response characteristics of a short range high resolution digital sonar altimeter abstract the datasonics model asa 920 digital sonar altimeter dsa is a compact high frequency 1 mhz short range 0 5 5 m underwater sonar device originally designed as an altimeter for submersibles the dsa has previously been successfully used on a bottom mounted tripod to measure changes in relative bed elevation at a point on the shoreface prior to and during a storm fixed to a rigid mounting on the seabed the dsa produces a digital output that is proportional to the transducer elevation above the bed the purpose of this report is to describe the response characteristics of the dsa tests using a flat steel plate and a flat sand bed as targets showed that the dsa is capable of resolving differences in elevation of at least 0 5 cm a laboratory calibration demonstrated that the instrument response is linear because the acoustic pulse emitted by the transducer has a finite width the dsa is incapable of delineating undulating sand beds when the bedslope taken over the beamwidth is significant this limits the instrument s use over a bed of wave generated ripples in general the altimeter does not see into the troughs of ripples when its height above the bed is more than eight times the ripple wavelength the instrument stability is good over 12 operating hours 14 days of burst sampling the indicated elevation drifted by 0 3 cm in the field the acoustic pulse is susceptible to interference by suspended particulate matter and bubbles during deployment in a water depth of 8 m on the shoreface two problems occurred pulse scattering that caused a loss of echo detection which was manifested as spikes in the record and premature echoes that obscured the actual bed surface a second altimeter with an operating frequency of 300 khz datasonics model psa 900 also gave a linear response but with a reduced accuracy of approximately 1 cm

layered and laterally constrained 2d inversion of resistivity data in a sedimentary environment quasi layered models often can represent the actual geology more accurately than smooth minimum structure models we present a 2d inversion scheme with lateral constraints and sharp boundaries lci for continuous resistivity data all data and models are inverted as one system producing layered solutions with laterally smooth transitions the models are regularized through lateral constraints that tie interface depths or thicknesses and resistivities of adjacent layers a priori information used to resolve ambiguities and to add for example geological information can be added at any point of the profile and migrates through the lateral constraints to parameters at adjacent sites similarly information from areas with well resolved parameters migrates through the constraints to help resolve areas with poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result a simple synthetic model proves the need for a quasilayered 2d inversion when compared with a traditional 2d minimum structure inversion a 2d minimum structure inversion produces models with spatially smooth resistivity transitions making identification of layer boundaries difficult a continuous vertical electrical sounding field example from sweden with a depression in the depth to bedrock supports the conclusions drawn from the synthetic example a till layer on top of the bedrock hidden in the traditional inversion result is identified using the 2d lci scheme furthermore the depth to the bedrock surface is easily identified for most of the profile with the 2d lci model which is not the case with the model from the traditional minimumstructure inversion

groundwater salinity influenced by holocene seawater trapped in incised valleys in the red river delta plain brackish to salty waters have been found in inland areas of delta aquifers geophysical data and modelling suggest that salty groundwater in the red river delta originates from trapped seawater contained in underlying holocene marine deposits

building 3d shear wave velocity models using surface waves testing the tarcento basin case history the paper reports on the use of surface wave testing for the construction of a three dimensional 3d shear wave velocity model of an alluvial basin the town of tarcento italy is located in a region with a high level of seismic hazard and was strongly affected by the two friuli earthquakes in 1976 the seismic surveys were performed with surface wave multistation methods using a combination of active source and passive source experimental setup experimental data were collected at 16 sites and inversion of the data is based on an innovative procedure for spatially constrained inversion with a single objective function in which a priori information is included the method provides an improvement in the robustness of the solution mitigating solution nonuniqueness available borehole logs at different locations are integrated into the data set in terms of a priori bedrock information three independent cross hole tests are used for a posteriori comparison of the inverted one dimensional 1d profiles three dimensional interpolation of the obtained profiles leads to a shear wave velocity model that is internally consistent and complies with a priori information cross hole results and suitable boundary profiles the model is intended for numerical simulations of the seismic response of the basin online material figure showing the a priori bedrock surface

application of near surface seismic refraction tomography and multichannel analysis of surface waves for geotechnical site characterizations a case study in this case study two geophysical methods based on seismic waves were employed to evaluate the geotechnical properties of the soil deposits at a site for a planned wind farm regional geological information shows that the study area is mainly covered by recent alluvium which is classified as a mixture of fine sand and gravel twenty five seismic refraction surveys were carried out in the study area the acquired shot gathers were processed from which primary wave p wave and shear wave s wave velocities were derived the p wave velocities were obtained by using the seismic refraction tomography method srt while the s wave velocities were extracted by utilizing the multichannel analysis of surface waves masw technique which is established based on the dispersion characteristics of rayleigh waves seismic hazard at the site was evaluated according to the iranian code using the measured s wave velocities and the friction angles of the soil deposits were approximated using an empirical method and by making use of jaky s formula for earth pressure at rest which yielded similar values the deformation properties of the foundation soil were also estimated based on the correlations between seismic wave velocities and elastic properties of soil as well as janbu s formula for soil modulus the findings of this study may serve as references for economic and non destructive geotechnical site characterizations using seismic wave methods

integrated geophysical surveys at the archaeological site of tindari sicily italy abstract the results of geophysical survey carried out at the archaeological site of tindari located 70 km west north west of messina sicily italy are presented and discussed the site is one of the most important archaeological sites about 90 ha large on the north eastern side of sicily and it was one of the last greek settlements in sicily keeping in mind the vastness of the site according to the archaeologists an area of about 1200 m2 was selected for a geophysical survey electrical resistivity tomography ert including induced polarization ip measurements and seismic refraction tomography were applied in the course of geophysical exploration in the area the objective of this preliminary geophysical investigation was to verify the effectiveness of the technique for a spatial definition of the buried archaeological structures mostly walls columns etc to determine their characteristics and to study the presence of collapsed columns within the zone of archaeological interest in view of their application in the rest of the site that for obvious reasons could not be entirely excavated in brief times the geophysical data visualized in 3d space revealed a distribution of low contrast shallow anomalies that indicate the presence of different types of buried structures in the surveyed area also the probable accumulations of collapsed columns could be determined these results confirm the hypothesis of a large northern extension of the archaeological site and provide useful information to design a more efficient excavation plan

optimized fast hankel transform filters in the linear digital filter theory for calculation of hankel transforms it is possible to find explicit series expansions for the filter coefficients a method is presented for optimizing the hankel filters calculated in this way for a certain desired accuracy of computation the sampling density and filter length are minimized by choosing the parameters determining the filter characteristics according to the analytical properties of the input function a new approach to the calculation of the filter coefficients has been developed for these optimized filters the length of the filters may be further reduced by introducing a shift in the sampling scheme

thin fine grained storm layers in a muddy shelf sequence an example from the lower jurassic in the stenlille 1 well denmark thin storm sand layers are a characteristic feature of many sandy shelf sequences while little evidence of storm layers is preserved in muddy shelf deposits where bioturbation is often total the present study shows that storm generated depositional processes governed sedimentation in a muddy shelf environment the studied sequence is dominated by blackish mudshale and silt streaked mudshale with thinner intervals of pale fine grained heterolithic sandstone it represents the lower jurassic fjerritslev formation in the eastern part of the danish basin and has been studied in four cores from the stenlille 1 well within the muddy outer shelf association four sedimentary facies and 14 types of laminae 0 5 10 mm thick may be distinguished most of the laminae share the characteristics of graded bedding erosive bases and occasional fading ripples with storm layers of sand grade the structures indicate that the mudshale laminae formed by settling of the suspension load carried by storm generated currents this kind of episodic deposition of fine grained storm layers may be common though rarely preserved in outer shelf environments

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

a survey of current trends in near surface electrical and electromagnetic methods electricalandelectromagnetice emmethodsfornearsurface investigations have undergone rapid improvements over the past few decades besides the traditional applications in groundwater investigations natural resource exploration and geological mapping a number of new applications have appeared these include hazardous waste characterizationstudies precision agricultureapplications archeological surveys and geotechnical investigations the inclusion of microprocessors in survey instruments development ofnewinterpretationalgorithms andeasyaccesstopowerful computers have supported innovation throughout the geophysical community and the e em community is no exception most notable are development of continuous measurement systems that generate large dense data sets efficiently these have contributed significantly to the usefulness of e em methods by allowing measurements over wide areas without sacrificing lateral resolution the availability of theseluxuriantdatasetsinturnspurreddevelopmentofinterpretation algorithms including laterally constrained 1d inversionaswellasinnovative2d and3d inversionmethods taken together these developments can be expected to improve the resolution and usefulness of e em methods and permit them to be applied economically the trend is clearly towarddensesurveyingoverlargerareas followedbyhighly automated post acquisition processing and interpretation to provide improved resolution of the shallow subsurface in a cost effectivemanner

high resolution seismic refraction method using surface and borehole data for site characterization of rocks abstract the authors have developed a new method for the analysis of seismic refraction data which can handle both surface and borehole data simultaneously the main features of the method we developed are as follows 1 the algorithm of analysis is based on the tomographic reconstruction technique and refraction data can be analyzed almost automatically after traveltime picking 2 the method is applicable to both layered velocity structures and those showing a velocity gradient with depth 3 in order to apply the seismic refraction technique to a site that has a more complex structure the method can use the data obtained from sources and receivers on the surface as well as those within boreholes simultaneously numerical and actual field examples have shown that the method can greatly improve the accuracy and the reliability of the seismic velocity models obtained by the seismic refraction method as compared to the conventional analysis methods it can also shorten the data processing time drastically and reduce the survey cost

magnetic imaging and electrical resistivity tomography studies in a roman military installation found in satala archaeological site northeastern anatolia turkey abstract satala is one of the last great military centers in the roman east available for archaeological and historical investigations this archaeological site is situated on the crossing of two singularly important routes in north east asia minor only little archaeological fieldwork in and around satala has so far been carried out thus delimiting our knowledge of the site and its role within the roman military structure of the east in order to provide further data on the site we carried out geophysical surveys including the application of magnetic and electrical resistivity techniques in an area north of the sadak village the geophysical surveys within this area supposedly part of the roman military camp proceeded in two stages the first stage saw magnetic gradiometer imaging studies being carried out on 2 1 ha measured by a geoscan fm 36 fluxgate gradiometer by using 0 5 1 m grid intervals for the second stage a different geophysical technique was used resistivity tomography resistivity data were collected using a number of combined 2d resistivity pseudosections in the eastern part of the area which contained very regular magnetic anomalies the 3d data were obtained by the combination of all survey lines collected from 2d data sets and thereafter the arranged data were processed by using the 3d robust inversion modified from the smoothness constrained algorithm electrical resistivity tomography investigations revealed that the buried archaeological structures might be located near the surface except for some structures found in the middle of the studied area the archaeological structures were furthermore determined by realistic model sections and volumetric representations magnetic imaging and electrical resistivity tomography surveys show that the combined usage of these techniques advances the understanding of archaeological structures beneath the surface

