solidified lava the remnant of a once swollen river of molten rock the lava erupted from a fissure inundated the channels and drained downstream in geologically recent times purported ice features in athabasca valles and its distal basin cerberus palus are actually composed of this lava similar volcanic processes may have operated in other ostensibly fluvial channels which could explain in part why the landers sent to investigate sites of ancient flooding on mars have predominantly found lava at the surface instead

mars paleostratigraphic restoration of buried surfaces in tharsis montes volcanism in the tharsis province of mars occurred in several different areas and was generally continuous without large time intervals between eruptive episodes major lava flow units are numerous and extensive but relatively thin in many places impact craters on buried surfaces project above younger flows that overlie them a new application of crater dating methods has been developed to aid in the identification of these buried surfaces and to determine their lateral extent the technique is especially adaptable to the tharsis region where the stratigraphic succession of major flow units has been established by detailed geologic mapping knowledge of the overall stratigraphy allows correlations to be made between known and unknown surfaces by comparing their crater frequencies at diameters large enough to insure their recognition on the buried unit the method has been applied to aid in the restoration of buried rock units and to construct a series of paleostratigraphic maps showing the sequence of major eruptive events in the tharsis region

investigating mercury s south polar deposits arecibo radar observations and high resolution determination of illumination conditions there is strong evidence that mercury s polar deposits are water ice hosted in permanently shadowed regions in this study we present new arecibo radar observations of mercury s south pole which reveal numerous radar bright deposits and substantially increase the radar imaging coverage we also use images from messenger s full mission to determine the illumination conditions of mercury s south polar region at the same spatial resolution as the north polar region enabling comparisons between the two poles the area of radar bright deposits in mercury s south is roughly double that found in the north consistent with the larger permanently shadowed area in the older cratered terrain at the south relative to the younger smooth plains at the north radar bright features are strongly associated with regions of permanent shadow at both poles consistent with water ice being the dominant component of the deposits however both of mercury s polar regions show that roughly 50 of permanently shadowed regions lack radar bright deposits despite some of these locations having thermal environments that are conducive to the presence of water ice the observed uneven distribution of water ice among mercury s polar cold traps may suggest that the source of mercury s water ice was not a steady regular process but rather that the source was an episodic event such as a recent large impact on the innermost planet

sounding the subsurface of athabasca valles using marsis radar data exploring the volcanic and fluvial hypotheses for the origin of the rafted plate terrain 1 to test the volcanic and fluvial hypotheses for the origin of the rafted plate terrain observed in the vicinity of athabasca valles 5 n 150 e central elysium planitia we investigated the subsurface radar echo from the mars advanced radar for subsurface and ionosphere sounding marsis 5 mhz band data over this area the backscattered signal losses were compared to finite difference time domain fdtd simulations of those arising from three hypothetical geoelectrical subsurface models which differed in their assumed composition percentage basalt versus ice and assumed mode of origin fluvial discharge frozen sea mudflow and low viscosity lavas the dielectric values used in these models are derived from laboratory measurements of mars analog materials under mars like conditions fdtd simulations suggest that if the near surface environment is ice rich it will result in an average loss rate of 0 053 db m for massive ice having less than 1 of suspended particulates and 0 065 db m for a mudflow consisting of a 50 50 mixture of ice and basaltic dust whereas the losses associated with a lava flow model increase to 0 19 db m in comparison the actual signal losses experienced by marsis within this region were on the order of 0 18 db m within the first 160 m beneath the surface this suggests that propagation characteristics of athabasca s near subsurface are more consistent with a volcanic rather than a fluvial or mudflow origin of the rafted plate terrain although limitations on radar sounding depth in this region cannot rule out the possibility of more deeply buried massive ice deposits

