alternative waveform inversion for surface wave analysis in 2 d media in the context of near surface seismic imaging a few hundreds of metres we propose an alternative approach for inversion of surface waves in 2 d media with laterally varying velocities it is based on full waveform inversion fwi but using an alternative objective function formulated in the frequency wavenumber f k domain the classical fwi objective function suffers from severe local minima problems in the presence of surface waves it thus requires a very accurate initial model the proposed objective function is similar to the one used in classical surface wave analysis in this approach the data are first split using sliding windows in the time space t x domain for each window the amplitude of the f k spectrum is computed the objective function measures the least squares misfit between the amplitude of observed and modelled 2 d fourier transformed data sets we call this formulation the windowed amplitude waveform inversion w awi the w awi objective function reduces some local minima problems as shown here through numerical examples the global minimum basin is wider in the w awi approach than in fwi synthetic examples show that w awi may achieve convergence if the lowest data frequency content is twice higher than the one needed by fwi for elastic inversion w awi can be used to reconstruct a velocity model explaining surface waves this surface wave inversion procedure can be used to retrieve near surface model parameters in lateral varying media

modeling of sh wave propagation in an irregularly layered medium application to seismic profiles near a dome campillo m 1987 modeling of sh wave propagation in an irregularly layered medium application to seismic profiles near a dome geophysical prospecting 35 236249 an approach that relies on a discrete representation of seismic wavefields allows the computation of synthetic sh seismograms in a laterally varying medium with plane and curved interfaces in the two dimensional 2 d case the diffracting interfa is represented by an array of body forces located along the interfa at equal spacing the numerical treatment is limited to the irregular boundary while the propagation in fiat layered zones is obtained by the refiection transmission matrix method as an example we have studied the case of a dome in a stratified medium the solutions obtained verify the reciprocity theorem with good accuracy the computation of vertical profiles and of surface refiection profiles illustra tes the effects of diffraction and the importance of lateral propagation in such a structure

a boundary element approach to ocean seismoacoustic facet reverberation a numerically efficient hybrid method is introduced for modeling of short and long range seismoacoustic facet reverberation in the ocean environment the method combines the global matrix approach to the solution of the wave equation in horizontally stratified media with a boundary element formulation of the boundary conditions at a contour surrounding the facet the present paper describes a two dimensional formulation for facets within an elastic seabed or an elastic ice cover but allows for simulation of the reverberant field within the water column as well the approach is directly extendable to treat reverberation from seabed penetrating facets as well as three dimensional elastic facets in contrast to discrete methods such as the finite element and finite difference approaches the solution obtained with the present hybrid approach is not only efficient for short as well as long range reverberation but inherently decomposes the total solution in the temporal and spatial spectral components of

full traveltime inversion abstractmany previously published wave equation based methods which attempt to automatically invert traveltime or kinematic information in seismic data or migrated gathers for smooth velocities suffer a common and severe problem the inversions are involuntarily and unconsciously hijacked by amplitude information to overcome this problem we have developed a new wave equation based traveltime inversion methodology referred to as full traveltime i e fully dependent on traveltime inversion fti to automatically estimate a kinematically accurate velocity model from seismic data the key idea of fti is to make the inversion fully dependent on traveltime information and thus prevent amplitude interference during inversion under the assumption that velocity perturbations cause only traveltime changes we have derived the fti method in the data and image domains which are applicable to transmitted arrivals and reflected waves respectively fti does not require an accurate initial velocity model or