acoustic imaging of sea bed geometry a high resolution remote tracking sonar hrrts ii abstract a high resolution remote tracking sonar hrrts ii is described which is capable of measuring a 2 d profile of the sea bed over a maximum distance of 5 m under conditions of significant sediment transport the backscattered signal from a pulsed 30 s 5 mhz sonar provides acoustic range measurements of the small scale topography generated by bedforms at any point in time as well as changes in this small scale topography and the average elevation of sections of the sea bed over time bedform height and spacing can be determined accurately although bedform shape is distorted by smoothing of large slope changes as a result of the finite size of the footprint of this narrow beamed 0 74 sonar the system operates on command from a shore based micro computer and topographic resolution of the order of a few millimetres is possible resolution deteriorates as wave energy increases to levels where vibration of the transducer and large concentrations of sediment in the water column result in signal attenuation and a decrease in the signal to noise ratio

piecewise 1d laterally constrained inversion of resistivity data in a sedimentary environment layered models are often capable of representing the actual geology more accurately than smooth minimum structure models furthermore interval thicknesses and resistivities are often the parameters to which non geophysicist experts can relate and base decisions on when using them in waste site remediation groundwater modelling and physical planning we present a laterally constrained inversion scheme for continuous resistivity data based on a layered earth model 1d all 1d data sets and models are inverted as one system producing layered sections with lateral smooth transitions the models are regularized through laterally equal constraints that tie interface depths and resistivities of adjacent layers prior information e g originating from electric logs migrates through the lateral constraints to the adjacent models making resolution of equivalences possible to some extent information from areas with well resolved parameters will migrate through the constraints in a similar way to help resolve the poorly constrained parameters the estimated model is complemented by a full sensitivity analysis of the model parameters supporting quantitative evaluation of the inversion result examples from synthetic 2d models show that the model recognition of a sublayered 2d wedge model is improved using the laterally constrained inversion approach when compared with a section of combined 1d models and when compared with a 2d minimum structure inversion case histories with data from two different continuous dc systems support the conclusions drawn from the synthetic example

subgrid modeling of moveable bed bottom friction in wind wave models a subgrid moveable bed bottom friction model is developed for use in large scale wind wave models this model defines a representative bottom roughness based on the local application of a discontinuous roughness model and a statistical description of depth sediment and wave parameters for a finite area within the model i e a grid box the model reproduces the discontinuous attenuation behavior of swell in conditions of initial ripple formation as predicted by a small scale model it furthermore suppresses non physical oscillations of swell energy and unrealistically strong dependencies of depth limited wave heights on sediment parameters an alternative interpretation of the model explains the continuous transition between the no ripple and ripple regimes as sometimes observed in nature

quaternary normal faulting in southeastern sicily italy a seismic source for the 1693 large earthquake summary we present geological and morphological data combined with an analysis of seismic reflection lines across the ionian ovshore zone and information on historical earthquakes in order to yield new constraints on active faulting in southeastern sicily this region one of the most seismically active of the mediterranean is avected by wnw ese regional extension producing normal faulting of the southern edge of the siculo calabrian rift zone our data describe two systems of quaternary normal faults characterized by diverent ages and related to distinct tectonic processes the older nw se trending normal fault segments developed up to 400 kyr ago and striking perpendicular to the main front of the maghrebian thrust belt bound the small basins occurring along the eastern coast of the hyblean plateau the younger fault system is represented by prominent nnw sse trending normal fault segments and extends along the ionian ovshore zone following the ne sw trending avola and rosolini ispica normal faults these faults are characterized by vertical slip rates of 0 7 3 3 mm yr 1 and might be associated with the large seismic events of january 1693 we suggest that the main shock of the january 1693 earthquakes m 7 could be related to a 45 km long normal fault with a right lateral component of motion a long term net slip rate of about 3 7 mm yr 1 is calculated and a recurrence interval of about 550 50 yr is proposed for large events similar to that of january 1693

bottom boundary layer measurements on the continental shelf off the ebro river spain abstract measurements of currents waves and light transmission obtained with an instrumented bottom tripod geoprobe were used in conjunction with a theoretical bottom boundary layer model for waves and currents to investigate sediment transport on the continental shelf south of the ebro river delta spain the current data show that over a 48 day period during the fall of 1984 the average transport at 1 m above the seabed was alongshelf and slightly offshore toward the south southwest at about 2 cm s a weak storm passed through the region during this period and caused elevated wave and current speeds near the bed the bottom boundary layer model predicted correspondingly higher combined wave and current bottom shear velocities at this time but the geoprobe optical data indicate that little to no resuspension occurred this result suggests that the fine grained bottom sediment which has a clay component of 80 behaves cohesively and is more difficult to resuspend than noncohesive materials of similar size model computations also indicate that noncohesive very fine sand in shallow water 20 m deep was resuspended and transported mainly as bedload during this storm fine grained materials in shallow water that are resuspended and transported as suspended load into deeper water probably account for the slight increase in sediment concentration at the geoprobe sensors during the waning stages of the storm the bottom boundary layer data suggest that the belt of fine grained bottom sediment that extends along the shelf toward the southwest is deposited during prolonged periods of low energy and southwestward bottom flow this pattern is augmented by enhanced resuspension and transport toward the southwest during storms

evaluation of infiltration from losing disconnected rivers using a geophysical characterisation of the riverbed and a simplified infiltration model summary despite their significance to alluvial aquifer water balances there are few field derived estimates of infiltration from losing disconnected rivers infiltration was estimated over a 2 km section of billabong creek murray darling basin australia using a combination of field measurements and modelling techniques a method was developed whereby in river and riverbank electrical resistivity surveys were used to map the spatial coverage and thickness of the riverbed clay layer thought to be the key control on infiltration in this environment inverted resistivity measurements were used to generate a surrogate for a spatial map of clay layer thickness with constraint provided by coring the riverbed at selected high and low resistivity locations to independently determine the thickness of the clay the survey showed that the clay layer was continuous across the study reach but varied in thickness 1 m to 4 m a simple infiltration model was developed for infiltration through a clay layer and shown to be accurate under steady state conditions when compared to estimates obtained using a variable saturation numerical model for idealised riverbed cross sections infiltration rates across the study reach were estimated to range between 1700 and 7800 m 3 km 1 year 1 with an average of 3400 m 3 km 1 year 1 a sensitivity analysis showed that infiltration rates were most sensitive to clay hydraulic conductivity not clay layer thickness however it is anticipated that when applied at a larger scale 10 100 km infiltration rates will be more sensitive to the presence or absence of a clay layer in the riverbed the proposed methodology can provide independent estimates of infiltration in losing disconnected rivers at a scale suitable for the calibration of regional groundwater models

storm dominated bottom boundary layer dynamics on the northern california continental shelf measurements and predictions measurements of near bottom velocity profiles in 85 m water depth during a storm on the continental shelf off northern california using the geoprobe tripod in december 1979 provided estimates of shear velocities u and roughness lengths z0 when the near bottom velocity profiles were logarithmic these estimates agree within 90 confidence intervals with values computed from a simple near bottom combined wave current model that includes movable bed effects the reasonably good comparison between model and profile estimates of u suggests that such models can be used to predict bed shear stresses or shear velocities under combined flows of waves and currents typical of stormy conditions on continental shelves if stratification corrections to the velocity profile resulting from suspended sediment are small the repeated occurrences of storms of similar intensities and wind velocities during the winter months off northern california suggest that the resultant high bottom stresses due to the combined effects of waves and currents are major factors in controlling the distribution of surficial sediment on the central portion of the northern california shelf

the role of wave reworking on the architecture of storm sandstone facies bell island group lower ordovician eastern newfoundland stacked shallow marine cycles in the lower ordovician bell island group of bell island newfoundland show upward thickening and upward coarsening sequences which were deposited on a storm affected shelf in the beach formation each cycle has a facies sequence comprised from base to top of dark grey mudstones light grey mudstones tabular sandstones and mudstones lenticular sandstones and mudstones and thick bedded lenticular sandstones reflecting a progressive increase of wave orbital velocities at the sediment surface the mudstones and tabular sandstones reflect an environment in which the sea floor lay in the lower part of the wave orbital velocity field and in which tempestites were deposited as widespread sheets from weak combined flow currents the lenticular sandstones in the succeeding facies are wave reworked sands commonly lying in erosional hollows and having erosional tops and internal hummocky cross stratification planar lamination is relatively uncommon and sole marks are mainly absent in this facies oscillatory currents were dominant and accumulated sand in patches generally 10 30 m in diameter the facies formed on the inner shelf where the oscillatory currents generated by storm waves had powerful erosional effects and also determined the depositional bedforms mud partings and second order set boundaries within sandstone beds are believed to separate the products of individual storms so that many lenticular sandstone beds represent the amalgamation of several event beds this interpretation has important implications for attempts to estimate event frequency by counting sandstone beds within a sequence and for estimates of sand budgets during storm events the thick bedded lenticular facies appears to have been formed by erosion of the mud beds between the lenticular sands leading to nearly complete amalgamation of several lenticular sand bodies except for residual mud partings in the overlying redmans formation the process of amalgamation progressed even further so that nearly all the mud partings were removed resulting in the formation of thick bedded tabular sandstones sequence stratigraphic analysis of the cyclical sequence suggests that the cycles were eustatically controlled the rising limb of the sea level curve produced only the dark grey mudstone part of the cycle while the remainder of the cycle was deposited on the falling limb there is a gradational but rapid facies transition from the tabular to the lenticular sandstone facies which is interpreted as occurring at the inflexion point on the falling limb the thick bedded facies of the beach formation and the thick bedded tabular facies of the redmans formation represent periods of maximum sea level fall the stacked cycles in the beach formation are interpreted as an aggradational high frequency sequence or parasequence set bounded at the top by a sequence boundary and succeeded by the three aggradational parasequences of the redmans formation the recognition of storm facies with sandstone beds of very different bed length has important implications for the reservoir modelling of such facies

integrated near surface geophysical survey of the cathedral of mallorca abstract this paper describes an integrated near surface geophysical study carried out in order to obtain high resolution images of the shallow subsurface under and around the cathedral of mallorca the study was a part of a global project focused on determining the state of the building structure and on evaluating the cathedral s dynamical behaviour natural frequencies and vibration modes ground penetrating radar gpr and the capacitively coupled resistivity method were used to obtain 2d images of the shallow subsurface refraction microtremor array measurements remi were also used to characterize the rock and soil properties and several invasive boreholes provided detailed and exact information on the stratigraphy the information from the geophysical data was used to determine a final model of the ground with indications of the most likely vulnerable zones as a part of this final model gpr profiles enabled us to delineate the superficial ground structure and to detect some archaeological features electrical resistivity imaging data were in good agreement with the gpr results and showed shallow major changes in the soil and rock under the filling materials the refraction microtremor array remi results indicate the existence of compacted soils in different areas probably corresponding to old filled zones in good correlation with gpr and resistivity profiles in the most superficial part of the ground

