tidally modulated occurrence of megaripples in a saturated surf zone 1 an abstracted model for saturated surf zone megaripple occurrence based on the hypothesis that megaripples form and persist unless flow conditions change too rapidly or the bed passes through the swash zone correctly predicts the bed state presence or absence of megaripples for 73 of measurements over 1 year at scripps beach more than seven standard deviations above the agreement between a random model and the measurements transitions between bed states are predicted within 1 5 hours for 54 of measurements compared with 6 agreement for a random model the model is forced with a record of water depth over the beach h from offshore tide measurements and inferred changes in bed elevation assuming that changes in flow conditions and depth are determined by tide level alone in a saturated surf zone model parameter values are estimated independent of model results megaripple formation time t 2 5 hours maximum rms depth change over time t hrms 0 1 m and minimum depth averaged over time t below which megaripples are smoothed hsw 0 3 m allowing model parameters to vary increases agreement between measurements and model predictions to a maximum 82 for parameter values t 3 hours hrms 0 05 m and hsw 0 1 m neither bed state nor bed state transitions are correlated with offshore wave conditions

tandem x pol insar performance for forest height estimation tandem x and terrasar x platforms form together the first spaceborne single pass polarimetric interferometer in space this allows for the first time the acquisition of spaceborne polarimetric synthetic aperture radar interferometry pol insar data without the disturbing effect of temporal decorrelation this paper aims to assess the potential of such data for forest applications for this single and dual pol data acquired over a boreal a temperate and a tropical site were investigated to characterize x band penetration and polarization diversity of the interferometric coherence measurements pol insar forest height inversion schemes have been proposed and implemented for the single and dual pol cases and cross validated against lidar reference measurements for all sites the single pol inversion relies on an external ground digital terrain model dtm and performed well for all sites with correlation coefficients r 2 between 0 80 and 0 98 the dual pol inversion does not require an external dtm but depends on the visibility of the whole forest layer accordingly its performance varied with forest structure and season the best performance was achieved for the summer acquisition of the boreal test site r 2 0 86 and for the winter acquisition of the temperate test site r 2 0 77 for the tropical test site only a weak correlation r 2 sim 0 50 could be established

spaceborne tomography of multi species indian tropical forests abstract synthetic aperture radar sar backscatter is the coherent combination of the scattering from multiple individual scatterers within the radar resolution cell which results into a 2 d radar image tomographic sar tomosar takes advantage of multiple sar acquisitions to provide 3 d vertical structure of the imaged target over forests parameters such as canopy structure canopy density leaf area and phenology contribute to different sar scattering mechanisms along the vertical dimension of the trees tomography has been demonstrated in various earlier works for forest bio physical parameter estimation using airborne data in this research work multi polarimetric space borne tandem x tomograms are examined for the first time over a multi species indian tropical forest multiple tandem x acquisitions are focused using capon beamforming at five polarimetric channels hh hv vv hh vv and hh vv four distinct forest species compartments are selected representing different canopy structure and density the tomograms obtained in different polarizations for these species are analyzed in detail to understand the scattering patterns across different forest species field surveys carried out in several forest locations provide in situ observations of forest height and vertical structure it was observed that canopy gaps and leaf density play a crucial role for x band sar signal penetration through ground for dense canopy species the backscatter contributions are spread through the canopy while in case of sparse canopy species the ground scattering is dominant vertical profiles obtained at surveyed plot locations are plotted in all polarizations and provide a good agreement with field observations further the obtained tomosar backscatter layers have a good correlation with field measured above ground biomass agb the agb is modeled from tomosar with the hh pol tomosar backscatter layer at 27 m canopy height leading to an agb estimation with correlation r 0 76 and rmse of 50 4 t ha

single and multipolarimetric sar tomography of forested areas a parametric approach in this paper a technique is described for the tomographic characterization of forested areas through multiple synthetic aperture radar sar observations based on either single or multipolarimetric acquisitions this technique is based on the idea of characterizing the fourier spectrum of the multibaseline data as being constituted by two effective scattering centers displaced along the vertical direction plus the associated decorrelation terms as a result sar tomography will be formulated as the problem of detecting the number of scattering centers within the resolution cell estimating the parameters that describe their spatial structure and evaluating the associated backscattered powers parameter estimation is carried out through the covariance matching estimation technique which provides an asymptotically optimal solution the results of an experiment performed on a real p band multibaseline fully polarimetric data set relative to the forested site of remningstorp sweden are reported

the topology of evolving rift fault networks single phase vs multi phase rifts rift fault networks can be complex particularly those developed by multiple periods of non coaxial extension comprising non colinear faults with many interactions thus topology rather than simple geometry is required to characterise such networks as it provides a way to describe the arrangement of individual faults in the network topology is analysed here in terms of nodes isolated i nodes or connected y or x nodes and branches i i i c c c branches in map view the relative proportions of these parameters vary in natural single and multi phase rift fault networks and in scaled physical models at different stages of development and strain interactions in single phase rifting are limited to fault splays and along strike fault linkage i node and i i or i c branch dominated networks whereas in multi phase rifting the topology evolves towards y node and c c branch dominated networks with the degree of connectivity increasing with greater strain the changes in topology and network connectivity have significant implications for fluid flow and reservoir compartmentalisation studies furthermore topology helps to distinguish single and multiple phase extension i e tectonic histories and thus provide constraints on the geodynamic context of sedimentary basins

forest height estimation by means of pol insar data inversion the role of the vertical wavenumber this paper examines the multifaceted effect of the effective spatial baseline as expressed through the vertical interferometric wavenumber on the inversion of forest height from polarimetric interferometric synthetic aperture radar pol insar data first the role of the vertical wavenumber in relating forest height to the interferometric volume coherence is introduced through the review of the forest height inversion from pol insar data the effect of the vertical wavenumber on the inversion performance is evaluated the selection of optimum with respect to forest height inversion performance vertical wavenumbers is discussed the impact of the acquisition geometry and terrain slopes on the vertical wavenumber and their consideration in the inversion methodology is addressed the individual effects discussed are demonstrated by means of airborne repeat pass pol insar acquisitions in l and p band acquired over different forest conditions including a boreal a temperate and a tropical forest test site the achieved forest height inversion performance is validated against reference height data derived from airborne lidar acquisitions

inclusion of topological measurements into analytic estimates of effective permeability in fractured media we demonstrate how topology based measures of connectivity can be used to improve analytical estimates of effective permeability in 2 d fracture networks which is one of the key parameters necessary for fluid flow simulations at the reservoir scale existing methods in this field usually compute fracture connectivity using the average fracture length this approach is valid for ideally shaped randomly distributed fractures but is not immediately applicable to natural fracture networks in particular natural networks tend to be more connected than randomly positioned fractures of comparable lengths since natural fractures often terminate in each other the proposed topological connectivity measure is based on the number of intersections and fracture terminations per sampling area which for statistically stationary networks can be obtained directly from limited outcrop exposures to evaluate the method numerical permeability upscaling was performed on a large number of synthetic and natural fracture networks with varying topology and geometry the proposed method was seen to provide much more reliable permeability estimates than the length based approach across a wide range of fracture patterns we summarize our results in a single explicit formula for the effective permeability

