orbital forcing of the martian polar layered deposits since the first images of polar regions on mars revealed alternating bright and dark layers there has been speculation that their formation might be tied to the planet s orbital climate forcing1 2 3 4 but uncertainties in the deposition timescale exceed two orders of magnitude estimates based on assumptions of dust deposition ice formation and sublimation and their variations with orbital forcing suggest a deposition rate of 10 3 to 10 2 cm yr 1 refs 5 6 whereas estimates based on cratering rate result in values as high as 0 1 to 0 2 cm yr 1 ref 7 here we use a combination of high resolution images of the polar layered terrains8 high resolution topography9 and revised calculations of the orbital and rotational parameters of mars to show that a correlation exists between ice layer radiance as a function of depth obtained from photometric data of the images of the layered terrains and the insolation variations in summer at the martian north pole similar to what has been shown for palaeoclimate studies of the earth10 11 12 for the best fit between the radiance profile and the simulated insolation parameters we obtain an average deposition rate of 0 05 cm yr 1 for the top 250 m of deposits on the ice cap of the north pole of mars

new martian climate constraints from radar reflectivity within the north polar layered deposits the north polar layered deposits npld of mars represent a global climate record reaching back millions of years potentially recorded in visible layers and radar reflectors however little is known of the specific link between those layers reflectors and the global climate to test the hypothesis that reflectors are caused by thick and indurated layers known as marker beds the reflectivity of three reflectors was measured mapped and compared to a reflectivity model the measured reflectivities match the model and show a strong sensitivity to layer thickness implying that radar reflectivity may be used as a proxy for short term accumulation patterns and that regional climate plays a strong role in layer thickness variations comparisons to an orbitally forced npld accumulation model show a strong correlation with predicted marker bed formation but dust content is higher than expected implying a stronger role for dust in mars polar climate than previously thought

wave attenuation in coastal mangroves in the red river delta vietnam abstract wave attenuation was studied in a coastal mangrove system in the red river delta vietnam on the coast north of do son from sea towards land the study area consisted of a bare mudflat covered by a sandy layer with embryonic cheniers abruptly changing into a muddy tidal flat overgrown with mangroves three instrumented tripods a c placed in a cross shore profile were used to measure current velocity and water level at the open tidal flat at the beginning of the mangrove vegetation and in the mangrove vegetation respectively measurements were conducted in the wet season in july and august 2000 the elevation of the area was surveyed using a levelling instrument over the bare sandy surface of the mudflat the incoming waves are reduced in height and energy density due to bottom friction this reduction decreases with increasing water depth in the mangrove vegetation the bottom friction exerted by the clay particles is very low however the dense network of trunks branches and above ground roots of the mangrove vegetation causes a much higher drag force for the mangrove vegetation which mainly consists of kandelia candel the drag force can be approached by the function c d 0 6e 0 15 a with a being the projected cross sectional area of the under water obstacles at a certain water depth for the same muddy surface without mangroves the function would be c d 0 6

earliest accumulation history of the north polar layered deposits mars from sharad abstract the approximately 2 km thick north polar layered deposits npld are often considered to contain the most complete and detailed stratigraphic records of recent climate of mars exposures of the dense layering within troughs and scarps allowed detailed reconstructions of the latest accumulation history of these water ice deposits but we lack knowledge of their initial emplacement the shallow radar sharad onboard mars reconnaissance orbiter mro penetrates the npld to their base and detects their internal layering overcoming the limitation of scarce and scattered visible outcrops of the lowermost sequences in this study we map reflectors in sharad data that result from discrete stratigraphic horizons in order to delineate the three dimensional stratigraphy of the lowermost 500 m npld sequence and reconstruct their accumulation history we confirm the large scale lateral continuity and thickness uniformity of the deposits previously detected within the lowermost npld however stratigraphic complexity in the form of pinch outs and significant thickness variations arises when we examine single radar units we find evidence of an initially limited geographic stability of water ice within two deposits that are centered at the north pole and present day gemina lingula a period of lateral ice sheet growth followed interrupted only once by a retreat episode lower net accumulation is observed on pre existing slopes suggesting a reduction of water ice stability due to increased solar radiation incidence and or transport by katabatic winds lateral transport of water ice by wind is also suggested by thickness undulations toward the top of the sequence resembling cyclic steps water ice accumulation models based on orbital forcing predict a sequence of deposition and retreat events that is generally compatible with our reconstructed accumulation history therefore we interpret the stratigraphic complexity that we observe as regional and possibly global climate change induced by orbital forcing we also find that at least two units are completely buried within the npld and do not outcrop and that npld deposition in some places was contemporaneous with deposition of the stratigraphically underlying cavi unit in other places both of these findings show that radar reflector mapping is a necessary complement to any stratigraphic reconstruction based on visible exposures

on water detection in the martian subsurface using sounding radar several radar experiments are planned to map the martian subsurface down to several kilometers searching for subsurface liquid water reservoirs using different concepts and techniques all based on the penetration property of radio frequency waves in arid soils the penetration depth of low frequency radar is mainly related to the electromagnetic properties of the investigated medium thus a good knowledge of the martian subsurface dielectric profile along the first few kilometers is necessary for future water identification and data interpretation in this work we have investigated the electrical and magnetic properties of the martian surface and subsurface using terrestrial laboratory analogues in the frequency range 1 500 mhz covering the frequency domain of the mars advanced radar for subsurface and ionosphere sounding marsis experiment on board the mars express mission esa 2003 the netlander ground penetrating radar gpr cnes 2007 and future sounding radar that may be updated to the mars exploration program in the follow the water strategy in our approach we constructed experimentally the most common dielectric profile representative of the martian subsurface by measuring the electric permittivity and magnetic permeability of well defined mixtures of basaltic volcanic and sedimentary materials that have been reported for mars we also considered iron oxides hematite and maghemite and evaporites that may be present such as gypsum and their mixtures with representative amounts of the martian geological context under the most common petrophysical and geophysical conditions along the subsurface profile this led to synthetic representative samples of the martian subsurface materials under adequate conditions of porosity and temperature that should exist in the first 2 5 km of the upper crust dielectric measurements show that the first layers of the martian subsurface a few hundred meters which are mainly composed of volcanic iron rich materials could dramatically decrease the radar penetration depth initially foreseen thus limiting deep subsurface exploration we also investigated the constraints on subsurface water detectability in a radar lossy medium and its dielectric identification among surrounding geological materials

flexural rigidity and shoot reconfiguration determine wake length behind saltmarsh vegetation patches vegetation patches play an important role in controlling sediment deposition in shallow aquatic environments such as coastal saltmarshes and fluvial systems however predicting deposition around vegetation patches is difficult due to the complexity of patch morphology and their dynamic interaction with the flow here we incorporate a biomechanical model parameterized using field data within a 3d computational fluid dynamics cfd model which allows prediction of individual shoot reconfiguration within patches due to flow forcing the model predicts velocity attenuation and bed shear stresses within the wake of the patch which agree spatially with accretion patterns measured in the field using terrestrial lidar the model is applied to sparse patches of suaeda maritima located in saltmarshes of coastal habitats to explore the role of i shoot distribution ii patch geometry iii shoot flexural rigidity and iv bulk flow velocity in determining the length of the predicted wake region we demonstrate that for suaeda maritima with intermediate rigidity the vertical shear layer over the vegetation controls the length of the predicted wake region consequently reconfiguration due to flexural rigidity strongly impacts on wake length confounding the relationship between patch height and wake length a simplified model for predicting wake length based on shoot reconfiguration is applied to the simulation data and shows good agreement the results demonstrate that the observed wake characteristics can be well explained by intraspecific variability in flexural rigidity thus demonstrating the importance of biomechanical traits in determining flow vegetation sediment interactions

radar evidence of subglacial liquid water on mars the presence of liquid water at the base of the martian polar caps has long been suspected but not observed we surveyed the planum australe region using the marsis mars advanced radar for subsurface and ionosphere sounding instrument a low frequency radar on the mars express spacecraft radar profiles collected between may 2012 and december 2015 contain evidence of liquid water trapped below the ice of the south polar layered deposits anomalously bright subsurface reflections are evident within a well defined 20 kilometer wide zone centered at 193 e 81 s which is surrounded by much less reflective areas quantitative analysis of the radar signals shows that this bright feature has high relative dielectric permittivity 15 matching that of water bearing materials we interpret this feature as a stable body of liquid water on mars

the chemical composition of martian soil and rocks returned by the mobile alpha proton x ray spectrometer preliminary results from the x ray mode the alpha proton x ray spectrometer apxs on board the rover of the mars pathfinder mission measured the chemical composition of six soils and five rocks at the ares vallis landing site the soil analyses show similarity to those determined by the viking missions the analyzed rocks were partially covered by dust but otherwise compositionally similar to each other they are unexpectedly high in silica and potassium but low in magnesium compared to martian soils and martian meteorites the analyzed rocks are similar in composition to terrestrial andesites and close to the mean composition of earth s crust addition of a mafic component and reaction products of volcanic gases to the local rock material is necessary to explain the soil composition

experimental study on vegetation flexibility as control parameter for wave damping and velocity structure abstract vegetation can contribute to coastal defence by damping incoming waves however prior studies have shown that attenuation varies greatly among plant species plant flexibility is a mechanical property that is commonly omitted but varies considerably between shrubs and grasses on salt marshes therefore we present an experimental study in a laboratory wave flume with artificial vegetation that differs in flexibility only we measured wave attenuation and water particle velocities around rigid and flexible salt marsh vegetation waves were measured using a series of gauges and particle image velocimetry piv was used to measure spatio temporal variations of water particle velocities in the x z plane around the vegetation our results show that flexible vegetation attenuates waves up to 70 less than rigid vegetation due to swaying of flexible plants furthermore we find that rigid vegetation modifies the velocity structure whereas flexible vegetation does not specifically a mean current in the direction of wave propagation develops around the canopy and the horizontal particle velocities are amplified directly above the canopy these results indicate that plant flexibility is a key parameter in the wave vegetation interaction that controls wave damping and velocity structure

