3d wave equation interferometric migration of vsp free surface multiples interferometric migration of free surface multiples in vertical seismic profile vsp data has two significant advantages over standard vsp imaging 1 a significantly larger imaging area compared to migrating vsp primaries and 2 less sensitivity to velocity estimation and static errors than other methods for migration of multiples in this paper we present a 3d wave equation interferometric migration method that efficiently images vsp free surface multiples synthetic and field data results confirm that a reflectivity image volume comparable in size to a 3d surface seismic survey around the well can be computed economically the reflectivity image volume has less fold density and lower signal to noise ratio than that obtained by a conventional 3d surface seismic survey because of the relatively weak energy of multiples and the limited number of geophones in the well however the efficiency of this method for migrating vsp multiples suggests that it might sometimes be a useful tool for 4d seismic monitoring where reflectivity images can be computed quickly for each time lapse survey

least squares reverse time migration of multiples abstractthe theory of least squares reverse time migration of multiples rtmm is presented in this method least squares migration lsm is used to image free surface multiples where the recorded traces are used as the time histories of the virtual sources at the hydrophones and the surface related multiples are the observed data for a single source the entire free surface becomes an extended virtual source where the downgoing free surface multiples more fully illuminate the subsurface compared to the primaries since each recorded trace is treated as the time history of a virtual source knowledge of the source wavelet is not required and the ringy time series for each source is automatically deconvolved if the multiples can be perfectly separated from the primaries numerical tests on synthetic data for the sigsbee2b and marmousi2 models show that least squares reverse time migration of multiples lsrtmm can significantly improve the image quality compared to rtmm or standard reverse time migratio

interferometric daylight seismic imaging summary claerbout s daylight imaging concept is generalized to a theory of interferometric seismic imaging ii interferometric seismic imaging is defined to be any algorithm that inverts correlated seismic data for the reflectivity or source distribution as examples we show that ii can image reflectivity distributions by migrating ghost reflections in passive seismic data and generalizes the receiver function imaging method used by seismologists interferometric seismic imaging can also migrate free surface multiples in common depth point cdp data and image source distributions from passive seismic data both synthetic and field data examples are used to illustrate the different possibilities of ii the key advantage of ii is that it can image source locations or reflectivity distributions from passive seismic data where the source position or wavelet is unknown in some cases it can mitigate defocusing errors as a result of statics or an incorrect migration velocity the main drawback with ii is that severe migration artefacts can be created by partial focusing of virtual multiples

reverse time migration of multiples for subsalt imaging some hydrocarbon reservoirs are trapped beneath salt bodies where seismic imaging is greatly challenged due to poor illumination multiple reflections have different propagation wave paths from primary reflections and thus can be used to complement the illuminations where primary reflections from beneath the salt are not acquired consequently migration of multiples can sometimes provide better subsalt images compared to conventional migration which uses primary reflections only in this paper we propose to modify conventional reverse time migration so that multiples can be used as constructive reflection energy for subsalt imaging this new approach replaces the impulsive source wavelet with the recorded data containing both primaries and multiples and uses predicted multiples as the input data instead of primary reflections in the reverse time migration process multiples recorded on the surface are extrapolated backward in time to each depth level and the observed data with both primaries and mult

investigating peatland stratigraphy and hydrogeology using integrated electrical geophysics hydrology has been suggested as the mechanism controlling vegetation and related surficial pore water chemistry in large peatlands peatland hydrology influences the carbon dynamics within these large carbon reservoirs and will influence their response to global warming a geophysical survey was completed in caribou bog a large peatland in maine to evaluate peatland stratigraphy and hydrology geophysical measurements were integrated with direct measurements of peat stratigraphy from probing fluid chemistry and vegetation patterns in the peatland consistent with previous field studies ground penetrating radar gpr was an excellent method for delineating peatland stratigraphy prominent reflectors from the peat lake sediment and lake sediment mineral soil contacts were precisely recorded up to 8 m deep two dimensional resistivity and induced polarization imaging were used to investigate stratigraphy beneath the mineral soil beyond the range of gpr we observe that the peat is chargeable and that ip imaging is an alternative method for defining peat thickness the chargeability of peat is attributed to the high surface charge density on partially decomposed organic matter the electrical conductivity imaging resolved glaciomarine sediment thickness a confining layer and its variability across the basin comparison of the bulk conductivity images with peatland vegetation revealed a correlation between confining layer thickness and dominant vegetation type suggesting that stratigraphy exerts a control on hydrogeology and vegetation distribution within this peatland terrain conductivity measured with a geonics em31 meter correlated with confining glaciomarine sediment thickness and was an effective method for estimating variability in glaciomarine sediment thickness over approximately 18 km 2 our understanding of the hydrogeology stratigraphy and controls on vegetation growth in this peatland was much enhanced from the geophysical study

integrated approach to subsalt depth imaging synthetic case study prestack depth migration has become almost mandatory in areas of complex geology for reasons that are abundantly clear in structurally complex media cmp traveltime curves differ significantly from hyperbolae thus when using standard time processing techniques we cannot produce a time section containing all information related to the medium that is in the prestack gathers

reverse time migration a prospect of seismic imaging methodology abstract reverse time migration rtm is a seismic imaging method to map the subsurface reflectivity using recorded seismic waveforms the practice in exploration seismology has long established a two fold approach of seismic imaging using velocity modeling building to establish the long wavelength reference velocity models and using seismic migration to map the short wavelength reflectivity structures among various seismic migration methods for different situations rtm is the only method that is capable to use all seismic wave types that can be computed numerically being initiated in early 1980 s rtm seeks an image of the subsurface reflectivity as the best match in an image space between the extrapolation of time reversed waveform data and the prediction based on estimated velocity model and source parameters judging the image quality in the same space of forming the images is more advantageous than the approaches of modeling and inversion which seek the solution in the model space but judge its fitness in data space considering that most seismic migration applications today still use primary reflection as the only signal the capability of rtm to use all computable wave types is unique and helpful reducing the imaging artifacts due to mistaking non primary waves as primary reflections hence we refer to those rtm algorithms using only primary reflections as the first generation rtm methods and the rtm algorithms making a full use of primary reflections multiple reflections and other non primary waveform data as the second generation rtm methods this paper reviews the development history of the rtm along with its major challenges current solutions and future perspectives

origin and movement of groundwater and major ions in a thick deposit of champlain sea clay near montreal at a site near montreal piezometers and core samples were used to assess the origin age and rate of groundwater movement in a 28 m thick deposit of champlain sea clay 3h occurs only within the upper 3 4 m which indicates that groundwater below this surficial weathered zone originated prior to 1952 concentrations of 18o na and cl in water from the deepest piezometer suggest that the deep clay was deposited in a mixture of about 33 seawater and 67 freshwater profiles of several major ions show a gradual increase in concentration with depth mathematical simulations of vertical migration of ca2 mg2 k na and cl provide close matches to the field profiles when only upward diffusion of these ions into the surficial freshwater zone is included in the model with a diffusion time of approximately 10 000 a when the downward advection rate of 0 13 cm a 1 obtained from field measurements of hydraulic gradient and hydraulic conductivity is included in the model the simulated major ion profile

