tower ocean wave and radar dependence experiment an overview the tower ocean wave and radar dependence experiment toward is a coordinated effort involving both field experimentation and theoretical investigations to address the divergent hypotheses on the mechanisms involved in synthetic aperture radar sar imaging of the ocean surface in the formulation of the experiment it was recognized that three distinct disciplines were to be addressed 1 hydrodynamics 2 radar backscatter and 3 sar image processing the field operations were executed in three 6 week segments during the period october 1984 to january 1986 the naval ocean systems center tower located offshore of mission beach san diego california was used as the focal point for the field operations the primary measurements included in situ capillary and short gravity waves long surface waves and internal waves ambient current and detailed meteorological measurements stereophotography tower based multifrequency radars and an l band sar deployed on board the nasa cv 990 the single most significant result is the determination that none of the available hypotheses on sar imaging of long surface waves could be demonstrated to explain all the sar observations obtained in toward specific results are reported

resurfacing history of europa from pole to pole geological mapping abstract we produced geologic maps from two regional mosaics of galileo images across the leading and trailing hemispheres of europa in order to investigate the temporal distribution of units in the visible geologic record five principal terrain types were identified plains bands ridges chaos and crater materials which are interpreted to result from 1 tectonic fracturing and lineament building 2 cryovolcanic reworking of surface units with possible emplacement of sub surface materials and 3 impact cratering the geologic histories of both mapped areas are essentially similar and reflect some common trends tectonic resurfacing dominates the early geologic record with the formation of background plains by intricate superposition of lineaments the opening of wide bands with infilling of inter plate gaps and the buildup of ridges and ridge complexes along prominent fractures in the ice it also appears that lineaments are narrower and more widely spaced with time the lack of impact craters overprinted by lineaments indicate that the degree of tectonic resurfacing decreased rapidly after ridged plains formation in contrast the degree of cryovolcanic resurfacing appears to increase with time as chaos formation dominates the later parts of the geologic record these trends and the transition from tectonic to cryovolcanic dominated resurfacing could be attributed to the gradual thickening of europa s cryosphere during the visible geologic history that comprises the last 2 or 30 80 myr of europa s history an originally thin brittle ice shell could be pervasively fractured or melted through by tidal and endogenic processes the degree of fracturing and plate displacements decreased with time in a thickening shell and lineaments became narrower and more widely spaced formation of chaos regions could have occurred where the thickness threshold for solid state convection was exceeded and can be aided by preferential tidal heating of more ductile ice in a long term context it is not clear at this point whether this inferred thickening trend would reflect a drastic change in the thermal evolution of the satellite or cyclic or irregular episodes of tectonic and cryovolcanic activity

comments on on the focusing issue of synthetic aperture radar imaging of ocean waves by c bruning et al in the above named work see ibid vol 29 p 120 8 1991 c bruning et al present results that show the application of the velocity bunching model to synthetic aperture radar sar images obtained during the tower ocean wave and radar dependence toward experiment the commenters argue that some of the observations presented require classification and discussion an attempt is made in this comment to clarify the issues and to present some new relevant results obtained from the sar x band and ocean nonlinearities chesapeake light tower saxon clt experiment

experimental and analytical framework for modelling soil compaction abstract compacted materials are fundamentally unsaturated soils whose behaviour can be expansive or collapsible depending upon changes in water content or stresses their behaviour is strongly dependent upon matric suction water content and stress history this paper presents a methodology for investigating the stress strain and suction water content paths during one dimensional compaction of unsaturated soils it focuses on anisotropic behaviour the testing programme was carried out in a new automated oedometer apparatus that allows measurement of axial strain radial and axial stresses suction and water content during tests the laboratory component used in this study involves kaolin compacted with different water contents after compaction the soil was subjected to wetting while the volumetric changes and stress paths were being examined the results were interpreted within an anisotropic elasto plastic framework the proposed methodology provides new insights into the behaviour of unsaturated soils during compaction and wetting

the effective stress concept in saturated sand clay buffer uncertainty has existed about the applicability of the effective stress concept to dense compacted plastic clays to examine this a series of tests has been performed on mixtures of sand and bentonite specimens were made by combining equal weights of the dry components with water and compacting the mixture to 85 or 95 astm modified maximum dry density the tests investigated the proposition that the behaviour of the mixture can be expressed in terms of effective stresses defined as the tensor difference between externally applied total stresses and pore water pressures measured outside the cell the proposition cannot be examined directly but must be studied through a series of corollaries that is statements of behaviour that would be expected if the proposition were true the testing considered the behaviour of specimens in consolidation and shear effective consolidation pressures were from 0 3 to 3 0 mpa with back pressures from 0 2 to 7 0 mpa within acceptable bounds of experimental error t

azimuthal ocean wave emerged in sar image spectra under specific condition velocity bunching causes nonlinear modulations in synthetic aperture radar sar images of oceanic scenes sar images for the azimuth waves exhibit destructive wavy patterns because of azimuthal distortion caused by velocity bunching meanwhile velocity bunching creates constructive wavy patterns for long waves in certain cases this paper aims to provide a simple indication for practical interpretation of plausible wavy patterns a numerical simulation had been performed to address how velocity bunching forms a clear wave like pattern caused by orbital motions of a long single swell under a certain condition more specifically when the azimuth shifts caused by the orbital motions of the azimuth wave concentrate in the wave trough or crest the bunching causes a strong single peak in the sar images this paper explains the mechanism of displaying plausible wavy patterns from the viewpoint of the ocean wave spectra and this specific condition first the simulation was validated for irregular waves generated from ocean wave spectra matching actual buoy data from which sar images were simultaneously obtained the sar image spectra showed longer waves than those of the ocean wave spectra estimated via buoy data the simulated spectra exhibited a similar trend to the actual sar image thus validating the numerical simulation next an additional numerical simulation was conducted for irregular waves under the specific condition the simulated results suggest that if a significant wave height and wavelength match the specific condition the long waves in sar image spectra can be similar to the original ocean wave spectra