north polar cap of mars polar layered deposit characterization and identification of a fundamental climate signal of the cap 6 10 5 km 2 in the 13 images analyzed to date 3 assessment of geometric relationships shows that layers are not horizontal but rather have an apparent dip of approximately 0 5 degrees we interpret these results as follows 1 the fundamental 30 m signal is interpreted as a climate signal that may correspond to a 51 kyr insolation cycle 2 the lateral correlation and broad distribution of these layer sequences strongly imply that layer accumulation processes are widespread across the cap rather than confined within a single trough or region 3 local to regional variability in individual layer thicknesses and thus accumulation and sublimation rates is typically less than a factor of 2 5 providing the ability to study regional trends but often making it difficult to correlate visually the vertical sequences in individual cores finally initial examination of layers located deeper in the stratigraphic sequence within the north polar cap than the 300 m thick zone 1 provides evidence for a unit less than 100 m thick zone 2 in which the fundamental 30 m sequence is not detected we interpret this as a deposit having formed during a recent high obliquity phase of mars during which time polar volatiles underwent mobilization and were transport equatorward leaving a polar lag of dust rich material the most recent ice age 0 5 2 ma offers a plausible candidate for this period of ice cap removal and lag deposit formation an underlying zone 3 200 m contains a dominant 35 m signal and a lowermost zone 4 200 m contains multiple signals but no dominant one together these four zones represent 800 m of vertical stratigraphic section about one fourth of the total thickness of the cap these findings support earlier interpretations that orbital parameter variations could cause significant erosion and possibly complete removal of the polar caps the interpreted crater retention ages of the layered terrain are consistent with the correlations and vertical sequences described here suggesting that the polar caps wax and wane throughout geological history depending on the evolution of orbital parameters definition of the 30 m unit signal holds promise for determining 1 the detailed origin of individual layer types 2 the nature of deposition and sublimation processes and their relation to insolation geometry across the polar cap and 3 correlation with and comparison to the south polar layered terrain record

refined data of alpha proton x ray spectrometer analyses of soils and rocks at the mars pathfinder site implications for surface chemistry 1 an extensive recalibration of the alpha proton x ray spectrometer apxs was performed to improve the data evaluation of the mars pathfinder mpf rock and soil in situ measurements many samples and geostandards were measured with an mpf identical spare apxs under simulated martian atmospheric pressure and low night temperature conditions precise calibration curves for major and minor elements were obtained using an improved spectral evaluation method for the original mpf spectra refined and new elemental compositions of the mpf rocks and soils were derived however all initial conclusions about soils and rocks remained valid the mpf soil composition revealed the mafic nature of the surface as inferred from the results of viking 1 and 2 data however the mpf rocks reflect a felsic composition for all samples linear correlations of sulphur with all other elements were noticed reflecting the fact that the rocks were covered with varying degrees of soil which compared to the rocks is rich in sulphur extrapolating to low sulphur abundance 0 3 the composition of a soil free rock was calculated the mpf rock composition is high in si and k and low in mg and fe compared to the soil using elemental data from mpf and martian meteorites a global estimation of the martian crust composition was derived the crust is of basaltic nature with a high abundance of incompatible elements k rb nd u th and volatile elements s cl while carbonates are lower or absent

monitoring the perennial martian northern polar cap with mgs moc abstract we have used the mars global surveyor mars orbiter camera wide angle mgs moc wa dataset to study albedo trends on the martian northern residual cap six study regions were selected the chasma boreale source region three regions near the center of the cap fish hook region latitude 87 bottle opener region latitude 87 steep shallow region latitude 85 and two lower latitude regions crater latitude 77 and polar outlier latitude 82 and the albedos of these six regions were examined these regions were chosen due to their good temporal coverage in the moc dataset as well as having been studied by other researchers bass et al 2000 icarus 144 382 396 calvin and titus 2004 lunar planet sci xxxv abstract 1455 the picture which emerges is complex most areas experience a combination of darkening and brightening through the northern summer only one area consistently brightens the polar outlier region a good deal of interannual repeatability in each region s albedo behavior is seen however possible causes for the observed complex behaviors include dust deposition from late summer storms sintering of frost grains over the course of the summer and cold trapping of volatiles on bright cold surfaces

onset and migration of spiral troughs on mars revealed by orbital radar the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years a pinwheel array of deep troughs has been one of the most perplexing features of the north polar layered deposits on mars many ideas have been put forward about how it formed but there is as yet no consensus here penetrating radar has been used to rule out erosional cutting as a mechanism for the formation of the array instead it is concluded that the troughs are largely depositional in origin and have migrated to the poles and upwards in elevation over the past two million years or so the landscape of the north polar layered deposits of mars npld is dominated by a pinwheel array of enigmatic spiral troughs1 the troughs have intrigued planetary scientists since the mariner 9 spacecraft returned the first close up image in 1972 but conclusive evidence of their origin has remained elusive debate continues regarding all aspects of the troughs including the possibility that they have migrated2 3 4 5 their age in relation to the current npld surface6 and whether they are fundamentally erosional6 7 or constructional2 4 features the troughs are probably related to climatic processes2 8 yet the nature of this relationship has remained a mystery previous data characterizing only the exposed nlpd surface were insufficient to test these hypotheses here we show that the central spiral troughs initiated after deposition of three quarters of the npld quickly reached a stable morphology and migrated approximately 65 kilometres poleward and 600 metres in altitude over the past two million years or so our radar stratigraphy rules out hypotheses of erosional incision post dating deposition6 7 9 10 and instead largely validates an early hypothesis for constructional trough migration2 3 4 5 with wind transport and atmospheric deposition as dominant processes these results provide hard constraints for palaeo climate models and a new context for evaluating imagery spectral data and now radar sounding data the better to understand the link between orbital parameters and climate the role of climate in shaping the polar ice of mars and eventually the age of the polar deposits themselves8 11 12 13

radar detectability of a subsurface ocean on europa abstract a spacecraft in orbit around jupiter s moon europa can use ice penetrating radar to probe for a possible liquid water ocean beneath europa s surface ice and to characterize other important subsurface structure consideration of available constraints on the properties of europa s ice possible subsurface temperature gradients and possible impurities in the ice places an upper limit of about 10 km on the depth to which an ocean might be detectable with an orbiting radar

an ice age recorded in the polar deposits of mars layered ice deposits at the poles of mars record a detailed history of accumulation and erosion related to climate processes radar investigations measure these layers and provide evidence for climate changes such as ice advance and retreat we present a detailed analysis of observational data showing that 87 000 cubic kilometers of ice have accumulated at the poles since the end of the last ice age 370 000 years ago this volume is equivalent to a global layer of 60 centimeters the majority of the material accumulated at the north pole these results provide both a means to understand the accumulation history of the polar deposits as related to orbital milankovitch cycles and constraints for better determination of mars past and future climates

non linear wave attenuation quantification model improves the estimation of wave attenuation efficiency of mangroves abstract the wave attenuation function of mangroves follows the dalrymple model but changes nonlinearly with vegetation structure in various places which has not been fully addressed here taking the da guan sha of beihai city china as a case study the landscape metrics characterizing mangrove structures including the diameter at breast height dbh crown breadth crown density and rhizome and stem systems were obtained through remote sensing and field measurements then the nonlinear spatiotemporal pattern of the wave attenuation function decreasing rate of wave height was explored and revealed among six 20 200 m parallel transects passing through mangroves along the direction of the current the results showed the following 1 the dbh and crown breadth first increased and then decreased from the seaward to landward side of each transect showing a nonlinear inverted u pattern of distribution 2 the wave attenuation function of mangroves was dominated by the canopy at high tide but significantly affected by the structure of the rhizome or stem system at low tide the wave height during a specific storm surge could decrease by nearly 97 among the six transects at high tide but by only 87 at low tide on average if the wave crossed through the mangroves over a distance of 100 m from the seaward side of the mangroves edge 3 the wet surface width of a major part of mangrove trees with wave attenuation functions would change with the distribution of the dbh crown breadth and tree height along the transects which would also change with the dynamics of the water level the wave attenuation of mangroves ranged from 85 to 90 at low tide and from 96 to 97 at high tide if the wave crossed through mangroves at a distance of 100 m from the seaward side of the mangrove edge 4 the predicted practical decreasing rate of wave height based on the forward differencing method a method that considered the varied vegetation structure along transects in the model during the calculation of wave attenuation which would be close to reality would be 12 and 9 higher at low and high tide respectively than those estimated by the simplified calculation method a method of taking the average value of the vegetation structure of each transect to calculate wave attenuation if the wave crossed through mangroves at a distance of 200 m from the seaward side of the mangrove edge the integration of mangrove structures into the established empirical models improves our understanding of the nonlinear wave attenuation function of mangroves and may provide decision makers with more valuable information on restoring mangrove ecosystems to protect against storm surges

mars north polar deposits stratigraphy age and geodynamical response the shallow radar sharad on the mars reconnaissance orbiter has imaged the internal stratigraphy of the north polar layered deposits of mars radar reflections within the deposits reveal a laterally continuous deposition of layers which typically consist of four packets of finely spaced reflectors separated by homogeneous interpacket regions of nearly pure ice the packet interpacket structure can be explained by approximately million year periodicities in mars obliquity or orbital eccentricity the observed 100 meter maximum deflection of the underlying substrate in response to the ice load implies that the present day thickness of an equilibrium elastic lithosphere is greater than 300 kilometers alternatively the response to the load may be in a transient state controlled by mantle viscosity both scenarios probably require that mars has a subchondritic abundance of heat producing elements