a study of the geoelectrical properties of peatlands and their influence on ground penetrating radar surveying1 geophysical surveys and chemical analyses on cores were carried out in three ontario peatlands from which we have gained a better understanding of the peat properties that control the geophysical responses the electrical conductivity depends linearly on the concentration of total dissolved solids in the peat pore waters and the pore waters in turn bear the ionic signatures of the underlying mineral sediments the ionic concentration and thus the electrical conductivity increase linearly from the surface to basement the average bulk electrical conductivity of peatlands at ellice marsh near stratford and at wally creek area forest drainage project near cochrane are of the order of 25 ms m the mer bleue peatland near ottawa has extremely high electrical conductivity reaching levels of up to 380 ms m near the base of the peat the mer bleue peatland water has correspondingly high values of total dissolved solids which originate from the underlying champlain sea glaciomarine clays the dielectric permittivity in peats is largely controlled by the bulk water content ground penetrating radar can detect changes in water content greater than 3 occurring within a depth interval less than 15 cm the principal peatland interfaces detected are the near surface aerobic to anaerobic transition and the peat to mineral basement contact the potential for the successful detection of the basement contact using the radar can be predicted using the radar instrument specifications estimates of the peatland depth and either the bulk peat or the peat pore water electrical conductivities predicted depths of penetration of up to 10 m for ellice marsh and wally creek exceed the observed depths of 1 to 2 m at mer bleue on the other hand we observe that as predicted a 100 mhz signal will penetrate to the base of a 2 m thick peat but a 200 mhz signal will not

subsalt imaging using tti reverse time migration tti depth imaging technology is routinely applied to image structures that lie beneath dipping anisotropic overburden in the canadian foothills vestrum and vermeulen 2004 the north sea hawkins et al 2002 and offshore west africa ball 1995 until now ray based migration algorithms served as the only choice for tti imaging because upgrading ray based imaging algorithms for tti is straightforward and incurs minor additional computational cost unlike ray based algorithms tti wave based algorithms are difficult to formulate and their implementations are often unstable and computationally intensive unfortunately ray based algorithms perform poorly in comparison to wave based algorithms in imaging structures beneath a complex overburden such as the salt canopy in the gulf of mexico however the use of tti imaging in this area is impeded by the lack of appropriate check shots and offset vsps that can constrain anisotropic parameters

ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

elastic reverse time migration elastic prestack reverse time finite difference migration of two component seismic surface data requires data extrapolation and application of an imaging condition data extrapolation involves synchronous driving of the vertical component and horizontal component finite difference meshes with the time reverse of the recorded vertical and horizontal traces respectively extrapolation uses the coupled elastic wave equation for variable velocity solved with a second order explicit finite difference scheme the imaging condition at any point in the grid is the one way traveltime from the source to that point elastic migrations of both synthetic test data and real two component common source gathers produce simpler images than acoustic migrations because of the coalescing of double reflections compressional waves and shear waves into single loci

pool patterning in a northern peatland geophysical evidence for the role of postglacial landforms a hydrogeophysical study conducted in a 2200 ha peatland in central maine shows evidence that a laterally continuous esker deposit extends below the peat soil following the direction of glacier retreat and coinciding with the presence of a pool system ground penetrating radar gpr electrical resistivity er imaging and terrain conductivity measurements were constrained with limited hydrological measurements direct sampling of inorganic sediments and radiocarbon dating of peat soils to develop a conceptual model for pool formation that could explain the unique pool patterning observed in other northern peatlands gpr profiles revealed three dimensional images of two esker crests below the easternmost edge of the pool area gpr data was supported by er imaging and terrain conductivity data and allowed for facies differentiation to infer processes related to esker formation during the glacier front retreat hydrologic data showed preferential flow of groundwater towards the esker suggesting that pools may persist as a result of enhanced peat decomposition and carbon loss due to oxygenation and or upward supply of alternative electron acceptors from the mineral soil along narrow permeable inorganic esker crests variations in pool depths and radiocarbon dating of peat samples from the pool bottom support a model whereby pools originate at a focus centered along the two esker crests and subsequently spread laterally outwards

acquisition and processing of wide aperture ground penetrating radar data a 40 channel wide aperture ground penetrating radar gpr data set was recorded in a complicated fluvial aeolian environment in eastern canada the data were collected in the multichannel format usually associated with seismic reflection surveys and were input directly into a standard seismic processing sequence filtering static corrections common midpoint gathering velocity analysis normal and dip moveout corrections stacking and depth migration the results show significant improvements over single channel recordings in noise reduction and depth of penetration by stacking and in spatial positioning and reduction of diffraction artifacts by migration these characteristics increase the potential for reliable interpretation of structural and stratigraphic details thus without having to develop any new software gpr data processing technology is brought to the same level of capability flexibility and accessibility that is current in seismic exploration

hillslope runoff processes and models abstract hillslope hydrology is concerned with the partition of precipitation as it passes through the vegetation and soil between overland flow and subsurface flow flow follows routes which attenuate and delay the flow to different extents so that a knowledge of the relevant mechanisms is important in the 1960s and 1970s hillslope hydrology developed as a distinct topic through the application of new field observations to develop a generation of physically based forecasting models in its short history theory has continually been overturned by field observation thus the current tendency particularly among temperate zone hydrologists to dismiss all hortonian overland flow as a myth is now being corrected by a number of significant field studies which reveal the great range in both climatic and hillslope conditions some recent models have generally attempted to simplify the processes acting for example including only vertical unsaturated flow and lateral saturated flows others explicitly forecast partial or contributing areas with hindsight the most complete and distributed models have generally shown little forecasting advantage over simpler approaches perhaps trending towards reliable models which can run on desk top microcomputers the variety now being recognised in hillslope hydrological responses should also lead to models which take account of more complex interactions even if initially with a less secure physical and mathematical basis than the richards equation in particular there is a need to respond to the variety of climatic responses and to spatial variability on and beneath the surface including the role of seepage macropores and pipes which call into question whether the hillside can be treated as a darcian flow system

time domain inversion of gpr data containing attenuation resulting from conductive losses many seismic data processing and inversion techniques have been applied to ground penetrating radar gpr data without including the wave field attenuation caused by conductive ground neglecting this attenuation often reduces inversion resolution this paper introduces a gpr inversion technique that accounts for the effects of attenuation the inversion is formulated in the time domain with the synthetic gpr waveforms calculated by a finite element method fem the jacobian matrix can be computed efficiently with the same fem forward modeling procedure synthetic data tests show that the inversion can generate high resolution subsurface velocity profiles even with data containing strong random noise the inversion can resolve small objects not readily visible in the waveforms further the inversion yields a dielectric constant that can help to determine the types of material filling underground cavities