scaling and connectivity of joint systems in sandstones from western norway abstract the scaling properties of a joint system in devonian sandstones in western norway have been investigated using seven maps covering areas from 18 to 720 m across which were generated by mapping in the field and from low level aerial photography taken from different heights each map represent a scale window on the fracture population bounded by resolution at small scales and the sample size at large scales a power law relationship between fracture trace length and critical observation height maximum height at which a trace can be identified is derived and used to create a statistical model for the resolution effects the model indicates that a continuous smooth curve without a straight line segment on a log log cumulative frequency distribution plot does not necessarily rule out a power law as the underlying population distribution together the maps indicate a powerlaw trace length distribution with an exponent of 2 1 this power law may be valid over four or more orders of magnitude with natural lower cut off of around 1 m the exponent is significantly different from 2 0 strictly selfsimilar case and is reflected in a decrease in the abundance of fractures with length comparable to map size as map scale decreases the fracture trace length distribution results in a decrease in apparent connectivity with decreasing scale high resolution large scale maps are well connected while the lowest resolution map smallest scale is unconnected fractures in the smallest scale map are however connected by small fractures below the limit of resolution represented by the largest scale map the variation in apparent connectivity with scale has implications for fluid flow when fractures are open to fluid flow the scaling properties of apparent connectivity imply that beyond a certain scale the size of fracture controlling flow will be scale independent in this fracture system this appears to occur in sample areas of around 300 m across

geometry and topology of tectonolineaments in the gorce mts outer carpathians in poland abstract the present study was focused on analysis of the geometrical and topological features of the lineament network in the gorce mountains polish outer carpathians the source data was a 1m high resolution lidar digital elevation model dem network topology was analysed using the networkgt toolset for arcgis software the topological analysis represented the first attempt to apply research of this type in the polish carpathians five lithostratigraphic units occurring in the research area characteristic of the krynica zone of the magura nappe were selected for analysis topology was studied for each of the units separately as well as for the whole area it was found that the units were differentiated in terms of some topological parameters such as 2d intensity moreover latitudinal trends were observed due to the presence of wide fault zones the geometry of the network is consistent with the general carpathian overview sets of conjugate strike slip faults with splaying ends were identified in the southern part of the area the strike of the oldest faults was e w this shows that on the scale of the observation hundreds to thousands of metres the network was a product of general thrusting processes rather than derivative of a local structural plan the applicability of both topological analyses and high resolution dem as supplementary to classical methods in a study of the outer carpathians was confirmed with analysis conducted despite the identification of some limitations such as gis operator related bias the scale of the analyses is linked in a multi scale approach to structural network analyses

a unified model for subaqueous bed form dynamics 1 bed form evolution remains dynamic even in the special case of steady uniform flow data from the sandy braided north loup river nebraska show that roughness features on the channel bottom display a statistical steady state and robust scaling that are maintained through the collective interactions of transient short lived bed forms motivated by such field data and laboratory observations of bed form growth we develop a nonlinear stochastic surface evolution model for the topography of bed load dominated sandy rivers in which instantaneous sediment flux explicitly depends on local elevation and slope this model quantitatively reproduces laboratory observations of initial growth and saturation of bed forms from a flat surface and also generates long term dynamical behavior characteristic of natural systems we argue that the variability in geometry and kinematics of bed forms in steady flow and the existence of roughness at all wavelengths up to the largest dunes are a consequence of the nonlinear relationship between sediment flux and topography subject to noise

analyzing tomographic sar data of a forest with respect to frequency polarization and focusing technique forest canopies are semitransparent to microwaves at both l and p bands thus a number of scattering sources and different types of scattering mechanisms may contribute to a single range cell of a synthetic aperture radar sar image by appropriately combining the sar data of multiple parallel flight paths a large 2 d aperture is synthesized which allows for tomographic imaging of the 3 d structure of such semitransparent media and the underlying ground a separate paper deals with the actual tomographic imaging part that leads to the 3 d data cube in particular three focusing techniques are described and analyzed multilook beamforming robust capon beamforming and multiple signal classification beamforming in this paper the resulting data products obtained by tomographically focusing two airborne multibaseline sar data sets of a partially forested area one at l band and another at p band are subject to a detailed analysis with respect to the location and the type of backscattering sources in particular the following aspects are investigated 1 the forest structure as obtained from the vertical profiles of intensities at sample plot locations within the forest is compared to the height distribution of the top of the forest canopy as derived from airborne laser scanning data and profiles are presented for all polarimetric channels and focusing techniques as well as at both frequencies 2 the type and location of scattering mechanisms are analyzed as functions of height for the two frequencies namely l and p bands and using the polarimetric channels as well as the pauli and cloudepottier decompositions thereof and 3 the accuracy of the ground elevation estimation obtained from the different focusing techniques and the two frequencies is assessed with the help of a lidar derived digital elevation model

a note on megaripples in the surf zone evidence for their relation to steady flow dunes megaripples in the combined flow environment of the nearshore are proposed to behave like dunes or large ripples in rivers tidal estuaries and deserts their profile basically is symmetric and thus significantly different from the traditional asymmetric triangular features observed in steady flows similarly their planform often exhibits little directionality unlike crescentic or lunate steady flow dunes that point in the downstream direction these characteristics are the result of complex combined flows in the nearshore including oscillatory flows wave skewness and steady currents undertow rips and alongshore flows recent observations of megaripples in the nearshore suggest that they occur frequently however they are rarely considered in studies of flow resistance or sediment transport in addition megaripples are thought to be the source of hummocky cross stratification in sedimentary sequences and are generally attributed to storm waves on inner continental shelves however observations show that they also exist inside the surf zone and under lower energy conditions a better understanding of their dynamics and thus their occurrence and characteristics would improve the understanding of nearshore wave and circulation dynamics sediment transport large scale morphodynamics and the resulting sedimentary sequences it is hypothesized that megaripples in the nearshore are dynamically similar to steady flow features which are observed in rivers estuaries and deserts and have been studied in much more detail

a temporal decorrelation model for polarimetric radar interferometers this paper describes a physical model of the temporal changes that occur in vegetated land surfaces observed by a repeat pass radar interferometer we assume the temporal changes to be caused by a gaussian statistic motion of the vegetation elements with motion variance changing along the vertical direction we show that the temporal correlation between two interferometric radar signals is affected by the structural parameters of the vegetation such as canopy height and varies with the wave polarization we validate the model using l band data acquired by the jet propulsion laboratory with the uninhabited aerial vehicle synthetic aperture radar airborne radar this work provides new insights into the role of temporal decorrelation in interferometric radar applications

naturally occurring scour pits in nearshore sands 1 depressions 10 50 cm in diameter and o 10 cm deep were observed in rotary acoustic imagery of the seafloor during sandyduck97 the rotary sonar record spans a 77 day period and 13 storm events the depressions occurred during both the wave growth and the wave decay phases of each storm and over a relatively narrow range of wave energies urms 0 32 cm s 0 05 cm s standard deviation and grain roughness shields parameters 0 7 0 2 the observations are mainly from the outer surf zone in 3 m mean water depth at two stations separated by 40 m cross shore distance depressions were 6 5 times more frequent at the inner station n 485 than at the outer n 75 areal densities were small o 0 1 m 2 depressions were also observed in the inner surf zone at a third station for which the data record is less complete the probability distribution of the locations of depression first occurrences is nonrandom i e non poisson due to 50 reoccurrence in roughly the same positions from storm to storm the geometry and temporal development of the depressions are similar to scour pits formed by cylindrical piles and other objects on the basis of these similarities and the clustering of first occurrence locations we conclude that the likely origin of the depressions is scour about compact semimobile obstacles on or embedded within the sandy seafloor possible candidate obstacles include pebbles large shells or large shell fragments and the chimney structures left by burrowing organisms importantly 13 of the pits evolved into meter scale lunate megaripples indicating that these features can act as megaripple precursors