north polar stratigraphy and the paleo erg of mars an accurate self consistent way of coregistering the imaging and topographic data sets of the mars global surveyor mission was developed and used to begin a stratigraphic analysis of the northern polar region a distinct change in the layering style exists at a definite stratigraphic horizon near the base of the north polar layered deposits occurrences of the contact between two distinct layered units can be mapped hundreds of kilometers apart at nearly the same mars orbiter laser altimeter mola elevation the lower layered unit has a consistent association with sand dunes leading to the conclusion that it is an eroding sand rich deposit that predates most of the overlying north polar layered deposits which exhibits the expected features of a dust ice mixture these results suggest that an areally extensive erg was in existence before the present ice cap and that the present circumpolar erg is likely composed of material reworked from this older deposit the volume of this lower unit is estimated to be on the order of 10 5 km 3 the presence of this deposit implies that there existed a period in mars history when there was no icy polar cap a dramatic climatic change leading to the deposition of the upper layered icy unit in the present day polar layered deposits represents a major event in mars history however owing to uncertainties in the mechanics of layered deposits formation such an event cannot be dated at this time

three dimensional radar imaging of structures and craters in the martian polar caps abstract over the last decade observations acquired by the shallow radar sharad sounder on individual passes of the mars reconnaissance orbiter have revealed the internal structure of the martian polar caps and provided new insights into the formation of the icy layers within and their relationship to climate however a complete picture of the cap interiors has been hampered by interfering reflections from off nadir surface features and signal losses associated with sloping structures and scattering foss et al the leading edge 36 43 57 2017 https doi org 10 1190 tle36010043 1 addressed these limitations by assembling three dimensional data volumes of sharad observations from thousands of orbital passes over each polar region and applying geometric corrections simultaneously the radar volumes provide unprecedented views of subsurface features readily imaging structures previously inferred from time intensive manual analysis of single orbit data e g trough bounding surfaces a buried chasma and a basal unit in the north massive carbon dioxide ice deposits and discontinuous layered sequences in the south our new mapping of the carbon dioxide deposits yields a volume of 16 500 km 3 11 larger than the prior estimate in addition the radar volumes newly reveal other structures including what appear to be buried impact craters with no surface expression our first assessment of 21 apparent craters at the base of the north polar layered deposits suggests a hesperian age for the substrate consistent with that of the surrounding plains as determined from statistics of surface cratering rates planned mapping of similar features throughout both polar volumes may provide new constraints on the age of the icy layered deposits the radar volumes also provide new topographic data between the highest latitudes observed by the mars orbiter laser altimeter and those observed by sharad in general mapping of features in these radar volumes is placing new constraints on the nature and evolution of the polar deposits and associated climate changes

numerical simulation of nonlinear long waves in the presence of discontinuous coastal vegetation abstract we presented numerical simulations of long waves interacting with arrays of emergent cylinders inside regularly spaced patches representing tsunamis interacting with discontinuous patchy coastal vegetation we employed the fully nonlinear and weakly dispersive serre green naghdi equations sgn until the breaking process starts while we changed the governing equations to nonlinear shallow water equations nsw at the vicinity of the breaking wave peak and during the run up stage we modeled the cylinders as physical boundaries rather than approximating them as macro roughness friction our results show that the cylinders provide protection for the areas behind them however they might also cause amplification in local water depth in those areas the presented results are extensively validated against the existing numerical and experimental data our results demonstrate the capability and reliability of our model in simulating wave interaction with emergent cylinders

global mineral distributions on mars 1 determining the mineralogy of mars is an essential part of revealing the conditions of the surface and subsurface a deconvolution method was used to remove atmospheric components and determine surface mineralogy from thermal emission spectrometer data at 1 pixel per degree ppd minerals are grouped into categories on the basis of compositional and spectral similarity and global concentration maps are produced all binned pixels are fit well with rms errors of 0 005 in emissivity higher rms errors are attributed to short wavelength particle size effects on dust covered surfaces significant concentrations 0 10 of plagioclase high ca pyroxene sheet silicates high si glass and hematite are detected and display distributions consistent with previous studies elevated concentrations of plagioclase and high ca pyroxene are consistent with basaltic surfaces and are located in low albedo highlands regions north of 45 s significant concentrations of plagioclase and sheet silicates high si glass and low concentrations of high ca pyroxenes are consistent with andesitic surfaces and are concentrated in both southern and northern high latitude low albedo regions andesitic surfaces in the southern hemisphere have a lower spectral contrast than northern surfaces an isolated surface located in solis planum is spectrally distinct but compositionally similar to other surfaces interpreted to be andesitic in composition concentrations of olivine below the detection limit correctly identify its presence in two of three locations potassium feldspar low ca pyroxene basaltic glass olivine sulfate carbonate quartz and amphibole are not detected with confidence at 1 ppd the results presented here indicate a predominance of volcanic compositions within martian dust free surfaces

sharad detection and characterization of subsurface water ice deposits in utopia planitia mars morphological analyses of utopia planitia mars have led to the hypothesis that the region contains a substantial amount of near surface ice this paper tests this hypothesis using ground penetrating radar techniques we have identified an expansive radar reflective region spanning approximately 375 000 km2 in shallow radar sharad data over western utopia planitia the sharad reflective regions coincides with high densities of scalloped depressions and polygonal terrain the reflectors are associated with layered mesas 80 170 m thick we find a value of 2 8 0 8 for the dielectric constant of the material overlying the reflectors this work finds that the dielectric constant is consistent with a mixture of ice air and dust containing a water ice volume up to 14 300 km3 in this unit

yearly comparisons of the martian polar caps 1999 2003 mars orbiter camera observations abstract the mars global surveyor mars orbiter camera wide angle cameras were used to obtain images of the north and south seasonal and residual polar caps between 1999 and 2003 wide angle red camera images were used in assembling mosaics of the north and south polar recessions and regression rates were measured and compared there are small variations in the north polar recession between 2000 and 2002 especially between l s 7 and l s 50 however there is no evidence for the plateau in the recession curves that has been observed in some prior years the south polar recession changes very little from year to year and the 2001 dust storm had little if any effect on the average cap recession that year albedo values of the geographic north pole were measured using wide angle red and blue camera images and the residual south polar cap configuration was compared between the three years observed by moc the albedo of the geographic north pole generally varies between 0 5 and 0 6 as measured from moc wide angle red camera images there were only minor variations near the edges of the residual south polar cap between the three years examined

mars landscape evolution influence of stratigraphy on geomorphology in the north polar region abstract lithology and physical properties of strata exposed at the earth s surface have direct influence on the erosion and geomorphic expression of landforms while this is well known on our planet examples on mars are just coming to light among the tens of thousands of airphoto quality images resolutions 1 5 12 m pixel acquired since 1997 by the mars global surveyor mgs mars orbiter camera moc specific examples occur among martian north polar layered materials which moc images reveal are divided into two distinct stratigraphic units a lower dark toned layered unit and a younger upper lighter toned layered unit the lower unit is less resistant to wind erosion than the upper unit the upper unit most likely consists of stratified dust and ice while the lower unit contains abundant poorly cemented sand sand is more easily mobilized by wind than dust the lower resistance to erosion of the lower unit results from the presence of sand where wind erosion in polar troughs has penetrated to the lower unit geomorphic change has proceeded more rapidly sand has been liberated from the lower unit and arcuate scarps have formed as the upper unit has been undermined wind erosion of the lower unit thus influences the geomorphology of the north polar region this result likely explains the genesis of the large polar trough chasma boreale and the relations between dunes and arcuate scarps that have puzzled investigators for nearly three decades the properties of the stratigraphic units suggest that the upper limit for the amount of water contained in the north polar layered materials may be 30 50 less than previously estimated

large scale 3 d experiments of wave and current interaction with real vegetation part 2 experimental analysis abstract this paper assesses the influence of different flow and vegetation parameters on the wave attenuation provided by two contrasting salt marsh species puccinellia maritima and spartina anglica different water depths and wave parameters height and period are considered for both regular and irregular waves with and without an underlying uniform current coming from different directions the study of the submergence ratio h h v influence shows that wave damping coefficient rapidly decreases as the plant submergence ratio increases the high nonlinearities found in the wave current interaction lead to different wave damping patterns in comparison to wave only conditions a smaller wave damping is found for waves and current acting in the same direction and an increase in the wave damping rate is obtained for waves and current flowing in the opposite direction these wave and current tests allow for the studying of the energy dissipation produced by the vegetation increasing our knowledge about flow and plant interaction in estuarine conditions the biomechanical properties of the two real salt marshes used in the experiments are also evaluated and related to wave damping revealing a higher attenuation for stiffer vegetation both the vegetation density and the biomass strongly influence wave damping higher density and biomass values lead to higher attenuation rates for both species

assessing the impact of extreme storms on barrier beaches along the atlantic coastline application to the southern rhode island coast abstract in this work we use the 2d model xbeach to dynamically simulate coastal erosion due to a synthetic 100 year storm impacting a typical north atlantic barrier beach located in southern ri this storm was extracted from the north atlantic coast comprehensive study naccs database based on results of an extreme value analysis of more than 1000 naccs storms xbeach parameters are first calibrated validated by simulating hurricane irene august 2011 for which both nearshore wave data and pre and post storm beach profiles were available in the study area comparing results to observations allowed calibration of the wave asymmetry and skewness parameter u a 0 3 in the model resulting in a 6 mean relative error between the simulated and measured subaerial eroded volumes along 4 transects in the 100 year storm xbeach simulations that include overwash effects of land cover on beach erosion in particular vegetation are assessed by specifying a spatially varying bed friction function of high resolution land cover results show that healthy back dune vegetation is essential to prevent the dune crest from being fully eroded down to its toe level the predicted median 100 year eroded volume is 46 m3 m for the entire barrier beach in good agreement with fema s empirical value of 50 m3 m at the two official 1d transects within the study area mean post storm reductions in dune crest elevations are in similar agreement the model however predicts very large alongshore variations of these parameters with eroded volumes over 1000 m3 m where breaching and the opening of surge channels occurs overall dune segmentation simulated in the model for the 100 year storm appears to be realistic and consistent with dune topography and land cover xbeach thus provides an improved 2d methodology for assessing the impact of extreme storms on atlantic barrier beaches predicting changes in dune morphology and quantifying the protective role of vegetation and effects of land cover in general