mapping groundwater salinization using transient electromagnetic and direct current resistivity methods in azraq basin jordan abstracthydrogeophysical characterization using the transient electromagnetic method tem and the dc resistivity sounding ves method was implemented in the central part of azraq basin qa basin jordan to identify and map the spatial distribution of shallow fresh and saline groundwater in the upper aquifer systems the alluvium al and chert limestone urc shallow aquifers show different degrees of groundwater salinization the range of groundwater resistivity varies from 0 06 to 10 8 ohm m saline groundwater was detected at depths between 5 to 30 m where the aquifers have a wide spectrum of resistivity values from 0 14 to 120 ohm m the integrated geophysical and hydrogeologic models are significantly correlated in chloride concentration groundwater resistivity and aquifer resistivity using 1d inversion results from the tem and ves soundings in addition to quasi 3d modeling 1d spatially constrained inversion at selected tem sites groundwater resistivity variation was attributed to two diffe

quantifying geophysical inversion uncertainty using airborne frequency domain electromagnetic data applied at the province of zeeland the netherlands an accurate understanding of the fresh saline distribution of groundwater is necessary for effective groundwater management airborne electromagnetic aem surveys offer a rapid and cost effective method with which to map this offering valuable additional information about the subsurface to convert aem data into electric conductivity and ultimately groundwater salinity an inversion is undertaken a number of algorithms are available for this purpose however these are affected by significant uncertainty owing to inherent nonunique characteristics of this process the most commonly used inversion codes in hydrogeophysical studies were quantitatively tested using frequency domain aem and ground data from the province of zeeland the netherlands these include ubc1dfm code and quasi 2d laterally constrained inversions following an investigation of inversion parameter settings data were inverted for four inversion methods and interpolated into 3 d volumes using geological data and empirical electrical conductivity and water salinity relationships each inversion was converted into groundwater electrical conductivity and split into fresh brackish saline regions for groundwater volume estimates out of a total volume of 2 8 billion m3 a fresh groundwater estimate could differ by as much as 178 million m3 depending on the inversion used the primary factor here was the choice of model smoothness which was shown to affect the thickness of the brackish interval fresh brackish saline interfaces were consistently mapped with an accuracy of 3 m the brackish being the most accurately resolved the few layer method was less successful at resolving smoothly varying salinity distributions but more successful at mapping the brackish interface at greater depth

shallow geophysical survey at the archaeological site of san miguel tocuila basin of mexico abstract a combined near surface geophysical survey conducted in san miguel tocuila show that geophysical methods offer the possibility to characterize and reconstruct the geometry of subsurface structures without destroying the deposits providing a way to find solutions to the questions of archaeological or engineering significance the survey consisted of the application magnetometry seismic refraction tomography srt and ground penetrating radar gpr within a depth range of 10 m before spanier conquest san miguel tocuila was a very prominent suburb of the main aztec ceremonial complex located on the eastern margin of lake texcoco central mexico where several mounds known as tlateles in nahuatl language have been identified nowadays the rapid expansion of mexico city s metropolitan area within the last four decades has strongly influenced tocuila s environment and has compromised several of its archaeological and ancient human settlements this study shows how the high resolution imagining of non invasive geophysical methodologies in addition with surface archaeological studies parsons j r 1971 prehistoric settlement patterns in the texcoco region mexico memoirs of the museum of anthropology university of michigan number 3 provide different kinds of information that characterize the subsoil and a buried structure based on the history of the ancient settlements in the zone and considering the characteristics of shape and height of the structure we interpreted that the subsurface images obtained depict a buried tlatel which corresponds to a ceremonial civic center of late aztec times

a glimpse beneath antarctic sea ice platelet layer volume from multifrequency electromagnetic induction sounding in antarctica ice crystals emerge from ice shelf cavities and accumulate in unconsolidated layers beneath nearby sea ice such sub ice platelet layers form a unique habitat and serve as an indicator for the state of an ice shelf however the lack of a suitable methodology impedes an efficient quantification of this phenomenon on scales beyond point measurements in this study we inverted multifrequency electromagnetic em induction soundings obtained on fast ice with an underlying platelet layer along profiles of 100 km length in the eastern weddell sea em derived platelet layer thickness and conductivity are consistent with other field observations our results suggest that platelet layer volume is higher than previously thought in this region and that platelet layer ice volume fraction is proportional to its thickness we conclude that multifrequency em is a suitable tool to determine platelet layer volume with the potential to obtain crucial knowledge of associated processes in otherwise inaccessible ice shelf cavities

effects of biological activity on the entrainment of marine sediments nowell a r m jumars p a and eckman j e 1981 effects of biological activity on the entrainment of marine sediments mar geol 42 133 153 the effects of animal tracks and fecal pellet production on the critical entrainment velocity of marine sediments were examined experimentally laboratory measurements in a free surface seawater flume were made using three sediment sizes effects of three species of polychaetes and two species of bivalves were tested boundary shear velocity was calculated from the mean velocity profile in the logarithmic region of the boundary layer measurements were made with a hot film anemometer tracking doubled the boundary roughness and decreased the critical entrainment velocity by 20 ambient or free sediments were more easily entrained than fecal mounds which were restrained from movement by mucous adhesion between the fecal coils isolated pellets such as those egested by amphicteis scaphobranchiata transported readily as bedload over a cohesive sediment surface

illuminating and optimising a three dimensional model of an oil shale seam and its volume distribution using the transient electromagnetic induction method central part of jordan the oil shale exploration program in jordan is undertaking great activity in the domain of applied geophysical methods to evaluate bitumen bearing rock in the study area the bituminous marl or oil shale exhibits a rock type dominated by lithofacies layers composed of chalky limestone marls clayey marls and phosphatic marls the study aims to present enhancements for oil shale seam detection using progressive interpretation from a one dimensional inversion to a three dimensional modelling and inversion of ground based transient electromagnetic data at an area of stressed geological layers the geophysical survey combined 58 transient electromagnetic sites to produce geoelectrical structures at different depth slices and cross sections were used to characterise the horizon of the most likely sites for mining oil shale the results show valuable information on the thickness of the oil shale seam at 3 7 m which is correlated to the geoelectrical layer between 2 ms and 4 ms transient time delays and at depths ranging between 85 m and 105 m the 300 m penetrated depth of the transient electromagnetic soundings allows the resolution of the main geological units at narrow resistivity contrast and the distinction of the main geological structures that constrain the detection of the oil shale seam this geoelectrical layer at different depth slices illustrates a localised oil shale setting and can be spatially correlated with an area bounded by fold and fault systems also three dimensional modelling and inversion for synthetic and experimental data are introduced at the faulted area the results show the limitations of oil shale imaging at a depth exceeding 130 m which depends on the near surface resistivity layer the low resistivity contrast of the main lithological units and the degree of geological detail achieved at a suitable model s misfit value this article is protected by copyright all rights reserved

marine transient electromagnetic sounding of deep buried hydrocarbon reservoirs principles methodologies and limitations the possibility of a time domain electromagnetic sounding method using excitation and measurement of vertical electric fields to search for and identify deeply buried reservoirs of hydrocarbons offshore is investigated the method operates on source receiver offsets which are several times less than the depth of the reservoir geoelectric information is obtained from the transient responses recorded in the pauses between the pulses of electric current in the absence of the source field the basics of the method as well as its sensitivity resolution and the highest accessible depth of soundings for various geological conditions in a wide range of sea depths are analyzed for the analysis 1d and 3d geoelectric models of hydrocarbon reservoirs are used it is shown that under existing technologies of excitation and measurement of vertical electric fields the highest accessible depth of soundings can be up to 4 km technology for the inversion and interpretation of transient responses is demonstrated on experimental data

interactions between waves sediment and turbulence on a shallow estuarine mudflat measurements were collected on a shallow estuarine mudflat in northern san francisco bay to examine the physical processes controlling waves turbulence sediment resuspension and their interactions tides alone forced weak to moderate currents of 10 30 cm s 1 in depths of 0 3 m and maintained a background suspension of 30 50 mg l 1 of fine sediment in the presence of wind waves bottom orbital velocities spanned 20 30 cm s 1 suspended sediment concentrations ssc at 15 and 30 cm above the bed cmab increased by 1 2 orders of magnitude and vertical gradients in ssc were strong enough to produce turbulence limiting stratification with gradient richardson numbers exceeding 0 25 simultaneously turbulent stresses decomposed from wave motions increased by an order of magnitude the apparent contradiction of energetic turbulence in the presence of strong stratification was reconciled by considering the turbulent kinetic energy tke budget in general dissipation and buoyancy flux were balanced by local shear production and each of these terms increased during wave events the classic wave current boundary layer model represented the observations qualitatively but not quantitatively since the velocity profile could not be approximated as logarithmic rather the mean shear was elevated by the stokes drift return flow and wind generated surface stress which diffused sediment upward and limited stratification our findings highlight a pathway for waves to supply energy to both the production and destruction of turbulence and demonstrate that in such shallow depths tke and ssc can be elevated over more of the water column than predicted by traditional models

on the salt water intrusion into the durusu lake istanbul a joint central loop tem and multi electrode ert field survey durusu lake is the biggest and most important freshwater source supplying drinking water to the european side of istanbul in this study electrical resistivity tomography ert and transient electromagnetic tem measurements were applied to detect a possible salt water intrusion into the lake and to delineate the subsurface structure in the north of durusu lake the ert and tem measurements were carried out along six parallel profiles extending from the sea coast to the lake shore on the dune barrier tem data were interpreted using different 1 d inversion methods such as occam marquardt and laterally constrained inversion lci ert data were interpreted using 2 d inversion techniques the inversion results of ert and tem data were shown as resistivity depth sections including topography the sand layer spreading over the basin has a resistivity of 150 400 omega m with a thickness of 5 10 m the sandy layer with clay silt and gravel has a resistivity of 15 100 omega m and a thickness of 10 40 m followed by a clay layer of a resistivity below 10 omega m when the inversion of these data is interpreted along with the hydrogeology of the area it is concluded that the salt water intrusion along the dune barrier is not common and occurs at a particular area where the distance between lake and sea is very close using information from boreholes around the lake it was verified that the common conductive region at depths of 30 m or more consists of clay layers and clay lenses