migration methods for imaging different order multiples multiples contain valuable information about the subsurface and if properly migrated can provide a wider illumination of the subsurface compared to imaging with vsp primary reflections in this paper we review three different methods for migrating multiples the first method is model based and it is more sensitive to velocity errors than primary migration the second method uses a semi natural green s function for migrating multiples where part of the traveltimes are computed from the velocity model and part of the traveltimes i e natural traveltimes are picked from the data to construct the imaging condition for multiples the third method uses cross correlation of traces the last two methods are preferred in the sense that they are significantly less sensitive to velocity errors and statics because they use natural data to construct part of the migration imaging conditions compared with the interferometric i e crosscorrelation imaging method the semi natural green s function method is more computationally efficient and is sometimes less prone to migration artifacts numerical tests with 2 d and 3 d vsp data show that a wider subsurface coverage higher fold and more balanced illumination of the subsurface can be achieved with multiple migration compared with migration of primary reflections only however there can be strong interference from multiples with different orders or primaries when multiples of high order are migrated one possible solution is to filter primaries and different orders of multiples before migration and another possible solution is least squares migration of all events a limitation of multiple migration is encountered for subsalt imaging here the multiples must pass through the salt body more than twice which amplifies the distortion of the image

geophysical surveys of burial sites a case study of the oaro urupa a maori family burial site was surveyed using shallow electromagnetic em magnetometer gradiometer and ground penetrating radar gpr techniques the locations of some older graves are no longer known partly through the loss of markers and partly through the loss of the oral record there are at least 150 such burial sites throughout new zealand and similar problems occur elsewhere in the world the knowledge that maori graves are traditionally set out facing east made survey design easier background trends are removed and possible anomalous features are identified despite the complicating presence of metal fencing the em in phase response the vertical gradient of the total magnetic field and the gpr response were particularly useful in combination gpr surveys were carried out using two frequencies 450 and 200 mhz the higher frequency radar surveys were limited in extent because these data had a limited depth of penetration and were prone to signal ringing in the surficial clay the lower

imaging with deep water multiples acquisition of on bottom hydrophone data recording of a near surface source provides an opportunity to treat water column multiples as useful signal a ray equation based kirchhoff depth migration is used to image primary reflections and deep water multiples recorded on an ocean bottom hydrophone obh the image of the subbottom sediments is shown to be improved by inclusion of the deep water multiple in the imaging process field data jointly acquired by woods hole oceanographic institute and university of texas institute for geophysics at austin and consisting of an obh 2300 m depth recording a 10 800 cubic inch air gun array are used to illustrate the feasibility of the technique images are obtained from both the primary reflections and from energy that has undergone an additional passage through the water column comparison of these images reveals an excellent correlation of reflectors with the predicted polarity reversal observed in the multiple s image synthetic data are used to examine the d

elastic p and s wave autofocus imaging with primaries and internal multiples conventional seismic imaging methods rely on the singlescattering born approximation requiring the removal of multiply scattered events from reflection data prior to imaging additionally many methods use an acoustic approximation representing the solid earth as an acoustic fluid medium we have developed imaging methods for solid elastic media that use primaries and internal multiples including their ps and sp conversions thus obviating the need for internal multiple removal and improving handling of internal conversions our methods rely on the elastic autofocusing method which estimates full multicomponent elastodynamic green s functions from virtual sources interior to the medium to receivers placed on the surface they require only surface seismic reflection data and estimates of the direct waves from virtual sources interior to the medium both of which are commonly available at the imaging step of seismic processing we tested our methods on a synthetic model with constant p and s velocities and vertical and horizontal density variations by producing for the first time to our knowledge pp and ss images from elastic autofocusing that are compared to reference seismic images based on conventional methods the effects of multiples are greatly attenuated in the images with fewer spurious reflectors than are observed when using born imaging

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

ground penetrating radar examination of thin tsunami beds a case study from phra thong island thailand coastal overwash deposits from tsunamis and storms have been identified and characterised from many coastal environments to date these investigations have utilised ad hoc time energy and cost intensive invasive techniques such as pits and trenches or taking core samples here we present the application of high frequency ground penetrating radar gpr to identify and characterise the 2004 indian ocean tsunami iot and palaeotsunami deposits from phra thong island thailand this site is one of the most intensively studied palaeotsunami sites globally and preserves a series of late holocene stacked sandy tsunami deposits within an organic muddy low energy backbeach environment using 100 500 and 1000 mhz gpr antennas 29 reflection profiles were collected from two swales x and y inland of the modern beach and two common mid point cmp profiles using the 200 mhz antennas were collected from swale y detailed examination of the cmps allowed accurate velocity estimates to be applied to each profile the reflection profiles included across swale profiles and a high resolution grid in swale x and were collected to investigate the feasibility of gpr to image the palaeotsunami deposits and two profiles from swale y where the tsunami deposits are poorly known the 500 mhz antennas provided the best stratigraphic resolution which was independently validated from the stratigraphy and sedimentology recovered from 17 auger cores collected along the profiles it is clear from the augers and gpr data that the different dielectric properties of the individual layers allow the identification of the iot and earlier tsunami deposits on phra thong island although applied in a coastal setting here this technique can be applied to other environments where thin sand beds are preserved in order to prioritise sites for detailed examination

stratigraphy and soil properties of fens geophysical case studies from northeastern germany abstract the determination of the total carbon storage of peatlands is of high relevance in the context of climate change mitigation efforts this determination relies on data about stratigraphy and peat properties which are conventionally collected by coring ground penetrating radar gpr and electrical resistivity imaging eri can support these point data by providing subsoil information in two dimensional cross sections in this study gpr and eri were conducted at two groundwater fed fen sites located in the temperate zone in north east germany the fens of this region are embedded in low conductive glacial sand and are characterised by thick layers of gyttja which can be either mineral or organic the two study sites are representative of this region with respect to stratigraphy total thickness peat and gyttja types and ecological conditions ph value trophic condition the aim of this study is to assess the suitability of gpr and eri to detect stratigraphy and peat properties under these characteristic site conditions results show that gpr clearly detects the interfaces between i carex and brown moss peat ii brown moss peat and organic gyttja iii organic and mineral gyttja and iv mineral gyttja and the parent material glacial sand these layers differ in bulk density and the related organic matter content eri however does not delineate these layers rather it delineates regions of varying properties at our base rich site pore fluid conductivity and cation exchange capacity are the main factors that determine peat electrical conductivity reverse of resistivity whereas organic matter and water content are most influential at the more acidic site thus the correlation between peat properties and electrical conductivity are driven by site specific conditions which are mainly determined by the solute load in the groundwater at fens when the total organic deposits exceed a thickness of 5 m the depth of investigation by gpr is limited due to increasing attenuation this is not a limiting factor for eri where the transition from organic deposits to glacial sand is visible at both sites due to these specific sensitivities a combined application of gpr and eri meets the demand for up to date information on carbon storage of peatlands which is moreover very site specific because of the inherent variety of ecological conditions and stratigraphy between peatlands in general and between fens and bogs in particular