rotary sidescan images of nearshore bedform evolution during a storm abstract high resolution acoustic images are presented of bedform development on the crest of a nearshore bar during a storm the images were obtained using a 2 25 mhz rotating sidescan sonar the sonar system provides a continuous record of the evolution of the bedform field through time within a 10 m diameter field of view the images document the occurrence of ripples cross ripples and megaripples during the waning stages of the storm transitions among ripple types occurred on time scales of 1 3 h beginning with flat bed and culminating in highly 3 d short crested ripples

three dimensional multipass sar focusing experiments with long term spaceborne data synthetic aperture radar sar interferometry is a modern efficient technique that allows reconstructing the height profile of the observed scene however apart for the presence of critical nonlinear inversion steps particularly crucial in abrupt topography scenarios it does not allow one to separate different scattering mechanisms in the elevation height direction within the ground pixel overlay of scattering at different elevations in the same azimuth range resolution cell can be due either to the penetration of the radiation below the surface or to perspective ambiguities caused by the side looking geometry multibaseline three dimensional 3 d sar focusing allows overcoming such a limitation and has thus raised great interest in the recent research first results with real data have been only obtained in the laboratory and with airborne systems or with limited time span and spatial coverage spaceborne data this work presents a novel approach for the tomographic processing of european remote sensing satellite ers real data for extended scenes and long time span besides facing problems common to the airborne case such as the nonuniformly spaced passes this processing requires tackling additional difficulties specific to the spaceborne case in particular a space varying phase calibration of the data due to atmospheric variations and possible scene deformations occurring for years long temporal spans first results are presented that confirm the capability of ers multipass tomography to resolve multiple targets within the same azimuth range cell and to map the 3 d scattering properties of the illuminated scene

observations and predictions of fluid velocities in the surf and swash zones 1 surfzone and swashzone water level fluctuations and cross shore fluid velocities observed at seven cross shore locations for 139 51 min periods on a low sloped fine grained sandy beach are shown to be modeled well by the depth averaged nonlinear shallow water equations the model initialized with observations about 150 m from the shoreline in 300 cm water depth accurately predicts the observed decrease in sea swell wave heights and orbital velocities with decreasing water depth across the surf zone and the observed maxima in infragravity orbital velocities and offshore directed mean flows near the outer edge of the swash zone in the surf zone both the observed and predicted velocity fluctuations are dominated by sawtoothed shaped pitched forward asymmetrical sea swell waves in the swash zone infragravity waves contribute substantially to the total velocity variance and asymmetry shoreward of the outer swash zone observed and predicted total and infragravity velocity asymmetry decrease onshore changing sign from positive to negative in the upper swash

the connectivity of two dimensional networks of spatially correlated fractures 1 continuum percolation thresholds for fracture systems are based on models with random fracture locations resulting in uniformly clustered systems in which all connections are fracture intersections fractures in natural systems can be either clustered or anticlustered and a significant portion of the connectivity is achieved through fracture abutments or splays analytical and numerical methods are combined to define critical properties of isotropic networks of constant length lines as a function of fracture clustering and of the ratio of abutments to intersections a second suite of numerical results indicates that the influence of these parameters varies as a function of the fracture length distribution a preliminary predictor of critical density of anisotropic nonrandom systems with lognormal length distributions is derived and applied to a suite of natural fracture systems predicted connectivities are closer to the observed connectivities when the predictor is used than when connectivity is estimated from the random threshold

observations of megaripples in the surf zone abstract bedform measurements were obtained under shoaling and breaking wave conditions using a pencil beam sonar in the intertidal zone at skallingen denmark measurements were made during four individual tidal cycles starting from flat bed conditions at low tide and as the tide rose and the instruments entered the surf zone megaripples appeared when the mobility number exceeded 240 which equates to the classic flat bed criterion proposed by dingler and inman 1976 the megaripples were oriented cross shore and their wavelength scaled with the wave orbital diameter wave ripples were observed when the mobility number was smaller which occurred mainly under shoaling waves since all bedforms were erased as the seabed became dry at low tide and perpendicular longshore currents were occasionally strong the megaripples were of small amplitude but their dimensions were consistent with predictions from the literature their migratory behaviour in the first few hours of existence appeared more strongly related to self organisation rather than to ambient hydrodynamics a clear gap in bedform spacing at 120 cm was identified between wave ripples and megaripples

sand bed roughness in the nearshore 1 measurements made using sonar altimeters mounted on an amphibious surveying vehicle are analyzed for root mean square rms bedform roughness observations for 22 days over a 500 m 700 m area are used to quantify the cross shore distribution of roughness and its variability large bedforms with amplitudes 5 50 cm occur frequently in shallow water 2 m water depth however the patchiness of these bedforms is also largest in shallow water this is likely owing to the spatial and temporal variability of the waves and currents of the sediment grain size distributions and of the large scale nearshore morphology large bedforms were observed to exist only for mobility numbers 150 above this threshold the rms roughness was 2 cm and the bed was interpreted to have transitioned to sheet flow conditions however the state of the bed e g large ripples small ripples flat bed was not predictable for mobility numbers between about 30 and 150 existing models for orbital ripples do not predict the observed large bedforms and have little predictive skill for these data

tidal induced large scale regular bed form patterns in a three dimensional shallow water model the three dimensional model presented in this paper is used to study how tidal currents form wave like bottom patterns inclusion of vertical flow structure turns out to be necessary to describe the formation or absence of all known large scale regular bottom features the tide and topography are treated as a coupled system and the potential free instabilities in this system are investigated a linear stability analysis is used to study the dynamics of bed forms this yields information on the role of physical mechanisms such information cannot be obtained by direct numerical nonlinear simulation the basic state represents a horizontal elliptical flow veering in vertical direction over a flat bottom it is shown that in such a system modes can grow which have characteristics of both tidal sand banks and sand waves the model predictions are compared with observations and show good agreement

bar trough generation on a natural beach mechanisms for bar trough generation are examined using velocities measured in the field applied to the bowen 1980 bailard 1981 energetics based sediment transport model measurements consist of a cross shore array of nine electromagnetic current meters spanning the surf zone and daily bathymetric surveys during a 10 day period during which two storms occurred when the bathymetry evolved from a three dimensional terrace to a well developed linear bar the model predicts bed and suspended load transport separately based on various velocity moments the velocities are partitioned into mean currents low frequency infragravity and shear instabilities 0 05 hz to determine the relative importance of various mechanisms to the total transport velocity moments are computed over 90 min intervals to resolve tidal fluctuations tidal signatures were apparent in all modes of transport predicted transport rates are integrated and compared with daily cross shore bathymetric profiles averaged over a 400 m length of beach the suspended load terms were an order of magnitude greater than bed load terms owing to the low fall velocity of the fine grain sand within the surf zone model results for this experiment indicate the dominant mechanism for bar development was sediments mobilized by the strong longshore current and incident short waves within the surf zone and transported offshore by the mean undertow and shoreward transport onshore due to short wave velocity skewness using standard coefficients the model correctly predicted the first order movement of the bar during storms but underpredicted trough development and did not always perform well during mild wave conditions