the influence of subaquatic springs in lacustrine sedimentation origin and paleoenvironmental significance of homogenites in karstic lake banyoles ne spain abstract banyoles 42 08 n 2 45 e is the largest and deepest lake of karstic tectonic origin in the iberian peninsula the lake comprises two basins and six sub circularly shaped sub basins fed by subaquatic springs periods of intense groundwater inflow in the deepest sub basins lead to the fluidization and re suspension of previously deposited sediments and subsequent settling forming homogenite deposits on the southern basin intermediate platforms the multiproxy analysis of sediment cores combined with high resolution seismic stratigraphy 3 5 khz pinger and multi frequency chirp surveys allows a precise reconstruction of depositional environments and related hydrological variability and groundwater inflow during the last ca 7 6 cal kyr bp according to the age model based on 137cs 210pb and ams 14c dating homogenite deposition occurred between 7 2 and 5 5 cal kyr bp stopped during the middle holocene 5 5 2 8 cal kyr bp and greatly increased during the last two millennia with a total of 17 homogenite layers individually up to 75 cm thick the onset of this unique sedimentation mode at ca 3 cal kyr bp coincides with an increase in lake level evidenced by the onlapping of fine grained distal sediments over coarser massive carbonate rich littoral deposits a detailed multidisciplinary study of the homogenites sedimentology physical properties high resolution elemental geochemistry mineral composition grain size organic matter content and sem combined with seismic stratigraphy demonstrates that the fluidization events triggering the formation of the homogenites were caused by higher and more intense local groundwater inflow related to increased rainfall during the late holocene and likely intensified by land use changes during the last millennium

mars orbital synthetic aperture radar obtaining geologic information from radar polarimetry 1 radar penetration of mantling layers and scattering from buried objects or interfaces is a topic of current interest in both terrestrial and planetary remote sensing we examine the behavior of surface and subsurface scattering interfaces and the types of information that may be obtained from observations in different polarizations and wavelengths these results are applied to the design of a future mars orbital synthetic aperture radar sar for which we draw the following conclusions 1 mapping of buried geologic features is best accomplished using vv polarization at an optimal wavelength determined by the competing effects of antenna gain attenuation in the dust and the reduction in effective surface roughness with wavelength p band frequencies 1 ghz or less offer the best opportunity for detection of moderately rough buried features 2 the relative roles of surface and subsurface scattering may be determined using measurements in hh and vv polarization with a channel gain calibration better than 0 5 db 3 the thickness of a mantling layer or ice mass cannot be directly inferred from multiwavelength observations layer thickness may be inferred from the interferometric correlation of backscatter measurements collected on suitably spaced orbital passes though the required phase measurement accuracy is challenging while additional information may be gained by collecting scattering data in more polarizations or wavelengths we suggest that the primary science goals of a mars orbiting radar could be accomplished by a single wavelength system capable of collecting vv and hh polarizations with the calibration and orbit control needed to permit interferometric analysis

shallow radar sharad pedestal craters and the lost martian layers initial assessments 1 since their discovery martian pedestal craters have been interpreted as remnants of layers that were once regionally extensive but have since been mostly removed pedestals span from subkilometer to hundreds of kilometers but their thickness is less than 500 m except for a small equatorial concentration in the medusae fossae formation the nearly exclusive occurrence of pedestal craters in the middle and high latitudes of mars has led to the suspicion that the lost units bore a significant fraction of volatiles such as water ice recent morphological characterizations of pedestal deposits have further supported this view here we employ radar soundings obtained by the shallow radar sharad to investigate the volumes of a subset of the pedestal population in concert with high resolution imagery to assist our interpretations from the analysis of 97 pedestal craters we find that large pedestals diameter 30 km are relatively transparent to radar in their majority with sharad being able to detect the base of the pedestal deposits and possess an average dielectric permittivity of 4 0 5 in one of the cases of large pedestals in malea planum layering is detected both in sharad data and in high resolution imagery of the pedestal margins we find that clutter is a major issue in the analysis of radar soundings for smaller pedestals and tentative detection of the basal reflection occurs in only a few of the cases examined these detections yield a higher average permittivity of 6 the permittivity value derived for the larger pedestals for which a basal reflection is unambiguous is higher than that of pure water ice but lower than that of most silicate materials a mixture of ice and silicates or an ice free porous silicate matrix can explain a permittivity of 4 and radar alone cannot resolve this nonuniqueness data from the compact reconnaissance imaging spectrometer crism tentatively confirms a mafic component in at least one pedestal in malea planum interpretation of sharad results can support either a mixture of ice and silicates or a porous silicate the former is compatible with a model where nonpolar ice is periodically deposited in the midlatitudes as a result of obliquity variations the latter is compatible with ash deposits at least in where pedestals appear in volcanic centers such as malea planum