thermokarst lake to lagoon transitions in eastern siberia do submerged taliks refreeze as the arctic coast erodes it drains thermokarst lakes transforming them into lagoons and eventually integrates them into subsea permafrost lagoons represent the first stage of a thermokarst lake transition to a marine setting and possibly more saline and colder upper boundary conditions in this research borehole data electrical resistivity surveying and modelling of heat and salt diffusion were carried out at polar fox lagoon on the bykovsky peninsula siberia polar fox lagoon is a seasonally isolated water body connected to tiksi bay through a channel leading to hypersaline waters under the ice cover the boreholes in the centre of the lagoon revealed floating ice and a saline cryotic bed underlain by a saline cryotic talik a thin ice bearing permafrost layer and unfrozen ground the bathymetry showed that most of the lagoon was ice grounded in spring in bedfast ice areas the electrical resistivity profiles suggest that an unfrozen saline layer was underlain by a thick layer of refrozen talik the modelling suggests thermokarst lake taliks refreeze when submerged in saltwater with mean annual bottom water temperatures below or slightly above 0 c this occurs because the top down chemical degradation of newly formed ice bearing permafrost is slower than the cooling of the talik hence lagoons may pre condition taliks with a layer of ice bearing permafrost before encroachment by the sea and this frozen layer may act as a cap on gas migration out of the underlying talik

wave formed structures and paleoenvironmental reconstruction clifton h e and dingier j r 1984 wave formed structures and paleoenvironmental reconstruction in b greenwood and r a davis jr editors hydrodynamics and sedimentation in wave dominated coastal environments mar geol 60 165 198 wave formed sedimentary structures can be powerful interpretive tools because they reflect not only the velocity and direction of the oscillatory currents but also the length of the horizontal component of orbital motion and the presence of velocity asymmetry within the flow several of these aspects can be related through standard wave theories to combinations of wave dimensions and water depth that have definable natural limits for a particular grain size threshold of particle movement and that of conversion from a rippled to fiat bed indicate flow velocity limits the ratio of ripple spacing to grain size provides an estimate of the length of the near bottom orbital motion the degree of velocity asymmetry is related to the asymmetry of the bedforms though it presently cannot be estimated with confidence a plot of water depth versus wave height h h diagram provides a convenient approach for showing the combination of wave parameters and water depths capable of generating any particular structure in sand of a given grain size natural limits on wave height and inferences or assumptions regarding either water depth or wave period based on geologic evidence allow refinement of the paleoenvironmental reconstruction the assumptions and the degree of approximation involved in the different techniques impose significant constraints inferences based on wave formed structures are most reliable when they are drawn in the context of other evidence such as the association of sedimentary features or progradational sequences

quantification of modeling errors in airborne tem caused by inaccurate system description beingabletorecoveraccurateandquantitativedescriptionsof the subsurface electrical conductivity structure from airborne electromagneticdataisbecomingmoreandmorecrucialinmany applications such as hydrogeophysical and environmental mapping but also for mining exploration the effect on the inverted models of inaccurate system description in the 1d forward modeling of helicopter time domain electromagnetic tem data was studied the most important system parameters needed for accurate description of the subsurface conductivity were quantified using a nominal airborne tem system and three different reference models to ensure the generality of the conclusions by calculating forward responses the effect of changing the system transfer function of the nominal airbornetem system was studied in detail the data were inverted and the consequences of inaccuratemodelingofthesystemtransferfunctionwerestudiedin themodelspace errorsinthedescriptionofthetransferfunction influence the inverted model differently the low pass filters current turn off and receiver transmitter rx tx timing issues primarily influenced the early time gates the waveform repetition gate integration altitude and geometry mainly influenced thelatetimegates depthofinvestigationishighlymodeldependent but in general the early times hold information on the shallower parts of the model and the late times hold information on thedeeperpartsofthemodel amplitude gain andcurrentvariations affect the entire sounding and therefore the entire model the results showed that all of these parameters should be measured and modeled accurately during inversion of airbornetem data if not the output model can differ quite dramatically from the true model layer boundaries can be inaccurate by tens of meters and layer resistivities by as much as an order of magnitude in the worst cases the measured data simply cannot be fittedwithinnoiselevel

hydrogeophysical investigations in the western and north central okavango delta botswana based on helicopter and ground based transient electromagnetic data and electrical resistance tomography abstractthe okavango delta is a huge alluvial megafan in northwestern botswana despite numerous geologic geochemical geophysical and hydrologic investigations over the past half century the sedimentary units underlying the delta are largely unknown to address this issue helicopter transient electromagnetic data htem have been collected across the entire delta and coincident ground based electrical resistance tomographic ert and transient electromagnetic tem data have been acquired at two locations one along the delta s western margin and one in its north central region inversions of the htem data have yielded three layer resistivity models in which a relatively homogeneous conductive layer is sandwiched between two resistive layers the three layer htem model is reproduced in models obtained from independently and jointly inverting the ground based data the conductive layer s low resistivities and depths to its upper and lower boundaries are practically equal in the htem and ground based m

quasi 3d modeling of airborne tem data by spatially constrained inversion we present a new methodology spatially constrained inversion sci that produces quasi 3d conductivity modeling of electromagnetic em data using a 1d forward solution spatial constraints are set between the model parameters of nearest neighboring soundings data sets models and spatial constraints are inverted as one system the constraints are built using delaunay triangulation which ensures automatic adaptation to data density variations model parameter information migrates horizontally through spatial constraints increasing the resolution of layers that would be poorly resolved locally sci produces laterally smooth results with sharp layer boundaries that respect the 3d geological variations of sedimentary settings sci also suppresses the elongated artifacts commonly seen in interpretation results of profile oriented data sets in this study sci is applied to airborne time domain em data but it can also be implemented with other ground based or airborne data types

suspended particle movement in and around quinault submarine canyon abstract time and space dependent light transmission temperature salinity and velocity data obtained during two winter experiments in the vicinity of quinault submarine canyon are used to examine processes controlling subtidal cpd fluctuations in suspended particulate concentration in the region in particular local resuspension of particles by waves and currents horizontal advection and vertical advection data include time series from four to eight mooring locations as many as 16 current meters and 10 transmissometers on the shelf over the open slope and in the canyon during each experiment spatial distributions from five ctd transmission surveys and gravity wave information particle concentration in the bottom boundary layer at the shelf edge was dominated by resuspension events the mechanism for resuspension had a large inter annual variation in the first year wave induced resuspension dominated whereas in the second year current induced resuspension dominated the cut off depth for storm related resuspension was generally m subtidal advection across isobaths upwelling downwelling accounted for 20 of the variance in concentration fluctuations at the shelf edge in the bottom boundary layer horizontal advection of material suspended in the bottom nepheloid layer on the shelf resulted in the formation of shelf break depth intermediate nepheloid layers over the canyon in regions where the flow crosses isobaths the existence strength onshore offshore extent and vertical structure of such nepheloid layers at a given time in this asymmetrical canyon appear to be a function of the direction of flow over the outer shelf and over the upper slope in the canyon whether active resuspension is occurring over the shelf and the maximum resuspension depth and magnitude of the active resuspension event the frequency timing and magnitude of previous resuspension events spatial and temporal continuity magnitude and direction of flow over the open slope north and south of the canyon vertical settling and upwelling or downwelling related to the along isobath flow over the upper slope fluctuations in particle concentration below the shelf break depth over the canyon slope were controlled by vertical rather than horizontal advection vertical excursions by the water mass of 100 m occurred both as a result of isopycnal adjustment to the quasi geostrophic along isobath flow and as a result of semidiurnal tidal oscillations when an overhead nepheloid layer was present such water mass excursions produced concentration fluctuations at depths below the maximum depth of storm related local resuspension in open slope regions where strong inls intermediate depth nepheloid layers were absent the portion of concentration variance that could be explained by advective models with constant spatial gradients was almost negligible only one resuspension event was documented in the bottom boundary layer within the deep canyon bottom depth 1000 m suggesting that advection must account for the observed variance in particle concentration however the large scale gradients at these depths are sufficiently weak cf the smaller scale gradients or noise that advective control could only be demonstrated during the second winter experiment when velocities along the canyon axis were relatively large finally the data demonstrate that subtidal concentration fluctuations within 50 m of the canyon floor are correlated to those at the shelf edge this correlation reflects a correlation in the velocity field rather than a transfer of particles as might occur with a turbidity current

rapid 1d 3d inversion of shallow resistivity multipole data examples in archaeological prospection fifteen years ago the introduction of mobile multipole arrays led to substantial improvements in shallow electric prospection because it allowed information related to thevertical distribution of ground resistivity in complement to the horizontal pattern of the detected features to be extracted however to make full use of this wealth of information further progress is needed to extendthequalitativeinterpretationofdatatoamorequantitative evaluation of the explored terrain to that intent we developed a two step process in the first step a 1d electric model is fitted to the data over the full explored area and in the second step using the moment method localized 3d interpretation is applied to limited areas for which the characteristics of a given feature require closer scrutiny after a first test with synthetic data generated using the surface integral 3d modeling method this process was applied to three different archaeological sites and one test site for both handheld pole pole array systems and a multipole continuous electric profiling mechanically pulled system at the test site the characteristics of a known wall were accurately recovered at the duntzenheim site the thickness and width of the archaeological remains determined by 3d interpretation corresponded to the features observedthrough excavation at the other two sites 3d interpretation made it possible to establish that the conductive features extend across the full extent of the superficial resistive second layers

quasi 2d block inversion of large scale surface nuclear magnetic resonance profile data using a laterally constrained model abstractthe water content of underground structures can be imaged using surface nuclear magnetic resonance nmr in one dimension two dimensions or recently three dimensions the maximum efficiency can be obtained with a coincident loop configuration in a large scale area although the resolution is limited we have developed a quasi 2d block inversion to characterize a horizontal continuous underground aquifer using a laterally constrained model to improve the resolution of thin aquifers and deep aquifers through the simulation of flat surface and irregular surface models a horizontally layered aquifer with continuously variable water content and t2 can be imaged through quasi 2d block inversion which is more optimized than the traditional 1d block or 1d or 2d smooth inversion methods finally using a series of profile data obtained from surface nmr field measurements in mongolia we determine that quasi 2d block inversion based on a laterally constrained model can significantly improve the disco

tidal asymmetry in sediment resuspension on a macrotidal beach in northwestern australia abstract a field experiment was conducted on a macrotidal beach in northwestern australia to investigate the relation between sediment resuspension and sea bed morphology continuous measurements of waves currents and suspended sediment concentrations were carried out over a period of several hours around high tide concurrent with half hourly visual observations of the sea bed morphology the incident waves had a significant wave height of 0 35 m and period 11 s most of the data were collected outside the surf zone where sediment resuspension was mainly by wave groups and suspended sediment transport was primarily accomplished by mean longshore and cross shore currents the sediment resuspension process was further characterised by a pronounced tidal asymmetry with suspended sediment concentrations and transport rates during the falling tide significantly larger than during the rising tide the asymmetry is attributed to the combined effects of a larger bed roughness and stronger mean nearshore flows during the falling tide the increase in bed roughness occurred during the rising tide under the influence of decreasing bed shear stresses when post vortex ripple morphology developed on a previously plane bed around high tide the ripples were fully developed and had attained a ripple height of approximately 0 005 m and a ripple length of 0 06 0 08 m application of the van rijn van rijn l c 1989 handbook sediment transport by currents and waves delft hydraulics report h461 sediment transport model further confirmed that enhanced sediment resuspension during the falling tide was primarily the result of the development of ripple morphology with increased mean current strengths playing a secondary role the results have major implications for modelling suspended sediment transport on macrotidal beaches