modeling of vortex ripple morphodynamics 1 a new morphology module has been developed in order to perform simulations of the bed form evolution under hydrodynamic forcing this module has been implemented into the numerical model dune2d which solves the reynolds averaged navier stokes rans equations in the boundary layer and resolves sediment transport over moving sand beds the morphology module is composed of a modified central scheme and a routine that simulates avalanches and has been successfully applied to the study of orbital ripples evolution ripple growth from a quasiflat bed have been simulated and the growth behavior has been compared to previous experimental measurements the simulated ripples reach an equilibrium state where energy damping processes avalanches compensate energy production processes flux of sediment these processes have been analyzed during ripple creation growth merging and annihilation furthermore sandy bed evolutions have been simulated with random initial bed forms in order to examine the influence of the bed history on the final solution and the wave energy dissipated during these evolutions

relaxation time effects of wave ripples on tidal beaches 1 seabed roughness due to wave ripples is a key factor in controlling sediment transport processes in the nearshore zone roughness is commonly considered a function of the ripple geometry which in turn can be predicted from sediment and hydrodynamic parameters existing ripple predictors consider the bed morphology to be in equilibrium with the hydrodynamics whereas recent laboratory measurements show that the time scale for ripple development is of the order of tens of minutes to hours here we show that wave ripples on tidal beaches are significantly affected by relaxation time effects with ripple height and length progressively increasing during the rising tide and remaining constant during the falling tide moreover we examine the ripples in the context of existing empirical models and suggest how the temporal evolution over a tidal cycle may be predicted

the drag coefficient bottom roughness and wave breaking in the nearshore the bottom drag coefficient in the nearshore has been suggested to depend on bottom roughness bedforms or alternatively on wave breaking the hypothesis that bottom drag coefficient depends on bottom roughness is tested with 2 months of field observations collected on a sandy ocean beach during the duck94 field experiment both the drag coefficient estimated from alongshore momentum balances and bottom roughness estimated from fixed altimeters are larger within the surfzone than in the region farther seaward although the drag coefficient increases with roughness seaward of the surfzone no relationship was found between the drag coefficient and roughness related quantities within the surfzone these results suggest that breaking wave generated turbulence increases the surfzone drag coefficient

phenomenology of ground scattering in a tropical forest through polarimetric synthetic aperture radar tomography this paper aims at characterizing the scattering mechanisms occurring at the ground level in a tropical forest illuminated by a p band synthetic aperture radar sar the analysis is carried out based on the multibaseline fully polarimetric data set collected by onera over paracou french guyana in the frame of the european space agency campaign tropisar the favorable baseline distribution of this data set results in the possibility of removing most contributions from the vegetation layer by tomographic techniques thus allowing the generation of a new fully polarimetric single look complex sar image relative to scattering contributions from the ground level only such a ground layer image is then analyzed by considering the variation of its polarimetric signature with respect to terrain local slope and radar look angle two major conclusions are drawn 1 double bounce scattering from trunk ground interactions is observed to be the dominant scattering mechanism at the ground level on flat terrains whereas it rapidly tends to vanish as the topographic slope increases and 2 the characteristic parameter that rules trunk ground scattering is not the tree height but rather the available free path facing the tree as a result of the presence of nearby trees undulating topography or understory preventing double bounce scattering from taking place whenever the ground bounce occurs too far away from the considered tree the mean free path length resulting from the analysis of this data set is found to be l 7 m finally we discuss how the concept of free path length can be accounted for in simple terms by assuming an equivalent extinction model characterized by a variation along the horizontal dimension

three dimensional geometry and growth of conjugate normal faults abstract good quality 2 d and 3 d seismic reflection data from the timor sea are used to determine the threedimensional geometry displacement patterns and development of intersecting conjugate normal faults these data are supplemented by data from previous physical modelling studies conjugate structures which comprise two intersecting opposed dipping normal faults or fault sets form synchronously on a geological time scale and develop due to the incidental intersection of the faults factors which affect both the formation and imaging of these structures include the fault density the spatial distribution of opposed dipping faults the seismic resolution and the vertical extent of the imaged fault data large conjugate structures grow from smaller ones larger conjugates are associated with more numerous and larger faults than small structures on the scale of the seismic data fault throws range from ca 10 400 m synchronous fault movements are accommodated by a reduction of displacements on discrete fault surfaces towards the fault intersection zone and a corresponding increase in ductile strain of this region high strains in the volume proximal to the fault intersection zone are expressed as thinning of stratigraphic units between the conjugate faults and are believed to be accommodated by numerous small sub seismic faults intersection of two opposed dipping faults does not prevent their continued synchronous movement and does not result in mechanical locking of the system

measurement and characterisation of spatial distributions of fractures abstract a variety of line sample 1 d and map 2 d datasets of faults and joints has been used to investigate the spatial distributions of fractures and to test techniques of fractal analysis the natural fracture datasets have been supplemented by synthetic datasets with known characteristics the fault datasets investigated range in scale from regional to outcrop and the joint datasets are derived from outcrop 1 d datasets were analysed by the spacing population interval counting and fracture number interval counting techniques 2 d datasets were analysed by box counting and fracture number box counting techniques results indicate that fracture spacing can be characterised in line samples using either the 1 d interval counting technique or more simply by measuring the spacing population as the cumulative frequency distribution of spaces between adjacent fractures tectonic faults frequently show a power law spacing population indicating fractal dimensions of between 0 4 and 1 0 but except for outcrop data truncation effects degrade the analysis unrefined joint datasets commonly show negative exponential or lognormal spacing cumulative frequency distributions however single orientation joint sets are characterised by a regular spacing and are therefore non fractal for both fault and joint map data box counting techniques do not yield the power law relationship between box size and the number of boxes that is expected of fractal geometries it is concluded that 2 d box counting techniques are too insensitive to characterise the many different parameters of a fracture array the fracture density technique appears not to discriminate between very different fracture patterns and therefore does not provide useful results a fracture pattern incorporates several attributes e g size distribution orientation linkage density roughness each of which may scale independently and each of which may be fractal with its own fractal dimension full characterisation of fracture patterns will therefore require independent analysis of each of these attributes

very high resolution spaceborne sar tomography in urban environment synthetic aperture radar tomography tomosar extends the synthetic aperture principle into the elevation direction for 3 d imaging it uses stacks of several acquisitions from slightly different viewing angles the elevation aperture to reconstruct the reflectivity function along the elevation direction by means of spectral analysis for every azimuth range pixel the new class of meter resolution spaceborne sar systems terrasar x and cosmo skymed offers a tremendous improvement in tomographic reconstruction of urban areas and man made infrastructure the high resolution fits well to the inherent scale of buildings floor height distance of windows etc this paper demonstrates the tomographic potential of these sars and the achievable quality on the basis of terrasar x spotlight data of urban environment a new wiener type regularization to the singular value decomposition method equivalent to a maximum a posteriori estimator for tomosar is introduced and is extended to the differential case 4 d i e space time different model selection schemes for the estimation of the number of scatterers in a resolution cell are compared and proven to be applicable in practice two parametric estimation algorithms of the scatterers elevation and their velocities are evaluated first 3 d and 4 d reconstructions of an entire building complex including its radar reflectivity with very high level of detail from spaceborne sar data by pixelwise tomosar are presented