revealing the temporal dynamics of subsurface temperature in a wetland using time lapse geophysics summary there is growing recognition of the need to understand the subsurface hydrological mechanisms within wetlands given their potentially significant role in the hydrological and biogeochemical function of catchments as well as their effects on the wetland habitat itself conventional subsurface hydrological sampling and monitoring techniques are often limited in such environments because of the invasive nature of such approaches and the sensitivity of the environment in this study we use ground penetrating radar gpr and electrical resistivity tomography ert to characterise the stratigraphy at a small riparian wetland site then through time lapse ert measurements over a 12 month period we demonstrate how changes in resistivity may provide additional value about localised recharge we compare direct measurements of water table depth and pore fluid electrical conductivity and temperature with subsurface resistivity derived from the ert measurements and reveal that temporal fluctuations in temperature of the subsurface dominates the change in resistivity over the monitored period from this we use the ert images of resistivity to estimate spatio temporal changes in subsurface temperature and thus infer localised zones of groundwater recharge due to suppressed seasonal variation in temperature although we focus here on one 2 d vertical profile through the wetland the results highlight the potential value of non invasive time lapse geoelectrical surveys for mapping 3 d thermal patterns within a wetland environment

investigating thickness and internal structure of alpine mires using conventional and geophysical techniques article i nfo we investigated the thickness and composition of five small alpine mires in tyrol austria performing a combination of conventional techniques telescope rods drilling and geophysical methods gpr surveys were carried out using 100 and 200 mhz antennas geoelectrical profiles supplemented the gpr at two sites the 2d surveys were enhanced by additional 1d profiling the aim was to achieve data on mire thickness to cross check the methods and to find reasons for different performance at the five sites the investigations contribute to establishing a future protection concept the formation history of the mires probably goes back to the early holocene the three larger mires are terrestrialisation mires while two mires are formed by paludification probing with a metal rod was subject to considerable errors in both directions caused by obstacles and soft underlying layers thus gpr proved to be a favourable addition to conventional depth assessment at four of five sites gpr made it possible to depict the base layer of the mires at a high accuracy while detecting peat internal interfaces was less successful 2d resistivity profiling supplemented with 1d modelling provided excellent additional informa tion on mire base and deeper subsurface at one site where minerogenic material is washed in 2d resistivity proved to be the better choice compared to gpr

the lamu basin deepwater fold and thrust belt an example of a margin scale gravity driven thrust belt along the continental passive margin of east africa in recent decades advances in seismic processing and acquisition of new data sets have revealed the presence of many deepwater fold and thrust belts dw ftbs often developing along continental passive margins these kinds of tectonic features have been intensively studied due to their substantial interest this work presents a regional scale study of the poorly explored lamu basin dw ftb a margin scale gravity driven system extending for more than 450 km along the continental passive margin of kenya and southern somalia east africa a 2 d seismic data set was analyzed consisting of both recently acquired high quality data and old reprocessed seismic profiles for the first detailed structural and stratigraphic interpretation of this dw ftb the system originated over an early to mid cretaceous shale detachment due to a mainly gravity spreading mechanism analysis of synkinematic strata indicates that the dw ftb was active from the late cretaceous to the early miocene but almost all of the deformation occurred before the late paleocene the fold and thrust system displays a marked n s variation in width the northern portion being more than 150 km wide and the southern portion only a few dozen kilometers wide this along strike variation is thought to be related to the complex tectonosedimentary evolution of the continental margin at the somalia kenya boundary also reflected in the present day bathymetry locally a series of volcanic edifices stopped the basinward propagation of the dw ftb a landward change in the dominant structural style from asymmetric imbricate thrust sheets to pseudo symmetric detachment folds is generally observed related to the landward thickening of the detached shales

variations in free phase gases in peat landforms determined by ground penetrating radar 1 the spatial variability of biogenic gas produced by methanogenic archaea is difficult to assess within saturated peat soils and is often poorly quantified this study uses ground penetrating radar to noninvasively estimate the vertical distribution of biogenic free phase gas fpg in two distinct peat landform types in the glacial lake agassiz peatland minnesota a near crest bog and a midslope lawn i e both as defined by surface vegetation communities ground penetrating radar velocities retrieved from common midpoint surveys were modeled using the complex refractive index model to estimate free phase gas volumes along one dimensional vertical profiles near crest bog landforms are characterized by vertical variability in gas content with accumulations along the peat column up to 24 by volume of fpg localized within the deep peat e g 2 4 m depth midslope lawn sites show lower total volumes up to 12 free phase gas and less variability that result in a more even free phase gas distribution throughout the vertical profile high resolution data also suggests the presence of thinner layers 1 m containing up to 40 free phase gas at a near crest site our results suggest that spatial distribution of free phase gas along the peat column may vary in the glacial lake agassiz peatlands depending on peat landform statistical analysis supports vertical variability of ground penetrating radar velocity data with a 95 confidence limit our results could potentially be upscaled using surface vegetation communities to estimate landscape scale gas storage potential in peat landforms

buffered lagged or cooled disentangling hyporheic influences on temperature cycles in stream channels 1 we monitored summertime base flow water temperatures of hyporheic discharge to surface water in main side and spring channels located within the bank full scour zone of the gravel and cobble bedded umatilla river oregon usa diel temperature cycles in hyporheic discharge were common but spatially variable relative to the main channel s diel cycle hyporheic discharge locations typically had similar daily mean temperatures but smaller diel ranges compressed by 2 to 6 c and desynchronized phases offset by 0 to 6 h in spring channels which received only hyporheic discharge surface water diel cycles were also compressed by 2 to 6 c and desynchronized by 4 to 6 h relative to the main channel creating diverse daytime and nighttime mosaics of surface water temperatures across main side and spring channels despite only minor differences 1 c in daily mean temperatures among the channels the river s hyporheic zone received and stored heat from the channel yet hyporheic return flows carried heat back to the channel minutes to months after removal associated surface water temperature dynamics were therefore complex hyporheic discharge was not simply cooler or warmer than main channel water instead instantaneous temperature differences between channel water and hyporheic discharge typically arose from diel temperature cycles in hyporheic discharge that were buffered and lagged relative to diel cycles in the main channel