tides in the black sea observations and numerical modelling longterm hourly data from 28 tide gauges were used to examine the main features of tides in the black sea the tides in this basin are directly caused by tide generating forces and the semidiurnal tides prevail over diurnal tides based on the princeton ocean model pom a numerical model of tides in the black sea and adjacent sea of azov was developed and found to be in good agreement with tide gauge observations detailed tidal charts for amplitudes and phase lags of the major tidal harmonics in these two seas were constructed the results of the numerical modelling and observations reveal for the semidiurnal tides the presence of an amphidromy with clockwise rotation and another one with counterclockwise rotation for the diurnal tides both located in the central part of the sea near the crimean peninsula therefore for this part of the sea the amplitudes of harmonics m2 and k1 are less than 0 1 cm relatively larger m2 amplitudes are observed on the east and west coasts of the sea 2 3 cm the maximum amplitude of the harmonic m2 was found at karkinit bay up to 4 5 cm while the maximum tidal range varies from 1 cm near the crimean peninsula to 18 19 cm in the dnieper bug estuary and karkinit bay radiational tides initiated mainly by sea breezes make an important contribution to the formation of tidal oscillations in the dnieper bug estuary

spatial coherence and rough bottom scattering in shallow water shallow water acoustic data collected off mallorca in march 1993 are analyzed for spatial coherence and their relation to rough bottom scattering is investigated bistatic reverberation data were collected by a horizontal receiver array with equispaced hydrophones suspended 1 m above the bottom a flextentional transducer towed behind the ship was used as a source generating a 209 db source level at center frequency of 400 hz with 5 ms signal length and 10 s interval the ship made a hexagonal run with the horizontal receiver array inside the track a theoretical source model has been designed to approximate the actual source pulse and is used to match filter the data the modal arrivals are clearly identified in the resulting impulse responses allowing for mode by mode analysis the total field is decomposed into a mean field coherent field and scattered field incoherent field by a stacking procedure the spatial coherence is then calculated using a correlation and a coherence function the mag

the carbon dioxide system on the mississippi river dominated continental shelf in the northern gulf of mexico 1 distribution and air sea co2 flux river dominated continental shelf environments are active sites of air sea co2 exchange we conducted 13 cruises in the northern gulf of mexico a region strongly influenced by fresh water and nutrients delivered from the mississippi and atchafalaya river system the sea surface partial pressure of carbon dioxide pco2 was measured and the air sea co2 flux was calculated results show that co2 exchange exhibited a distinct seasonality the study area was a net sink of atmospheric co2 during spring and early summer and it was neutral or a weak source of co2 to the atmosphere during midsummer fall and winter along the salinity gradient across the shelf the sea surface shifted from a source of co2 in low salinity zones 0 s 17 to a strong co2 sink in the middle to high salinity zones 17 s 33 and finally was a near neutral state in the high salinity areas 33 s 35 and in the open gulf s 35 high pco2 values were only observed in narrow regions near freshwater sources and the distribution of undersaturated pco2 generally reflected the influence of freshwater inputs along the shelf systematic analyses of pco2 variation demonstrated the importance of riverine nitrogen export that is riverine nitrogen enhanced biological removal along with mixing processes dominated pco2 variation along the salinity gradient in addition extreme or unusual weather events were observed to alter the alongshore pco2 distribution and to affect regional air sea co2 flux estimates overall the study region acted as a net co2 sink of 0 96 3 7 mol m 2 yr 1 1 15 4 4 tg c yr 1

estimating advective near surface currents from ocean color satellite images abstract improved maximum cross correlation mcc techniques are used to retrieve ocean surface currents from the sequential ocean color imagery provided by multiple newer generations of satellite sensors on hourly scales in the yellow sea and the u s east and gulf coasts the mcc calculation is validated in a series of bio optical forecasting biocast experiments with predetermined synthetic velocities and its products are evaluated by examining the errors and biases with respect to the high frequency radar hfradar measurements the root mean square rms errors in our best current products derived from the overlap of satellite sensor swath between the viirs sequential orbits are less than 0 17 m s 1 in the evaluation area outside of the chesapeake bay the most accurate current products are those derived from the imagery data of r rs 551 b b 551 and c 551 while the image sequences of b b 551 and z eu lee are identified as the most suited products for the retrieval of currents because of their best production capacities of valid velocity vectors mechanisms between the advective processes and the dynamic changes of bio optical properties are discussed regarding the performances of various color products on the retrieval of currents similarities of velocity distribution in the retrieved vector arrays are collected across different mcc products derived from ocean color datasets that are of different types and derived from different spectral channels of satellite overpasses the inter product similarities themselves can be used to characterize the near surface advection as well and usually have smaller errors than each of the individual mcc currents moreover efforts are also under way to improve the ocean color derived currents by merging several of the mcc products with similarities to increase the total spatial coverage this study not only seeks the image derived products best representing the sea surface current structures in coastal areas but also exploits how these currents can be improved or optimized to support the ocean forecasts