cross shore migration of lunate megaripples during duck94 1 remote acoustic observations of lunate megaripple migration are presented from two storm events during the duck94 nearshore dynamics experiment for time periods during which longshore currents were weak 20 cm s during these periods significant wave orbital velocities were 50 80 cm s megaripple heights were 0 05 0 5 m megaripple horns were directed shoreward the crest to trough slope of the shoreward advancing ripple face was close to the angle of repose and migration speeds were 10 40 cm h onshore the observations also indicate that the megaripples stalled and may have begun to migrate offshore when the mean offshore flow exceeded 20 cm s during the second storm stress based bed load sediment transport models are moderately successful in predicting the observed dependence of migration velocity on measured fluid velocities separated into zero mean current infragravity wave and sea and swell wave frequency bands wave and mean current friction factors fw and fc are obtained by best fit between the predicted and observed migration velocities for two choices 3 2 and 5 2 for the stress exponent in the bed load transport part of the model net transport is computed using wave velocity amplitudes determined from both run length statistics and wave by wave improved agreement with observations is obtained for the wave by wave net transport predictions and for the wave like treatment of the infragravity band the level of agreement is relatively insensitive to the value of the best fit current and wave friction factor values for 5 2 and 3 2 are fc 4 3 10 3 and 8 0 10 3 and fw 1 7 10 2 and 4 8 10 2 respectively

scaling of fracture connectivity in geological formations a new method to quantify fracture network connectivity is developed and applied to analyze two classical examples of fault and joint networks in natural geological formations the connectivity measure accounts for the scaling properties of fracture networks which are controlled by the power law length distribution exponent a the fractal dimension d and the fracture density the connectivity behavior of fracture patterns depends on the scale of measurement for a d 1 analysis of the san andreas fault system shows that a d 1 and that the connectivity threshold is reached only at a critical length scale in contrast for a typical sandstone joint pattern a d 1 which is on the cusp where the connectivity threshold is highly sensitive to the minimum fracture length in the system

forest height inversion using high resolution p band pol insar data in this paper a high resolution p band pol insar data set acquired by the airborne ramses system over pine forest stands of different height is investigated a significant penetration depth in all the polarimetric channels and a wide range of polarimetric phase center heights are observed attesting of an interaction of the radar waves with different forest structural elements the main objective of this paper concerns forest height inversion at p band first forest modeling assumptions are evaluated using a priori information such as ground level and forest height measurements the full extend of the forest height is shown to be responsible of the volume decorrelation and a significant orientation effect is clearly identified over the highest stands as a consequence the oriented volume over ground model ovog is determined to be the most appropriated model for the forest height inversion at p band the ground contribution is present in all the polarimetric channels due to the important penetration at this frequency to overcome this difficulty a time frequency optimization method based on sublook decomposition is developed to separate the pure ground and canopy contributions allowing forest height estimation with ovog with an rms error on the order of 2 m in the last section of this paper a sensitivity analysis of the inversion with respect to two important system parameters the signal to noise ratio and the resolution is presented leading to a discussion on the inversion robustness in spaceborne conditions where these system parameters are the most deteriorated as compared to airborne configurations

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

critical stress localization of flow associated with deformation of well fractured rock masses with implications for mineral deposits fluid flow and deformation of fractured rock masses is investigated using numerical models based on distinct element methods udec which couple mechanical and hydraulic behaviour a series of numerical experiments is presented in which diffuse flow through fracture networks changes to highly localized flow at a critical stress state slip on parts of the fracture network causes the opening up of some fractures often at fracture intersections thus a change in the stress state results in a sudden localization of deformation and fluid flow a series of plots of hydraulic conductivity v differential stress are presented for some natural fracture networks to demonstrate the influence of fracture network geometry and in situ stress on the critical phase boundary between diffuse and localized flow the onset of localized deformation and fluid flow is a critical point phenomenon resulting in fractal properties fractal and multifractal techniques are used to characterize heterogeneity of the flow in order to generalize the results of the modelling of discrete systems to a continuum based description of the flow the significance of the models and their implications for crustal behaviour are discussed in relation to hydrothermal mineralization and natural vein systems

c band repeat pass interferometric sar observations of the forest properties of ers 1 c band repeat pass interferometric sar information for a forested area are studied the intensity information is rather limited but including coherence and effective interferometric sar insar height more information about the forest parameters can be obtained via satellite such information is also important for correction of insar derived topographic maps coherence properties have been used to identify forested nonforested areas and the interferometric effective height of the forest determined by comparison to a dem of the area the authors have developed a model to relate basic forest properties to insar observations these show that the coherence and interferometric effective height of a forested area change between image pairs the model demonstrates how these properties are related to the temporal decorrelation and the scattering from the vegetation canopy and the ground surface gaps in the vegetation are found to be important in the characterization of boreal forests

linkage and evolution of conjugate strike slip fault zones in limestones of somerset and northumbria conjugate strike slip fault zones that cover metre scale areas at beadnell northumbria and kilve somerset were initiated as conjugate vein arrays early conjugate faults are linked by the propagation of one fault that eventually by passes the other fault a model for the development of strike slip faults is presented using fault and vein geometries and the position of damage zones with respect to the master faults as an indication of the propagation direction this model includes the evolution of networks from 1 the initial random development of vein arrays to 2 the isolated development of several unconnected conjugate fault segments that pass into vein arrays through 3 the intersection of a conjugate set of master faults and linkage with minor antithetic faults and the formation of new vein arrays with extensional geometries after a linked network of faults is established to 4 breaching of intersection points by dominant faults and finally 5 the propagation towards oversteps that are breached to form a through going fault the geometry of the active structures simplifies with time as strain is localised along the master fault but the complexities are preserved in the fault walls

volume loss and deformation around conjugate fractures comparison between a natural example and analogue experiments abstract in well stratified sedimentary rocks measurement of the bedding offsets along fractures gives a value for the relative displacement at each location to restore the undeformed geometry of the layers the offset along each fracture must be cancelled restoration of the geometry enables the location of places where shortening is concentrated to be established namely at the fracture intersection and at fracture tips slow displacement during deformation is demonstrated by the growth of fibres on the fault surfaces pressure solution inside the layers is responsible for the internal strain with associated volume loss this mechanism is compatible with low strain rates giving aseismic displacements along the fractures to model rock rheology dominated by pressure solution a viscous material paraffin wax has been employed in the analogue model volume loss in nature is represented by area changes during the analogue experiments in the experiments shortening is concentrated around the fractures in exactly the same geometrical positions as in nature when the amount of displacement is different on each of the two fractures one of the fractures is observed to offset its conjugate fracture when this is the case relative timing of displacement along conjugate fractures cannot be determined without ambiguity from the observation of fracture offsets