modification of the quaternary stratigraphic framework of the inner continental shelf by holocene marine transgression an example offshore of fire island new york abstract the inner continental shelf off fire island new york was mapped in 2011 using interferometric sonar and high resolution chirp seismic reflection systems the area mapped is approximately 50 km long by 8 km wide extending from moriches inlet to fire island inlet in water depths ranging from 8 to 32 m the morphology of this inner continental shelf region and modern sediment distribution patterns are determined by erosion of pleistocene glaciofluvial sediments during the ongoing holocene marine transgression much of the shelf is thus an actively forming ravinement surface remnants of a pleistocene outwash lobe define a submerged headland offshore of central fire island east of the submerged headland relatively older pleistocene outwash is exposed over much of the inner continental shelf and covered by asymmetric sorted bedforms interpreted to indicate erosion and westward transport of reworked sediment erosion of the eastern flank of the submerged pleistocene headland over the last 8000 years yielded an abundance of modern sand that was transported westward and reworked into a field of shoreface attached ridges offshore of western fire island west of the submerged headland erosion of pleistocene outwash continues in troughs between the sand ridges resulting in modification of the lower shoreface comparison of the modern sand ridge morphology with the morphology of the underlying ravinement surface suggests that the sand ridges have moved a minimum of 1000 m westward since formation comparison of modern sediment thickness mapped in 1996 1997 and 2011 allows speculation that the nearshore shoreface sedimentary deposit has gained sediment at the expense of deflation of the sand ridges

dynamics of large and small scale bedforms on a macrotidal shoreface under shoaling and breaking waves abstract bedform dimensions bed position changes near bed velocities and suspended sand concentrations are analyzed from measurements at a single location on a macro tidal beach in the south west of england the study was conducted in 0 5 2 25 m water depth under both swell and wind generated storm waves with both weak and strong currents present bed positions and suspended sand concentrations were measured using the 3 transducers of a multi frequency acoustic backscatter sensor with 5 mm vertical resolution two distinct bed types based on wavelength were observed each with two or more subtypes possible i small scale bedforms 20 cm which include two dimensional 5 forms and three dimensional vortex 6 forms small scale forms were dominant under non breaking conditions while the large scale forms occurred under both non breaking and breaking waves the large scale forms dominate under breaking conditions both types but particularly low steepness forms were highly mobile with maximum horizontal migration rates of 5 cm min 1 large upto 15 cm and rapid upto 3 0 cm min 1 changes in vertical bed elevation were also observed in association with the development and migration of large scale forms large scale bedforms were also highly variable spatially often being interspersed with smaller scale forms under decaying flow regimes and with areas of flat bed under increasing regimes observations suggest these forms are present even under high energy surf zone conditions wave shields 1 models for predicting ripple dimensions did not perform well in this environment this lack of agreement reflects the complex hydrodynamic regimes associated with random grouped shoaling and breaking waves together with the presence of currents often at large angles to the waves as well as the rapid rates of change in the wave forcing associated with tidal cycle oscillations in this macrotidal environment suspended sediment concentrations and transport rates are particularly sensitive to the bedforms present and also to bed position changes associated with ripple migration estimates of transport rates are subject to potentially large errors upto 30 without compensation for bed elevation changes relative to sensor position

quasi 2d inversion of dcr and tdem data for shallow investigations joint or sequential inversion of direct current resistivity dcr and time domain electromagnetic tdem data commonly are performed for individual soundings assuming layered earth models dcr and tdem have different and complementary sensitivity to resistive and conductive structures making them suitable methods for the application of joint inversion techniques this potential joint inversion of dcr and tdem methods has been used by several authors to reduce the ambiguities of the models calculated from each method separately a new approach for joint inversion of these data sets based on a laterally constrained algorithm was found the method was developed for the interpretation of soundings collected along a line over a 1d or 2d geology the inversion algorithm was tested on two synthetic data sets as well as on field data from saudi arabia the results show that the algorithm is efficient and stable in producing quasi 2d models from dcr and tdem data acquired in relatively complex environments

suspended sediment transport under estuarine tidal channel conditions abstract a modified version of the geoprobe tripod has been used to monitor flow conditions and suspended sediment distribution in the bottom boundary layer of a tidal channel within san francisco bay california measurements were made every 15 minutes over three successive tidal cycles they included mean velocity profiles from four electromagnetic current meters within 1 m of the seabed mean suspended sediment concentration profiles from seven miniature nephelometers operated within 1 m of the seabed near bottom pressure fluctuations vertical temperature gradient and bottom photographs additionally suspended sediment was sampled from four levels within 1 m of the seabed three times during each successive flood and ebb cycle while the instrument was deployed std nephelometer measurements were made throughout the water column water samples were collected each 1 2 hours and bottom sediment was sampled at the deployment site from these measurements estimates were made of particle settling velocity ws from size distributions of the suspended sediment friction velocity u from the velocity profiles and reference concentration ca was measured at z 20 cm these parameters were used in the suspended sediment distribution equations to evaluate their ability to predict the observed suspended sediment profiles three suspended sediment particle conditions were evaluated 1 individual particle size in the 4 11 62 5 0 5 m range with the reference concentration ca at z 20 cm c 2 individual particle size in the 4 6 size range flocs representing the 7 11 size range with the reference concentration ca at z 20 cm cf and 3 individual particle size in the 4 6 size range flocs representing the 7 11 size range with the reference concentration predicted as a function of the bed sediment size distribution and the square of the excess shear stress in addition computations of particle flux were made in order to show vertical variations in horizontal mass flux for varying flow conditions

identifying seawater intrusion in coastal areas by means of 1d and quasi 2d joint inversion of tdem and ves data abstract seawater intrusion is an increasingly widespread problem in coastal aquifers caused by climate changes sea level rise extreme phenomena like flooding and droughts and groundwater depletion near to the coastline to evaluate and mitigate the environmental risks of this phenomenon it is necessary to characterize the coastal aquifer and the salt intrusion geophysical methods are the most appropriate tool to address these researches among all geophysical techniques electrical methods are able to detect seawater intrusions due to the high resistivity contrast between saltwater freshwater and geological layers the combination of two or more geophysical methods is recommended and they are more efficient when both data are inverted jointly because the final model encompasses the physical properties measured for each methods in this investigation joint inversion of vertical electric and time domain soundings has been performed to examine seawater intrusion in an area within the ferragudo albufeira aquifer system algarve south of portugal for this purpose two profiles combining electrical resistivity tomography ert and time domain electromagnetic tdem methods were measured and the results were compared with the information obtained from exploration drilling three different inversions have been carried out single inversion of the ert and tdem data 1d joint inversion and quasi 2d joint inversion single inversion results identify seawater intrusion although the sedimentary layers detected in exploration drilling were not well differentiated the models obtained with 1d joint inversion improve the previous inversion due to better detection of sedimentary layer and the seawater intrusion appear to be better defined finally the quasi 2d joint inversion reveals a more realistic shape of the seawater intrusion and it is able to distinguish more sedimentary layers recognised in the exploration drilling this study demonstrates that the quasi 2d joint inversion improves the previous inversions methods making it a powerful tool applicable to different research areas

improvement in mrs parameter estimation by joint and laterally constrained inversion of mrs and tem data we developed a new scheme for joint and laterally constrained inversion lci of magnetic resonance sounding mrs data and transient electromagnetic tem data which greatly improves the estimation of the mrs model parameters during the last few decades electrical and electromagnetic methods have been widely used for groundwater investigation but they suffer from some inherent limitations for example equivalent layer sequences furthermore the water content information is only empirically correlated to resistivity of the formation mrs is a noninvasive geophysical technique that directly quantifies the water content distribution from surface measurements the resistivity information of the subsurface is obtained from a complementary geophysical method such as tem or dc resistivity methods the conventional inversion of mrs data assumes the resulting resistivity structure to be correct and considers a constant mrs kernel through the inversion we found that this assumption may introduce an error to the forward modeling and consequently could result in erroneous parameter estimations in the inversion process we investigated the advantage of tem for the joint inversion compared to dc resistivity a fast and numerically efficient mrs forward routine made it possible to invert the mrs and tem data sets simultaneously along profiles furthermore by application of lateral constraints on the model parameters lateral smooth 2d model sections could be be obtained the simultaneous inversion for resistivity and mrs parameters led to a more reliable and robust estimation of all parameters and the mrs data diminished the range of equivalent resistivity models we examined the approach through synthetic data and a field example in denmark where good agreement with borehole data was demonstrated with clear correlation between the relaxation time

three dimensional image of seismic refraction tomography and electrical resistivity tomography survey in the castle of occhiola sicily italy a geophysical survey was carried out at the ruins of occhiolacastle sicily italy a medieval village located at the north western part of a hill named terravecchia at 491 m asl in order to map the archaeological structures such as walls and burrows electrical resistivity to mography ert and seismic refraction tomography methods were used the resistivity variations are known to correlate quite well with the lithology thus providing important information for identifying the buried archaeological remains on the other hand seismic velocity variations provide information about the geometrical features of the remains the two geophysical methods are used in an enjoined way to better aid the interpretation and evaluate the significance and reliability of the results obtained with each single method the electrical and seismic data are displayed in three dimensions by using the iso resistivity and iso velocity surfaces respectively this allows us to effectively define the location of the anomalies present in the single electrical and seismic sections the results obtained in the survey highlight the presence of structures of regular shape probably due to features of archaeological interest 2006 elsevier ltd all rights reserved

challenges in geophysical mapping of glaciotectonic structures abstractglaciotectonic complexes have been recognized worldwide traditionally described on the basis of outcrops or geomorphological observations in the past few decades geophysics has become an integral part of geologic mapping which enables the mapping of buried glaciotectonic complexes the geophysical methods provide different types of information and degrees of resolution and thus a different ability to resolve the glaciotectonic structures we evaluated these abilities on the basis of an integrated application of four commonly used geophysical methods airborne transient electromagnetics high resolution reflection seismic geoelectrical and ground penetrating radar gpr we covered an area of 100 km2 in a formerly glaciated region in the western part of denmark the geologic setting was highly heterogeneous with glaciotectonic deformation observed in the form of large scale structures in the seismic and airborne transient electromagnetic data to small scale structures seen in the gpr and g