seismic velocities of upper oceanic crust new measurements are reported for the seismic velocities in upper oceanic crust layer 2a at off axis sites along a track at 34 n in the pacific where the sediments were thin 33m and the crustal age increased from 42 to 63 m y the data were obtained in experiments designed to measure the reflection coefficient at each site using a horizontal line array the reflection coefficient versus angle information was inverted for the seismic velocities using a nonlinear inversion technique based on a simulated annealing search algorithm the p wave velocity increased from 2 7 to 3 1 km s along the track and the shear velocity in creased from about 1 0 to 1 6 km s these results suggest that the aging process controlled by passive hydrothermal circulation is continuing at these sites

bottom reflection coefficient measurement and geoacoustic inversion at the continental margin near vancouver island with the aid of spiking filters this paper presents the results of an experiment to measure the reflection coefficient versus grazing angle at the continental margin west of vancouver island the measured reflection coefficients are inverted and estimates of the surficial sediment geoacoustic properties obtained the receiver used in this experiment was a long towed array with the source in aft endfire aspect the acoustic sources for this experiment were explosives that produced direct path arrivals approximately 0 1 s in length bottom and sub bottom arrivals continued for several seconds duration explosives were detonated at intervals such that bottom reflected energy received at the array sampled grazing angles in the interval 10 80 source receiver ranges were computed by measuring arrival time differences at each of the array elements comparing these time differences with those computed using a ray tracing propagation model and globally minimizing the accumulated squared time difference residuals to aid in the measurement of

high resolution seismic characterization in an urban area subway tunnel construction in barcelona spain traveltime seismic tomography used to aid subway tunnel drilling in barcelona spain provides a detailed characterization of the shallow subsurface including a complex network of faults and dikes we encountered many difficulties while working in this urban setting such as cultural noise and the inability to deploy instruments along much of the tunnel trace because of the street layout furthermore the shallow subsurface is highly heterogeneous because of gas and water lines building foundations and the sewage system obscuring deeper structures we acquired seismic data using a 10 s vibroseis sweep that provided relatively good signal to noise s n ratio first arrival traveltime tomography proved to be a key tool to differentiate rock vol umes characterized by different physical properties in particular the contact between the weathered upper layer and the more competent rock below we interpreted the seismic results using surface geologic observations and borehole cores low seismic velocit

source levels of shallow explosive charges experimental measurements are reported in this article for the source levels of 0 82 kg signals underwater sound sus charges detonated at nominal depths of 18 3 91 and 183 m the data were recorded in the farfield using a high resolution digital data acquisition system that provided good reproduction of both the high and low frequency components of the signal from the explosion the results are presented in 1 3 octave bands from 5 630 hz and represent the mean values of samples of at least 30 charges for each depth group the standard deviations were within 1 db for most frequency bands analysis of the distribution of explosion depths indicated that the average detonation depths were consistently deeper than the nominal depths this result was attributed to the effect of the relatively cold water temperatures at the experimental site in addition to the measured source levels estimates for 0 82 kg sus charges at 244 m were scaled from the experimental data using a method suggested by hughes r hu