bedform transport rates for the lowermost mississippi river 1 new methods of data collection and processing are developed to provide quantitative reach scale measurements of bedform transport mass within the tidally influenced mississippi river a multibeam swath profiler was used to collect daily bathymetry over a range of water discharges and bed elevation changes induced by dune migration are measured these values are coupled with bulk physical properties of the bed sediment to constrain mass flux and annual bedform transport is estimated at 2 2 x 10 6 metric tons mt the total annual sand flux from the mississippi river calculated by combining measured bedform transport rates and suspended sediment flux is estimated to be 20 x 10 6 mt survey data also provide information about the spatial distribution of dunes across the channel bottom straight reach segments are commonly mantled by dunes for the entire cross section while bends are typically areas of focused scour devoid of bedforms presumably any sediments associated with migrating dunes are propelled into suspension within bends before redepositing in the subsequent straight reach movement via suspension is therefore an important component for the downriver transport of bed materials in the lower mississippi river

influence of bed roughness on dune and megaripple generation richards 1980 conjectured that megaripples of the continental shelf are due to a seabed instability in the presence of seabed ripples towards a better understanding of this megaripple formation process we use a morphodynamical numerical model to investigate the bed roughness influence on the bed load induced linear stability of a sandy bed we find that the linearly most amplified mode shifts from a dune mode grain roughness towards a megaripple mode large bed roughness then we discuss how megaripples could be generated over a flat bed and over dunes

computer simulations of self organized megaripples in the nearshore 1 megaripples are bed forms with heights of 20 50 cm and lengths of 1 10 m that are common in the surf zone of natural beaches they affect sediment transport flow energy dissipation and larger scale hydro and morphodynamics they are thought to be dynamically similar to bed forms in deserts rivers and deeper marine environments here a self organization model similar to models for subaerial bed forms is used to simulate the formation and development of megaripples in the surf zone sediment flux is determined from combined wave and current flows using stream power and bed shear stress formulations as well as a third formulation for transport based on simple rules which represent sheet flow random bed irregularities either imposed or resulting from small variations in transport representing turbulence are necessary seeds for bed form development feedback between the bed and the flow in the form of a shadow zone downstream of a bed form and increasing flow acceleration with elevation over the crests of bed forms alter the transport such that organized bed forms emerge modeled bed form morphology including cross sectional shape and plan view and dynamics including growth and migration are similar to natural megaripples the model can be used to extend the field observations of clarke and werner 2004 which suggest that if conditions remain the same megaripples will continue to grow contrary to many bed form models this model supports the idea that bed form spacing grows continually

bedform spacing from defect dynamics spacing is a time varying characteristic of bedform fields deriving from the behavior of defects ends of crest lines in the bedform pattern in a model based on this hypothesis crest line length is lost and spacing increases because bedform defects which are smaller in height and faster migrating than surrounding bedform crest lines merge with larger bedforms as defects migrate through bedform fields spacing in large bedform fields asymptotically increases with the logarithm of time as pairs of oppositely facing defects meet and annihilate spacing in small bedform fields such as flumes exponentially approaches a fixed value as defects are eliminated at the boundaries of the field model predictions are compatible with observed spacing of transverse bedforms ripples formed under waves and linear dunes calling into question the widespread assumption that bedform spacing approaches a steady state value characteristic of fluid flow and sediment transport over two dimensional bedforms

understanding coastal morphodynamic patterns from depth averaged sediment concentration this review highlights the important role of the depth averaged sediment concentration dasc to understand the formation of a number of coastal morphodynamic features that have an alongshore rhythmic pattern beach cusps surf zone transverse and crescentic bars and shoreface connected sand ridges we present a formulation and methodology based on the knowledge of the dasc which equals the sediment load divided by the water depth that has been successfully used to understand the characteristics of these features these sand bodies relevant for coastal engineering and other disciplines are located in different parts of the coastal zone and are characterized by different spatial and temporal scales but the same technique can be used to understand them since the sand bodies occur in the presence of depth averaged currents the sediment transport approximately equals a sediment load times the current moreover it is assumed that waves essentially mobilize the sediment and the current increases this mobilization and advects the sediment in such conditions knowing the spatial distribution of the dasc and the depth averaged currents induced by the forcing waves wind and pressure gradients over the patterns allows inferring the convergence divergence of sediment transport deposition erosion occurs where the current flows from areas of high to low low to high values of dasc the formulation and methodology are especially useful to understand the positive feedback mechanisms between flow and morphology leading to the formation of those morphological features but the physical mechanisms for their migration their finite amplitude behavior and their decay can also be explored

fractal and multifractal measures of natural and synthetic fracture networks we have analyzed the fractal and multifractal nature of a series of 17 natural fracture trace maps representing a wide variety of scales geological settings and lithologies as well as a number of typical synthetic fracture networks in which fracture locations orientations and lengths are drawn from various probability distribution functions recent studies have shown that multifractal methods can be used to investigate fracture networks at greater depth since the fractal dimension represents only part of the scaling spectrum characterizing each network we find that the real and synthetic fracture maps display fractal and multifractal properties moreover the properties of the synthetic networks are very similar to those of the real networks with nontrivial fractal dimensions and multifractal spectra we suggest that different fracturing mechanisms can lead to two or more distinct subranges over which a fractal dimension can be defined while the heterogeneity of the rock and the nature of the fracturing mechanisms lead to multifractal properties we also find that the fractal dimension of a synthetic fracture network is relatively insensitive to parameters such as fracture length and orientation but can be controlled by appropriate choice of the relative fracture density

vertical profiles of longshore currents and related bed shear stress and bottom roughness the vertical structure of the mean wave driven longshore current over a barred beach is examined on three strong current days during the duck94 experiment and it is found that the bottom boundary layer is well described by a logarithmic profile mean correlation coefficient for all 22 profiles 0 98 the logarithmic profile fits better in the trough where turbulent bottom boundary layer processes predominate than over the bar where breaking wave induced turbulence generated at the surface modifies the profile the surface layer in the presence of waves is well described by adjusting the logarithmic profile for the intermittent presence of water and adding the alongshore component of the mass transport velocity slope of the least squares linear regression between model predictions and observations 1 005 and root mean square rms error of 7 bed shear stresses calculated from logarithmic velocity profiles are equated to a quadratic bottom shear stress formulation the associated bed shear stress coefficients vary by more than an order of magnitude across the surf zone 0 0006 0 012 bottom roughness was measured throughout the nearshore using a sonic altimeter mounted on a moving platform the bed shear stress coefficients are positively correlated with bottom roughness linear correlation coefficient 0 6 a higher linear correlation coefficient 0 8 is obtained by subtracting skin friction from the total bed shear stress

multibaseline polarimetric sar tomography of a boreal forest at p and l bands longer wavelength synthetic aperture radars sars are precious in the remote sensing of forested areas being sensitive to contributions from the whole vegetation layer and from the ground below the electromagnetic properties of such contributions are retrieved from multipolarimetric acquisitions whereas their vertical structure is retrieved from multibaseline acquisitions through tomographic imaging combining baseline and polarization diversity provides most information allowing the decomposition of the sar signal into ground and volume only contributions a formal treatment of this problem is provided with the algebraic synthesis technique which extends the concepts of polinsar the decomposition however is shown to be ambiguous in that different solutions are equally consistent with the data the main goal of this paper is to discuss this topic in light of the experimental results from a tomographic and polarimetric analysis of the boreal forest within the krycklan river catchment northern sweden investigated at p and l bands during the esa campaign biosar 2008 different solutions to the decomposition problem will be discussed by examining the corresponding vertical structures accessible through tomographic techniques elements are shown supporting the idea that ground volume interactions play a nonnegligible role at p band and a solution is proposed to isolate contributions from direct volume backscattering the retrieval of forest top height is discussed as well leading to the conclusion that such parameter is robust against erroneous choices in the identification of volume only contributions thus corroborating the polinsar approach for the analysis of single baseline data