improved 1d inversions for sea ice thickness and conductivity from electromagnetic induction data inclusion of nonlinearities caused by passive bucking the porosity of sea ice is a fundamental physical parameter that governs the mechanical strength of sea ice and the mobility of gases and nutrients for biological processes and biogeochemical cycles in the sea ice layer however little is known about the spatial distribution of the sea ice porosity and its variability between different sea ice types an efficient and nondestructive method to measure this property is currently missing sea ice porosity is linked to the bulk electrical conductivity of sea ice a parameter routinely used to discriminate between sea ice and seawater by electromagnetic em induction sensors here we have evaluated the prospect of porosity retrieval of sea ice by means of bulk conductivity estimates using 1d multifrequency em inversion schemes we have focused on two inversion algorithms a smoothness constrained inversion and a marquardt levenberg inversion which we modified for the nonlinear signal bias caused by a passive bucking coil operated in such a highly conductive environment using synthetic modeling studies 1d inversion algorithms and multiple frequencies we found that we can resolve the sea ice conductivity within 0 01 s m using standard assumptions for the conductivity porosity relation of sea ice we were able to estimate porosity with an uncertainty of 1 2 which enables efficient and nondestructive surveys of the internal state of the sea ice cover

resistivity mapping with geophilus electricus information about lateral and vertical soil heterogeneity abstract geophilus electricus nickname geophilus is a novel system for mapping the complex electrical bulk resistivity of soils rolling electrodes simultaneously measure amplitude and phase data at frequencies ranging from 1 mhz to 1 khz the sensor s design and technical specifications allow for measuring these parameters at five depths of up to ca 1 5 m data inversion techniques can be employed to determine resistivity models instead of apparent values and to image soil layers and their geometry with depth when used in combination with a global positioning system gps and a suitable cross country vehicle it is possible to map about 100 ha day assuming 1 data point is recorded per second and the line spacing is 18 m the applicability of the geophilus system has been demonstrated on several sites where soils show variations in texture stratification and thus electrical characteristics the data quality has been studied by comparison with static electrodes by repeated measurements and by comparison with other mobile conductivity mapping devices veris3100 and em38 the high quality of the conductivity data produced by the geophilus system is evident and demonstrated by the overall consistency of the individual maps and in the clear stratification also confirmed by independent data the geophilus system measures complex values of electrical resistivity in terms of amplitude and phase whereas electrical conductivity data amplitude are well established in soil science the interpretation of phase data is a topic of current research whether phase data are able to provide additional information depends on the site specific settings here we present examples where phase data provide complementary information on man made structures such as metal pipes and soil compaction

an electrostratigraphic cross section across the central po plain bearings on subsurface geology and hydrostratigraphy a 72 km long n s cross section was surveyed with direct current resistivity soundings through the quaternary clastic infill of the apennine foredeep in the po plain of lombardy northern italy the aims are 1 to test the potential of dc resistivity methods at the regional scale 2 to draw the electrostratigraphic picture of the basin fill down to the pre quaternary substratum 3 to refine and test the methodology and concepts of hierarchic electrostratigraphy at the basin scale 4 to contribute to characterize the regional hydrostratigraphy of a relevant hydrogeological basin 163 resistivity versus depth profiles with a maximum investigation depth of 450 m were obtained from vertical electrical soundings to draw the electrostratigraphic cross section the polarity of the resistivity contrast across resistivity interfaces i e resistive over conductive layers or vice versa was considered and the discontinuities were correlated according to the persisting pattern from north to south doing so the hierarchic assemblage of four major electrostratigraphic boundaries and the five intervening groups of electrostratigraphic units esus was established the resulting picture was compared to the available subsurface reconstructions from the literature using the 1 d borehole data only to check the geophysical image at some random sample sites the results show that the electrostratigraphic picture captures the geological and hydrostratigraphic complexity of the subsurface of the basin comparing well with the available direct subsurface geological and hydrostratigraphic reconstructions at the regional scale of the cross section two hierarchic orders of esus and correlative boundaries could be drawn first order groups and second order individual esus while the lowermost third order rank the electrolayer is recognized at the single ves sites only

high sea floor stress induced by extreme hurricane waves 1 strong surface waves and currents generated by major hurricanes can produce extreme forces at the seabed that scour the seafloor and cause massive underwater mudslides our understanding of these forces is poor due to lack of concurrent measurements of waves and currents under these storms using unique observations collected during the passage of a category 4 hurricane ivan bottom stress due to currents and waves over the outer continental shelf in the gulf of mexico was examined during the passage of ivan the bottom stress was highly correlated with the wind with a maximum of about 40 of the wind stress the bottom stress was dominated by the wave induced stresses and exceeded critical levels at depths as large as 90 m surprisingly the bottom damaging stress persisted after the passage of ivan for about a week and was modulated by near inertial waves

the benthic boundary layer and sediment transport the major problems facing scientists studying marine boundary layer fluid mechanics in 1979 concerned the specific mechanismic operating in the regions of the top and the bottom of the boundary layer at the top the mechanisms of fluid escapement from the boundary layer and mixing into the ocean interior could only be postulated approximations of diffusivity across the top of the layer were being debated the values of which were more articles of faith than physically validated estimates cf armi 1979 garrett 1979 at the bottom the intermittent generation of stress cf gordon 1975 heathershaw and simpson 1979 was held responsible for the wide variability observed in the drag coefficient and the thickness of the viscous sub layer was claimed to be greater than that traditionally found from laboratory studies caldwell and chriss 1979

palaeoseismicity of the oquirrh fault utah from shallow seismic tomography the magnitude and frequency of normal fault palaeoearthquakes are usually determined by trenching studies that ascertain the size and number of colluvial wedges along the fault such information can be invaluable in predicting the seismic hazard and potential for a future earthquake in that region digging trenches across normal faults however is environmentally intrusive expensive and limited in the penetration depth to overcome these problems we propose the use of 3 d seismic tomography as a means to identify the shapes and sizes of colluvial wedges along normal faults as an example 2 d and 3 d seismic surveys were conducted across the oquirrh fault utah with the purpose of imaging the normal fault structure to a depth of about 10 m results show that the 3 d tomogram clearly delineates the fault zone and a colluvial wedge both of which correlate extremely well with the geological cross section interpreted from an adjacent trench the thickness of the colluvial wedge image is used in conjunction with a seismic section to compute an estimate of a 6 8 moment magnitude earthquake for the most recent event on this fault which is in close agreement with the 7 0 estimate based on a nearby trenching study these tomographic results demonstrate for the first time that seismic imaging methods can be used in some cases to estimate unambiguously the shapes of colluvial wedges and the sizes of prehistoric earthquakes thus seismic tomography has the possibility of providing cheaper deeper and wider but less resolved images of fault systems than the intrusive excavation of trenches across faults

sediment transport events on the northern california continental shelf abstract a long term monitoring tripod has been maintained in 60 m water depth at the northern end of the strataform study site on the northern california continental shelf as part of this ongoing study tripod data for 1 year beginning 24 september 1995 are used to provide a sediment transport analysis on an event by event basis the objective of this paper is to highlight the energetic nature of this shelf region in terms of the frequency duration and magnitude of sediment suspension events and the associated particle flux analyses are based on measurements from two current meters and two optical backscatterance sensors located at 30 and 100 cm above the bed data from these instruments and a pressure sensor were averaged over 7 5 min every hour during the year of record 41 distinct sediment suspension events occurred i e sustained suspended sediment concentrations greater than 20 mg l above background level at 100 cm above bed suspended sediment events were associated with significant wave activity tidal currents and river discharge the average duration of a sediment suspension event was 3 1 days and varied from 0 7 to 8 days during events mean suspended sediment concentrations of 110 mg l were observed with peak hourly observations exceeding 1000 mg l concentrations between events averaged 35 mg l the overall sediment flux for the period of record was directed seaward and southward the distribution and magnitude of sediment suspension events and particle flux showed a strong seasonality for example of the sediment transport during events 98 of the net along shelf and 73 of the net across shelf sediment transport occurred in the winter three major winter storms could account for 72 of the total along shelf transport but only 10 of the across shelf transport the across shelf flux was more evenly distributed over the year and occurred as a result of mean currents and very low frequency seaward flows associated with mesoscale circulation patterns

a comparison of helicopter borne electromagnetic systems for hydrogeologic studies the increased application of airborne electromagnetic surveys to hydrogeological studies is driving a demand for data that can consistently be inverted for accurate subsurface resistivity structure from the near surface to depths of several hundred metres we present an evaluation of three commercial airborne electromagnetic systems over two test blocks in western nebraska usa the selected test blocks are representative of shallow and deep alluvial aquifer systems with low groundwater salinity and an electrically conductive base of aquifer the aquifer units show significant lithologic heterogeneity and include both modern and ancient river systems we compared the various data sets to one another and inverted resistivity models to borehole lithology and to ground geophysical models we find distinct differences among the airborne electromagnetic systems as regards the spatial resolution of models the depth of investigation and the ability to recover near surface resistivity variations we further identify systematic biases in some data sets which we attribute to incomplete or inexact calibration or compensation procedures

slopes of an airborne electromagnetic resistivity model interpolated jointly with borehole data for 3d geological modelling we investigate a novel way to introduce resistivity models deriving from airborne electromagnetic surveys into regional geological modelling standard geometrical geological modelling can be strengthened using geophysical data here we propose to extract information contained in a resistivity model in the form of local slopes that constrain the modelling of geological interfaces the proposed method is illustrated on an airborne electromagnetic survey conducted in the region of courtenay in france first a resistivity contrast corresponding to the clay chalk interface was interpreted confronting the electromagnetic soundings to boreholes slopes were then sampled on this geophysical model and jointly interpolated with the clay chalk interface documented in boreholes using an implicit 3d potential field method in order to evaluate this new joint geophysical geological model its accuracy was compared with that of both pure geological and pure geophysical models for various borehole configurations the proposed joint modelling yields the most accurate clay chalk interface whatever the number and location of boreholes taken into account for modelling and validation compared with standard geological modelling the approach introduces in between boreholes geometrical information derived from geophysical results compared with conventional resistivity interpretation of the geophysical model it reduces drift effects and honours the boreholes the method therefore improves what is commonly obtained with geological or geophysical data separately making it very attractive for robust 3d geological modelling of the subsurface

movable bed roughness in unsteady oscillatory flow a model to predict the roughness in unsteady oscillatory flows over movable noncohesive beds is presented the roughness over movable beds is shown to be a function of the boundary shear stress rather than a fixed geometrical scale as is the case for fully rough turbulent boundary shear flows over immobile beds the model partitions the roughness into two distinct contributions these two contributions are due to the form drag around individual bed forms and to the near bed sediment transport the form drag over the bed forms is treated explicitly as a function of the boundary geometry and shear stress the ripples are predicted as a function of the local skin friction and a semiempirical expression is derived using standard law of the wall arguments which gives the ripple or form roughness as a function of the boundary geometry the ripple roughness is found to be proportional to the product of the ripple steepness and height favorable comparison of the form drag model with the results of bagnold s 1946 fixed ripple study is found the value of z0 associated with intense sediment transport in oscillatory flow over a flat bed is determined from carstens et al s 1969 experiments this value is found to be 7 or 8 grain diameters an expression is derived for the roughness associated with the maximum thickness of a near bottom sediment transporting layer consistent with owen s 1964 roughness hypothesis for saltation of uniform grains in air at large values of the boundary shear stress relative to the critical value for initial sediment motion the derived expression is similar to the results of smith and mclean s 1977 unidirectional flow approach modified for oscillatory flow the total roughness model is found to compare favorably with carstens et al s 1969 data in contrast to smith and mclean s 1977 steady flow findings the results here show that when ripples are present they account for a significant portion of the boundary roughness

