removing tidal period variations from time series data using low pass digital filters abstract several low pass digital filters are examined for their ability to remove tidal period variations from a time series of water surface elevation for san francisco bay the most efficient filter is the one which is applied to the fourier coefficients of the transformed data and the filtered data recovered through an inverse transform the ability of the filters to remove the tidal components increased in the following order 1 cosine lanczos filter 2 cosine lanczos squared filter 3 godin filter and 4 a transform fitter the godin fitter is not sufficiently sharp to prevent severe attenuation of 2 3 day variations in surface elevation resulting from weather events

descriptive physical oceanography of great entry lagoon gulf of st lawrence this study describes some aspects of the physical oceanography of great entry lagoon gel canada using sea level current salinity and temperature time series recorded in 1988 and 1989 gel is part of a communicating two lagoon system each having one opening with the gulf of st lawrence the length of gel is 25 km its surface area is 58 km2 and its mean depth is 3 m a navigation channel divides the lagoon into a relatively deep basin 4 6 m to the east and a shallow 1 3 m region to the west leading to the second lagoon water in the lagoon is generally well mixed in the vertical but can remain horizontally stratified harmonic analysis reveals that gel is a leaky lagoon that tides are mixed and predominantly semi diurnal and that the tide progresses from the inlet to the adjacent lagoon in about 3 h this sets up tidal currents reaching 0 5 m s 1 at the entrance and in the western section in the basin however tidal currents remain weak 0 05 m s 1 low frequency currents have typical speeds of 0 05 0 1 m s 1 they respond to non local sea level fluctuations at the entrance and to local winds in the form of downwind currents in shallow areas and upwind currents at depth inside the basin atmospheric pressure plays a major role in the renewal of waters through an inverse barometer effect acting at time scales of 3 to 15 days the low salinity signature of the st lawrence river freshet reaches the lagoon at the beginning of august using this natural tracer in conjunction with spectral analysis a renewal time for waters in the deeper basin is estimated to lie in the range of 10 to 20 days

perturbation solution for dam break floods a solution for the complete and instantaneous collapse of a dam in a prismatic infinitely long sloping channel is found by using the method of matched asymptotic expansions the outer solution is a kinematic wave approximation and an inner solution that includes a depth gradient term in the momentum equation is calculated for the region near the moving kinematic shock front the reservoir is modeled with a point mass source and the solution is believed to become asymptotically valid after the shock front has advanced about four reservoir lengths downstream a comparison with experiment shows good qualitative agreement but more comparisons with experiment should be made in order to assess the qualitative accuracy of the solution

constraints on lake agassiz discharge through the late glacial champlain sea st lawrence lowlands canada using salinity proxies and an estuarine circulation model during the last deglaciation abrupt freshwater discharge events from proglacial lakes in north america such as glacial lake agassiz are believed to have drained into the north atlantic ocean causing large shifts in climate by weakening the formation of north atlantic deep water and decreasing ocean heat transport to high northern latitudes these discharges were caused by changes in lake drainage outlets but the duration magnitude and routing of discharge events factors which govern the climatic response to freshwater forcing are poorly known abrupt discharges called floods are typically assumed to last months to a year whereas more gradual discharges called routing events occur over centuries here we use estuarine modeling to evaluate freshwater discharge from lake agassiz and other north american proglacial lakes into the north atlantic ocean through the st lawrence estuary around 11 5 ka bp the onset of the preboreal oscillation pbo faunal and isotopic proxy data from the champlain sea a semi isolated marine brackish water body that occupied the st lawrence and champlain valleys from 13 to 9 ka indicate salinity fell about 7 8 range of 4 11 around 11 5 ka model results suggest that minimum 1600 km3 and maximum 9500 km3 estimates of plausible flood volumes determined from lake agassiz paleoshorelines would produce the proxy reconstructed salinity decrease if the floods lasted 1 day to 5 months and 1 month to 2 years respectively in addition champlain sea salinity responds very quickly to the initiation within days and cessation within weeks of flooding events these results support the hypothesis that a glacial lake flood rather than a sustained routing event discharged through the st lawrence estuary during the pbo