an application of ground penetrating radar to peat stratigraphy of ellice swamp southwestern ontario ground penetrating radar gpr has been applied to the mapping of stratigraphy and peat thickness of a large bog in southwestern ontario the gpr survey was undertaken in conjunction with a conventional coring survey and measurement of peat physical properties the results indicate that gpr responds to peat moisture content and bulk density which vary with stratigraphic changes in particular the acrotelm catotelm boundary and the basal clay are gpr reflectors the presence of gyttja above the clay is indicated by complex basal reflections ground penetrating radar is a viable alternative to an intensive coring survey for evaluating peat depth and extent

prestack depth migration of primary and surface related multiple reflections part i imaging surface related multiples i e all seismic waves reflected at the free surface at least once often severely contaminate seismic recordings because conventional imaging techniques require input data that consist of primary reflections only significant processing effort is commonly dedicated to attenuating multiples prior to migration on the other hand surface related multiples provide additional illumination of the subsurface and therefore should not be considered as noise we present a prestack depth migration method that allows primary and multiple reflections to be imaged simultaneously depth imaging using primary and multiple reflections dipmr involves decomposing the datainto upgoing and downgoing wave constituents followed by downward extrapolation artifacts generated by interference of upgoing and downgoing events not associated with the same subsurface reflection points crosstalk are attenuated by using a 2d deconvolution imaging condition in contrast to existing methods dipmr doe

observations and modeling of hillslope throughflow temperatures in a coastal forested catchment a growing body of research on stream thermal regimes has highlighted the importance of heat advection associated with surface water and groundwater interactions such as hyporheic exchange groundwater discharge and hillslope throughflow inputs existing catchment models that predict stream temperature use a variety of approaches to estimate throughflow temperatures but none has been evaluated against field measurements of throughflow temperature in this study throughflow temperatures were monitored over two winters at 50 locations adjacent to a headwater stream 11 ha catchment area located in the rain on snow zone of the pacific northwest existing approaches to estimate throughflow temperature under or overpredicted throughflow temperatures by up to 5 c or were unable to represent the influence of transient snow cover therefore a conceptual parametric model that is computationally efficient was developed that simulates hillslope hydrology and throughflow temperatures the model structure includes an upslope reservoir that drains into a downslope reservoir that in turn drains into the stream vertical and lateral energy and water fluxes are simulated using simplified process representations the model successfully predicts throughflow temperatures and highlights the dominant role of throughflow advection and the influence of snow cover on stream thermal regimes during high flow periods and rain on snow events

identifying causes of ground penetrating radar reflections using time domain reflectometry and sedimentological analyses ground penetrating radar gpr is a geophysical technique widely used to study the shallow subsurface and identify various sediment features that reflect electromagnetic waves however little is known about the exact cause of gpr reflections because few studies have coupled wave theory to petrophysical data in this study a 100 and 200 mhz gpr survey was conducted on aeolian deposits in a quarry time domain reflectometry tdr was used to obtain detailed information on the product of relative permittivity er and relative magnetic permeability lr which mainly controls the gpr contrast parameter in the subsurface combining tdr data and lacquer peels from the quarry wall allowed the identification of various relationships between sediment characteristics and erlr synthetic radar traces constructed using the tdr logs and sedimentological data from the lacquer peels were compared with the actual gpr sections numerous peaks in erlr which are superimposed on a baseline value of 4 for dry sand are caused by potential gpr reflectors these increases in erlr coincide with the presence of either organic material having a higher water content and relative permittivity than the surrounding sediment or iron oxide bands enhancing relative magnetic permeability and causing water to stagnate on top of them sedimentary structures as reflected in textural change only result in possible gpr reflections when the volumetric water content exceeds 0ae055 the synthetic radar traces provide an improved insight into the behaviour of radar waves and show that gpr results may be ambiguous because of multiples and interference

effects of stream morphodynamics on hyporheic zone thermal regime 1 we develop a heat transport model to study the impact of streambed morphology on temperature distribution within the hyporheic zone of gravel bed rivers the heat transport model which includes conduction diffusion and advection is solved by a lagrangian approach neglecting transverse dispersion and considering stream water temperature as boundary condition at the streambed first we show that the model accurately reproduces the temperature distribution measured within the hyporheic zone of a reach of the bear valley creek idaho usa our model reveals spatially complex patterns of hyporheic water temperatures that vary with time within the hyporheic zone and at the streambed surface the analysis shows that temperature distributions are primarily related to the hyporheic residence time and consequently to the bed morphology and in stream flow discharge results show that the hyporheic temperature amplitudes are smaller than the surface water temperature and they decrease with stream size leading hyporheic zones of large streams to be independent from in stream daily temperature fluctuations

increasing illumination and sensitivity of reverse time migration with internal multiples reverse time migration is a two way time domain finite frequency technique that accurately handles the propagation of complex scattered waves and produces a bandlimited representation of the subsurface structure that is conventionally assumed to be linear in the contrasts in model parameters because of this underlying linear singlescattering assumption most implementations of this method do not satisfy the energy conservation principle and do not optimally use illumination and model sensitivity of multiply scattered waves migrating multiply scattered waves requires preserving the non linear relation between the image and perturbation of model parameters i modify the extrapolation of source and receiver wavefields to more accurately handle multiply scattered waves i extend the concept of the imaging condition in order to map into the subsurface structurally coherent seismic events that correspond to the interaction of both singly and multiply scattered waves this results in an imaging process referred to here as non linear reverse time migration it includes a strategy that analyses separated contributions of singly and multiply scattered waves to a final non linear image the goal is to provide a tool suitable for seismic interpretation and potentially migration velocity analysis that benefits from increased illumination and sensitivity from multiply scattered seismic waves it is noteworthy that this method can migrate internal multiples a clear advantage for imaging challenging complex subsurface features e g in salt and basalt environments the results of synthetic seismic imaging experiments including a subsalt imaging example illustrate the technique

can we image beneath salt a decade has passed since petroleum geologists first recognized that jurassic salt in the extensional gulf of mexico often appeared to be thrust between layers of younger sediments since then many teams of geoscientists have been faced with the problems of either 1 improving subsalt quality through better data collection or 2 making subsalt interpretations from data of very poor quality these problems aren t new in fact they have faced the seismic industry from the beginning in the gulf of mexico however the cause of the problem salt is obvious in particular high velocity structurally contoured salt bodies act as sonic lenses that disperse or concentrate seismic signals in haphazard ways many advances in seismic imaging technology have been in response to these salt related problems of velocity and structure