multiscale spectral analysis of bathymetry on the flank of the mid atlantic ridge modification of the seafloor by mass wasting and sedimentation the results of a multiscale spectral analysis of bathymetric data on the flank of the mid atlantic ridge are described data were collected during two cruises using hydrosweep multibeam tens of kilometers to 0 2 km scale range and mesotech scanning pencil beam sonar attached to remotely operated vehicle jason 1 km to 0 5 m scale range these data are augmented by visual data which enabled us to identify bathymetric profiles which are over unsedimented or thinly sedimented crust our analysis therefore is focused primarily on statistical characterization of basement morphology work is concentrated at two sites site b on 24 ma crust in an outside corner setting and site d on 3 ma crust in an inside corner setting at site b we find that an anisotropic band limited fractal model i e the von karman model proposed for abyssal hill morphology by goff and jordan 1988 is not sufficient to describe the full range of scales observed in this study our observations differ from this model in two ways 1 strike and cross strike dip spectral properties converge for wavelengths smaller than 300 m and 2 in both strike and dip directions the fractal dimension changes at 10 m wavelength from 1 27 at larger scales to 1 0 at smaller scales the convergence of strike and dip spectral properties appears to be associated with destruction of ridge parallel fault scarps by mass wasting which develops canyon like incisions that cross scarps at high angles the change in fractal dimension at 10 m scale appears to be related to a minimum spacing of significant slope breaks associated with scarps which are created by faulting and mass wasting at site d although there is no significant abyssal hill anisotropy the spectral properties at all scales are consistent with the von karman model the fractal dimension at this site 1 15 is less than at site b this difference may be reflect different morphology related to crustal formation at inside corner versus outside corner position or more likely differences in the degree of mass wasting the smoothing of seafloor morphology by sediments is evident in hydrosweep periodograms where relative to basement roughness spectral power decreases progressively with decreasing wavelength

advective surface velocities derived from sequential infrared images in the southwestern atlantic ocean abstract sequential infrared satellite images between november 1995 and august 1996 have been used to derive sea surface advective velocities in the southwestern atlantic ocean using the maximum cross correlation mcc technique the infrared images geometrically corrected and accurately registered to a map grid are masked for land and cloud cover the linear displacements of the sea surface thermal features are determined by locating the maximum cross correlation in windowed portions of successive images the advective velocities are estimated for each pair of images based on regular grids incoherent vectors are eliminated from these fields using a statistical method after this a visual inspection by the operator is completed to remove the remaining fictitious vectors the region studied includes the southern brazilian uruguayan and northern argentinian shelves and the neighboring oceanic area known as the brazil malvinas confluence despite the rather complex circulation of this region the advective surface currents calculated by the mcc method are consistent with the shapes of the sea surface temperature features the general patterns of the surface circulation estimated by the mcc agree well with previous studies that used direct measurements hydrographic data and or modeling efforts in the shallower areas of the study region the mcc technique is less applicable due to the predominance in violation of the assumptions of the method of nonadvective processes

short term changes in seafloor character due to flood derived hyperpycnal discharge typhoon mindulle taiwan july 2004 during typhoon mindulle in early july 2004 the choshui river central western taiwan discharged similar to 72 mt of sediment to the eastern taiwan strait peak concentrations were g 200 g l similar to 35 40 of which was sand box core samples and chirp compressed high intensity radar pulse sonar records taken just before and after the typhoon indicate that the hyper pycnal sediment was first deposited adjacent to the mouth of the choshui subsequently resuspended and transported northward via the taiwan warm current and redeposited as a patchy coastal band of mud dominated sediment that reached thicknesses of 1 2 m within megaripples within a month most of the mud was gone probably continuing its northward transit but more mud appeared in late august in response to typhoon aere following autumn and winter storms the entire nearshore area was again sand dominated by early spring

new curvilinear scheme for elastic wave propagation in presence of curved topography we study a new curvilinear scheme for wave propagation modelling in presence of topography the discrete scheme takes advantage of recent developments in areoacoustics our new scheme relies on the conventional grid coupled with optimized filters to remove numerical noise in case of strong material heterogeneity we used non centred stencils for free surface implementation and optimized the explicit runge kutta scheme for the time differencing we performed a complete theoretical stability and dispersion analysis of the discrete scheme finally we illustrate the numerical accuracy of the new scheme by intensive experiments