layover in satellite radar images of ocean waves present models explaining radar imaging of ocean surface waves have considered variations in radar cross section of the tilted or roughened surface and velocity bunching effects caused by the doppler shifts of moving scatterers it is pointed out here that simple layover effects will cause an additional significant modulation of the image brightness that increases the visibility of range traveling waves

fluid volcanism on miranda and ariel flow morphology and composition several types of volcanic units have been recognized on the icy uranian satellites miranda and ariel on miranda ridges characterized by crest grooves are up to 10 km wide and 500 m high a continuous flat topped flow band also 10 km wide and 500 m high forms the outer southern margin of elsinore corona elsinore coronae at least appears to comprise coalesced flow bands and ridges on ariel in addition to at least one ridge unit similar to these on miranda flood plains material has covered the floors of deep chasmata grabens and an irregular depression flows on both satellites are characterized by linear vent geometries and distinct topographic margins which indicate extrusion of a relatively viscous material the topography of the flows can be used to estimate flow viscosity or yield strength using a bingham plastic model extrusion viscosity estimates incorporating plausible volcanologically based emplacement time scales and a rigid crust correction range from 107 to 109 p 1013 p in the unlikely absence of a chilled crust viscosity estimates are dependent on the assumed emplacement time scale however and could be as high as 1016 p if a solid stale based time scale is assumed bingham models indicate that it is yield strength that controls the final flow width and thickness that we see yield strength estimates are probably more reliable because of uncertainties in the viscous flow time scale yield strength estimates range from 10 1 to 10 2 bars consistent with yield strengths of partially crystallized silicate melts on other planets nevertheless both the viscosities and yield strengths are well within the range of and in some cases lower than silicate flows silicate compositions are not possible for these flows because of the ice rich composition of these satellites measured properties of ammonia water liquid crystal mixtures are consistent with the observed and estimated flow rheologic properties however and extrusion of such material s is a viable alternative to solid state extrusion for the origin of these flow features

energy density directional spectra of a nearshore wave field measured by interferometric synthetic aperture radar the nearshore wave field within monterey bay california is studied using remote sensing imaging by an interferometric synthetic aperture radar insar and simultaneous ground based measurements it is shown that insar imagery of the ocean surface offers some advantages over conventional synthetic aperture radar because of the direct imaging mechanism of insar quantitative information about the complicated wave field can be obtained the insar derived directional energy density spectra and the corresponding ground based spectra compare well

models for synthetic aperture radar imaging of the ocean a comparison theoretical comparisons are made of different models for synthetic aperture radar sar imaging of ocean waves the velocity bunching model distributed surface model lyzenga model canadian center for remote sensing radarsat ccrs radarsat model and the ocean research and engineering ore model are compared analytically with respect to their description of the sar imaging process and the radar backscatter process the study concentrates on the temporal description of the backscatter process and its impact on sar imaging of the ocean sample simulations are conducted so as to quantify some of the similarities and differences of the aforementioned models other sar imaging models are discussed as they pertain to the comparisons noted above the analytical and numerical simulations show that the lyzenga model the ccrs radarsat model and the ore model are similar for most commonly occurring sea states the velocity bunching model is similar to these models when the sar integration time is small but it tends to deviate for long integration times the distributed surface model is shown to describe the imaging process adequately when the radar backscatter is highly correlated in space and time

solid state ice volcanism on the satellites of uranus voyager images of the uranian satellites ariel and miranda show flow features with morphologies indicating that ice has been extruded to the satellites9 surfaces in the solid state these images provide the first observational evidence for solid state ice volcanism in the solar system topographic profiles have been measured across a number of flow features on ariel with a simple model of extrusion spreading and cooling of a viscous flow the initial viscosity of the flow material is found to have been no more than about 10 16 poise far lower than expected for h 2 o ice at the ambient surface temperatures in the uranian system sharply reduced viscosities may have resulted from incorporation of ices like nh 3 or ch 4 in the uranian satellites

focusing simulations of synthetic aperture radar ocean images the sar ocean images obtained in the tower ocean wave and radar dependence experiment toward are carefully analyzed at different focus settings and compared with simulated results based on various theories for imaging surface waves the agreement between the experimental data and all of the sar simulations except one is found to be favorable there is also surprisingly close agreement among the different theoretical models themselves suggesting a closer fundamental similarity among the contending theories than was previously thought it is shown that the width of the focusing curve has an inverse dependence on the sar integration time for the toward conditions it is found that the image modulation due to azimuth traveling surface waves is greater than that due to range traveling waves