formation of a jump by the dam break wave over a granular bed a previously unreported shock feature associated with the scouring of a horizontal granular bed by a dam break wave is discussed near the wave centre the present study shows the free surface breaks backward and a hydraulic jump forms this behaviour is described from the standpoint of shallow water theory suitably extended to deal with non equilibrium sediment transport the shock formation involves a particularly strong coupling between flow free surface evolution and bed morphodynamics support for our conclusions is sought through experimental and numerical approaches in order to magnify the observed phenomena measurements were performed for the case of light bed particles moving in sheet and debris flow modes a detailed picture of the transient two phase flow is presented based on whole field acquisition of the grain motions by particle tracking techniques corresponding shallow water solutions are constructed numerically using a shock capturing scheme finally an interpretation of the jump formation is proposed based on the theory of characteristics

timescale dependency of spatial patterns in the variability of the northern hemisphere winter slp field 1 the arctic oscillation ao the north atlantic oscillation nao and the cold ocean warm land pattern cowl have been identified as important modes of variability in the northern hemisphere winter sea level pressure field however which one is most fundamental in describing this variability and the relationship between them are still important open questions a key uncertainty is our lack of knowledge of the linkages between the arctic north atlantic and north pacific oceans that are manifest in these modes in this study the authors investigate these linkages through a frequency dependent decomposition of the variability in the northern hemisphere sea level pressure field in particular the authors show that the spatial expression of the variability in this field has a frequency dependence that results in a nao like pattern on inter annual timescales an ao like pattern on inter decadal timescales and a cowl like pattern on multi decadal timescales

efficient 3 d frequency domain mono parameter full waveform inversion of ocean bottom cable data application to valhall in the visco acoustic vertical transverse isotropic approximation computationally efficient 3 d frequency domain full waveform inversion fwi is applied to ocean bottom cable data from the valhall oil field in the visco acoustic vertical transverse isotropic vti approximation frequency domain seismic modelling is performed with a parallel sparse direct solver on a limited number of computer nodes a multiscale imaging is performed by successive inversions of single frequencies in the 3 5 10 hz frequency band the vertical wave speed is updated during fwi while density quality factor qp and anisotropic thomsen s parameters and are kept fixed to their initial values the final fwi model shows the resolution improvement that was achieved compared to the initial model that was built by reflection traveltime tomography this fwi model shows a glacial channel system at 175 m depth the footprint of drifting icebergs on the palaeo seafloor at 500 m depth a detailed view of a gas cloud at 1 km depth and the base cretaceous reflector at 3 5 km depth the relevance of the fwi model is assessed by frequency domain and time domain seismic modelling and source wavelet estimation the agreement between the modelled and recorded data in the frequency domain is excellent up to 10 hz although amplitudes of modelled wavefields propagating across the gas cloud are overestimated this might highlight the footprint of attenuation whose absorption effects are underestimated by the homogeneous background qp model qp 200 the match between recorded and modelled time domain seismograms suggests that the inversion was not significantly hampered by cycle skipping however late arrivals in the synthetic seismograms computed without attenuation and with a source wavelet estimated from short offset early arrivals arrive 40 ms earlier than the recorded seismograms this might result from dispersion effects related to attenuation the repeatability of the source wavelets inferred from data that are weighted by a linear gain with offset is dramatically improved when they are estimated in the fwi model rather than in the smooth initial model the two source wavelets estimated in the fwi model from data with and without offset gain show a 40 ms time shift which is consistent with the previous analysis of the time domain seismograms the computational efficiency of our frequency domain approach is assessed against a recent time domain fwi case study performed in a similar geological environment this analysis highlights the efficiency of the frequency domain approach to process a large number of sources and receivers with limited computational resources thanks to the efficiency of the substitution step performed by the direct solver this efficiency can be further improved by using a block low rank version of the multifrontal solver and by exploiting the sparsity of the source vectors during the substitution step future work will aim to update attenuation and density at the same time of the vertical wave speed