roughness and near surface density of mars from sharad radar echoes 1 we present a technique for estimating mars topographic roughness on horizontal scales from about 10 m to 100 m using shallow radar sharad sounding data our results offer a view of surface properties complementary to mars orbiter laser altimeter mola pulse width or baseline roughness maps and can be compared to sharad peak echo properties to infer deviations from the average near surface density latitudinal averaging of sharad derived roughness over arabia and noachis terrae shows good agreement with mola derived roughness and provides clear evidence for latitude dependent mantling deposits previously inferred from image data in northwestern gordii dorsum we find that bulk density in at least the upper few meters is significantly lower than in other units of the medusae fossae formation we observe the same behavior indicative of low near surface density in wind eroded crater fill in the southern highlands combining surface properties analysis subsurface sounding and high resolution optical images we show that the pavonis mons fan shaped deposit differs significantly from lobate debris aprons which sharad has shown to be ice cored there are no internal radar reflections from the smooth facies portion of the pavonis mons fan shaped deposit and we suggest that these deposits are either quite thin or have little dielectric i e density contrast with the underlying terrain future application of these techniques can identify other low density units across mars assist in the mapping of regional volatile rich mantling units and provide new constraints on the physical properties of the polar layered terrain

young lava flows on the eastern flank of ascraeus mons rheological properties derived from high resolution stereo camera hrsc images and mars orbiter laser altimeter mola data 1 we report on estimates of the rheological properties of late stage lava flows on the eastern flank of ascraeus mons mars from previous studies it is known that the dimensions of flows reflect rheological properties such as yield strength effusion rates and viscosity our estimates are based on new high resolution images obtained by the high resolution stereo camera hrsc on board the european space agency s mars express spacecraft in combination with mars orbiter laser altimeter mola data compared to earlier studies the high spatial resolution of the hrsc and mola data allowed us to map 25 late stage lava flows and to measure their dimensions as well as their morphological characteristics in greater detail our estimates of the yield strengths for these flows range from 2 0 102 pa to 1 3 105 pa with an average of 2 1 104 pa these values are in good agreement with estimates for terrestrial basaltic lava flows and are comparable to previous estimates derived for a small number of lava flows on ascraeus mons our investigation indicates that the effusion rates for the studied ascraeus mons flows are on average 185 m3 s 1 ranging from 23 m3 s 1 to 404 m3 s 1 these results are higher than earlier findings that indicate effusion rates of 18 60 m3 s 1 with an average of 35 m3 s 1 however our effusion rates are similar to terrestrial effusion rates of kilauea and mauna loa and other martian volcanoes on the basis of our estimates of the effusion rates and the measured dimensions of the flows we calculated that the time necessary to emplace the flows is on average 26 days viscosities were estimated on the basis of yield strengths and effusion rates yielding average values of 4 1 106 pa s and ranging from 1 8 104 pa s to 4 2 107 pa s on the basis of newly available data sets e g hrsc mola we are now able not only to identify possible differences in eruptive behavior between ascraeus mons and elysium mons but also to study such differences over time

bistatic radar observations of the moon using mini rf on lro and the arecibo observatory the miniature radio frequency mini rf instrument aboard nasa s lunar reconnaissance orbiter lro is a hybrid dual polarized synthetic aperture radar sar that operated in concert with the arecibo observatory to collect bistatic radar data of the lunar nearside from 2012 to 2015 the purpose of this bistatic campaign was to characterize the radar scattering properties of the surface and near surface as a function of bistatic angle for a variety of lunar terrains and search for a coherent backscatter opposition effect indicative of the presence of water ice a variety of lunar terrain types were sampled over a range of incidence and bistatic angles including mare highland pyroclastic crater ejecta and crater floor materials responses consistent with an opposition effect were observed for the ejecta of several copernican aged craters and the floor of the south polar crater cabeus the responses of ejecta material varied by crater in a manner that suggests a relationship with crater age the response for cabeus was observed within the portion of its floor that is not in permanent shadow the character of the response differs from that of crater ejecta and appears unique with respect to all other lunar terrains observed analysis of data for this region suggests that the unique nature of the response may indicate the presence of near surface deposits of water ice