validation and assimilation of seasat altimeter wave heights using the wam wave model the mutual consistency of the seasat global data sets of scatterometer winds and altimeter wave heights is investigated for the complete seasat period using the third generation wave model wam the wave model was driven by surface 1000 hpa wind and surface stress fields constructed by the goddard laboratory for atmospheres gla by assimilation of the scatterometer winds in an atmospheric model for the 10 day period september 7 17 the intercomparison was extended to two further scatterometer wind fields a 1000 hpa assimilated wind field from the european centre for medium range weather forecasts and a subjectively analyzed 19 5 m height surface wind field from the jet propulsion laboratory on the global average the modeled and observed wave heights agree reasonably well regional differences however can be large and sometimes exceed 40 the errors are attributed mainly to deficiencies in the forcing wind fields low wind speeds are found to be overestimated and high wind speeds underestimated by the seasat scatterometer algorithm the friction velocities of the gla model are found to be significantly underestimated in the high wind belt of the southern hemisphere the analysis demonstrates the diagnostic advantages of applying a wave model for the quality assessment of satellite wind and wave data a preliminary wave data assimilation scheme is presented in which the wave field is updated without changing the forcing wind field a considerable improvement of the computed wave field is achieved particularly in regions in which the wave energy is dominated by swell however a more general assimilation scheme including modifications of the wind field is needed to upgrade wind sea forecasts

the two scale radar wave probe and sar imagery of the ocean a two scale formulation of oceanic backscatter of microwave radiation which has previously been applied to the dual frequency scatterometer is applied here to the two scale radar wave probe and sar imagery of the ocean a two scale radar wave probe is a microwave system which coherently detects signals scattered from a very small patch of the ocean surface it is shown that a sar image may be described as a convolution of the am part of the output of a two scale wave probe with the power spectrum of the fm part of the output thus sar images are not faithful reproductions of cross section variations over the surface distortions occur as a result of variable surface velocities examples of this distortion are derived from two scale wave probe data taken in the gulf of mexico application of a focusing correction does not remove the distortion from the simulated image of a nearly sinusoidal azimuth traveling wave large v r0 ratios minimize the distortion however

on ocean sar raw signal simulation simulation of synthetic aperture radar sar raw signal pertaining to an ocean scene is presented it embodies the distributed surface model the hydrodynamic modulation and the bragg dominant scattering mechanism simulation experiments are provided

estimating ocean coherence time using dual baseline interferometric synthetic aperture radar a new technique for measuring the coherence time of the ocean surface at radar wavelengths has been developed and tested this technique requires an interferometric synthetic aperture radar system with at least two unique baselines along the direction of platform motion the coherence time of the surface may be presented as a high resolution coherence time map this technique was tested using the jpl airsar along track interferometer measurements of the ocean coherence at the l band were made at high spatial resolution under a variety of conditions a new operating technique that results in the required two baselines is described some parametric analysis is performed pertaining to the design of such a system a representative interferometric data set acquired at the strait of messina in 1991 is presented to illustrate the technique the interferometric phase data reveal and measure tidal currents flowing through the strait while the coherence time image shows considerable structure not visible in the backscatter or phase image coherence times in and around the strait were measured to be of the order of 0 1 s at the l band which is in agreement with previous estimates and measurements

focusing of synthetic aperture radar ocean images with long integration times synthetic aperture radar sar images obtained in the sar and x band ocean nonlinearities chesapeake light tower saxon clt experiment are processed with long integration times 6 s and analyzed to study the effects of focusing two images with near azimuth traveling waves were chosen for the study the first image consists of relatively short wavelength wind waves traveling in the same general direction as the aircraft the second image consists of a long atlantic swell traveling in the opposite direction to the aircraft at these long integration times the image spectral intensities are found to be sensitive to the focus setting the spectral intensity at the optimum focus is 400 of that at zero focus for the first image and 167 for the second image the focusing curves for both images agree well with those predicted by a model developed by several groups and referred to here as the consensus model this model predicts an optimum focus setting that is equal to one half of the effective phase speed of the dominant wave in the azimuth direction the velocity bunching model underpredicts the optimum focus setting significantly the study concludes that in long integration time sar processing of surface waves such as the spotlight mode the image contrast is sensitively dependent on the focus setting and that the optimum focus setting is given by one half of the effective phase speed of the dominant surface wave

theory for synthetic aperture radar imaging of the ocean surface with application to the tower ocean wave and radar dependence experiment on focus resolution and wave height spectra a one dimensional model is developed to simulate azimuthal synthetic aperture radar sar imaging of the ocean surface the model developed here is general and can admit both the distributed surface and the velocity bunching approaches computer simulations are performed to test the validity of this model the simulations show that the time dependent modulation patterns due to the radar cross section variation and the velocity bunching effects give optimum focusing around half the phase velocity of the long wave it is shown that the focus dependence is due to an incoherent integration process and not due to motion induced phase errors it is argued that the radar reflectivity is correlated over distances small in comparison with the sar resolution in the simulations the radar reflectivity is assumed to be spatially decorrelated also given are the relative importance of the various effects that degrade the azimuthal resolution it is shown that the limited radar temporal coherence due to the velocity spread of short waves degrades the azimuthal resolution of the sar this coherence time depends on sea state and radar wavelength it is shown that the orbital acceleration effects are small in comparison with the smearing due to the velocity spread it is found that the degraded azimuthal resolution of the radar minimizes the nonlinear effects of velocity bunching the simulations show that in the tower ocean wave and radar dependence experiment toward sar imaging at l band is reasonably linear

influence of suction on the strength and stiffness of compacted sand bentonite this paper examines the constitutive behaviour of unsaturated mixtures of compacted sand bentonite material two different techniques have been used to modify soil suction in laboratory specimens to examine the influence of suction on the behaviour of compacted materials the two methods generated inherent differences in material fabric and therefore in stress strain behaviour the difference in microstructure generated by these two preparation techniques created different properties for the two series of specimens this paper compares the behaviour of the two series of specimens and relates the observed mechanical behaviour to the initial soil fabric created by the two different preparation techniques specimens of similar compacted material were taken from two full scale in ground experiments conducted at atomic energy of canada limited s underground research laboratory at lac du bonnet manitoba and sheared using the same triaxial equipment the results are compared to the results of shearing laborator