upper pleistocene to holocene peatland evolution in southern brazilian highlands as depicted by radar stratigraphy sedimentology and palynology paleoenvironmental interpretation of proxy data derived from peatlands is largely based upon an evolutionary model for ombrotrophic bogs in which peat accumulates in still environments reports on proxies obtained from minerotrophic fens where hydrologic inputs are variable are less common in this study a highland peatland in southern brazil is presented through ground penetrating radar gpr and sedimentological palynological and geochronologic data the radar stratigraphic interpretation suggests a relatively complex history of erosion and deposition at the site since the beginning of marine isotope stage 3 mis 3 interstadial period in spite of this radar stratigraphic and palynologic interpretations converge electromagnetic reflections tend to group in clusters that show lateral coherence and correlate with different sediment types while pollen grains abound and are well preserved as a result the study of minerotrophic fens provides a source of proxies suggesting that ombrotrophic bogs are not the only reliable source of data in wetlands for palynological analysis

relations between topography and water table depth in a shallow forest soil the relations between water table depth in a shallow forest soil and topographic characteristics derived from a raster digital elevation model dem were studied water table depths at times of observation and peak levels between times of observation were measured weekly during an autumn winter rainy season at 59 wells in a catchment ca 0 04 km 2 drained by an ephemeral stream located 80 km east of vancouver canada digital elevation models with grid spacings of 4 8 and 16 m were derived from a ground survey and values of a upslope contributing area per unit contour length tan surface slope and x a measure of surface curvature were computed from the dems to avoid problems with data censoring when the water table dropped below the bottom of some wells the depths were discretized into classes and discriminant analysis was used to relate water table depth classes to the topographic indices the relations were derived using data from 30 wells and were tested on data from the other 29 wells to provide an independent test of predictive capability the index in a tan provided more reliable classifications than a multiple discriminant analysis using in a tan and x as separate predictor variables water table depths at some wells were consistently misclassified e g 0 3 correct classifications whereas at others they were classified correctly in up to 100 of cases consistent misclassification at individual wells could reflect either the effects of errors in the derived topographic indices through errors in the dem or the algorithms used to calculate the indices or phenomena not related to surface topography such as variability in soil properties or differences between the surface topography and the topography of the base of the soil profile the predictive accuracy and statistical significance of derived relations decreased as the dem grid size increased from 4 to 8 to 16 m these results are valid only for predictions of water table depths at points further research should explore the effect of grid scale on relations between grid averaged water table depths and topographic indices and on methods to parameterize subgrid scale variability

generalized staining algorithm for seismic modeling and migration abstractthe staining algorithm is introduced to improve the signal to noise ratio s n of poorly illuminated subsurface structures in seismic imaging however the amplitudes of the original and the stained wavefield i e the real and the imaginary wavefields differ by several orders of magnitude and the waveform of the stained wavefield may be greatly distorted we have developed a generalized staining algorithm gsa to achieve amplitude preservation in the stained wavefield the real wavefield and the stained wavefield propagate in the same velocity model a source wavelet is used as the source of the real wavefield however the real wavefield is extracted from the stained area as the source of the stained wavefield the gsa maintains some properties of the original staining algorithm the stained wavefield is synchronized with the real wavefield and it contains only information relevant to the target region by imaging with the stained wavefield we obtain higher s ns in images of target struct

influence of organic matter in soils on radar wave reflection sedimentological implications abstract soils are excellent reflectors of ground penetrating radar gpr signals because of the ability of organic matter to hold water in this paper gpr profiles of an eolian sedimentary succession are combined with textural dielectric and moisture retention characteristics to illustrate the influence of soil moisture on radar wave reflection organic matter in this succession varies strongly from lt 0 15 for clean sand to 7 for the most prominent soil whereas grain size distributions are comparable moisture retention curves show a complex relationship between suction potential pf and volumetric water content as a result of their uniform pore size distribution clean sand and weakly developed soils with lt 1 organic matter experience a sudden loss of water between pf 1 5 and pf 1 8 going directly from saturated to almost dry conditions in contrast the most prominent soil shows a more gradual decrease in with increasing suction potential it follows that the dielectric contrast between clean sand and this soil increases sharply above pf 1 5 reaches a maximum value at field capacity conditions and then decreases slowly synthetic gpr images for different suction potentials show that field capacity conditions when reflection coefficients are high are favorable for tracing one single soil dry sediments are preferable when imaging widely spaced soils whereas saturated sediments are best when imaging closely spaced soils

geophysical evidence for peat basin morphology and stratigraphic controls on vegetation observed in a northern peatland vegetation patterns in peatlands suggest autogenic peatland development and hydrological processes are controlling factors in peatland evolution these processes regulate vegetation ordination by influencing ph and nutrient availability at the peat surface geophysical studies in caribou bog a 2200 hectare peatland in central maine indicate a close correlation between underlying geologic deposits and dominant vegetation type the location of pools within the bog also appears to be related to subsurface geologic materials electrical resistivity imaging along a 1 km transect across the central unit of caribou bog resolved underlying lake sediment and glacio marine clay thickness as well as variability in depth to glacial till ground penetrating radar precisely defined the organic rich lake sediment the glacio marine interface and elevated till surfaces where peat thickness is less than 10 m direct verification of peat and lake sediment thickness in addition to samples of the glacio marine and till deposits constrained the geophysical interpretation wooded heath wh interspersed with occasional sphagnum lawn occurs where lake sediment and glacio marine clay accumulation is thickest abrupt thinning of both layers such that peat rests directly on till in places correlates with a sharp transition to shrub heath dominated vegetation a major open pool area located within the wh coincides with a localized sandy mineral soil lake sediment contact at the base of the bog the geophysical data suggest the underlying double basin system influences peatland development and dictates vegetation patterning limited groundwater elevation data suggest that sub organic sediment stratigraphy mapped with geophysics regulates water levels at the peat surface exerting a control on vegetation patterning the major pool area located between the basins appears to reflect isolation of stagnant water at a point where peat development is incomplete and thus suggests that pools exist concurrent with peatland formation

do peatland microforms move through time examining the developmental history of a patterned peatland using ground penetrating radar using ground penetrating radar gpr to map subsurface patterns in peat physical properties we investigated the developmental history of meso scale surface patterning of microforms within a raised bog common offset gpr measurements were obtained along a 45 m transect at frequencies ranging from 100 to 900 mhz we found that low frequency central frequency 240 mhz showed a striking pattern of subsurface reflections that dip consistently in a northerly direction the angle of these dipping reflectors is calculated using a semblance algorithm and was shown to average 3 9 degrees between a depth of 1 0 and 2 5 m these dipping reflectors may indicate downslope migration of surface microforms during the development of the peatland based on the estimated angle and the rate of peat accumulation the average rate of downslope propagation of these surface microforms is calculated at 9 8 mm per year further survey work is required to establish whether the downslope migration is common across the peatland