mars global surveyor bistatic radar probing of the mpl ds2 target area abstract mars global surveyor bistatic radar was used to probe the mars polar lander and deep space 2 target areas 76 s 195 w in may 2000 the behavior of quasi specular echoes at wavelength 3 6 cm indicates that the top few centimeters of regolith are similar in their reflecting properties everywhere along a track of approximately 1000 km which crosses the mpl ds2 area our provisional estimate of surface dielectric constant e 2 25 is consistent with loose soil moderately packed h 2 o snow solid co 2 or a mixture of at least two but other data rule out both h 2 o and co 2 near the surface in late southern summer l s 351 leaving dry soil with density 1 4 g cm 3 as the most likely material

radar imaging of asteroid 7 iris arecibo radar images of iris obtained in november 2006 reveal a topographically complex object whose gross shape is approximately ellipsoidal with equatorial dimensions within 15 of 253 228 km the radar view of iris was restricted to high southern latitudes precluding reliable estimation of iris entire 3d shape but permitting accurate reconstruction of southern hemisphere topography the most prominent features three roughly 50 km diameter concavities almost equally spaced in longitude around the south pole are probably impact craters in terms of shape regularity and fractional relief iris represents a plausible transition between 50 km diameter asteroids with extremely irregular overall shapes and very large concavities and very much larger asteroids ceres and vesta with very regular nearly convex shapes and generally lacking monumental concavities

kilometer scale roughness of mars results from mola data analysis the mars orbiter laser altimeter mola data are used to characterize the kilometer scale surface roughness of mars the median absolute value of the differential slope at a given baseline is proposed as a data derived measure of the surface roughness at this scale study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for mola ranging accuracy the baseline lengths from 0 6 to 20 km are used and kilometer scale roughness is mapped for the entire surface the maps show that different geological units have distinctive roughness characteristics scale dependence of roughness for a number of geological units is presented and discussed the southern polar cap is rougher than the northern at kilometer and subkilometer scale which suggests differences in the sublimation condensation balance the vastitas borealis formation has a distinctive 3 km scale background surface topography which suggests a nonvolcanic origin for its upper layer young volcanic plains in amazonis planitia and the eastern part of elysium planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on mars which suggests a distinctive eruption style there are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands terrains at high latitude are smoother at short baselines the characteristic vertical scale related to this difference is several meters processes that could be responsible for formation of this trend include creep of ice rich near surface material at high latitudes treatment of the surface with repetitive deposition and sublimation of seasonal frost climate controlled deposition and or cementation of dust at high latitudes and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations all mechanisms of origin could operate more effectively under different climate conditions relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes

circular polarization radar properties of high altitude ice western kunlun shan and central andes full polarization synthetic aperture radar images of high altitude glaciers and ice fields in the western kunlun shan of tibet and the central andes near santiago chile made with the shuttle imaging radar display regions with circular polarization ratios c in excess of unity the mountainous topography at both locales allows reconstruction of the angular scattering behavior the behavior is very similar to that displayed by greenland s percolation zone glaciologic evidence from the tibetan site confirms ice pipes and lenses embedded in the firn which have been identified as the scatterers producing c 1 in greenland this demonstrates that the cold snow percolation facies radar signature exists outside of greenland the greenland radar behavior had been suggested as an analogue for that of the icy galilean satellites we like previous workers find that the near nadir backscatter is too specular to be considered analogous to that of the jovian moons we also present a crevasse region in tibet that exhibits c 1 and a possible detection of the ice substrate of a rock covered glacier in the andes