evaluation of the transitional inelastic behaviour of unsaturated clay sand mixtures this paper examines and compares the mechanical behaviour of two different unsaturated clay mixtures comprised of bentonite clay saskatchewan or wyoming and quartz sand the two mixtures have bee

experimental observations of the stress regime in unsaturated compacted clay when laterally confined construction processes often involve reformation of the landscape which will inevitably encompass compaction of artificially placed soils a common application of fill materials is their use as backfill in many engineering applications for example behind a retaining wall the post construction behaviour of clay fills is complex with respect to stresses and deformation when the fills become saturated over time heavily compacted fills swells significantly more than the lightly compacted fills this will produce enhanced lateral stresses if the fill is laterally restrained the work presented in this paper examines how the stress regime in unsaturated clay fills changes with wetting under laterally restrained conditions specimens of compacted kaolin with different initial conditions were wetted to various values of suction under zero lateral strain at constant net overburden pressure which allowed the concept of k0 the ratio between the net horizontal stress and the net vertical stress to be examined

on the focusing issue of synthetic aperture radar imaging of ocean waves it is widely accepted that the imaging of ocean surface waves by synthetic aperture radar sar can be adequately described by velocity bunching theory in conjunction with the two scale wave model however it has been conjectured that this theory is incapable of explaining why under certain conditions the image contrast of airborne sar imagery of ocean waves can be enhanced by defocusing the sar processor in the present study the velocity bunching theory is defended

voyager 2 in the uranian system imaging science results voyager 2 images of the southern hemisphere of uranus indicate that submicrometersize haze particles and particles of a methane condensation cloud produce faint patterns in the atmosphere the alignment of the cloud bands is similar to that of bands on jupiter and saturn but the zonal winds are nearly opposite at mid latitudes 70 degrees to 27 degrees where winds were measured the atmosphere rotates faster than the magnetic field however the rotation rate of the atmosphere decreases toward the equator so that the two probably corotate at about 20 degrees voyager images confirm the extremely low albedo of the ring particles high phase angle images reveal on the order of 10 2 new ringlike features of very low optical depth and relatively high dust abundance interspersed within the main rings as well as a broad diffuse low optical depth ring just inside the main rings system nine of the newly discovered small satellites 40 to 165 kilometers in diameter orbit between the rings and miranda the tenth is within the ring system two of these small objects may gravitationally confine the e ring oberon and umbriel have heavily cratered surfaces resembling the ancient cratered highlands of earth s moon although umbriel is almost completely covered with uniform dark material which perhaps indicates some ongoing process titania and ariel show crater populations different from those on oberon and umbriel these were probably generated by collisions with debris confined to their orbits titania and ariel also show many extensional fault systems ariel shows strong evidence for the presence of extrusive material about halfof miranda s surface is relatively bland old cratered terrain the remainder comprises three large regions of younger terrain each rectangular to ovoid in plan that display complex sets of parallel and intersecting scarps and ridges as well as numerous outcrops of bright and dark materials perhaps suggesting some exotic composition

reconciliation of theories of synthetic aperture radar imagery of ocean waves several theories of synthetic aperture radar sar imagery of ocean waves especially those dealing with the focusing issue are examined we show that the time dependent theories of lyzenga 1988 and of kasilingam and shemdin 1988 and the velocity bunching theory of bruning alpers and shroter 1991 are identical for short integration times but diverge on the focusing issue for long integration times the reason for the divergence is simply that velocity bunching theory assumes that integration times are short compared with ocean wave periods the inference is that the phase speed of the ocean wave plays a secondary nearly negligible role to that of orbital velocity and acceleration in determining the optimum focus setting for short integration times but becomes dominant as integration times are increased for the case of zero focus adjustment these focus dependent theories are shown to reduce to those of plant and keller 1983 and of hasselmann et al 1985 thus several of the apparently differing theories of sar imagery of the ocean are reconciled and shown to be a single consistent theory

extensional tilt blocks on miranda evidence for an upwelling origin of arden corona subparallel ridges and troughs in the outer belt of arden corona on the uranian satellite miranda are interpreted as tilt blocks formed by extension and normal faulting fault scarps generally face outward from the corona exposing dark material in the subsurface reconstruction of faults along a deep rift zone bounding the corona suggests initial dips of 50 local extension reaches 70 extremely high in comparison to previous estimates of strain on icy satellites a rise adjacent to the rift zone is modeled as flexural and indicates an effective elastic lithospheric thickness of 2 km at the time of flexure the assumption that faulting has significantly weakened the lithosphere suggests a mechanical lithosphere thickness of 5 to 10 km corresponding thermal gradients in a frictionally controlled ice lithosphere are 8 to 20 k km 1 and lithospheric tensional strength is 0 4 to 1 8 mpa normal faulting in arden corona indicates that internal upwelling likely formed the corona and the outward facing direction of faults is consistent with such a model an upwelling origin of miranda s coronae eliminates the need to invoke catastrophic breakup and reaccretion of the satellite as an explanation for its surface geology