predicting ripple roughness and sand resuspension under combined flows in a shoreface environment ripple measurements and flow and sediment dynamical data obtained from the shoreface of the middle atlantic bight using instrumented tripods were analyzed to evaluate various predictors of ripple geometry and roughness ripple roughness controls on sand resuspension and suspended sediment concentration profiles under combined waves and currents were also evaluated the limited observation of sand ripples in the field indicates that the grant and madsen 1982 method overestimates ripple roughness while the nielsen 1981 method tends to under predict ripple roughness a modified ripple predictor is thus proposed based on the grant and madsen method and it is shown to give reasonable predictions under the present experiment conditions this modified ripple prediction along with wave current and suspended sediment concentration data recorded by the tripods were then brought into the combined flow bottom boundary layer model of grant and madsen 1986 and the modified rouse equation of glenn and grant 1987 to calculate sand resuspension coefficient 0 and to predict suspended sediment concentration profiles it was found that under low energy fair weather conditions sand ripples are in the equilibrium range and ripple roughness increases with the bed shear stress this causes strong vortex activity close to seabed and thus higher resuspension coefficient reference concentrations are moderate due to this high resuspension coefficient even though bed shear stresses are low under moderate storm conditions ripple break off occurs and ripple roughness will decrease with bed shear stress this reduces the vortex activity and hence sand resuspension coefficient 0 the combination of this moderately high bed shear stress and reduced but still moderate ripple roughness favours sand suspension and produces the highest reference concentration for the encountered experimental conditions as bed shear stress is further increased ripples are nearly washed out and sand resuspension coefficient is further decreased approaching the previously suggested constant value of 1 3 10 4 this corresponds with the lowest reference concentration despite the high bed shear stress suspended sediment concentrations predicted by the modified rouse equation using this time variable resuspension coefficient and properly calculated bottom boundary layer parameters are reasonable compared to the field measured concentration profiles

sharp spatially constrained inversion with applications to transient electromagnetic data time domain electromagnetic data are conveniently inverted by using smoothly varying 1d models with fixed vertical discretization the vertical smoothness of the obtained models stems from the application of occam type regularization constraints which are meant to address the ill posedness of the problem an important side effect of such regularization however is that horizontal layer boundaries can no longer be accurately reproduced as the model is required to be smooth this issue can be overcome by inverting for fewer layers with variable thicknesses nevertheless to decide on a particular and constant number of layers for the parameterization of a large survey inversion can be equally problematic here we present a focusing regularization technique to obtain the best of both methodologies the new focusing approach allows for accurate reconstruction of resistivity distributions using a fixed vertical discretization while preserving the capability to reproduce horizontal boundaries the formulation is flexible and can be coupled with traditional lateral spatial smoothness constraints in order to resolve interfaces in stratified soils with no additional hypothesis about the number of layers the method relies on minimizing the number of layers of non vanishing resistivity gradient instead of minimizing the norm of the model variation itself this approach ensures that the results are consistent with the measured data while favouring at the same time the retrieval of horizontal abrupt changes in addition the focusing regularization can also be applied in the horizontal direction in order to promote the reconstruction of lateral boundaries such as faults we present the theoretical framework of our regularization methodology and illustrate its capabilities by means of both synthetic and field data sets we further demonstrate how the concept has been integrated in our existing spatially constrained inversion formalism and show its application to large scale time domain electromagnetic data inversions

measurements of storm generated bottom stresses on the continental shelf large values of bottom friction velocity u and roughness length z0 determined from burst averaged speed data taken on the continental shelf in outer norton sound alaska with the geoprobe tripod during a storm in september 1977 are correlated with extremely large values of near bottom concentration of total suspended particulate matter tsm combined wind driven and tidal currents exceeding 30 cm s at 1 m above the bottom and intense oscillatory bottom currents with maxima above 45 cm s were associated with the largest measured values of tsm at 2 m above the sea floor the values of u and z0 obtained from the law of the wall velocity depth relationship are diminished substantially throughout the storm period average reduction of 44 when the turbulence reducing effects of the vertical concentration gradient of tsm are considered the form of the latter correction was adapted from smith and mclean 1977a values of the mean u computed from the theory of grant and madsen 1979 which predicts an enhanced shear stress due to nonlinear wave current interactions compare favorably with the u values determined from the measured velocity profiles the measured values of z0 however are considerably larger than any of the estimates based on 1 the actual scales of the physical roughness elements 2 the apparent roughness of grant and madsen 1979 or 3 the thickness of the bed load layer as formulated by smith and mclean 1977a

an improved ert approach for the investigation of subsurface structures the joint use of multiple geophysical data types has been proven to be a powerful tool to both improve subsurface imaging and help in the interpretation process the main goal of this paper is to develop a multi geophysical approach for subsurface experimental investigations in which seismic data are used to improve electrical resistivity tomography quality the basic philosophy of the method is that seismic travel time data will be used to construct the prior model for the resistivity inversion synthetic data were employed to demonstrate the improvements enabled by the use of this strategy afterwards the scheme was applied successfully on field data from northwestern china the outcomes reveal that the multi geophysical approach improves the interpretation of the subsurface over a single source

laterally constrained inversion of ground roll from seismic reflection records seismic reflection data contain surface waves that can be processed and interpreted to supply shear wave velocity models along seismic reflection lines the coverage of seismic reflection data allows the use of automated multifold processing to extract high quality dispersion curves and experimental uncertainties in a moving spatial window the dispersion curves are then inverted using a deterministic laterally constrained inversion to obtain a pseudo 2d model of the shear wave velocity a monte carlo global search inversion algorithm optimizes the parameterization when the strategy is used with synthetic and field data consistent final models with smooth lateral variations are successfully retrieved this method constitutes an improvement over the individual inversion of single dispersion curves

breaks in lithology interpretation problems when handling 2d structures with a 1d approximation most airborne electromagnetic aem data are processed using successive 1d approximations to produce stitched conductivity depthsections becausethecurrentinducedinthenearsurface by an aem system preferentially circulates at some radial distancefromahorizontallooptransmittersometimescalledthe footprint the section plotted directly below a concentric transmitter receiver system actually arises from currents induced in the vicinity rather than directly underneath detection of paleochannels as conduits for groundwater flow is a common geo

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

a numerical comparison of 2d resistivity imaging with 10 electrode arrays numerical simulations are used to compare the resolution and efficiency of 2d resistivity imaging surveys for 10 electrode arrays the arrays analysed include polepole pp pole dipole pd half wenner hw wenner wn schlumberger sc dipole dipole dd wenner wb array gm multiple or moving gradient array gd and midpoint potential referred measurement mpr arrays five synthetic geological models simulating a buried channel a narrow conductive dike a narrow resistive dike dipping blocks and covered waste ponds were used to examine the surveying efficiency anomaly effects signal to noise ratios and the imaging capabilities of these arrays the responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust l1 norm inversion and smoothness constrained least squares l2 norm inversion for the five synthetic models the results show the following i gm and wn are less contaminated by noise than the other electrode arrays ii the relative anomaly effects for the different arrays vary with the geological models however the relatively high anomaly effects of pp gm and wb surveys do not always give a high resolution image pd dd and gd can yield better resolution images than gm pp wn and wb although they are more susceptible to noise contamination sc is also a strong candidate but is expected to give more edge effects iii the imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi electrode layout within the tested ranges iv the robust inversion generally gives better imaging results than the l2 norm inversion especially with noisy data except for the dipping block structure presented here v gd and mpr are well suited to multichannel surveying and gd may produce images that are comparable to those obtained with dd and pd accordingly the gd pd dd and sc arrays are strongly recommended for 2d resistivity imaging where the final choice will be determined by the expected geology the purpose of the survey and logistical considerations

marine electrical resistivity tomography for shipwreck detection in very shallow water a case study from agropoli salerno southern italy abstract a marine electric resistivity survey was carried out over a submerged beach along the agropoli shore salerno italy to detect buried objects of archaeological interest below the sandy seabed we found a shipwreck a military vessel that probably sunk during the salerno landing operations of the allied forces in the second world war resistivity data provide information on the vertical and horizontal extension of the shipwreck which is characterized by very low calculated resistivity values about 2 5 ohm m such values differ significantly from the sand and the bedrock values 5 40 ohm m although the presence of the shipwreck is clearly visible from geoelectric data the joint application of electric magnetic and multibeam bathymetric techniques reduces the ambiguities inherent in each method as shown in the electrical resistivity tomography ert and confirmed by the digital elevation model obtained from the processing of bathymetric data the shipwreck extends more than 30 m in ne sw direction and it is about 13 m wide the global extension of the relic is consistent with the magnetic data that are characterized by a magnetic anomaly with an amplitude of about 1800 nt and similar dimension as inferred from the estimation of source boundaries obtained from the computation of the analytic signal the results of our survey encourage the use of marine geoelectrical methods for the detection of buried archaeological targets particularly in locations where the use of seismic prospecting is not effective e g very shallow water with sandy sea bottoms the integration of different geophysical methods allows to better define the extension depth and thickness of buried objects suggesting that such an approach is the most effective for underwater archaeological investigations

laterally filtered 1d inversions of small loop frequency domain emi data from a chemical waste site we made a study in the backyard of an agrochemical plant using a small loop frequency domain electromagnetic induction emi system such systems are very sensitive to conductive structures buried at shallow depths frequently they are only used to locate and delimit these structures by direct observation of data however much more information can be obtained by applying numerical modeling techniques to the data first we mapped an anomalous zone that indicates the possible presence of buried waste or some other underground contamination by visualizing data then we applied a 1d inversion method to the data from this zone by joining 1d inversion results this method builds 2d images of the subsoil structure below survey lines because the code applies smoothness constraints to the 1d inversions the subsoil properties in these 2d images change gradually with depth the code does not impose any correlation between the data or 1d models corresponding to neighboring points so sharp lateral changes can appear several of them do not represent real features of the subsoil we designed and applied two spatial filters to smooth the spurious lateral variations in our models one correlates the data acquired at adjacent points prior to inversions the other applies an analogous correlation to the inverse models obtained from the original data both filters greatly improve the quality of the 2d images compiling these results we obtained a 3d model of the subsoil that characterizes the anomalous structure excavations made later at the site confirmed the results