experimental insights on geomorphological processes within dam break outburst floods summary hydraulic behavior and unsteady sediment transport within dam break outburst floods are inherently inter dependent yet poorly constrained this study experimentally determined how the mobility and clast size of channel bed sediments affected the peak flow depth and flow velocities wave propagation and attenuation sediment entrainment and duration of transport flood power energy transfer and geomorphological impact of outburst floods due to our choice of clast size and of a unimodal size distribution the predominant sediment transport mechanism was bedload we found that frontal wave propagation was slower and attenuated faster for flows over a mobile bed versus those over a fixed bed peak flow depth was greater and was attained earlier for flows over a mobile bed and with increased clast size geomorphological power declined logarithmically with time after an initial period where gravitational forces exceeded frictional forces both peak and time to peak geomorphological power varied inversely with clast size peak deposition rates were greatest with coarser bed sediment but time to peak deposition rate was inversely proportional to clast size volume changes down channel were described by an exponential curve which we suggest indicates that sediment transport proceeded in waves via both translation and dispersion mechanisms peak suspended load occurred coincident with peak flow velocity peak bedload occurred coincident with peak flow depth and peak sediment discharge lagged behind peak water discharge these descriptions of kinematic transformation multi phase flow and of geomorphological work due to outburst floods help to provide data for numerical modelling for mitigating outburst flood hazards and for informing on the immediate and longer term geological legacy of outburst floods

response of the mediterranean mean sea level to atmospheric pressure forcing the response of the mediterranean mean sea level to atmospheric pressure forcing is analyzed using 3 years of topex poseidon data coherence analysis between mean sea level and atmospheric pressure shows a significant departure from a standard inverse barometer effect at frequencies higher than 30 days at high frequencies the phase difference between sea level and pressure is about 100 o while it should be 180 o for a perfect inverse barometer response this result is in agreement with previous findings and confirms the role of the straits of gibraltar and sicily in limiting the water exchange and thus the response to atmospheric pressure forcing at high frequencies the response of the mediterranean mean sea level is then investigated using the candela 1991 analytical model which takes account of friction in the straits of gibraltar and sicily the model explains a large part of the variance in topex poseidon mean sea level variations 50 for the western basin and 38 for the eastern basin compared to an inverse barometer correction it gives a smoother response with a phase delay at high frequencies it also explains more variance in topex poseidon mean sea level variations 5 cm 2 and 7 cm 2 for the western and eastern basins respectively this demonstrates that this simple model provides an improved correction of atmospheric pressure effects in topex poseidon data as the two corrections have an rms difference of 2 3 cm with maximum differences of up to 10 cm the impact on the mapping of oceanic circulation is not negligible this is exemplified through the comparison of sea level anomaly derived from the two corrections

ambient seismic noise eikonal tomography for near surface imaging at valhall the permanent ocean bottom array at the valhall field in norway provides an excellent source of passive seismic data to test what might be accomplished with seismic interferometry the array was installed in 2003 kommedal et al 2004 and data can be recorded for long periods in all weather conditions the subsurface structure is well known both from numerous wells and from seismic imaging during periods without active seismic acquisition at valhall there is abundant passive energy in the data over a wide range of fre quencies

experimental study of flash flood surges down a rough sloping channel flood waves resulting from flash floods and natural dam overtopping have been responsible for numerous losses in the present study surging waters down a flat stepped waterway slope 3 4 degrees were investigated in a 24 m long chute wave front propagation data were successfully compared with hunt s 1982 1984 theory visual observations highlighted strong aeration of the leading edge instantaneous distributions of void fractions showed a marked change in shape for t ts g do 1 3 which may be caused by some major differences between the wave leading edge and the flow behind including non hydrostatic pressure distributions plug slug flow regime and different boundary friction regime practically the results quantified the large amount of entrained air i e white waters at the wave front which in turn reduces buoyancy and could affect sediment motion at the leading edge because the sediment relative density is inversely proportional to the entrained air content

a model for estimating cross shore surface transport with application to the new jersey shelf 1 a one dimensional steady state numerical model is developed for estimating cross shore surface transport in shallow waters where the water depth is comparable to boundary layer thickness the model is used to solve a momentum equation which describes the cross shore balance to validate the model acoustic doppler current profiler adcp current data collected during an experiment off the new jersey shelf in the summer of 1996 are used to estimate the cross shore surface transport during that period and then compared with model predictions based on the local wind the success of the model in estimating the cross shore surface transport leads to an improved version of the conventional upwelling index i e the bakun index particularly for coastal areas with wide and shallow shelves such as the east coast of the united states finally the model because of its simplicity is well suited for operational applications where computational resources may be limited