reverse time migration of internal multiples for subsalt imaging abstractinternal multiple reflections have different propagation paths than primary reflections and surface related multiples thus they can complement illumination where other waves are unavailable consequently migration of internal multiples may provide vital images in the shadow zone of primary reflections we have developed an approach to image structures with internal multiples with this method internal multiples can be separated and used as data for reverse time migration instead of applying the imaging condition directly to the source and receiver wavefields we decomposed the extrapolated source and receiver waves into up and downgoing waves then we applied the imaging condition to upgoing source and receiver waves to form an up up uu image and also to downgoing source and receiver waves to form a down down dd image the image of the true reflector and the artifacts behave differently in the dd and uu images a similarity analysis is conducted to the uu and dd images to separate true i

storage outflow modelling of streamflow recessions with application to a shallow soil forested catchment abstract the objectives of this study were to introduce an alternative to the matching strip correlation and parameter averaging methods for deriving master recession characteristics from a set of recession segments and to apply the method to streamflow recession segments for a small forested catchment in which baseflow is provided by drainage of the saturated zone in the shallow permeable soil the method involves fitting conceptual storage outflow models using an iterative algorithm diagnostic plots revealed that the recessions were non linear and that the recessions did not follow a common single valued storage outflow relation a model involving two linear reservoirs provided substantially better fit than three single reservoir models indicating that the form of the recession curve probably depends not just on the volume of subsurface storage but also on its initial distribution amongst reservoirs

determining the number of manual measurements required to improve peat thickness estimations by ground penetrating radar ground penetrating radar gpr is often used for investigating peat thickness the quality of gpr measurements depends on electromagnetic wave emw velocity estimates the objective of this study is to determine the number of manual measurements required to minimize emw velocity error in peatlands a total of 175 manually measured peat thicknesses are used with a depth to target method to assess emw velocity in two southern quebec peatlands mean measured emw velocities are 0 040 and 0 039 m ns 1 with standard deviations of 0 013 and 0 008 m ns 1 statistical analyses show that at least 30 calibration points are required to minimize the emw velocity error regardless of the geological setting copyright 2008 john wiley sons ltd

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

ecohydrologically important subsurface structures in peatlands revealed by ground penetrating radar and complex conductivity surveys 1 the surface pattern of vegetation influences the composition and humification of peat laid down during the development of a bog producing a subsurface hydrological structure that is expected to affect both the rate and pattern of water flow subsurface peat structures are routinely derived from the inspection of peat cores however logistical limits on the number of cores that can be collected means that the horizontal extent of these structures must be inferred we consider whether subsurface patterns in peat physical properties can be mapped in detail over large areas with ground penetrating radar gpr and complex conductivity by comparing geophysical measurements with peat core data along a 36 m transect through different microhabitats at caribou bog maine the geophysical methods show promise peat horizons produced radar reflections because of changes in the volumetric moisture content although these reflections could not be directly correlated with the peat core data they were related to the depth averaged peat properties which varied markedly between the microhabitats well decomposed peat below a hollow was characterized by a discontinuous sequence of chaotic wavy reflections while distinct layering of the peat below an area of hummocks coincided with a pattern of parallel planar reflections the complex conductivity survey showed spatial variation in the real and imaginary conductivities which resulted from changes in the pore water conductivity peat structures may also have influenced the spatial pattern in the complex conductivity the gpr and complex conductivity surveys enabled the developmental history of the different microhabitats along the studied transect to be inferred

throughflow variability on a forested hillslope underlain by compacted glacial till this study examined the spatial and temporal variability of throughflow in a shallow forest oil in terms of the controls exerted by topography soil properties and the shape of the water table hillslope outflow was measured at nine troughs installed at a road cut and hydraulic head was measured at 37 piezometers installed to the confining till surface at the base of the soil at the lowest flows the distribution of throughflow across the hillslope conformed reasonably to the distribution of upslope contributing area computed from the topography of the confining basal till layer at higher flows however the distribution of throughflow shifted partly as a result of changes in the orientation in flow tubes as the piezometric surface changed at high flows surface topography appeared to provide a reasonable proxy for the shape of the water table shunting of water through discrete macropores however can apparently overwhelm topographic controls on throughflow at least for slope widths less than about 10 m effective hydraulic conductivities computed at the scale of the troughs varied over two orders of magnitude and displayed no consistent relationship with the thickness of the saturated layer estimates at the plot scale c 10 m hillslope width were far less variable and for higher flows displayed an approximately linear relationship with saturated zone thickness copyright 2000 john wiley sons ltd

geophysical and hydrological evaluation of two bog complexes in a northern peatland implications for the distribution of biogenic gases at the basin scale 1 ground penetrating radar gpr was used to determine peat basin geometry and the spatial distribution of free phase biogenic gasses in two separate units of a northern peatland central and southern unit of caribou bog maine the central unit is characterized by a deep basin structure 15 m maximum depth and a raised eccentric bog topographic profile up to 2 m topographic variation here numerous regions of electromagnetic em wave scattering are considered diagnostic of the presence of extensive free phase biogenic gas in contrast the southern unit is shallower 8 m maximum depth and has a slightly convex upwards bog profile less than 1 m topographic variation and areas of em wave scattering are notably absent the biogenic gas zones interpreted from gpr in the central unit are associated with 1 wooded heath vegetation at the surface 2 open pools at the surface 3 high water table elevations near the center of the basin and 4 a region of overpressure at approximately 5 m depth immediately below the zone of free phase gas accumulation the latter suggests 1 a transient pressure head associated with low hydraulic conductivity resulting from the biogenic gasses themselves or confining layers in the peat that restrict both gas release and groundwater flow and or 2 overpressure in the peat column as a result of the gas buildup itself in contrast the southern unit where zones of em scattering are absent is characterized by 1 predominantly shrub vegetation 2 a lack of open pools 3 only minor variations less than 1 m in water table elevation throughout the entire unit and 4 generally upward groundwater flow throughout the basin the results illustrate the nonuniformity of free phase biogenic gas distribution at the peat basin scale and provide insights into the processes and controls associated with ch4 and co2 accumulation in peatlands

application of ground penetrating radar to the identification of subsurface piping in blanket peat natural soil pipes are common and significant in upland blanket peat catchments yet there are major problems in finding and defining the subsurface pipe networks this is particularly important because pipeflow can contribute a large proportion of runoff to the river systems in these upland environments and may significantly influence catchment sediment and solute yields traditional methods such as digging soil pits are destructive and time consuming particularly in deep peat and only provide single point sources of information this paper presents results from an experiment to assess the use of ground penetrating radar gpr to remotely sense pipes in blanket peat the technique is shown to be successful in identifying most of the pipes tested in the pilot catchment comparison of data on pipes identified by gpr and verified by manual measurement suggests that pipes can be located in the soil profile with a depth accuracy of 20 to 30 cm gpr identified pipes were found throughout the soil profile however those within 10 20 cm of the surface could not be identified using the 100 or 200 mhz antennae due to multiple surface reflections generally pipes smaller than 10 cm in diameter could not be identified using the technique although modifications are suggested that will allow enhanced resolution future work would benefit from the development of dual frequency antennae that will allow the combination of high resolution data with the depth of penetration required in a wetland environment the gpr experiment shows that pipe network densities were much greater than could be detected from surface observation alone thus gpr provides a non destructive fast technique which can produce continuous profiles of peat depth and indicate pipe locations across survey transects copyright 2002 john wiley sons ltd