derivation of martian surface slope characteristics from directional thermal infrared radiometry abstract directional thermal infrared measurements of the martian surface is one of a variety of methods that may be used to characterize surface roughness and slopes at scales smaller than can be obtained by orbital imagery thermal emission spectrometer tes emission phase function epf observations show distinct apparent temperature variations with azimuth and emission angle that are consistent with the presence of warm sunlit and cool shaded slopes at typically 0 1 m scales a surface model of a gaussian distribution of azimuth independent slopes described by bar is combined with a thermal model to predict surface temperature from each viewing angle and azimuth of the tes epf observation the models can be used to predict surface slopes using the difference in measured apparent temperature from 2 separate 60 70 emission angle observations taken 180 in azimuth relative to each other most martian surfaces are consistent with low to moderate slope distributions the slope distributions display distinct correlations with latitude longitude and albedo exceptionally smooth surfaces are located at lower latitudes in both the southern highlands as well as in high albedo dusty terrains high slopes are associated with southern high latitude patterned ground and north polar sand dunes there is little apparent correlation between high resolution imagery and the derived bar with exceptions such as duneforms this method can be used to characterize potential landing sites by assuming fractal scaling behavior to meter scales more precisely targeted thermal infrared observations from other spacecraft instruments are capable of significantly reducing uncertainty as well as reducing measurement spot size from 10s of kilometers to sub kilometer scales

dual polarization radar observations of mars tharsis and environs abstract observations of the tharsis region of mars with the 12 6 cm radar at arecibo observatory have yielded radar echoes which are highly depolarizes and which are in terms of total echo power dominated by diffuse rather than quasi specular backscattering the observations were made on february 7 8 and 9 1980 and the subradar track extended from 77 to 126 w longitude at 22 n latitude dual polarized reception was employed i e the echo was received in the same sense of circular polarization as transmitted depolarized sense as well as in the opposite polarized sense the disk integrated ratio of depolarized power to polarized power averages 0 37 and the ratio of diffuse power to quasi specular power averages 3 2 the depolarized spectra are dominated by a broad enhancement identified primarily with echoes from the tharsis ridge implying that extensive areas of tharsis are rough on decimeter scales the major tharsis shield volcanoes are candidates for sources of strong depolarization although they alone cannot account for the entire depolarization enhancement

important role for ocean warming and increased ice shelf melt in antarctic sea ice expansion changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature in contrast to arctic sea ice sea ice surrounding antarctica has expanded1 with record extent2 in 2010 this ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling3 here we show that accelerated basal melting of antarctic ice shelves is likely to have contributed significantly to sea ice expansion specifically we present observations indicating that melt water from antarctica s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves simulating these processes in a coupled climate model we find that cool and fresh surface water from ice shelf melt indeed leads to expanding sea ice in austral autumn and winter this powerful negative feedback counteracts southern hemispheric atmospheric warming although changes in atmospheric dynamics most likely govern regional sea ice trends4 our analyses indicate that the overall sea ice trend is dominated by increased ice shelf melt we suggest that cool sea surface temperatures around antarctica could offset projected snowfall increases in antarctica with implications for estimates of future sea level rise

arecibo radar imagery of mars ii chryse xanthe polar caps and other regions abstract we conclude our radar imaging survey of mars which maps spatial variations in depolarized radar reflectivity using arecibo s band 12 6 cm observations from 2005 2012 whereas our earlier paper harmon et al 2012 arecibo radar imagery of mars the major volcanic provinces icarus 220 990 1030 covered the volcanic regions of tharsis elysium and amazonis this paper includes non volcanic regions where hydrologic and impact processes can be the dominant resurfacing agents affecting radar backscatter many of the more prominent and interesting radar bright features outside the major volcanic provinces are located in and around chryse planitia and xanthe terra these features are identified with a basin in northeast lunae planum containing the combined deposits from maja vallis and ganges catena outflows channel outwash plains in western and southern chryse basin plateaus bordering chasma chaos zones where surface modification may have resulted from hydrologic action associated with incipient chaos formation and some bright ejecta craters in chryse basin of a type otherwise rare on mars dark halo craters have also been identified in chryse and elsewhere that are similar to those seen in the volcanic provinces although the cratered highlands are relatively radar bland they do exhibit some bright depolarized features these include eroded crater rims several unusual ejecta flows and impact melts and terrain softened plains the rims of large impact basins hellas argyre isidis show a variety of radar bright features provisionally identified with massif slopes erosion sediments eroded pyroclastics impact melts and glacial deposits the interiors of these basins are largely radar dark which is consistent with coverage by rock free sediments tempe terra and acheron fossae show bright features possibly associated with rift volcanism or eroded tectonic structures and northwest tempe terra shows one very bright feature associated with glacial or other ice processes in the dichotomy boundary region the first delay doppler images of the radar bright features from the north and south polar icecaps are presented both poles show the circular polarization inversion and high reflectivity characteristic of coherent volume backscatter from relatively clean ice the south polar feature is primarily backscatter from the residual co 2 icecap with a lesser contribution from the polar layered deposits whose finite optical depth probably accounts for the feature s strong s x band wavelength dependence conversely the north polar radar feature appears to be mostly backscatter from the h 2 o ice rich polar layered deposits rather than from the thin residual h 2 o cap the north polar region shows additional radar bright features from korolev crater and a few other outlying circumpolar ice deposits