geographic and hydrodynamic characteristics of shallow coastal lagoons abstract coastal lagoons can be conveniently separated based on geomorphology into leaky restricted or choked systems this subdivision orders coastal lagoons hydrodynamically according to water exchange with the coastal ocean leaky systems have the shortest turnover time restricted lagoons have a longer turnover time and choked lagoons have the longest turnover time in leaky coastal lagoons oscillating tidal currents account for most of the flow variance and mask residual currents due to wind and freshwater induced density gradients in restricted lagoons tides winds and freshwater runoff drive components of the circulation winds are usually dominant in causing circulation and mixing in choked lagoons and water exchange with the coastal ocean largely depends on the hydrologic cycle coastal lagoons are usually well mixed but can exhibit significant horizontal gradients due to freshwater runoff and vertical gradients due to solar radiation or surface cooling in general river inflow and heat balance induce stratification in coastal lagoons whereas winds and tides cause mixing coastal lagoons usually trap inorganic sediment and organic matter thus serving as material sinks on a geologic time scale they are short lived landscape features with an existence intrinsically linked to filtering efficiency and relative sea level change as a result of glacioeustatic cycles and local tectonic activity

tidal and residual circulations in coupled restricted and leaky lagoons abstract finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of a coupled restricted and leaky coastal lagoon system located in the magdalen islands gulf of saint lawrence havre aux maisons lagoon hml is of a restricted nature with a neutral inlet in terms of tidal asymmetry grande entree lagoon gel is of a leaky nature with a marked ebb dominance at the inlet due to direct interactions between the main astronomical tidal constituents the imbalance caused by the different tidal filtering characteristics of both inlets combines with the internal morphological asymmetries of the system to produce a residual throughflow from hml to gel the residual circulation is also characterized by strongest values at both inlets very weak residual currents in hml deep basin and a dipole of residual eddies over the deeper areas of gel further investigations including numerical tracer experiments will be necessary to achieve a full understanding of the long term circulation of this lagoonal system

full 3 d tomography for crustal structure in southern california based on the scattering integral and the adjoint wavefield methods we have successfully applied full 3 d tomography f3dt based on a combination of the scattering integral method si f3dt and the adjoint wavefield method aw f3dt to iteratively improve a 3 d starting model the southern california earthquake center scec community velocity model version 4 0 cvm s4 in f3dt the sensitivity frechet kernels are computed using numerical solutions of the 3 d elastodynamic equation and the nonlinearity of the structural inversion problem is accounted for through an iterative tomographic navigation process more than half a million misfit measurements made on about 38 000 earthquake seismograms and 12 000 ambient noise correlagrams have been assimilated into our inversion after 26 f3dt iterations synthetic seismograms computed using our latest model cvm s4 26 show substantially better fit to observed seismograms at frequencies below 0 2 hz than those computed using our 3 d starting model cvm s4 and the other scec cvm cvm h11 9 which was improved through 16 iterations of aw f3dt cvm s4 26 has revealed strong crustal heterogeneities throughout southern california some of which are completely missing in cvm s4 and cvm h11 9 but exist in models obtained from previous crustal scale 2 d active source refraction tomography models at shallow depths our model shows strong correlation with sedimentary basins and reveals velocity contrasts across major mapped strike slip and dip slip faults at middle to lower crustal depths structural features in our model may provide new insights into regional tectonics when combined with physics based seismic hazard analysis tools we expect our model to provide more accurate estimates of seismic hazards in southern california

dam break surges with floating debris the effect of floating debris on dam break surges is studied experimentally hexahedron plastic particles having a specific gravity of 0 92 are used as debris in addition to qualitative investigation of the surge behavior the speed and height of the surges are plotted for various downstream to upstream depth ratios and debris concentration the results are compared with the clear water surges deceleration and the increase in height of the surge are more pronounced for smaller initial depths downstream of the gate in general the speed of the surge is found to be a function of downstream to upstream depth ratio the ratio of the mass of the debris per unit surface area to the mass or the water per unit surface area upstream of the gate and the particle size relative to the upstream depth the wave height on the other hand is found to be a function of the depth and concentration ratios for smaller initial downstream depths for higher initial downstream depths the wave height is a function of the depth ratio only