cryomagmatic mechanisms for the formation of rhadamanthys linea triple band margins and other low albedo features on europa we investigate cryomagmatic mechanisms for the formation of the diffuse low albedo margins of triple bands and haloes associated with elliptical lenticulae on europa one mechanism involves explosive venting of a gas particle spray derived from a subsurface body of volatile bearing water assuming the dark features represent cryoclastic deposits erupted from a medial or central vent modeling the dynamics of the eruptive plumes indicates that eruption velocities of 30 to 250 m s 1 and volatile contents of 0 1 to 20 wt are required to produce deposits having the observed dimensions calculated heights for ballistic plumes range from 1 to 25 km as an alternative mechanism we consider conductive heating of lithospheric ice by a subsurface heat source e g a warm ice diapir or cryomagmatic intrusion which promotes enhanced sublimation of surface ice producing local enrichment of nonice material an analytical model describing a constant temperature infinite heat source places lower bounds on the time scales required to produce a detectable feature a numerical treatment of more realistic geometries and boundary conditions allows cooling of the heat source to be modeled we find that the thermal model satisfactorily explains features with the dimensions of minor lineaments and lenticulae haloes a few kilometers over time intervals of 104 to 105 years the formation of a sublimation lag deposit proceeds rapidly once the ice temperature exceeds a threshold of 130 k however for triple bands measuring up to 25 km in width additional heat sources such as repeated or multiple intrusions are necessary to reproduce the observed dimensions this is consistent with the observation that well developed triple bands typically have multiple medial ridge sets each of which may represent a discrete tabular heat source although neither the volcanic nor intrusive thermal model can be ruled out at this stage the latter is a more satisfactory explanation for some characteristics of the low albedo features analyzed in this study

a three dimensional formulation for synthetic aperture radar images of ocean waves in orbital motions an analytic model of the ocean surface sar images with a three dimensional framework is developed following the formalism presented by swift and wilson 1979 a trochoidal swell propagates through a uniform field of bragg type distributed scatterers two dimensional sar images are calculated for the interpretation and prediction of actual sar images of the ocean surface as a function of ocean wave amplitude wave frequency propagation direction and radar frequency off nadir angle of the antenna and spatial resolutions

comparisons between measured and theoretical results for c and ku bands backscatter from naturally occurring internal wave current patterns predicted and measured values of radar backscatter and of internal wave surface currents are compared using data obtained during the scattmod internal wave experiment radar backscatter and surface truth measurements were obtained during six days in august 1985 and cover nine sets of tide generated internal waves in the georgia strait canada the radar portion of this data consists of approximately 75 sets each of c and ku band fanbeam airborne scatterometer signals each processed to 25 incidence angles and an along track resolution of either 12 5 or 6 25 m aircraft navigation data were also recorded simultaneous surface measurements including wave slope wave height current wind and ship position were obtained from the cfav endeavour current meter were located both fore and aft to allow internal wave phase velocity estimates to be computed

viscosity of rock ice mixtures and applications to the evolution of icy satellites theory and experiments are used to establish lower and upper bounds on the ratio of actual viscosity to pure ice viscosity for a suspension of rock particles in a water ice matrix for typical conditions encountered in icy satellites this ratio is of order ten or possibly larger depending on unknown factors such as the particle size distribution it is shown that even this modest increase in viscosity may be enough to have caused a failure of solid state convective self regulation early in the evolution of a homogeneous rock water ice satellite provided the satellite is large enough and sufficiently silicate rich the criteria for this failure are satisfied by ganymede and are marginal for callisto if the silicates are hydrated failure of self regulation means that the viscosity is too high for the interior to remain completely solid and eliminate the heat production of long lived radioisotopes by solid state convection partial melting of the ice then occurs it is further shown that satellites of this size may then undergo runaway differentiation into a rock core and almost pure ice mantle because the gravitational energy release is sufficient to melt nearly all the ice and the rayleigh taylor instability time scale is short although the high pressure phases of ice melt the resulting water quickly refreezes at a higher level it is conjectured that these results explain the striking surface dissimilarity of ganymede and callisto if these satellites accreted cold and undifferentiated ganymede may have gone supercritical melted and differentiated because of a failure of self regulation whereas callisto remained undifferentiated to the present day like all proposed explanations for the ganymede callisto dichotomy this conjecture cannot be quantified with confidence because of inadequate or incomplete observations theory and experimental data

the use of sar to measure ocean wave dispersion in frazil pancake icefields abstract icefields composed of frazil and pancake ice play important roles in both polar regions in winter during the early to midwinter period pancake ice is a major component of the antarctic sea ice cover while in the arctic the odden ice tongue in the greenland sea associated with deep convection is composed mainly of pancake ice the retrieval of sea ice thickness by remote sensing is in general a very difficult task in this paper the change in dispersion of ocean waves as they penetrate into pancake ice is considered so as to gain insight into its possible relationship with thickness spectral analysis of subscenes from ers 2 second european remote sensing satellite synthetic aperture radar sar images yields the wavelength and direction of the principal spectral component both outside and inside the ice cover there is a decrease of wavelength at the ice edge as well as refraction toward the normal and a loss of amplitude the analysis is complex because the true wave spectrum must be re

mobilization of cryogenic ice in outer solar system satellites voyager images of the uranian satellites show a diversity of geological features including clear evidence for the softening and mobilization of ice on miranda and ariel some of these features are similar to those seen on jovian and saturnian satellites where the mobile material is believed to be water or a water ammonia mixture however the extremely low temperatures and probable unavailability of large energy sources within the uranian satellites lead us to consider flow mechanisms that operate at very low temperature t 100 k we propose here a form of pressure solution creep in which very fine grained water ice or clathrate hydrate is mobilized by a small amount of intergranular cryogenic fluid ch 4 co or n 2 viscosities as low as 10 12 p are possible for a limited time sufficient to allow flooding of rift valleys and perhaps even substantial lateral flows glaciers