utilisation of the sedimentological and hydrochemical dynamics of the stump bay wetland along lake taupo new zealand for the recognition of paleo shoreline indicators abstract terrestrial sediments are generally simple to differentiate from lacustrine sediments but the interface between the two is difficult to recognise when clean beach sand is absent in addition tracing the dispersal of pollutant trace metals at this interface can be a major problem because toxic and natural metal cycles often take the same path to solve these problems we studied the natural geochemical processes in a wetland along the shore of lake taupo new zealand to characterise the surficial sediments that could be used as indicators of shoreline processes and to determine the variability of natural metals in the system lake taupo is new zealand s largest lake the stump bay wetland is part of the south taupo wetland which is situated along the southern edge of lake taupo and has an area of 15 4 km2 although much of the surrounding shoreline has been modified by human activity the stump bay wetland has retained its natural configuration to understand the variability at the terrestrial lacustrine interface we characterised the surficial sediments using shallow cores to learn the stratigraphy and geochemical make up of the sediment using x ray fluorescence xrf for major elements and selected metals fe mn zn cu ni ba in addition we installed shallow piezometers to relate the stratigraphy and geochemistry to groundwater flow and chemical composition ph alkalinity dissolved fe silt deposits derived from floods alternate with peat accumulations in shallow cores taken in the centre of the wetland the reduction of ferric iron to ferrous iron controls the south taupo wetland groundwater ph and total alkalinity sediment cores from the wetland have high iron concentrations up to 15 wt the abundance of iron in the cores does not correlate with either loss on ignition loi or silica abundance indicating that the iron is derived from a combination of decay of organic matter and leaching from volcanic rock material concentrations of sodium potassium and calcium and magnesium tend to increase with depth and reflect the increasing amount of inorganic matter in the core sulphur concentrations in the cores are relatively low and there is a weak correlation with loi although conditions for iron sulphide precipitation are possible in the wetland sediments it does not occur within the upper 1 m of the sediment the low topographic and groundwater gradient of the wetland area has led to a close interaction between sediment build up and the hydrochemistry of the water flowing into the lake in particular zones of iron rich diagenetic alteration of sediments at the surface water groundwater interface could be used to fix the position of the shoreline in paleo lake studies as long as the chemical interactions along the groundwater flow path are understood

elemental distribution and pyrite occurrence in a freshwater peatland alberta a continental minerotrophic peatland in alberta was studied for its botanical petrographical mineralogical and geochemical characteristics changes in peat stratigraphy and mineralogy are related and development toward oligotrophic conditions is recorded elemental concentration and distribution vary in the peat profile reflecting the influence of natural and anthropogenic factors on peat geochemistry many elements al as ba co cr fe mn th v accumulate in the zone of water table fluctuation as a result of changes in redox chemistry the relative elemental concentration at the surface and near surface e g as cr sb th ti v may also be attributed to atmospheric deposition related to anthropogenic activity chemical analysis al fe mg na si ti also reveals the presence of a non visible volcanic ash rich layer near the base of the peat profile possibly mazama tephra this study provides evidence of pyrite formation in a freshwater peat forming environment associated with high sul