on the footprint of anisotropy on isotropic full waveform inversion the valhall case study summary the validity of isotropic approximation to perform acoustic full waveform inversion fwi of real wide aperture anisotropic data can be questioned due to the intrinsic kinematic inconsis tency between short and large aperture components of the data this inconsistency is mainly related to the differences between the vertical and horizontal velocities in vertical transverse isotropic vti media the footprint of vti anisotropy on 2 d acoustic isotropic fwi is illus trated on a hydrophone data set of an ocean bottom cable that was collected over the valhall field in the north sea multiscale fwi is implemented in the frequency domain by hierar chical inversions of increasing frequencies and decreasing aperture angles the fwi models are appraised by local comparison with well information seismic modelling reverse time migration rtm and source wavelet estimation a smooth initial vti model parameterized by the vertical velocity v0 and the thomsen parameters andwere previously developed by anisotropic reflection traveltime tomography the normal moveout vnmo v0 1 2 and horizontal vh v0 1 2 velocity models were inferred from the anisotropic models to perform isotropic fwi the vnmo models allows for an accurate match of short spread reflection traveltimes whereas the vh model after updating by first arrival traveltime tomog raphy fatt allows for an accurate match of first arrival traveltimes ray tracing in the velocity models shows that the first 1 5 km of the medium are sampled by both diving waves and reflections whereas the deeper structure at the reservoir level is mainly controlled by short spread reflections starting from the initial anisotropic model and keeping fixed and models anisotropic fwi allows us to build a vertical velocity model that matches reasonably well the well log velocities isotropic fwi is performed using either the nmo model or the fatt model as initial model in both cases horizontal velocities are mainly reconstructed in the first 1 5 km of the medium this suggests that the wide aperture components of the data have a dominant control on the velocity estimation at these depths these high velocities in the upper structure lead to low values of velocity in the underlying gas layers either equal or lower than vertical velocities of the well log and or a vertical stretching of the structure at the reservoir level below the gas this bias in the gas velocities and the mispositioning in depth of the deep reflectors also shown in the rtm images are required to match the deep reflections in the isotropic approximation and highlight the footprint of anisotropy in the isotropic fwi of long offset data despite the significant differences between the anisotropic and isotropic fwi models each of these models produce a nearly equivalent match of the data which highlights the ill posedness of acoustic anisotropic fwi hence we conclude with the importance of considering anisotropy in fwi of wide aperture data to avoid bias in the velocity reconstruc tions and mispositioning in depth of reflectors designing a suitable parameterization of the vti acoustic fwi is a central issue to manage the ill posedness of the fwi

multiparameter full waveform inversion of multicomponent ocean bottom cable data from the valhall field part 2 imaging compressive wave and shear wave velocities

experimental study of bore driven swash hydrodynamics on impermeable rough slopes abstract a detailed experimental investigation of the hydrodynamics of large scale bore driven swash on impermeable rough beach slopes is described the experiments were carried out on 1 10 impermeable rough slopes with three different surface roughnesses based on 1 3 mm sand 5 4 mm gravel and 8 4 mm gravel the large scale discrete swash event was produced by the collapse of a dambreak generated bore on the beach simultaneous depths and velocities were measured using lif laser induced fluorescence and piv particle image velocimetry respectively yielding better resolution of the hydrodynamics than previous studies depth time series instantaneous velocity profiles depth averaged velocities instantaneous turbulent kinetic energy profiles depth averaged turbulent kinetic energy reynolds stress profiles and bed shear stresses are presented for five cross shore measurement locations in the swash the measurements resolve the backwash shoreline position and the late backwash period when depths are shallow and velocities are high the detailed data can be used to test and develop advanced numerical models for bore driven waves on rough slopes