martian north polar cap recession 2000 mars orbiter camera observations abstract the wide angle cameras of the mars orbiter camera moc on the mars global surveyor have recorded the 2000 recession of the seasonal co 2 cap in the north polar region from l s 330 to 90 in stark contrast to the asymmetric behavior of the south seasonal cap the seasonal north cap remains relatively circular and uniform until mid spring when the retreat reaches the circum polar dune field which is the one major nonuniformity in the cap the recession of cap edge latitude versus areocentric longitude l s is very well represented as a linear function until late spring there is no evidence for the plateau or standstill in the recession curve that has been observed in some prior years the lambert albedo of the seasonal frost deposits in the north polar region demonstrates the increase with insolation first observed by paige in 1985 increasing to approximately 0 57 at l s 40 the north polar cap near solstice visually appears smaller than that observed by moc at the start of mapping in 1999 but later images acquired in summer show the residual cap returning to its more usual shape the most likely explanation for these changes in albedo is precipitation and subsequent removal of dust on the cap as a result of frequent dust storms near the cap edge

soil like deposits observed by sojourner the pathfinder rover most of the soil like materials at the pathfinder landing site behave like moderately dense soils on earth with friction angles near 34 39 and are called cloddy deposits cloddy deposits appear to be poorly sorted with dust sized to granule sized mineral or rock grains they may contain pebbles small rock fragments and clods thin deposits of porous compressible drifts with friction angles near 26 28 are also present drifts are fine grained cohesions of both types of deposits are small there may be indurated soil like deposits and or coated or crusted rocks cloddy deposits may be fluvial sediments of the ares tiu floods but other origins such as ejecta from nearby impact craters should be considered drifts are probably dusts that settled from the martian atmosphere remote sensing signatures of the deposits inferred from rover observations are consistent with those observed from orbit and earth

flexure of the lithosphere beneath the north polar cap of mars implications for ice composition and heat flow the geodynamical response of the lithosphere under stresses imposed by the geologically young north polar cap is one of the few clues we have to constrain both its composition and the present day t

accumulation and erosion of mars south polar layered deposits mars polar regions are covered with ice rich layered deposits that potentially contain a record of climate variations the sounding radar sharad on the mars reconnaissance orbiter mapped detailed subsurface stratigraphy in the promethei lingula region of the south polar plateau planum australe radar reflections interpreted as layers are correlated across adjacent orbits and are continuous for up to 150 kilometers along spacecraft orbital tracks the reflectors are often separated into discrete reflector sequences and strong echoes are seen as deep as 1 kilometer in some cases the sequences are dipping with respect to each other suggesting an interdepositional period of erosion in australe sulci layers are exhumed indicating recent erosion

preservation of midlatitude ice sheets on mars national science foundation nsf dge 1143953 nasa earth and space sciences fellowship nessf nnx16ap09h nasa mars data analysis program mdap award nnx15am62g

massive co2 ice deposits sequestered in the south polar layered deposits of mars shallow radar soundings from the mars reconnaissance orbiter reveal a buried deposit of carbon dioxide co2 ice within the south polar layered deposits of mars with a volume of 9500 to 12 500 cubic kilometers about 30 times that previously estimated for the south pole residual cap the deposit occurs within a stratigraphic unit that is uniquely marked by collapse features and other evidence of interior co2 volatile release if released into the atmosphere at times of high obliquity the co2 reservoir would increase the atmospheric mass by up to 80 leading to more frequent and intense dust storms and to more regions where liquid water could persist without boiling

the polar deposits of mars the tantalizing prospect of a readable record of martian climatic variations has driven decades of work toward deciphering the stratigraphy of the martian polar layered deposits and understanding the role of the residual ice caps that cover them spacecraft over the past decade have provided a massive infusion of new data into mars science polar science has benefited immensely due to the near polar orbits of most of the orbiting missions and the successful landing of the phoenix spacecraft in the northern high latitudes topographic thermal radar hyperspectral and high resolution imaging data are among the datasets that have allowed characterization of the stratigraphy of the polar layered deposits in unprecedented detail additionally change within the residual ice caps has been monitored with spacecraft instruments for several years these new data have provided a golden opportunity to understand the interplay between the martian orbit climate and polar ice

integrating radar stratigraphy with high resolution visible stratigraphy of the north polar layered deposits mars abstract shallow radar sharad on board nasa s mars reconnaissance orbiter has successfully detected tens of reflectors in the subsurface of the north polar layered deposits npld of mars radar reflections are hypothesized to originate from the same material interfaces that result in visible layering as a first step towards verifying this assumption this study uses signal analyses and geometric comparisons to quantitatively examine the relationship between reflectors and visible layers exposed in an npld outcrop to understand subsurface structures and reflector geometry reflector surfaces have been gridded in three dimensions taking into account the influence of surface slopes to obtain accurate subsurface geometries these geometries reveal reflector dips that are consistent with optical layer slopes distance elevation profiling of subsurface reflectors and visible layer boundaries reveals that reflectors and layers demonstrate similar topography verifying that reflectors represent paleosurfaces of the deposit statistical and frequency domain analyses of the separation distances between successive layers and successive reflectors confirms the agreement of radar reflector spacing with characteristic spacing of certain visible layers direct elevation comparisons between individual reflectors and discrete optical layers while necessary for a one to one correlation are complicated by variations in subsurface structure that exist between the outcrop and the sharad observations as inferred from subsurface mapping although these complications have prevented a unique correlation a genetic link between radar reflectors and visible layers has been confirmed validating the assumption that radar reflectors can be used as geometric proxies for visible stratigraphy furthermore the techniques for conducting a stratigraphic integration have been generalized and improved so that the integration can be undertaken at additional locations

buried ice and sand caps at the north pole of mars revealing a record of climate change in the cavi unit with sharad nasa mars data analysis program nnx15am52g landmark software and services a halliburton company

origin and characteristics of the mars north polar basal unit and implications for polar geologic history building upon previous studies we have used mars orbiter camera and mars orbiter laser altimeter data to characterize in detail the newly discovered north polar basal unit lying stratigraphically between the polar layered deposits from which it is likely separated by an unconformity and the vastitas borealis formation this unit has introduced new complexity into north polar stratigraphy and has important implications for polar history exposures of the basal unit in olympia planitia and chasma boreale reveal relatively dark layers which exhibit differential erosion eroded primarily by wind the basal unit may be the major if not sole source for the north polar dunes and ergs and has contributed material to the lower polar cap layers we investigate four possible origins for the basal unit outflow channel oceanic deposits basal ice paleopolar deposits and eolian deposits the patchy layering within the unit its likely sandy grain size and presence only in the north polar basin suggest that it is primarily an eolian deposit supporting byrne and murray s 2002 earlier conclusion this implies that at some time during the early to late amazonian migrating sand was mixed with water ice forming a relatively dark sandy deposit during this time either no classic polar layered deposits were forming or smaller caps were growing and shrinking possibly adding material to the basal unit

method for anisotropic crystal orientation fabrics detection using radio wave depolarization in radar sounding of mars polar layered deposits the polar layered deposits plds provide a wealth of information about the past climate evolution of mars surface mass fluxes and ice flow mainly governed topography and layering of the pld china s mars probe including an orbiter and a landing rover will be launched by 2020 a new type satellite borne mars penetrating radar instrument has been selected to be a part of the payloads on the orbiter its main scientific objectives are to map the distribution of water water ice and to detect the soil characteristics at global scale on the martian crust compared with mars advanced radar for subsurface and ionospheric sounding and shallow radar the biggest difference is that the antenna system of this mars penetrating radar consists of two dipole antennas mutually perpendicular this special configuration enables the investigation of the ice flow of pld by detecting and analyzing the features of anisotropic crystal orientation fabric cof thus relying on the fact that the radio waves are depolarized while passing through an anisotropic cof layer in this paper a method for anisotropic cof detection based on this radar system is proposed the radar echo formulation of anisotropic cof is derived and the ratio of the signals measured by the two perpendicular antennas is used to analyze the anisotropy of cof we demonstrate that the ratio is an ideal criterion for the detection and analysis of cof since it contains all parameters about the anisotropy feature of cof and it is independent of the attenuation in the propagation path and the reflection coefficient in order to verify the validity of the derived analytical expression of the ratio for the detection of cof finite different time domain simulations are carried out based on a simple model of the subsurface of pld which contains an anisotropic cof layer the advantages of this method the potential application scenarios and the effects of the martian environment are also discussed

numerical model for coastal wave propagation through mild slope zone in the presence of rigid vegetation abstract the study of wave propagation on coastal vegetation field is fundamental to assessing the effectiveness and limitations of vegetation in coastal protection this paper presents a refraction diffraction wave model for the investigation of wave propagation through a coastal mild slope zone in the presence of rigid vegetation via numerical simulation the model is based on the implementation of a module for vegetation induced wave energy dissipation in the parabolic mild slope equation the model is capable of simulating both wave refraction and diffraction and economical in computation and may bridge the gap between the wave energy spectrum and the phase resolved models for wave propagation through coastal vegetation fields the model is validated through by comparison with experimental results the model is subsequently applied to a simulation of a wave propagating on a plane in the presence of different patterns of rigid vegetation the sensitivity of the wave height to the plant height the diameter and the stem density is investigated by comparison of the numerical results for wave height attenuation that results from different patterns of rigid vegetation the numerical results show that wave height attenuation due to rigid vegetation has a higher variability for the different rigid plant conditions and that the attenuation of the wave height due to the rigid vegetation increases alongside the plant height under water as well as the diameter and plant stem density the results further indicate that for wave propagates through coastal rigid vegetation zones with a high plant height under water large diameter and high stem density the wave height along the propagating direction is decreased nonlinearly with the increase of the wave propagating distance and nonlinearity is more obvious for the plant with a higher height under water as well as a larger diameter and higher stem density