impact of pore fluid salinity on the mechanical behavior of unsaturated bentonite sand mixture high salinity of local groundwater and the thermal gradient present within the deep geological repository environment make it necessary to investigate the effect of the pore fluid salinity on the hydro mechanical behavior engineered barriers at different degrees of saturation this study examines the impact of cacl2 salt solution at two concentrations i e 100 and 250 g l on the compressibility and shear strength behavior of the bentonite sand buffer bsb within a range of saturations both as compacted and desiccated bsb specimens were studied desiccated specimens were prepared in a constant suction environment using the vapor equilibrium technique and high pressure cells were used to carry out the triaxial shear experiments experimental results were compared with the available data from the literature for bsb materials prepared with distilled water in order to get a better understanding of the impact of the salinity the comparison shows that the existence of salt in the specimens has notable effect on the total suction levels compressibility and shear strength of the material

theory of synthetic aperture radar ocean imaging a marsen view this paper reviews basic synthetic aperture radar sar theory of ocean wave imaging mechanisms using both known work and recent experimental and theoretical results from the marine remote sensing marsen experiment several viewpoints that have contributed to the field are drawn together in a general analysis of the backscatter statistics of a moving sea surface a common focus for different scattering models is provided by the mean image impulse response function which is shown to be identical to the spatially varying frequency variance spectrum of the local complex reflectivity coefficient from the analysis has emerged a more complete view of the sar imaging phenomenon than has been previously available a new generalized imaging model is proposed

tower ocean wave and radar dependence experiment a synthesis the tower ocean wave and radar dependence experiment toward was conceived to provide an experimental data base to resolve the disparity among the different synthetic aperture radar sar imaging theories of the ocean surface this goal has been achieved through publication of two collections of scientific papers of which the second is part of this issue there is now a framework and consensus on how sar images the ocean surface

a new insight from space into swell propagation and crossing in the global oceans a half century ago it was recorded that ocean swells can propagate up to halfway around the globe however from a global perspective how ocean swells propagate in the global oceans has yet to be depicted to date synthetic aperture radar sar is the only available remote sensing instrument to measure the two dimensional information of ocean surface waves here a 10 year 2002 2012 global wave data set of the spaceborne advanced sar on board the european space agency s satellite envisat and the global wind data set of the windsat were used to 1 depict the propagation routes of ocean swells in the global oceans 2 identify four distinguished crossing swell pools and 3 interpret how these pools are formed together these findings yield a new insight into ocean swells propagation and the consequent occurrence of crossing swells on a global ocean scale from space which will further deepen our understanding of nature of ocean

an experimental investigation of the mechanical behaviour of an unsaturated gneiss residual soil the paper presents compression and triaxial tests conducted under controlled suction in horizons b and c of a residual soil gneissic rock profile from south east brazil horizon b found at the surface consists of a 2 m thick reddish lateritic clayey soil layer whereas horizon c is a saprolitic soil layer that reaches great depths the block samples representing horizons b and c were manually taken from depths of 1 m and 5 m respectively the test programme carried out consisted of isotropic and anisotropic compression tests as well as drained and constant water content triaxial tests tests were performed under saturated and unsaturated conditions at controlled suction strength parameters c and were shown to increase with matric suction the critical state parameters were shown to vary with suction which also expanded the yield curve data obtained may be useful for the development of soil constitutive models for unsaturated soils

the 2003 r m hardy lecture soil parameters for numerical analysis in clay engineers in geotechnical practice work on increasingly complex problems with increasingly powerful numerical tools effective solutions to design problems need good information about the site and parameters or functions that describe how the soil will behave under the proposed loadings these loadings can include heating drying or wetting time effects and chemical changes as well as the more common structural loads this paper outlines issues that need to be considered when laboratory tests are used to produce soil properties for use in numerical analyses the focus is on soft to moderately stiff saturated clays similar considerations for in situ tests stiff clays and sands are not considered key words clay testing characterization properties constitutive modeling

thermohydromechanical modelling of the buffer container experiment abstract in order to investigate how heat affects the performance of a dense bentonite sand buffer material a full scale in situ experiment the buffer container experiment bce was conducted by atomic energy of canada limited aecl in the bce an electric heater simulating the heat output of a disposal container of used fuel was installed vertically in a 1 24 m diameter by 5 m deep borehole surrounded by bentonite sand buffer the borehole was drilled in the floor of a room excavated in canadian shield granite on the 240 level of aecl s underground research laboratory url the thermal hydraulic and mechanical responses were monitored in the bentonite sand buffer and in the surrounding rock power was provided to the heater for approximately 896 days in order to get a better understanding of the coupled thermohydromechanical t h m process in the bce numerical simulations were conducted using code bright to model the evolution of the temperature thermally induced pore water pressure and mechanical response in the bentonite sand buffer and the surrounding rock the thermal response in the experiment was successfully modelled the simulated water seepage from the rock to the borehole was compared with measured results for the bce the thermally induced moisture movement in the buffer was also reasonably well simulated the comparison of the simulated pore water pressure in the rock with the measurement indicates that the influence of temperatures on the hydraulic parameters of rock should be further studied the modelled vertical displacements in the rock are also compared with the measured data in the bce and the analysis of the rock displacement suggested that the in situ thermal expansion coefficient of the rock could be much higher than the coefficient determined in the laboratory