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

building starting models for full waveform inversion from wide aperture data by stereotomography building an accurate initial velocity model for full waveform inversion fwi is a key issue to guarantee convergence of full waveform inversion towards the global minimum of a misfit function in this study we assess joint refraction and reflection stereotomography as a tool to build a reliable starting model for frequency domain full waveform inversion from long offset i e wide aperture data stereotomography is a slope tomographic method that is based on the inversion of traveltimes and slopes of locally coherent events in a data cube one advantage of stereotomography compare to conventional traveltime reflection tomography is the semi automatic picking procedure of locally coherent events which is easier than the picking of continuous events and can lead to a higher density of picks while conventional applications of stereotomography only consider short offset reflected waves we assess the benefits provided by the joint inversion of reflected and refracted arrivals introduction of the refracted waves allows the construction of a starting model that kinematically fits the first arrivals a necessary requirement for full waveform inversion in a similar way to frequency domain full waveform inversion we design a multiscale approach of stereotomography which proceeds hierarchically from the wide aperture to the short aperture components of the data to reduce the non linearity of the stereotomographic inversion of long offset data this workflow which combines stereotomography and full waveform inversion is applied to synthetic and real data case studies for the valhall oil field target the synthetic results show that the joint refraction and reflection stereotomography for a 24 km maximum offset data set provides a more reliable initial model for full waveform inversion than reflection stereotomography performed for a 4 km maximum offset data set in particular in low velocity gas layers and in the deep part of a structure below a reservoir application of joint stereotomography full waveform inversion and reverse time migration to real data reveals that the fwi models and the reverse time migration images computed from the stereotomography model shares several features with fwi velocity models and migrated images computed from an anisotropic reflection traveltime tomography model although stereotomography was performed in the isotropic approximation implementation of anisotropy in joint refraction and reflection stereotomography of long offset data is a key issue to further improve the accuracy of the method

waveform tomography of two dimensional three component seismic data for hti anisotropic media reservoirs with vertically aligned fractures can be represented equivalently by horizontal transverse isotropy hti media but inverting for the anisotropic parameters of hti media is a challenging inverse problem because of difficulties inherent in a multiple parameter inversion in this paper when we invert for the anisotropic parameters we consider for the first time the azimuthal rotation of a two dimensional seismic survey line from the symmetry of hti the established wave equations for the hti media with azimuthal rotation consist of nine elastic coefficients expressed in terms of five modified thomsen parameters the latter are parallel to the thomsen parameters for describing velocity characteristics of weak vertical transverse isotropy media we analyze the sensitivity differences of the five modified thomsen parameters from their radiation patterns and attempt to balance the magnitude and sensitivity differences between the parameters through normalization and tuning factors which help to update the model parameters properly we demonstrate an effective inversion strategy by inverting velocity parameters in the first stage and updates the five modified thomsen parameters simultaneously in the second stage for generating reliably reconstructed models

azimuthal anisotropy from the valhall 4c 3d survey recording and processing both the converted shear waves and the compressional waves from multicomponent ocean bottom seismic obs data provide additional opportunities to understand the subsurface the converted waves are generally used to provide complementary images and velocity information to support the conventional seismic model however they also provide a new opportunity to measure and understand shear wave azimuthal anisotropy this paper describes the results from an azimuthal anisotropy study on 3d 4c obs data from valhall field

multiparameter full waveform inversion of multicomponent ocean bottom cable data from the valhall field part 1 imaging compressional wave speed density and attenuation multiparameter full waveform inversion fwi is a challenging quantitative seismic imaging method for lithological characterization and reservoir monitoring the difficulties in multiparameter fwi arise from the variable influence of the different parameter classes on the phase and amplitude of the data and the trade off between these in this framework choosing a suitable parametrization of the subsurface and designing the suitable fwi workflow are two key methodological issues in non linear waveform inversion we assess frequency domain visco acoustic fwi to reconstruct the compressive velocity vp the density or the impedance ip and the quality factor qp from the hydrophone component using a synthetic data set that is representative of the valhall oil field in the north sea we first assess which of the vp and vp ip parametrizations provides the most reliable fwi results when dealing with wide aperture data contrary to widely accepted ideas we show that the vp parametrization allows a better reconstruction of both the vp and ip parameters first because it favours the broad band reconstruction of the dominant vp parameter and secondly because the trade off effects between velocity and density at short to intermediate scattering angles can be removed by multiplication to build an impedance model this allows for the matching of the reflection amplitudes while the broad band velocity model accurately describes the kinematic attributes of both the diving waves and reflections then we assess different inversion strategies to recover the quality factor qp in addition to parameters vp and a difficulty related to attenuation estimation arises because on the one hand the values of qp are on average one order of magnitude smaller than those of vp and and on the other hands model perturbations relative to the starting models can be much higher for qp than for vp and during fwi in this framework we show that an empirical tuning of the fwi regularization which is adapted to each parameter class is a key issue to correctly account for the attenuation in the inversion we promote a hierarchical approach where the dominant parameter vp is reconstructed first from the full data set i e without any data preconditioning to build a velocity model as kinematically accurate as possible before performing the joint update of the three parameter classes during a second step this hierarchical imaging of compressive wave speed density and attenuation is applied to a real wide aperture ocean bottom cable data set from the valhall oil field several geological features such as accumulation of gas below barriers of claystone and soft quaternary sediment are interpreted in the fwi models of density and attenuation the models of vp and qp that have been developed by visco acoustic fwi of the hydrophone data can be used as initial models to perform visco elastic fwi of the geophone data for the joint update of the compressive and shear wave speeds