color and albedo of the south polar layered deposits on mars five color albedo units including polar frost have been recognized and mapped in the southern layered deposits on mars atmospheric dust scattering was measured in shadows and modeled in order to remove the component of brightness in mars images due to the atmosphere and quantify the albedo and color of the surface the layered deposits appear to be mantled by red dust except where eolian stripping has exposed the underlying bedrock frost and bare ground are mixed below the resolution of the images in many areas adjacent to the polar cap some of which appear to be younger than the surrounding layered terrain dark material has been deposited in topographic depressions in much of the south polar region including the layered deposits the available observational data suggest that the layered deposits are composed of bright dust ice and a small amount of dark material if the dark material is sand a periodic change in polar winds seems required in order to transport the sand poleward into the layered terrain in any case the observations are not consistent with the layered deposits being composed only of bright dust and ice the mars observer camera and infrared instruments should be particularly useful in this investigation

probing supraglacial debris on mars 1 sources thickness and stratigraphy abstract geomorphic and geophysical evidence supports a debris covered glacier origin for a suite of landforms at the mid latitudes of mars including lobate debris aprons lda lineated valley fill lvf and concentric crater fill ccf these large reservoirs of ice and their near surface structure provide a rich record for understanding the planet s climate and history of global volatile exchange over the past billion years lda lvf and ccf are also potential sites for future robotic and human missions but the accessibility of glacial ice for direct sampling and in situ resource utilization depends largely on the geotechnical properties of the surface debris supraglacial debris including its thickness grain sizes and density structure the physical properties of this supraglacial debris layer have been poorly constrained we use images of morphology digital elevation models thermal inertia data and radar sounding data to probe the near surface of lda lvf and ccf in deuteronilus mensae in order to place constraints on the sources grain sizes thickness and stratigraphy of supraglacial debris we find evidence for at least a two layer stratigraphy layered mantle consisting of atmospherically emplaced dust and ice superposes boulder rich sediment sourced by rockfalls glacially transported downslope high thermal inertia boulder rich termini and debris bands reminiscent of medial moraines are found throughout the study region supporting a rockfall origin for at least a fraction of the debris exposed at the surface this supraglacial debris layer would have thickened with time from sublimation of glacial ice and liberation of englacial sediment and dust at present the entire supraglacial debris package is a minimum of a few meters in thickness and is likely tens of meters in thickness in many locations possibly thinning regionally at lower latitudes and locally thinning toward the headwalls the lack of terracing or interior structures in craters formed within lda lvf and ccf and the absence of near surface reflectors in sharad radar data further suggest that no strong contrasts in permittivity or strength occur at the interface of the layers

sharad sounding radar on the mars reconnaissance orbiter 1 sharad shallow radar is a sounding radar provided by agenzia spaziale italiana asi as a facility instrument on the mars reconnaissance orbiter mission its 20 mhz center frequency and 10 mhz bandwidth complement the lower frequency relatively narrower bandwidth capability of the marsis sounding radar a joint italian u s team has guided the experiment development and is responsible for data analysis and interpretation the radar transmits signals at a 700 hz pulse repetition frequency prf and collects reflections from both the surface and near subsurface of mars vertical and horizontal resolutions are respectively 15 m free space and 3 6 km cross track by 0 3 1 km along track the scientific objective of sharad is to map in selected locales dielectric interfaces to at least several hundred meters depth in the martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials including competent rock soil water and ice a signal to noise ratio of 50 db for a specular surface return is achieved with 10 w of radiated power by using range and azimuth focusing in ground data processing preprocessed data as well as range and azimuth focused data will be formatted according to planetary data system pds standards and be made available from the asi science data center asdc and from the geosciences node of the planetary data system pds important targets for sharad include the polar layered deposits sedimentary stacks especially in terra meridiani buried channel systems buried impact craters volcanic complexes and shallow ice deposits in equilibrium with the atmosphere

constraints on the composition of the martian south polar cap from gravity and topography abstract the polar caps of mars have long been acknowledged to be composed of unknown proportions of water ice solid co 2 dry ice and dust gravity and topography data are here analyzed over the southern cap to place constraints on its density and hence composition using a localized spectral analysis combined with a lithospheric flexure model of ice cap loading the best fit density of the volatile rich south polar layered deposits is found to be 1271 kg m 3 with 1 limits of 1166 and 1391 kg m 3 the best fit elastic thickness of this geologically young deposit is 140 km though any value greater than 102 km can fit the observations the best fit density implies that about 55 dry ice by volume could be sequestered in these deposits if they were completely dust free alternatively if these deposits were completely free of solid co 2 the dust content would be constrained to lie between about 14 and 28 by volume the bulk thermal conductivity of the polar cap is not significantly affected by these maximum allowable concentrations of dust however even if a moderate quantity of solid co 2 were present as horizontal layers the bulk thermal conductivity of the polar cap would be significantly reduced reasonable estimates of the present day heat flow of mars predict that dry ice beneath the thicker portions of the south polar cap would have melted depending on the quantity of solid co 2 in these deposits today it is even possible that water ice could melt where the cap is thickest if independent estimates for either the dust or co 2 content of the south polar cap could be obtained and if radar sounding data could determine whether this polar cap is presently experiencing basal melting or not it would be possible to use these observations to place tight constraints on the present day heat flow of mars

soils of eagle crater and meridiani planum at the opportunity rover landing site the soils at the opportunity site are fine grained basaltic sands mixed with dust and sulfate rich outcrop debris hematite is concentrated in spherules eroded from the strata ongoing saltation exhumes the spherules and their fragments concentrating them at the surface spherules emerge from soils coated perhaps from subsurface cementation by salts two types of vesicular clasts may represent basaltic sand sources eolian ripples armored by well sorted hematite rich grains pervade meridiani planum the thickness of the soil on the plain is estimated to be about a meter the flatness and thin cover suggest that the plain may represent the original sedimentary surface

surface wave attenuation by vegetation with the stem root and canopy abstract to experimentally study the performance of the stem root and canopy on wave attenuation by vegetation a total of 112 laboratory experiments were conducted with seven vegetation models four vegetation densities five wave heights and four water depths wave period was assumed constant limiting the understanding of wave attenuation phenomena by vegetation frictional energy losses from sidewall and bottom were measured and removed by comparing with non vegetated tests experimental results show that wave attenuation by vegetation with stems roots and canopies varied with wave conditions due to vertically non uniform physical vegetation properties the root significantly impacted wave dissipation when the relative root height was greater than 0 167 higher wave attenuation occurred when the still water level was located at the canopy geometrical centroid the transmission coefficients of vegetation of the stem root and canopy ranged from 0 21 to 0 83 an empirical formula for predicting transmission coefficients of vegetation with stems roots and canopies was obtained based on experimental data the wave energy dissipated by vegetation was estimated in terms of drag coefficients calculated by analytical models of dalrymple et al 1984 and kobayashi et al 1993 a semi empirical analytical equation was proposed on the basis of experimental data for predicting wave attenuation by vegetation of the stem root and canopy

saw tooth structures and curved veins related to folds in the south central pyrenees spain two generation of folds f1 and f2 and associated structures developed in the eocene turbidites of the south central pyrenees are analyzed in this paper f1 folds are close have sub horizontal axes and southwards vergence they have an associated cleavage s1 competent layers were folded by layer parallel shortening tangential longitudinal strain some possible flexural flow and an obliquely superimposed homogeneous strain due mainly to simple shear flexural slip is also an important mechanism in the whole multilayer f2 folds are gentle and scarce they fold the s1 cleavage among the structures associated with f1 folds there are sets of veins with curved form in the competent layers the displacement of each vein gave rise usually to a step in the layer boundary so that a set of veins produces a structure that is named saw tooth structure the veins initiated as small faults that made flexural slip difficult and gave rise to a concentration of stress on the steps leading to an opening of the fractures and a propagation of them along a curved path as suggested by a simple mechanical model this propagation agrees with finite element models developed by other authors

density variations within the south polar layered deposits of mars 1 the south polar layered deposits spld constitute the largest known reservoir of water on mars previous studies solved for the best fit uniform density of the deposits using a forward approach here we invert for the lateral density variations in the layered deposit using gravity data from radio tracking of mars reconnaissance orbiter topography from mola on board mars global surveyor and radar sounding data from marsis on board mars express we use the gravity anomalies outside the spld to construct a wiener filter which is applied to the gravitational signature of the spld to remove the short wavelength anomalies over the spld that are spectrally consistent with an origin in the crust or mantle we then use a constrained inversion for the vertically averaged density within the spld as a function of position the results suggest significant density variations within the spld an inverse relationship between the density and thickness of the spld suggests that thicker portions of the cap contain less dust alternatively the dorsa argentea formation may extend beneath the spld and result in the observed high gravity anomaly in the marginal area of the spld we find these conclusions to be robust against the choice of inversion constraint and perturbations to the applied filter a synthetic test is also performed to verify the recoverability of the density variation in our approach

exposed water ice discovered near the south pole of mars the mars odyssey thermal emission imaging system themis has discovered water ice exposed near the edge of mars southern perennial polar cap the surface h2o ice was first observed by themis as a region that was cooler than expected for dry soil at that latitude during the summer season diurnal and seasonal temperature trends derived from mars global surveyor thermal emission spectrometer observations indicate that there is h2o ice at the surface viking observations and the few other relevant themis observations indicate that surface h2o ice may be widespread around and under the perennial co2 cap