impact of pre existing fabrics and multi phase oblique extension on cenozoic fault patterns wichianburi sub basin of the phetchabun rift thailand abstract cenozoic fault patterns associated with rift development in the wichianburi sub basin show a wide range of controls at different scales including influence by the margin of a permian basin and nw se to ne sw trending triassic folds and faults during the late oligocene early miocene phase 1 normal faults nnw sse to nne ssw trends developed in response to e w extension faults predominantly trend nnw sse to n s during this phase during the middle miocene pliocene the extension direction rotated to a more nw se orientation the old fault orientations were reactivated and new faults also developed with predominantly nne ssw to ne sw orientations many new faults nucleated within the syn rift section and were not directly influenced by pre existing fabrics in the pre rift section four types of phase 2 fault can be identified type 1 newly formed faults that strike sub orthogonal to the phase 2 extension direction type 2 newly formed faults that strike between the phase 1 fault orientations and type 1 faults type 3 newly formed faults that strike at angles greater than 90 with respect to the phase 2 extension direction type 4 reactivated phase 1 faults local stress rotations and fault linkage rotations explain many of the type 2 and 3 fault orientations the stress rotation in the middle miocene is observed in other basins in central thailand notably the suphan buri and phitsanulok basins where a range of fault patterns are produced by the effects of inherited fabrics plus multi phase rifting

investigation of a self organization model for beach cusp formation and development a recent numerical investigation of self organization werner and fink 1993 suggests that the feedback process between currents and sediment response can result in self organized patterns and can be used to predict beach cusp formation and spacing a similar model based on self organization is tested here in order to understand the processes occurring during beach cusp formation and development to evaluate the sensitivity toward the parameters used and to examine how the model might relate to field observations results obtained confirm the validity of the self organization approach and its capacity to predict beach cusp spacing with values in fair agreement with the available field measurements with most of the input parameters primarily affecting the rate of the process rather than the final spacing however changes in the random seed and runs for large numbers of swash cycles reveal a dynamical system with significant unpredictable behavior cusp spacing tends to change with time and cusp regularity shows large long term variations cusps are found to be accretionary in the swash zone and in agreement with most observations mean flows are horn divergent over developed topography simulations over nonplanar slopes characterized by the presence of preexisting nonrhythmic or cuspate features have been performed results indicate that preexisting large amplitude cusps are destroyed if their spacing is substantially different from that expected under self organization and that the final spacing is consistent with that predicted by the model for an equivalent plane beach these findings support the hypothesis that self organization is a robust mechanism for beach cusp formation

self organization of sorted patterned ground striking circular labyrinthine polygonal and striped patterns of stones and soil self organize in many polar and high alpine environments these forms emerge because freeze thaw cycles drive an interplay between two feedback mechanisms first formation of ice lenses in freezing soil sorts stones and soil by displacing soil toward soil rich domains and stones toward stone rich domains second stones are transported along the axis of elongate stone domains which are squeezed and confined as freezing soil domains expand in a numerical model implementing these feedbacks circles labyrinths and islands form when sorting dominates polygonal networks form when stone domain squeezing and confinement dominate and stripes form as hillslope gradient is increased

investigating polygonal fault topological variability structural causes vs image resolution abstract the topology of three polygonal fault sets is investigated to determine potential causes of variations in connectivity as measured by nodes and branches between and vertically within the fault sets two faults sets from the great south basin gsb new zealand and southeast asia sea are imaged by 3d seismic reflection data a third data set al farafra oasis egypt is imaged from satellite data the values measuring connectivity for the gsb and sea polygonal fault sets plot in ternary diagrams in similar areas to other complex normal fault sets from rifts these data sets are dominated by faults with either isolated fault tips i nodes or with abutting or splaying geometries y nodes the similarities in node and branch topology of polygonal faults and complex fault patterns in rifts associated with multi phase rifting complex local stress rotations or inherited fabrics which are imaged on 3d seismic indicates that topology describes the complexity of fault connectivity but in general by itself cannot discriminate the causes of normal fault pattern variations the al farafra oasis faults sets areas 2 and 3 provide an end member example of fault patterns with a very high degree of connectivity associated with cross cutting fault sets x nodes that are more rarely present in other fault sets some faults forming x nodes may be hybrid tensile shear failure fractures or even calcite vein filled tensile fractures much of the difference between the seismic and satellite image data sets may be related resolution indicating that comparisons of topology characteristics are best made between data sets of similar resolution

deformation within a strike slip fault network at westward ho devon u k domino vs conjugate faulting abstract a system of ne trending left lateral faults and nw trending right lateral faults at westward ho north devon u k cut steeply dipping 60 strata faults were accurately mapped in the field and from aerial photography and lateral separations of marker beds measured along the fault traces these data are used to examine the displacements within the network of interacting faults and to calculate variations in the density and relative proportions of the fault sets the displacements are also used in a tensor analysis of the strain and together with block rotations used to restore the deformation the results show a range of heterogeneity within the fault network both in terms of the fault patterns and strain some sub areas show a dominance of one fault set with regularly spaced larger displacements separating relatively weakly deformed blocks with smaller antithetic faults within these areas up to 20 rotation of the faults and bedding produces a domino style deformation that accommodates up to 15 extension the domino regions are separated by areas of conjugate faulting in which both sets of faults are equally developed and have similar displacement ranges conjugate areas have little or no rotation of the bedding and generally lower strains than domino regions

first order seismic attributes for clastic seismic facies interpretation examples from the east china sea abstract seismic attributes for the interpreting explorationist are numerous some are useful some duplicative and some less useful however with respect to optimizing a systematic basin analysis approach which relies upon heavily upon integrating seismic facies there are eight particularly useful attributes which have clear geophysical meaning strong underlying geological rock fluid implications and which for clastic depositional environments greatly assist in determining seismic facies associated paleoenvironments and lessening the number of interpretive possibilities they are amplitude envelope chaos cosine of phase dip deviation instantaneous frequency q relative acoustic impedance and variance a systematic application of these first order attributes for the east china sea in particular and for other clastic environments in general allows a first pass assessment of a basin s exploration potential through seismic reconnaissance an interpretive reconnaissance whose accuracy is limited only by the seismic fidelity of the lines and logic of the assumed geology employed

analysis of a strike slip fault network using high resolution multibeam bathymetry offshore nw devon u k abstract imaging of the sea floor offshore from hartland point north devon u k using high resolution multibeam bathymetry reveals a strike slip fault network this consists of ne trending left lateral faults and nw trending right lateral faults that cut folded and steeply dipping strata 60 faults were accurately mapped using the multibeam imagery and lateral separations of marker beds measured along fault traces these data are used to examine the spatial arrangement fault displacement and strain distribution within the network at different displacement cut offs at high displacement cut offs the fault network is dominated by a few long isolated right lateral fault segments that bound fault blocks but at lower displacement cut offs shorter left lateral and right lateral fault segments make up fault tips and infill fault blocks the majority 70 of fault trace length is taken up by small fault segments that have 10 m displacement the topology and relative connectivity of the network is analysed in terms of a system of fault branches between tips i nodes or intersections x or y nodes the relative proportions of which reflect the connectivity of the network although the kinematic behaviour of the fault network is controlled by large fault segments connectivity is very dependent on the small fault segments a comparison with a similar nearby strike slip fault network at westward ho north devon shows many similarities and indicates that fault networks are better connected with increasing strain and that the network becomes better connected when strain is localized within damage zones rather than on individual faults