monitoring the 1979 1985 equatorial pacific current transports with expendable bathythermograph data geostrophic transports of the major equatorial currents including the equatorial undercurrent and the south equatorial current have been estimated on a bimonthly basis in the central and western pacific over the 1979 1985 period this was made possible by a collection of carefully checked expendable bathythermograph xbt data and a few hydrocast and conductivity temperature depth data this collection considerably improved the number and quality of temperature profiles of the original institut francais de recherche scientifique pour le developpement en cooperation orstom scripps institute of oceanography tropical pacific xbt ship of opportunity program the temperature profiles were first grouped independently of longitude in regions around mean xbt tracks dynamic heights were then calculated relative to 400 db through a t s relationship deduced from the climatological levitus file geostrophic currents were calculated along the roughly south north oriented fiji hawaii and new caledonia japan mean xbt tracks using a specific technique this technique which combines fourier filtering in the meridional direction and in time also ensures the continuity across the equator between geostrophic currents deduced from the first and second derivatives of the meridional pressure field the filter coefficients in the meridional direction were determined through an adjustment of geostrophic currents to directly measured currents using the mean of data collected along 165 e during six tropical ocean and global atmosphere toga orstom cruises finally transports of the main equatorial currents were computed in a subjective way between 20 n and 20 s 0 400 m using monthly charts of geostrophic currents along the two mean xbt tracks the transports in the central pacific were compared to the transports derived from the semicontinuous direct current measurements taken during the hawaii tahiti shuttle experiment in 1979 1980 and during the line island profiling project pacific equatorial ocean dynamics experiment in 1982 1983 reasonable agreement demonstrates that it is possible to use xbt data for transport indexes of the major equatorial currents in the central and western pacific

subtidal sea level and current variations in the northern reach of san francisco bay abstract analyses of sea level and current meter data using digital filters and a variety of statistical methods show a variety of phenomena related to non local coastal forcing and local tidal forcing in the northern reach of san francisco bay a partially mixed estuary low frequency variations in sea level are dominated by non local variations in coastal sea level and also show a smaller influence from tidally induced fortnightly sea level variations low frequency currents demonstrate a gravitational circulation which is modified by changes in tidal current speed over the spring neap tidal cycle transients in gravitational circulation induce internal oscillations with periods of two to four days

3d prestack plane wave full waveform inversion prestack depth migration has been used for decades to derive velocity distributions in depth numerous tools and methodologies have been developed to reach this goal exploration in geologically more complex areas exceeds the abilities of existing methods new data acquisition and data processing methods are required to answer these new challenges effectively the recently introduced wide azimuth data acquisition method offers better illumination and noise attenuation as well as an opportunity to more accurately determine velocities for imaging one of the most advanced tools for depth imaging is full waveform inversion prestack seismic full waveform inversion is very challenging because of the nonlinearity and nonuniqueness of the solution combined with multiple iterations of forward modeling and residual wavefield back propagation the method is computer intensive especially for 3d projects we studied a time domain plane wave implementation of 3d waveform inversion we found that plane wave gathers

time lapse full waveform inversion with ocean bottom cable data application on valhall field abstractknowledge of changes in reservoir properties resulting from extracting hydrocarbons or injecting fluid is critical to future production planning full waveform inversion fwi of time lapse seismic data provides a quantitative approach to characterize the changes by taking the difference of the inverted baseline and monitor models the baseline and monitor data sets can be inverted either independently or jointly time lapse seismic data collected by ocean bottom cables obcs in the valhall field in the north sea are suitable for such time lapse fwi practice because the acquisitions are of a long offset and the surveys are well repeated we have applied independent and joint fwi schemes to two time lapse valhall obc data sets which were acquired 28 months apart the joint fwi scheme is double difference waveform inversion ddwi which inverts differenced data the monitor survey subtracted by the baseline survey for model changes we have found that ddwi gave a cleaner and more easily interpr