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

wave attenuation by flexible idealized salt marsh vegetation abstract wave attenuation by vegetation is a highly dynamic process and its quantification is important for understanding shore protection potential and modeling coastal hydrodynamics data documenting the interactions of spartina alterniflora represented by polyolefin tubing and single and double peaked irregular waves were collected in a large scale laboratory flume the laboratory provided a controlled environment to evaluate wave attenuation including the parameters of stem density submergence wave height and peak period wave attenuation appeared to be most dependent on stem density and the ratio of stem length to water depth wave attention increased slightly with wave height while no clear trend with respect to wave period was seen treating double peaked spectra as superimposed wave systems revealed a preferential dissipation of the higher frequency wave system relative to the lower frequency wave system under emergent conditions wave energy loss occurred at all frequencies of both spectral types with dissipation increasing with frequency above the spectral peak parameterizing the spectral equilibrium range as a function of frequency showed a steepening of the spectral tail compared to the 4 power law under emergent conditions an empirical relationship defining the bulk drag coefficient for s alterniflora as a function of the stem reynolds number is found to serve as a first estimate for engineering applications

numerical investigation of wave induced flow in mound channel wetland systems abstract coastal wetlands are an important ecosystem in nearshore regions but they are also significant in affecting the flow patterns within these areas wave induced flow in wetlands has complex circulation characteristics because of the interaction between waves and plants especially in discontinuous vegetation here a numerical investigation is performed to analyze the wave averaged flow in vegetated mound channel systems different water levels vegetated conditions and mound configurations are studied with the coulwave cornell university long and intermediate wave boussinesq model model simulations show rip currents in the mound channel systems whose strength varies with different mound separation distances the relative influence of vegetation depends on both mound configuration and water level approximately a 15 change in significant wave height results as waves propagate over the vegetated mounds while up to a 75 decrease in the mean shoreward flow speed through vegetation is observed in addition vegetation influences the spatial distribution of mean water level within the wetlands dimensional analysis shows that rip current strength and primary circulation size depend on mound spacing water depth wave height and vegetation cover

effects of wave steepness and relative water depth on wave attenuation by emergent vegetation abstract a physical model experiment was conducted to investigate the effects of wave nonlinearity on the attenuation of irregular waves propagating through a stand of uniform emergent vegetation in constant water depth the experimental conditions spanned relative water depths from near shallow to near deep water waves 0 45

long waves through emergent coastal vegetation we study the effects of emergent coastal forests on the propagation of long surface waves of small amplitude the forest is idealized by an array of vertical cylinders simple models are employed to represent bed friction and to simulate turbulence generated by flow through the tree trunks a multi scale homogenization analysis similar to that for seepage flows is carried out to deduce the effective equations on the macro scale the effective coefficients are calculated by numerically solving the micro scale problem in a unit cell surrounding one or several cylinders analytical and numerical solutions for wave attenuation on the macro scale for different bathymetries and coastal forest configurations are presented for a transient incident wave analytical results are discussed for the damping of a leading tsunami for comparison series of laboratory data for periodic and transient incident waves are also presented good agreement is found even though some of the measured waves are short or nonlinear

regional stratigraphy of the south polar layered deposits promethei lingula mars discontinuity bounded units in images and radargrams abstract the mars south polar layered deposits spld are the result of depositional and erosional events which are marked by different stratigraphic sequences and erosional surfaces to unambiguously define the stratigraphic units at regional scale we mapped the spld on the basis of observed discontinuities i e unconformities correlative discontinuities and conformities as commonly done in terrestrial modern stratigraphy this methodology is defined as discontinuity bounded units or allostratigraphy and is complemented by geomorphological mapping our study focuses on promethei lingula pl and uses both high resolution images ctx hirise and radargrams sharad to combine surface and sub surface observations and obtain a 3d geological reconstruction of the spld one regional discontinuity named aur1 was defined within the studied stratigraphic succession and is exposed in several non contiguous outcrops around pl as well as observed at depth within the ice sheet this is the primary contact between two major depositional sequences showing a different texture at ctx resolution the lower sequence is characterized mainly by a ridge and trough morphology ridge and trough sequence rts and the upper sequence shows mainly by a stair stepped morphology stair stepped sequence sss on the basis of the observations we defined two regional discontinuity bounded units in pl respectively coinciding with rts and sss sequences our stratigraphic reconstruction provides new hints on the major scale events that shaped this region oscillations in martian axial obliquity could have controlled local climate conditions in the past affecting the pl geological record

marsis subsurface radar investigations of the south polar reentrant chasma australe 1 the mars express mars advanced radar for subsurface and ionospheric sounding marsis has conducted the first ever subsurface probing of the south polar layered deposits spld revealing internal structure that is rich in detail we report on subsurface features detected from a set of orbits that passed over the largest of the south polar reentrants chasma australe at the edge of the spld we present selected marsis overflights to both document the unique observations and gain insight into the possible origin of this feature we conclude that marsis observations clearly reveal new evidence of subsurface structure such as 1 internal bands 2 the continuation of the prometheus basin floor beneath the spld to form a prominent basal interface and 3 the presence of a possible ice rich layer on the prometheus basin floor extending to 500 m depth there is no obvious indication of a present day aquifer at the head of the chasma and identification of features associated with a past aquifer and water flow is ambiguous while marsis observations may not uniquely solve the chasma origin debate they do reveal the subsurface region beneath this very interesting feature for the first time

numerical simulations of wave propagation over a vegetated platform abstract vegetated platforms have been constructed in recent years for the purpose of shore protection this paper addresses some fundamental questions concerning the vegetated platform 1 what is the difference in wave attenuation between a vegetated platform and a simple platform and how much can vegetation increase the efficiency of reducing wave transmission 2 are there any differences between the effects of stems and roots on wave attenuation 3 does vegetation always reduce wave transmission 4 is it possible to develop an empirical formula for estimating the wave transmission of a vegetated platform to answer the above questions a numerical model solving the navier stokes equations for wave propagation over a vegetated platform is established and validated by several existing laboratory experiments a total of 244 numerical experiments based on this model have been carried out the simulated results suggest that the platform plays a major role and the vegetation plays a supporting role in reducing wave transmission except for some special cases stems tend to have a larger influence than roots in reducing wave transmission with the same height the roots always help reduce wave transmission while the stems may increase wave transmission when the platform width is in the range of 37 5 62 5 of the incident wavelength based on our numerical experiments and existing laboratory data the paper proposes a simple formula for predicting the wave transmission coefficient of a vegetated platform for engineering applications

geologic history of the polar regions of mars based on mars global surveyor data ii amazonian period based on mars orbiter laser altimeter mola and mars orbiter camera moc observations of amazonian polar layered deposits pld morphology composition and thickness we conclude that the plds are composed of porous unconsolidated layers that have not experienced significant basal melting or other glacial type processes morphologic features and associations within the pld chasmata including preserved craters and sinuous ridges indicate that the dominant process of chasmata formation is wind scouring our detailed analysis of south polar spiral trough topography in conjunction with the identification of similar layered stratigraphy within north polar spiral troughs suggests that trough migration due to preferential ablation of sun facing slopes cannot be demonstrated within the layered sequences we have not identified widespread unconformities discontinuities or pinch outs that would indicate an accublation origin of the plds we therefore postulate that the well defined plds at both poles eventually reached and maintained their present form following deposition without extensive deformation or redeposition large cuspate ridges in the ultimi lobe of planum australe appear to be layered and may be unusual erosional remnants of a once thicker pld in this area beneath the north polar layered deposits in planum boreum we have identified a platform of older highly degraded polar deposits as much as a kilometer thick that may have once covered an area larger than planum boreum

measurements of dielectric loss factors due to a martian dust analog 1 radar signals can penetrate loose sediments such as dust sand and alluvium to reveal buried geologic structures obscured in visible and infrared images in anticipation of data from instruments such as the marsis and sharad radar sounders and potential future imaging sar and rover mounted gpr instruments measurements have been made to characterize electrical loss factors of a martian dust analog and an iron rich soil this paper presents results from dielectric measurements of carbondale red clay crc and the palagonitic mars jsc 1 soil simulant from 0 2 to 1 3 ghz and from transmission measurements of radar penetration of crc up to 12 ghz attenuations predicted from dielectric measurements are compared to values measured in the experiment and are discussed relative to the frequencies at which imaging radars operate over the frequencies considered loss tangent tan decreases with increasing frequency but attenuation increases due to the influence of wavelength attenuation in crc ranges from 8 to 22 db m over p and l bands and jumps to 36 and 67 db m at c and x bands respectively mars jsc 1 has lower attenuation of 5 db m at p band and 12 db m at l band compared to attenuation measurements of sand both crc and mars jsc 1 cause significantly greater attenuation likely due to their compositions containing iron bearing minerals because martian fine sediments also contain ferric mineral components constraining higher losses of analogs for martian dust and fine sediments is important for predicting the performance of radar instruments operating in orbit or on the surface of mars

spectral wave flow attenuation within submerged canopies implications for wave energy dissipation 1 communities of benthic organisms can form very rough surfaces canopies on the seafloor previous studies have shown that an oscillatory flow induced by monochromatic surface waves will drive more flow inside a canopy than a comparable unidirectional current this paper builds on these previous studies by investigating how wave energy is attenuated within canopies under spectral wave conditions or random wave fields defined by many frequencies a theoretical model is first developed to predict how flow attenuation within a canopy varies among the different wave components and predicts that shorter period components will generally be more effective at driving flow within a canopy than longer period components to investigate the model performance a field experiment was conducted on a shallow reef flat in which flow was measured both inside and above a model canopy array results confirm that longer period components in the spectrum are significantly more attenuated than shorter period components in good agreement with the model prediction this paper concludes by showing that the rate at which wave energy is dissipated by a canopy is closely linked to the flow structure within the canopy under spectral wave conditions wave energy within a model canopy array is dissipated at a greater rate among the shorter period wave components these observations are consistent with previous observations of how wave energy is dissipated by the bottom roughness of a coral reef