tidal cycle changes in oscillation ripples on the inner part of an estuarine sand flat abstract oscillation ripples form on subaqueous sand beds when wave generated near bottom water motions are strong enough to move sand grains the threshold of grain motion is the lower bound of the regime of oscillation ripples and the onset of sheet flow is the upper bound based on the relation between ripple spacing and orbital diameter three types of symmetrical ripples occur within the ripple regime in the lower part of the ripple regime orbital ripples spacing is proportional to orbital diameter in the upper part anorbital ripples spacing is independent of orbital diameter between these regions occurs a transitional region suborbital ripples oscillation ripples develop on a sandy tidal flat in willapa bay washington as a result of waves traversing the area when it is submerged because wave energy is usually low within the bay the ripples are primarily orbital in type this means that their spacing should respond in a systematic way to changes in wave conditions during the high water parts of some tidal cycles ripples near the beach decrease in spacing during the latter stage of the ebb tide while ripples farther offshore do not change observations made over several tidal cycles show that the zone of active ripples shifts on or offshore in response to different wave conditions detailed bed profiles and current measurements taken during the high water part of spring tides show the manner in which the oscillation ripples change with changes in orbital diameter changes in ripple spacing at the study site could be correlated with changes in orbital diameter in the manner suggested by the criterion for orbital ripples however there appeared to be a lag time between a decrease in orbital diameter and the corresponding decrease in ripple spacing absence of change during a tidal cycle could be attributed to orbital velocities below the threshold for grain motion that negated the effects of changes in orbital diameter because changes in sand flat ripples depend both upon changes in orbital diameter and upon the magnitude of the orbital velocity exposed ripples were not necessarily produced during the preceding high tide in fact some ripples may have been just produced while others farther offshore may have been produced an unknown number of tides earlier therefore when interpreting past wave conditions over tidal flats from low tide ripples one must remember that wave periods have to be short enough to produce velocities greater than the threshold velocity for the orbital diameters calculated from the observed ripple spacings

2 5d resistivity modeling of embankment dams to assess influence from geometry and material properties repeated resistivity measurement is a potentially powerful method for monitoring development of internal erosion and anomalous seepage in earth embankment dams this study is part of a project to improve current longterm monitoring routines and data interpretation and increasing the understanding when interpreting existing data this is accomplished by modeling various occurrences typical of embankment structures using properties from two rockfill embankment dams with central till cores in the north of sweden the study evaluates the influence from 3d effects created by specific dam geometry and effects of water level fluctuations in the reservoir moreover a comparison between different layout locations is carried out and detectability of internal erosion scenarios is estimated through modeling of simulated damage situations software was especially developed to model apparent resistivity for geometries and material distributions for embankment dams the model shows that the 3d effect from the embankment geometry is clearly significant when measuring along dam crests for dams constructed with a conductive core of fine grained soil and high resistive rockfill the effect becomes greatly enhanced also water level fluctuations have a clear effect on apparent resistivities only small differences were found between the investigated arrays a layout along the top of the crest is optimal for monitoring on existing dams where intrusive investigations are normally avoided because it is important to pass the current through the conductive core which is often the main target of investigation the investigation technique has proven beneficial for improving monitoring routines and increasing the understanding of results from the ongoing monitoring programs although the technique and software are developed for dam modeling it could be used for estimation of 3d influence on any elongated structure with a 2d cross section

the use of reference models from a priori data to guide 2d inversion of electrical resistivity tomography data clay rich till plains cover much of the uk such sites are attractive locations for landfills since clay aquitards lower the risk of landfill leachate entering groundwater however such tills often contain sand and gravel bodies that can act as leachate flow routes such bodies may not be detected by conventional site investigation techniques such as drilling boreholes and trial pitting a method of guided inversion where a priori data are used to construct structural reference models for use in inverting electrical resistivity tomography data was proposed as a tool to improve the detection of sand and gravel bodies within clay rich till sequences following a successful 2d guided inversion synthetic modelling study a field study was undertaken wenner 2d electrical resistivity tomography lines resistivity cone penetrometry bores and electromagnetic induction ground resistivity data were collected over a site on the east yorkshire coast england where sand and gravel lenses were known to exist from cliff exposures a number of equally valid geoelectrical models were constructed using the electromagnetic and resistivity cone data these were used as structural reference models in the inversion of the resistivity tomography data blind inversion using an homogenous reference model was also carried out for comparison it was shown for the first time that the best solution model produced by 2d inversion of one data set with a range of structural reference models could be determined by using the l2 model misfit between the solution models and associated reference models reference misfit as a proxy for the l2 misfit between the solution models and the synthetic model or best guess geoelectrical model true misfit the 2d methodology developed here is applicable in clay rich till plains containing sand and gravel bodies throughout the uk

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

detecting palaeolithic activity areas through electrical resistivity survey an assessment from vale de obidos portugal abstract the open air late pleistocene campsite of vale de obidos provided an opportunity to systematically assess the utility of electrical resistivity surveying for activity area detection at palaeolithic sites detailed surface mapping facilitated the exploration of electrical resistivity effects caused by recent land use activities and post depositional processes at vale de obidos tree throw events ploughing and earth moving have a more significant impact on soil resistivity than increases in soil moisture associated with pine tree stumps and roots resistivity results successfully discriminate activity areas containing hearth features and high densities of fire cracked rocks and artifacts as an aid for understanding post depositional processes at archaeological sites and to design excavation and recovery efforts the technique has great potential for palaeolithic archaeology and in other prehistoric contexts that lack major architectural remains

use of transient electromagnetics to define local hydrogeology in an arid alluvial environment to characterize a local groundwater system in an arid alluvial environment a transient electromagnetic tem survey was performed with a dense station spacing along intersecting profiles structural features of significance to groundwater development were clearly evident in the color modulated apparent resistivity versus time pseudosections that were used to display the apparent resistivity data modeling results in conjunction with pseudosections were used to determine exploratory drill sites comparing the modeled results with electric logs from test holes demonstrated that 1 d modeling is not suitable for areas where rapid lateral change occurs these areas are easily identified in the apparent resistivity versus time pseudosections sites not located in fault zones with a resistivity greater than a few tens of ohm m were considered to be preferred locations for production wells hydraulic testing confirmed this interpretation philosophy the survey demonstrates the utility of closely spaced tem sound

assessing hydrological model predictive uncertainty using stochastically generated geological models in distributed and coupled surface water groundwater modelling the uncertainty from the geological structure is unaccounted for if only one deterministic geological model is used in the present study the geological structural uncertainty is represented by multiple stochastically generated geological models which are used to develop hydrological model ensembles for the norsminde catchment in denmark the geological models have been constructed using two types of field data airborne geophysical data and borehole well log data the use of airborne geophysical data in constructing stochastic geological models and followed by the application of such models to assess hydrological simulation uncertainty for both surface water and groundwater have not been previously studied the results show that the hydrological ensemble based on geophysical data has a lower level of simulation uncertainty but the ensemble based on borehole data is able to encapsulate more observation points for stream discharge simulation the groundwater simulations are in general more sensitive to the changes in the geological structure than the stream discharge simulations and in the deeper groundwater layers there are larger variations between simulations within an ensemble than in the upper layers the relationship between hydrological prediction uncertainties measured as the spread within the hydrological ensembles and the spatial aggregation scale of simulation results has been analysed using a representative elementary scale concept the results show a clear increase of prediction uncertainty as the spatial scale decreases copyright 2015 john wiley sons ltd

performance of a sonar altimeter in the nearshore abstract a 1 mhz sonar altimeter with automatic gain control is shown to provide accurate estimates of the distance between the instrument and the seafloor laboratory experiments indicate that distance estimates degrade slightly when the bottom is rough or sloped and when sediment is suspended in the water column results from field tests both within and seaward of the surf zone show some degradation owing to a combination of suspended sediment and bubbles bed undulations and perhaps the dynamic nature of the sand bottom under waves seaward of the surf zone the bottom can be located within 2 cm nearly continuously whereas inside the surf zone the bottom can be located only intermittently and the accuracy decreases to 3 cm a 300 m long cross shore transect of 16 altimeters was deployed from the shoreline to about 4 m depth for 3 months in summer fall 1994 near duck nc results show that the altimeters are robust and can usually provide estimates of the seafloor position every few minutes even in the surf zone during large storms

inversion of induced polarization data we present an algorithm for inverting induced polarization ip data acquired in a 3 d environment the algorithm is based upon the linearized equation for the ip response and the inverse problem is solved by minimizing an objective function of the chargeability model subject to data and bound constraints the minimization is carried out using an interior point method in which the bounds are incorporated by using a logarithmic barrier and the solution of the linear equations is accelerated using wavelet transforms inversion of ip data requires knowledge of the background conductivity we study the effect of different approximations to the background conductivity by comparing ip inversions performed using different conductivity models including a uniform half space and conductivities recovered from one pass 3 d inversions composite 2 d inversions limited aim updates and full 3 d nonlinear inversions of the dc resistivity data we demonstrate that when the background conductivity is simple reasonable ip results are obtainable without using the best conductivity estimate derived from full 3 d inversion of the dc resistivity data as a final area of investigation we study the joint use of surface and borehole data to improve the resolution of the recovered chargeability models we demonstrate that the joint inversion of surface and crosshole data produces chargeability models superior to those obtained from inversions of individual data sets

acoustic measurements of suspended sand on the shoreface and the control of concentration by bed roughness acoustic backscatter measurements of the concentrations of sand in suspension on the shoreface seawards of the breaking zone during a mild storm event show that sand concentrations increase initially but then rapidly decrease as the wave energy increases it is suggested that the bed roughness is a major control on suspended sand concentration and that the decrease in concentration is due to decreasing ripple steepness after the break off bed shear stress is exceeded no direct measurements of bedforms were available and the combined wave current interaction model of grant and madsen j geophys res vols 84 1979 and 87 1982 with extensions to movable bed roughness ripple dimensions from carstens et al s 1969 laboratory data u s army corps eng cerc tech mem 28 and to sediment induced self stratification glenn and grant j geophys res vol 92 1983 was used to predict the current and suspended sand concentration profile matching the measured and modeled concentrations at 2 cm above the bed the values of the resuspension coefficient 0 were found to decrease as excess skin friction increased in a manner similar to that suggested by drake and cacchione cont shelf res vol 9 1989 but were an order of magnitude larger using the much smaller ripple dimensions of nielsen j geophys res vol 86 1981 changed the model results very little significant differences were found between the time averaged suspended sand profiles and those predicted by the model sand transport fluxes have also been computed using the instantaneous products of measured suspended concentrations and currents the current being the sum of steady and wave induced components the wave induced fluxes show considerable variability from run to run but the general pattern is of a transport profile having a shoreward maximum at 5 10 cm above the bed and offshore transport in the few centimetres closest to the bed little net transport occurred above 15 cm these fluxes show a weak dependence on the wave energy becoming more shoreware and the height of the maximum shoreward transport decreasing as the wave energy increased again consistent with the influence of the ripple steepness