a comparison of time domain electromagnetic and surface nuclear magnetic resonance sounding for subsurface water on mars 1 the time domain electromagnetic tdem method has enjoyed wide success in terrestrial groundwater exploration and the contrast in electrical conductivity between dry overburden and groundwater containing even a small amount of dissolved solids on mars will yield a robust response however moist clays or even ores e g massive hematite will also be electrically conductive and could be mistaken for aquifers on mars if proper geologic context is lacking surface nuclear magnetic resonance snmr is the only noninvasive geophysical method that responds nearly uniquely to water as the measured emf is proportional to the proton precession frequency which in turn is proportional to the planet s static magnetic field snmr signals are comparatively weak using small systems of several kilograms and several watts the exploration depth of snmr is one to two orders of magnitude smaller than tdem the latter can detect water to depths up to a few kilometers whereas the former is limited to depths of a few tens of meters there is no improvement in snmr signal to noise with increasing static field where penetration is controlled by aquifer salinity skin depth as reasonable integration times cannot substantially increase the exploration depth much larger transmitter current or loop mass either requiring system masses of tens to hundreds of kilograms are the only way to implement snmr for exploration to depths of at least hundreds of meters in spite of some ambiguity in target identification tdem is recommended for the first generation of in situ active source em measurements for groundwater on mars

the taupo eruption new zealand i general aspects the ca a d 186 taupo eruption was the latest eruption at the taupo volcanic centre occurring from a vent at horomatangi reefs now submerged beneath lake taupo in the central north island of new zealand minor initial phreatomagmatic activity was followed by the dry vent 6 km 3 hatepe plinian outburst large amounts of water then entered the vent during the 2 5 km 3 hatepe phreatoplinian ash phase eventually stopping the eruption though large amounts of water continued to be ejected from the vent area causing gullying of the ash deposits after a break of several hours to weeks phreatoplinian activity resumed generating the 1 3 km 3 rotongaio ash notable for its fine grainsize and for containing significant quantities of non or poorly vesicular juvenile material the vent area then became dry again and eruption rates and power markedly increased into the 23 km 3 taupo ultraplinian phase which is the most powerful plinian outburst yet documented synchronous with this ultraplinian activity lesser volumes of non to partially welded ignimbrite were generated by diversion of ejecta from or partial collapse of the eruption column the rapid rate of magma withdraw al during this phase removed support from the vent area to trigger local vent collapse and initiate the catastrophic eruption of the ca 30 km 3 taupo ignimbrite finally after some years lava was extruded on to the floor of the reformed lake taupo and floating fragments derived from the lava carapace were driven ashore the known eruption volume is more than 65 km 3 while additional volumes are represented by primary material now beneath lake taupo and layer 3 to the ignim brite phases a total volume of more than 105 km 3 is likely equivalent to more than 35 km 3 of magma plus more than 3 km 3 of lithic debris airfall deposits more than 10 cm thick blanketed 30000 km 2 of land east of the vent while ignimbrite covers a near circular area of 20000 km 2 widespread and locally severe ground shaking occurred during but mostly after the eruption associated with subsidence in the lake taupo basin secondary deposits are abundant above and extending beyond the taupo ignimbrite consisting of the products of surface water interacting with the still hot ignimbrite and subsequent water reworking of the light pumiceous materials the complexity and size of this eruption preclude accurate forecasting of the size nature and return period of the inevitable next eruption from the taupo volcanic centre

ground penetrating radar as a tool for probing the shallow subsurface of mars 1 design and testing of an impulse ground penetrating radar gpr for possible rover deployment on mars in 2009 is well underway the gpr has mass power volume and data rate targets of 0 5 kg 3 w peak 3400 cm3 and 0 3 mb d and will possess easily modified bistatic high frequency e g 500 600 mhz and monostatic rat tail e g 100 mhz antennas the gpr should be capable of measuring in situ radar properties on mars to depths of up to 10 20 m thereby helping to constrain near surface geology and structure initial gpr tests at the site of the 2001 fido rover field trials near cronese lake california confirm the value of the instrument in defining local geologic setting and in providing context for data collected using other rover science payload elements a rover deployed gpr may enable three dimensional mapping of local stratigraphy which in turn can assist in evaluating the history of aqueous activity and the accessibility of near surface water