nature based flood protection the efficiency of vegetated foreshores for reducing wave loads on coastal dikes this paper analyses the effect of vegetation on wave damping under severe storm conditions based on a combination of field measurements and numerical modelling the field measurements of wave attenuation by vegetation were performed on two salt marshes with two representative but contrasting coastal wetland vegetation types cordgrass spartina anglica and grassweed scirpus maritimus the former is found in salty environments whereas the latter is found in brackish environments the measurements have added to the range with the highest water depths and wave heights presented in the literature so far a numerical wave model swan has been calibrated and validated using the new field data it appeared that the model was well capable of reproducing the observed decay in wave height over the salt marsh the model has been applied to compute the reduction of the incident wave height on a dike for various realistic foreshore configurations and hydraulic loading conditions additionally the efficiency of vegetated foreshores in reducing wave loads on the dike has been investigated where wave loads were quantified using a computed wave run up height and wave overtopping discharge the outcomes show that vegetated foreshores reduce wave loads on coastal dikes significantly also for the large inundation depths that occur during storms and with the vegetation being in winter state the effect of the foreshore on the wave loads varies with wave height to water depth ratio on the foreshore the presence of vegetation on the foreshore extends the range of water depths for which a foreshore can be applied for effective reduction of wave loads and prevents intense wave breaking on the foreshore to occur this research demonstrates that vegetated foreshores can be considered as a promising supplement to conventional engineering methods for dike reinforcement

the construction of chasma boreale on mars the northern polar cap of mars containing enough water to cover the entire planet to a depth of several metres features two major landforms that stand above all others these are the enormous canyon chasma boreale and a series of spiral troughs the processes leading to their formation have remained unclear now two papers in this issue present detailed histories of both systems john holt and colleagues use penetrating radar imagery from mars reconnaissance orbiter s radar sounder to show that depositional processes rather than a catastrophic event formed the chasma boreale isaac smith and john holt use mars reconnaissance orbiter data to rule out erosional cutting of polar ice as the cause of the central troughs and instead conclude that they too are largely depositional having migrated polewards and upwards in elevation in the past two million years the chasma boreale is a large canyon 500 km long up to 100 km wide and nearly 2 km deep that cuts into the north polar layered deposits on mars quite how it formed has been unclear however new penetrating radar imagery has now been used to show that depositional processes rather than catastrophic events were responsible the polar layered deposits of mars contain the planet s largest known reservoir of water ice1 2 and the prospect of revealing a detailed martian palaeoclimate record3 4 but the mechanisms responsible for the formation of the dominant features of the north polar layered deposits npld are unclear despite decades of debate stratigraphic analyses of the exposed portions of chasma boreale a large canyon 500 km long up to 100 km wide and nearly 2 km deep have led most researchers to favour an erosional process for its formation following initial npld accumulation candidate mechanisms include the catastrophic outburst of water5 protracted basal melting6 erosional undercutting7 aeolian downcutting7 8 9 and a combination of these processes10 here we use new data from the mars reconnaissance orbiter to show that chasma boreale is instead a long lived complex feature resulting primarily from non uniform accumulation of the npld the initial valley that later became chasma boreale was matched by a second equally large valley that was completely filled in by subsequent deposition leaving no evidence on the surface to indicate its former presence we further demonstrate that topography existing before the npld began accumulating influenced successive episodes of deposition and erosion resulting in most of the present day topography long term and large scale patterns of mass balance achieved through sedimentary processes rather than catastrophic events ice flow or highly focused erosion have produced the largest geomorphic anomaly in the north polar ice of mars

hydrodynamics induced by wind waves in a vegetation field the wave induced kinematics and dynamics of a submerged or emerged vegetation field is analyzed using potential flow and an eigenfunction expansion the problem is solved considering regular as well as irregular incident waves the model takes into account the vegetation motion and solves for the complete wave system on the vegetation field and in its vicinity the model is validated against experimental laboratory data obtained by other authors showing a much better agreement than previous theoretical models in this paper the model is used to evaluate wave height evolution damping vegetation and fluid motion and forces and moments on the vegetation furthermore the inclusion of irregular waves provides force and moment distributions on the vegetation field depending on the wave climate statistics

summer evolution of the north polar cap of mars as observed by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega visible infrared imaging spectrometer extensively observed regions of mars with latitudes above 70 n in late 2004 heliocentric longitude from ls 93 to ls 127 the extent of water ice at the surface and the size of ice grains were monitored as a function of time bright small grained frost which initially covered a large fraction of the polar cap waned in favor of large grained ice in outlying regions dominated by large grained ice the albedo increased over the period evaluating the dust content was model dependent however contamination of ice by dust was low

sulfates in the north polar region of mars detected by omega mars express the observatoire pour la mineralogie l eau les glaces et l activite omega imaging spectrometer observed the northern circumpolar regions of mars at a resolution of a few kilometers an extended region at 240 e 85 n with an area of 60 kilometers by 200 kilometers exhibits absorptions at wavelengths of 1 45 1 75 1 94 2 22 2 26 and 2 48 micrometers these signatures can be unambiguously attributed to calcium rich sulfates most likely gypsum this region corresponds to the dark longitudinal dunes of olympia planitia these observations reveal that water alteration played a major role in the formation of the constituting minerals of northern circumpolar terrains

radar soundings of the subsurface of mars the martian subsurface has been probed to kilometer depths by the mars advanced radar for subsurface and ionospheric sounding instrument aboard the mars express orbiter signals penetrate the polar layered deposits probably imaging the base of the deposits data from the northern lowlands of chryse planitia have revealed a shallowly buried quasi circular structure about 250 kilometers in diameter that is interpreted to be an impact basin in addition a planar reflector associated with the basin structure may indicate the presence of a low loss deposit that is more than 1 kilometer thick

sequence architecture of the cavi unit chasma boreale mars abstract the principles of terrestrial sequence stratigraphy provide a proven approach for evaluating the cavi unit where it transitions into the north polar layered deposits npld three cavi unit outcrops at the head of chasma boreale were examined using high resolution imagery and topography and interpreted in a sequence stratigraphic framework lithofacies present in the cavi unit were identified and consist of 1 dark lithic material 2 dark material with icy foresets 3 icy cavi 4 isolated dunes 5 dirty ice and 6 layered ice these lithofacies represent a progression in the dominance of aeolian to cryosphere processes and have analogs in the modern chasma boreale depositional environment parasequences were defined as aeolian units bounded by outcrop scale unconformities permafrost layers and layered ice deposits the northern outcrop is dominated by sandy lithofacies with large bodies of sand also dominating the northern parts of the central and southern outcrops in the central and southern outcrops sandy lithofacies yield southward to icier accumulations concurrently vertical trends in lithofacies distribution indicate an increasing prevalence of ice deposits through time considered across all three outcrops the parasequences form a set that expresses the northward retreat of the cavi aeolian system coincident with transgression of an ice sheet originating in gemini lingula this retrogradational stacking pattern of cavi aeolian parasequences with gradual transgression of the npld environment implies that the transitional cavi unit and npld form a single sequence that may correspond to allogenic forcing by orbital parameters the dynamics between aeolian and cryosphere processes revealed at the parasequence scale indicate that preservation of the stratigraphic record is driven by the ice transgression suggesting that during episodes of ice sheet collapse the north polar sedimentary environment reverts to one dominated by aeolian erosion and reworking as represented by the basal cavi unit

co2 snow depth and subsurface water ice abundance in the northern hemisphere of mars observations of seasonal variations of neutron flux from the high energy neutron detector hend on mars odyssey combined with direct measurements of the thickness of condensed carbon dioxide by the mars orbiter laser altimeter mola on mars global surveyor show a latitudinal dependence of northern winter deposition of carbon dioxide the observations are also consistent with a shallow substrate consisting of a layer with water ice overlain by a layer of drier soil the lower ice rich layer contains between 50 and 75 weight water indicating that the shallow subsurface at northern polar latitudes on mars is even more water rich than that in the south

subsurface structure of planum boreum from mars reconnaissance orbiter shallow radar soundings abstract we map the subsurface structure of planum boreum using sounding data from the shallow radar sharad instrument onboard the mars reconnaissance orbiter radar coverage throughout the 1 000 000 km2 area reveals widespread reflections from basal and internal interfaces of the north polar layered deposits npld a dome shaped zone of diffuse reflectivity up to 12 s 1 km thick underlies two thirds of the npld predominantly in the main lobe but also extending into the gemina lingula lobe across chasma boreale we equate this zone with a basal unit identified in image data as amazonian sand rich layered deposits byrne s murray b c 2002 j geophys res 107 5044 12 pp doi 10 1029 2001je001615 fishbaugh k e head j w 2005 icarus 174 444 474 tanaka k l rodriguez j a p skinner j a bourke m c fortezzo c m herkenhoff k e kolb e j okubo c h 2008 icarus 196 318 358 elsewhere the npld base is remarkably flat lying and co planar with the exposed surface of the surrounding vastitas borealis materials within the npld we delineate and map four units based on the radar layer packets of phillips et al phillips r j and 26 colleagues 2008 science 320 1182 1185 that extend throughout the deposits and a fifth unit confined to eastern gemina lingula we estimate the volume of each internal unit and of the entire npld stack 821 000 km3 exclusive of the basal unit correlation of these units to models of insolation cycles and polar deposition laskar j levrard b mustard j f 2002 nature 419 375 377 levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 is consistent with the 4 2 ma age of the oldest preserved npld obtained by levrard et al levrard b forget f montmessin f laskar j 2007 j geophys res 112 e06012 18 pp doi 10 1029 2006je002772 we suggest a dominant layering mechanism of dust content variation during accumulation rather than one of lag production during periods of sublimation