volcanic constructs on ganymede and enceladus topographic evidence from stereo images and photoclinometry paul m schenklunar and planetary institute houston texasjeffrey m moorespace sciences division and the seti institute nasa ames research center moffett field californiaabstract the morphology of volcanic features on ganymede differs significantly from that onthe terrestrial planets few if any major volcanic landforms such as thick flows or shieldvolcanoes have been identified to date using new stereo voyager images we have searchedganymede for relief generating volcanic constructs we observed seven major types of volcanicstructures including several not previously recognized the oldest are broad flat topped domespartially filling many older craters in dark terrain similar domes occur on enceladus togetherwith smooth dark deposits these domes indicate that the volcanic history of the dark terrain iscomplex bright terrain covers vast areas although the style of emplacement remains unclear smooth bright materials embay and flood older terrains and may have been emplaced as low viscosity fluids associated with smooth bright material are a number of scalloped shaped semi enclosed scarps that cut into preexisting terrain in planform these structures resemble terrestrialcalderas the youngest volcanic materials identified are a series of small flows that may haveflooded the floor of the multiring impact structure gilgamesh forming a broad dome theidentification of volcanic constructs up to 1 km thick is the first evidence for extrusion ofmoderate to high viscosity material on ganymede viscosity and yield strength estimates for thesematerials span several orders of magnitude indicating that volcanic materials on ganymede have arange of compositions and or were extruded under a wide range of conditions and or eruptive styles introductionthe voyager survey of the outer solar system has revealedan astonishing variety of endogenic landforms on the surfacesof icy satellites despite extensive endogenic resurfacing ofsomc satellites for example ganymede enceladus andtriton volcanism on these surfaces has little topographicexpression we do not see massive volcanic edifices similarto olympus mons or mauna kea even the best putativeexamples of volcanic landforms seen on ariel miranda triton and enceladus exhibit rarely more than 1 2 km ofrelief jankowski and squyres 1988 pozio and kargel 1989 schenk 1991a croft et al 1995 this may berelated to the soft theology of ice see poirier 1982 durham et al 1983 and kirby et al 1987 or torheology and volcanic styles peculiar to icy petrologicsystems e g kargel 1991 kargel et al 1991 well over half of the surface of ganymede radius 2634 kin has been covered by endogenic effusions it is now consideredlikely that ganymede experienced one or more episodes ofchaotic orbital behavior malhotra 1991 possiblyresulting in tidal heating volcanic resurfacing constitutes arecord of ganymede s compositional and thermal evolution andmay record some of these putative tidal heating events yetthis satellite has been the subject of morphological study for15 years without the unambiguous detection of relief copyright 1995 by the american geophysical union paper number 95je01854 0148 0227 95 95je 01854505 00generating volcanic constructions on its landscape the styleof emplacement and composition of those volcanic depositsthat have been identified remains unclear on any planetary surface volcanic and other nonimpactconstructs can be difficult to recognize in spacecraft images particularly those obtained under high sun conditions e g malin 1978 topography is especially low on the galileansatellites and imaging resolution is at best 500 m pixel major local albedo variations on ganymede further complicategeologic and topographic mapping with these problems inmind we have undertaken the production of stereo pairs ofvoyager images where coverage permits to aid in the searchfor and characterization of volcanic landforms on ganymede ssurface in addition to an examination of previously identifiedvolcanic materials we report the discovery of severalpreviously unrecognized volcanic landforms and at least twotypes with substantial relief and describe their morphologyand geologic setting morphology of volcanic depositsindicates that ganymede extrusions probably had a range oftheologies and may be compositionally variable we concludewith speculations and predictions regarding their mode ofemplacement and the implications of volcanic landforms forthe geologic evolution of ganymede stereo imaging with voyagerthis study was motivated by the recognition that asignificant fraction of the surfaces of most of the outer planetsatellites were imaged by voyager in stereo e g croft andsoderblom 1991 schenk and moore 1993 we can usestereo imaging to detect subtle topographic features that were19 009

an exact analytic representation of a regular or interferometric sar image of ocean swell the problem of obtaining quantitative data on spatial ocean wave spectra from the images of the ocean surface by either regular sar or along track interferometric sar insar is studied the dominant mechanism which allows imaging of ocean waves by sar insar is the so called velocity bunching this mechanism is essentially nonlinear the theoretical analysis of sar insar imagery of the ocean surface due to velocity bunching is performed and nonlinear solutions of the sar insar images of monochromatic waves and of the spectra of these images are obtained analytic expressions are presented which allow for the accurate simulation both sar and insar images of waves with arbitrary lengths heights and propagation directions it is demonstrated that a monochromatic wave expands in the sar insar images into an infinite number of harmonics in addition to the nonlinearity parameters of sar which is related to the velocity bunching mechanism it is shown that for complex insar the degree of nonlinearity depends also on separation time between the two antennas the results of the present study indicate that in addition to the prevailing practice to consider the phase component of the insar image an analysis of the imaginary part of the complex insar map of the ocean surface may provide some supplementary information beneficial in particular for rough sea

elastic plastic modelling of unsaturated soil using results from a new triaxial test with controlled suction this paper examines the constitutive behaviour of a compacted highly plastic sand clay mixture three series of tests evaluated components of a possible elastic plastic constitutive model for unsaturated stress strain behaviour the tests examined the influence of suction on yield stress under external isotropic loading and the influence of suction on shear strength the results examine the behaviour of highly plastic clay subjected to generalised triaxial stresses that include shear isotropic and suction loading the data represent an important new resource of information on a densely compacted strongly expansive sand bentonite mixture that was loaded independently by external stresses and internal suctions the suctions were also measured by sensors buried in the specimens they have been interpreted in an elastic plastic framework to produce values for some of the material properties needed for the model the results and associated discussion provide new insights into the behaviour of unsaturated