estimating nearshore bedform amplitudes with altimeters abstract estimates of the heights of large 0 1 0 4 m heights and 1 10 m horizontal lengths migrating bedforms on a sandy beach made with fixed single point altimeters are similar to heights estimated from profiles across the bedforms made with altimeters mounted on an amphibious vehicle that traversed the surf zone unlike many profiling systems the robust fixed altimeters can measure bedforms in bubbly sediment laden surf zone waters nearly continuously including during storms thus allowing investigation of the relationships between bedform heights and near bottom velocities to be extended to a wide range of wave conditions the fixed altimeter observations of migrating bedforms suggest a sandy surf zone seafloor is not always smooth during energetic conditions with strong mean currents and large wave orbital velocities

principal bed states during sandyduck97 occurrence spectral anisotropy and the bed state storm cycle 1 results are presented from 70 days of nearly continuous in situ acoustic imagery of the nearshore sandy seabed in 3 m mean water depth at two locations separated by 40 m cross shore distance the bottom sediments were 150 m median diameter sand with nearly identical size distributions at the two locations five principal bed states were observed irregular ripples cross ripples linear transition ripples lunate megaripples and flat bed the linear transition and flat bed states were the most frequent together accounting for 68 of the total time bed state occurrence was a strong function of incident wave energy each bed state occurring within a relatively narrow range of sea and swell energies during the 12 major storm events spanned by the record the bed response was characterized by a repeatable bed state storm cycle involving four of the five principal states lunate megaripples did not appear repeatedly and thus may be a special case with no obvious dependence of bed state occurrence on prior bed state or on third moment measures of wave nonlinearity radial spectra from the rotary acoustic images indicate pronounced differences in the anisotropy of spatial scales for the different bed states and exhibit onshore offshore differences which are likely related to ripple migration

development of subaqueous barchanoid shaped dunes due to lateral grain size variability in a tidal inlet channel of the danish wadden sea 1 high resolution bathymetry at centimeter scale accuracy acquired with a multibeam echo sounder system revealed the existence of barchanoid shaped large i e length 10 100 m to very large i e length 100 m dunes in the gradyb tidal inlet channel in the danish wadden sea the development of these dunes is due to an increase in dune celerity from 12 m yr in the center of the channel to around 30 m yr at the sides this increase in dune celerity can be explained by the fact that dune heights decrease from 3 1 m in the center of the channel to 1 4 m at the sides as a smaller sediment volume has to be moved per unit time for equal dune celerity water depth is uniform across the channel likewise high resolution acoustic doppler current profiler measurements across the channel showed a uniform distribution of both ebb and flood flow thus no correlation between dune dimensions and water depth or flow velocity was established instead high accuracy bed sampling along the crests of the dunes showed a decrease in mean grain size from 0 63 mm in the center to 0 36 mm at the sides of the channel the decrease in dune height is ascribed to this decrease in grain size given that flow depth and flow velocity are uniform across the channel the lateral decrease in grain size is suggested to result from sorting effects by secondary currents directed from the center toward the sides of the channel in the trough lee side region of the barchanoid shaped dunes

development of subaqueous barchanoid shaped dunes due to lateral grain size variability in a tidal inlet channel of the danish wadden sea development of barchanoid shaped dunes

megaripple migration in a natural surf zone migrating megaripples are bedforms that appear in the surf zone of sandy coasts1 with heights of 0 1 0 5 m and wavelengths of 1 5 m they are similar in size and shape to small dunes large ripples or sand waves such sedimentary bedforms have been studied in subaerial2 steady flow3 and intertidal4 environments as well as in laboratory flume experiments5 they affect overlying currents by introducing hydraulic roughness4 6 and may provide a mechanism for sediment transport7 8 as well as forming sedimentary structures in preserved facies9 10 the formation orientation and migration of such bedforms is not understood well11 12 dunes for example can be aligned with their crests perpendicular to steady unidirectional winds13 but in more complex wind fields their orientation becomes difficult to predict14 15 16 17 similarly it is not known how sea floor megaripples become aligned and migrate in the complex flows of the surf zone here we present observations in the surf zone of a natural beach which indicate that megaripples do not migrate in the direction of the vector sum of the currents but are aligned so that the sediment transport normal to the bedform crest is maximized17 this may need to be taken into account in modelling morphology change and interpreting existing and fossil morphologic patterns

scaling relationships of joint and vein arrays from the burren co clare ireland abstract we present a study of the systematics of veins and joints in carboniferous limestones of the burren ireland scaling relationships were established for fracture arrays mapped from low elevation aerial photographs that image fractures on numerous limestone pavements for areas up to ca 1 km2 the veins and joints occur in the same sequence but have contrasting scaling properties the veins strike north south and cut many beds to form vertically persistent non stratabound arrays they are strongly clustered and have scale invariant geometric properties vein geometries suggest they grew sub critically under relatively high differential stresses during north south directed variscan compression the joints form stratabound arrays with regular spacings that scale with bed thickness they show greater strike variation than the veins and have lognormal length distributions the joints formed during uplift under low differential stress conditions the contrasting scaling properties of the joints and veins are attributed to different overburden stresses at the time of formation the veins formed at greater depths than the joints in conditions that favoured fracture propagation across mechanical discontinuities resulting in the development of non stratabound scaling properties

eolian dunes computer simulations and attractor interpretation a simple computer simulation algorithm for the transport of sand by wind produces forms resembling barchan crescentic ridge linear and star natural dune classes sand is moved as slabs composed of many grains that are picked up at random transported in a specified direction and deposited 1 with a probability that depends on the local presence or absence of sand or 2 in shadow zones in the lee of dunes the simulated dune fields are interpreted as complex systems with sand dune classes being dynamical attractors of these systems the evolution of dunes once formed becomes decoupled from the details of eolian sand transport

first demonstration of airborne sar tomography using multibaseline l band data in synthetic aperture radar sar interferometry the phase differences between two different sensor positions are used to estimate the terrain topography although it is possible in this way to find a three dimensional 3d surface representation the distribution of the different scatterers in the height direction at a fixed range and azimuth position remains unknown contrary to this tomographic techniques enable a real geometric resolution capability in the height direction and introduce new possibilities for many applications and inversion problems even misinterpretations in sar images caused by layover and foreshortening effects can be solved by the tomographic processing in this paper the successful experimental realization of polarimetric airborne sar tomography is demonstrated for the first time the authors present the concept of aperture synthesis for tomographic imaging for the case of a multibaseline imaging geometry and discuss the constraints arising from the limited number of flight tracks they propose a method for reduction of the height ambiguities associated to the irregular and undersampled spatial distribution of the imaging positions finally they address the experimental requirements for polarimetric airborne sar tomography and show experimental results using a multibaseline data set acquired in l band by dlr s experimental sar e sar of a test site near oberpfaffenhofen germany