large scale deformational systems in the south polar layered deposits promethei lingula mars soft sediment and deep seated gravitational slope deformations mechanisms abstract the present study is the first attempt at a detailed structural and kinematic analysis of large scale deformational systems observed in the south polar layered deposits splds in the promethei lingula pl margins mars by systematically collecting attitude data referable to previously unknown deformational structures and defining the cross cut relationships of the structures we reconstructed a deformational history consisting of two superimposed well defined stages the first stage is dominated by large scale strike slip and transtensional faults arranged into conjugate systems and delimiting shear zones that show a wide range of subsidiary structures including normal and reverse faults drag folds boudins s c tectonites and sub horizontal interstratal shear planes marked by sygmoidal boudins other typical structures referable to this event are ductile folds locally true convolute folds and lobes ball and pillow structures affecting certain marker beds of the succession we suggest that the structural assemblage might be the expression of a shallow soft sediment tectonics that possibly occurred during warm periods of the south pole climate the second stage seems to affect the weaker and in certain cases pre deformed stratigraphic levels of the spld succession this stage is mainly characterized by extensional deformations caused by gravity the consequence of the deformations is the nucleation of deep seated gravitational slope deformations dsgsds marked by typical morphostructures such as scarps trenches and bulging basal contractant zones these phenomena were never observed within an ice cap according to terrestrial modeling these slow collapses were caused by 1 the presence of detachment levels i e subhorizontal bedding planes along which the ice sheet margins can slide and 2 the development of listric faults within the glacial mass which merge with sub horizontal shear planes in the subsurface the presence of complex deformational systems in the spld necessarily implies that a large scale dynamics of the ice sheet occurred in the past the relatively fast internal creep and basal internal sliding inferable from the structure assemblage can be due to partial melting of the ice possibly caused by climatic changes in the promethei lingula region in this manner we believe that climate heating which according to the literature is likely caused by orbital variations softened some of the spld layers triggering or accelerating the ice sheet s outward movement the evidence of a marked disharmonic deformational style through the spld succession suggests the possibility of local periodic compositional variations in the sequence

north south geological differences between the residual polar caps on mars polar processes can be sensitive indicators of global climate and the geological features associated with polar ice caps can therefore indicate evolution of climate with time the polar regions on mars have distinctive morphologic and climatologic features thick layered deposits seasonal co 2 frost caps extending to mid latitudes and near polar residual frost deposits that survive the summer the relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained mainly by the limited spatial resolution of the available data in particular it has not been known if the residual caps represent simple thin frost cover or substantial geologic features here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography this is very different from the residual cap on the north pole which grades into the underlying layered materials these findings indicate that the differences between the caps are substantial rather than reflecting short lived differences in frost cover and so support the idea of long term asymmetry in the polar climates of mars

basal mechanics of ice streams insights from the stick slip motion of whillans ice stream west antarctica the downstream portion of whillans ice stream west antarctica moves primarily by stick slip motion the observation of stick slip motion suggests that the bed is governed by velocity weakening physics and that the basal physics is more unstable than suggested by laboratory studies the stick slip cycle of whilla s ice plain exhibits substantial variability in both the duration of sticky periods and in slip magnitude to understand this variability we modeled the forces acting on the ice stream during the stick phase of the stick slip cycle the ocean tides introduce changes in the rate at which stress is applied to the ice plain increased loading rates promote earlier failure and vice versa results show that the bed of whillans ice stream strengthens over time healing during the quiescent intervals in the stick slip cycle with the bed weakening during slip events the time dependent strengthening of the ice plain bed following termination of slip events indicates that the strength of the bed may vary by up to 0 35 kpa during the course of a single day copyright 2009 by the american geophysical union

radar subsurface mapping of the polar layered deposits on mars 1 determining the three dimensional 3 d structure of the martian polar caps is fundamental to understanding their hydrologic history dynamic behavior past climatic changes and the underlying lithosphere and radar sounding is the most promising technique to do so we model the dielectric profile of the martian polar layered deposits pld apply it to a 1 d electromagnetic plane wave propagation model and calculate the relative strength of radar reflections produced by layering within these deposits variations in dust fraction with depth derive from albedo profiles of a northern polar trough and a radiative transfer model detection of the fine scale layering present in the polar deposits with sharad is likely under a wide range of possible dielectric properties of the ice and silicate inclusions as long as minimum inclusion volumetric fractions are larger than 10 3 our models indicate also that stratigraphic mapping of the pld is feasible with a vertical resolution of 20 m under ideal conditions penetration depths depend greatly on the dielectric properties of silicate inclusions reaching at least 250 m for ice rich in highly conductive altered basaltic dust to at least 2 km for weakly conducting silicate inclusions because of the wide parameter space and unconstrained composition interpretation of polar radar data will be best accomplished in conjunction with updated thermal models and other data sets such as the recently published results from orbital infrared remote sensing that impose limits on ice grain size and dust

h2o grain size and the amount of dust in mars residual north polar cap in mars north polar cap the probable composition of material residual from the annual condensation cycle is a mixture of fine dust and h2o grains of comparable size and abundance however metamorphism of such material will gradually lower its albedo by increasing the size of the h2o grains only if the cap is undergoing net annual sublimation as inferred from water vapor observations late summer observations should be of old ice with h2o grain sizes of 100 microns or more ice of this granularity containing 30 percent fine dust has a reflectivity similar to that of dust alone the observed albedo and computed ice grain size imply dust concentrations of 1 part per 1000 or less the brightness of the icy areas conflicts with what would be expected for a residual cap deposited by an annual cycle similar to that observed by viking and aged for thousands of years the residual cap surface cannot be old dirty ice it could be old coarse and clean or it could be young fine and dirty this brings into question both the source of the late summer water vapor and the formation rate of laminated terrain

permittivity estimation of layers beneath the northern polar layered deposits mars 1 martian polar layered deposits most likely dusty ice are transparent to radar waves in the north pole bedrock has been detected by marsis up to a depth about 2 km whereas in the south pole such interface has been located at about 3 7 km the reflected signal is generally above the noise and can be used to estimate the dielectric properties of the bedrock assuming the permittivity of the first layer is known we use a simplified inversion method to extract the bedrock relative dielectric permittivity as 4 9 below the north pld s these values are coherent with the basalt nature and so the approach could be used to identify the lithology beneath the martian poles

evidence from opportunity s microscopic imager for water on meridiani planum the microscopic imager on the opportunity rover analyzed textures of soils and rocks at meridiani planum at a scale of 31 micrometers per pixel the uppermost millimeter of some soils is weakly cemented whereas other soils show little evidence of cohesion rock outcrops are laminated on a millimeter scale image mosaics of cross stratification suggest that some sediments were deposited by flowing water vugs in some outcrop faces are probably molds formed by dissolution of relatively soluble minerals during diagenesis microscopic images support the hypothesis that hematite rich spherules observed in outcrops and soils also formed diagenetically as concretions

stratigraphy of promethei lingula south polar layered deposits mars in radar and imaging data sets 1 the south polar layered deposits spld of mars have been studied through imagery for decades now two subsurface sounding radar instruments have collected data the mars advanced radar for subsurface and ionospheric sounding marsis instrument on mars express and the shallow radar sharad instrument on mars reconnaissance orbiter are observing the spld at multiple frequencies 1 8 5 and 20 mhz respectively both instruments detect subsurface reflections in the promethei lingula region of the spld marsis detects up to three reflections within promethei lingula in addition to detecting the basal contact between the spld and the underlying plains sharad detects 10s of reflections without penetrating to the base of the spld marsis reflections likely correlate to the boundaries of packets of reflections in the sharad data whatever change in composition of the spld that causes the sharad reflections to occur in packets may also be the source of the marsis reflections in several locations sharad reflections can be compared directly with images of layers an individual reflection corresponds to 3 7 layers in images at resolutions of 6 m pixel reflection surfaces are calculated using the radar observations and extrapolated to the spld margins where they are compared to the stratigraphy observed in images we find that the marsis reflections and thus the packet structure within the sharad observations are likely related to distinctive groups of layers rather than individual layers the radar data sets allow us to confirm several predictions concerning the interior of the spld from stratigraphic studies of images including that most of the layers extend throughout the region and that they decrease in elevation toward the margin of the spld

wind flow and sedimentation in artificial vegetation field and wind tunnel experiments abstract the flow dynamics within and immediately above an artificial plastic vegetation canopy are measured in the field and wind tunnel artificial plants created from wooden dowels and cable zip ties were arranged in a variety of arrays on pegboards where plant cover or lateral cover could be accurately controlled plant covers examined ranged from 12 to 60 wind velocity profiles and the bedforms incipient dunes that developed within and beyond the vegetation in a few hours were measured the results indicate that flow deceleration and drag increases within the canopy as plant density increases in general there is a marked reduction and inflection in velocity at the canopy top and a second major inflection in the velocity profiles occurs immediately below the base of the four arrays equal or 23 density tall vegetation allows flow to sweep under the canopy and local high speed maxima flows may develop leading to minimal sedimentation in those canopies but deposition downwind beyond the canopies short vegetation where the leaves fill the canopy close to the ground display significantly greater drag and rapid rates of sand deposition flow velocities above the canopy increase as plant cover or density increases due to flow compression and acceleration bedform development is strongly correlated with plant cover density or lateral cover and short plants such that shorter length higher bedforms develop in higher density and or shorter plants the relationship between plant cover density or lateral cover and within canopy velocity is non linear and a new tentative flow regime is proposed canopy flow which may occur between wake interference flow and skimming flow this study further confirms that plant density plays a defining role in determining bedform and dune morphology the results also apply to flow in semi arid grasslands