large and small scale spatial evolution of digitally processed ocean wave spectra from seasat synthetic aperture radar precision digitally processed and corrected synthetic aperture radar sar image spectra along a large portion of seasat orbit 1339 september 28 1978 have revealed a number of unique potentials but also some substantial limitations of spaceborne sar for global ocean wave monitoring sar appears to be capable of monitoring the spatially evolving ocean wave number spectrum with high statistical reliability the large scale few hundred kilometer spatial evolution of the spectrum is generally consistent with the location in time and space of wave generating sources even when multiple wave systems are present on a more local scale of just a few tens of kilometers the nearshore wave number spectrum responds to local depth changes but is too noisy to respond reliably to local current changes the seasat sar was severely restricted in its ability to sense azimuthtraveling along track waves in high sea states azimuth waves corresponding to ocean wavelengths shorter than about 200 m were either undetected or severely attenuated in the higher sea states hs 2 m azimuth waves shorter than 100 m are not detectable in even the lowest sea states moreover there is a tendency for attenuated wave systems to be shifted toward the range direction this effect will significantly impede studies of spatial evolution of seasat sar spectra without some additional correction strategy

mapping surface currents and waves with interferometric synthetic aperture radar in coastal waters observations of wave breaking in swell dominant conditions airborne and spaceborne interferometric synthetic aperture radars insars produce surface velocity measurements at very high spatial resolutions over a large area the data allow construction of the velocity strain field for highlighting ocean surface processes such as wave breaking and rip currents also coherence between signals from two interferometric channels is a descriptor of the correlation condition of the surface roughness that scatters back the radar signals and it is an indication of the ocean surface turbulence wave breaking is a major turbulence source causing surface roughness decorrelation thus the coherence parameter serves as an independent means for detecting wave breaking the results of breaking detection using roughness decorrelation and critical local acceleration are comparable in this paper the breaking fraction in swell dominant mixed seas along a cross shore transect is compared with several steepness parameters characterizing different length scales of surface waves the highest correlation coefficient from 0 90 to 0 99 is between the breaking fraction and windsea mean square slope contributed primarily by short waves this result reinforces the previous field observations showing that the length scales of breaking waves are much shorter than the energetic components near the spectral peak although dominant waves and the associated wave group modulation are important in triggering the breaking process the large spatial coverage of airborne or spaceborne operation further offers the opportunity to investigate evolution of the surface wave spectrum in high spatial subkilometer resolution this capability is very useful for monitoring the coastal wave and current environment

use of numerical simulations to assess hydraulic and mechanical measurements of bentonite sand buffer in an in floor borehole abstract as part of the process of developing concepts for isolation of used nuclear fuel in a deep geological environment a large in ground experiment the isothermal test itt was conducted at atomic energy of canada limited s underground research laboratory this installation was designed and constructed to examine how a large mass of dense unsaturated bentonite sand buffer would take on water from the surrounding rock the itt was installed in a 1 24 m diameter by 5 m deep emplacement borehole drilled in the granite 240 m below the ground surface the lowermost 2 m of this borehole was filled with an in situ compacted bentonite sand buffer material this buffer material was capped by a 1 25 m thick plug of high performance concrete and the installation was left undisturbed for 6 5 years during this time the pore pressures total pressures water uptake and temperature in the buffer and the surrounding rock were continuously monitored numerical simulations were conducted using code bright to model the evolution of the pore pressure in the buffer and the surrounding rock as well as mechanical response of the buffer the simulated water seepage from the rock to the emplacement borehole was compared with measured results the simulated pore water pressure in the rock the pore water suction in the buffer and the earth pressure in the buffer were compared with data measured during the test and inferred from end of test water saturation measurements graphs of the simulated displacements in the buffer are presented

a simulation for spaceborne sar imagery of a distributed moving scene a computer simulation that is designed to represent aspects of spaceborn synthetic aperture radar sar imagery of the ocean surface is presented the simulation is unique in that a scatterer density per resolution cell is explicitly included thus allowing the incorporation of various scattering natures from purely specular to purely diffuse the simulation may be applied to ocean surface wave imaging since velocity bunching and scene coherence times are also included certain assumptions inherent in the velocity bunching formulation limit the applicability of the simulation in its present form to spaceborn sar systems only two experiments based on this simulation are considered 1 the effect of varying the target density and 2 the effect of the mean scene coherence time in the imaging of a ocean swell system

a semiparametric algorithm to retrieve ocean wave spectra from synthetic aperture radar a new wave retrieval method for the ers synthetic aperture radar sar wave mode is presented the new algorithm named semiparametric retrieval algorithm spra uses the full nonlinear mapping relations as proposed by hasselmann and hasselmann 1991 it differs from previous retrieval algorithms in that it does not require a priori information on the sea state instead it combines the observed sar spectrum with the collocated wind vector from the ers scatterometer to make an estimate of the wind sea spectrum the residual signal in the sar spectrum is interpreted as swell the method has been validated by collocating over 5 years of sar wave mode observations with spectral buoy measurements at 11 locations on the open ocean for wave components longer than 225 m the standard deviation between the retrieved spectra and buoy observations is 0 41 m which corresponds to a relative rms error of 29 about 10 of the observed sar spectra were rejected in particular in light wind conditions when nonwave features such as those caused by slicks dominated the imagette the bias and scatter in the results obtained under light wind conditions could be reduced by introducing a wind dependent tilt modulation this wind dependent tilt formulation is derived from the empirical cmod4 relation between the wind vector the incidence angle and the radar backscatter for the ers scatterometer