imaging internal multiples from subsalt vsp data examples of target oriented interferometry seismic interferometry has become a technology of growing interest for imaging borehole seismic data we demonstrate that interferometry of internal multiples can be used to image targets above a borehole receiver array by internal multiples we refer to all types of waves that scatter multiple times inside the model these include for instance interbed intrasalt and water bottom multiples as well as conversions among them we use an interferometry technique that is based on representation theorems for perturbed media and targets the reconstruction of specific primary reflections from multiply reflected waves in this interferometry approach we rely on shot domain wavenumber separation to select the directions of waves arriving at a given receiver using a numerical walkaway waw vsp experiment recorded by a subsalt borehole receiver array in the sigsbee salt model we use the interference of internal multiples to image the salt structure from below in this numerical example the interferometric i

stratigraphic controls on pool formation in a domed bog inferred from ground penetrating radar gpr ground penetrating radar gpr and terrain conductivity measurements reveal a close correlation between the location of water filled pools and stratigraphic lithologic features in caribou bog a 2200 hectare peatland in central maine the geophysical profiles supported by coring define the general peatland stratigraphy as till underlain by glacio marine sediment overlain by organic rich lake sediment transitioning into terrestrial peat gpr measurements show that open pools coincide with abrupt thinning of lake sediment and glaciomarine clay such that elevated mineral soil surfaces are in direct contact with the base of terrestrial peat the width of these features the gpr reflection patterns the anomalously low terrain conductivity and the core samples obtained support the interpretation of these elevated mineral surfaces as the extension of buried eskers that outcrop on the periphery of caribou bog the geophysical results indicate that two parallel esker ridges are orientated n s and dip towards the south we suggest that the distribution of open pools is related to the distribution of depressions and beads associated with a beaded esker deposit the pools possibly being maintained by local groundwater flow cells associated with the esker gpr and em31 surveys across sphagnum pools defined here as sphagnum filled wet depressions suggest a continuous sequence of underlying lake sediment and glacio marine deposits devoid of elevated mineral surfaces we suggest that sphagnum pools developed after peatland formation secondary features due to changes in water table peat accumulation and or climatic controls q 2005 elsevier b v all rights reserved

leda clay from deep boreholes at hawkesbury ontario part i geology and geotechnique the geologic and geotechnical characteristics of thick soft champlain sea clay deposits at hawkesbury ontario are presented in this paper a second paper will deal with the mineralogy and geochemistry of the same deposits a westerly clay plain at 50 m and an easterly plain at 75 m elevation occur in the area preconsolidation pressure versus depth curves obtained for clays from both deposits show marked preconsolidation near the top and bottom drainage boundaries and nearly normally consolidated conditions at the centre this suggests that both sites were loaded by sandy fluvial deltaic sediments that were eroded 70 years after deposition an ancestral meander of the ottawa river being responsible for the erosion on the lower clay plain two stratigraphic schemes compatible with the p versus depth profiles are presented for the lower elevation clay plain these schemes suggest erosion of 21 m of deltaic sands a value generally confirmed by field studies of deltaic sand terraces to the west the se

measuring thaw depth beneath peat lined arctic streams using ground penetrating radar in arctic streams depth of thaw beneath the stream channel is likely a significant parameter controlling hyporheic zone hydrology and biogeochemical cycling as part of an interdisciplinary study of this system we conducted a field investigation to test the effectiveness of imaging substream permafrost using ground penetrating radar gpr we investigated three sites characterized by low energy water flow organic material lining the streambeds and water depths ranging from 0 2 to 2 m we acquired data using a 200 mhz pulsed radar system with the antennas mounted in the bottom of a small rubber boat that was pulled across the stream while triggering the radar at a constant rate we achieved excellent results at all three sites with a clear continuous image of the permafrost boundary both peripheral to and beneath the stream our results demonstrate that gpr can be an effective tool for measuring substream thaw depth copyright 2005 john wiley sons ltd

least squares data to data migration an approach for migrating free surface related multiples free surface related multiples can provide extra illumination of the subsurface and thus can be usefully included in migration procedures however most multiple migration approaches require separation of primaries and free surface related multiples or at least prediction of multiples in advance which is time consuming and prone to errors the data to data migration ddm method migrates free surface related multiples by forward and backward propagating the recorded full data containing primaries and free surface related multiples for ddm there is no need to predict or separate multiples but the migration results suffer from the crosstalk generated by crosscorrelations of undesired seismic events e g primaries and second order free surfacerelated multiples we have developed least squares ddm lsddm for marine data to eliminate the crosstalk generated by ddm in each iteration the forward propagated primaries and free surface related multiples are crosscorrelated with the backward propagated primary and free surface related multiple residuals to form the reflectivity gradient we use a three layer model and the marmousi model for numerical tests the results validate that lsddm can provide a migrated image with higher signal to noise ratio and more balanced amplitudes than ddm the lsddm approach might be valuable for general subsurface imaging for marine seismic data when the migration velocity is accurate and the acquired data have sufficient recording time

staining algorithm for seismic modeling and migration abstractin seismic migration some structures such as those in subsalt shadow zones are not imaged well the signal in these areas may be even weaker than the artifacts elsewhere we evaluated a method to significantly improve the signal to noise ratio s n in poorly illuminated areas of the model we constructed a phantom wavefield an extension of the wavefield to the complex domain the imaginary wavefield was synchronized with the real wavefield but it contained only the events relevant to a target region of the model which was specified using a staining algorithm the real wavefield interacted with the entire model however all structures except for the target were transparent to the imaginary wavefield which is excited only when the real wavefront arrives at the target structure the real and the imaginary source wavefields were crosscorrelated with the regular receiver wavefield the results were revealed in two images the conventional reverse time migration image and an image of the target

ground penetrating radar and spring formation in a groundwater dominated peat wetland summary ground penetrating radar gpr was used to identify the thickness and geometry of peat in a groundwater fed wetland in northern wisconsin the low electrical conductivity of the water saturated peat permitted high resolution imaging to a depth of 16 m the gpr survey results delineated a break in slope in the interface between peat and the underlying sand gravel springs and ponds are located above the break in slope suggesting that thinning of the sand and gravel may focus groundwater flow upward to the wetland surface with emergence as springs the results of the gpr surveys suggests a potential mechanism that controls the formation of large springs and pools above the break in slope