retrieving 2d structures from surface wave data by means of space varying spatial windowing abstractsurface wave techniques are mainly used to retrieve 1d subsurface models however in 2d environments the 1d approach usually neglects the presence of lateral variations and because the surface wave path crosses different materials the resulting model is a simplified or misleading description of the site we tested a processing technique to retrieve 2d structures from surface wave data acquired with a limited number of receivers our technique was based on a two step process first we extracted several local dispersion curves along the survey line using a spatial windowing based on a set of gaussian windows with different shapes the window maxima span the survey line so that we were able to extract a dispersion curve from the seismic record for every window this provided a set of local dispersion curves each of them referring to a different subsurface portion this space varying spatial windowing provided a good compromise between wavenumber resolution and the lateral resolution of the obtain

high resolution sea ice motion estimation with optical flow using satellite spectroradiometer data the purpose of this paper is twofold 1 to propose an approach based on optical flow for the estimation of sea ice motion as an accurate dense and computationally efficient alternative to state of the art pattern matching approaches and 2 to investigate the potential of moderate resolution imaging spectroradiometer modis optical satellite data for combined daily and high resolution motion estimation a series of modis image pairs for a selected region in arctic ocean is employed and sparse pairwise correspondences between nonrigid patches are calculated an edge preserving sparse to dense interpolation is applied followed by variational energy minimization to compute the final optical flow a state of the art multiresolution pattern matching method based on phase correlation and normalized cross correlation is also implemented and evaluated for comparison thorough experimentation with different settings of input data preprocessing as well as varying scales of motion is performed the derived motion vectors are compared with coarser resolution operational sea ice motion vector products from combined buoy and microwave satellite data the proposed optical flow approach clearly outperforms the pattern matching method in most cases both in terms of accuracy and motion vector consistency the estimated motion vectors from the modis images highly correlate with the operational vector products in addition modis provides a vector field with spatial resolution two orders of magnitude higher than the operational products that are able to detect significantly smaller sea ice drifts

regularized elastic full waveform inversion using deep learning we thank y liu z wu and y choi for their helpful discussions we also thank e gasperikova a guitton and four anonymous reviewers for the effort put into the review of this paper we thank the king abdullah university of science technology kaust for its support and specifically the seismic wave analysis group members for their valuable insights for computer time this research used the resources of the supercomputing laboratory at kaust in thuwal saudi arabia we thank vecta oil and gas and especially b devault for the bigsky data and the helpful discussions

wave equation reflection traveltime inversion with dynamic warping and full waveform inversion abstractin reflection seismology full waveform inversion fwi can generate high wavenumber subsurface velocity models but often suffers from an objective function with local minima caused mainly by the absence of low frequencies in seismograms these local minima cause cycle skipping when the low wavenumber component in the initial velocity model for fwi is far from the true model to avoid cycle skipping we discovered a new wave equation reflection traveltime inversion werti to update the low wavenumber component of the velocity model while using fwi to only update high wavenumber details of the model we implemented the low and high wavenumber inversions in an alternating way in werti we used dynamic image warping diw to estimate the time shifts between recorded data and synthetic data when compared with correlation based techniques often used in traveltime estimation diw can avoid cycle skipping and estimate the time shifts accurately even when shifts vary rapidly hence by minimizing tr

modeling scattering from azimuthally symmetric bathymetric features using wavefield superposition in this paper an approach for modeling the scattering from azimuthally symmetric bathymetric features is described these features are useful models for small mounds and indentations on the seafloor at high frequencies and seamounts shoals and basins at low frequencies a bathymetric feature can be considered as a compact closed region with the same sound speed and density as one of the surrounding media using this approach a number of numerical methods appropriate for a partially buried target or facet problem can be applied this paper considers the use of wavefield superposition and because of the azimuthal symmetry the three dimensional solution to the scattering problem can be expressed as a fourier sum of solutions to a set of two dimensional scattering problems in the case where the surrounding two half spaces have only a density contrast a semianalytic coupled mode solution is derived this provides a benchmark solution to scattering from a class of penetrable hemispherical bosses or indentations the details and problems of the numerical implementation of the wavefield superposition method are described example computations using the method for a simple scattering feature on a seabed are presented for a wide band of frequencies

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

thin sediment shear induced effects on low frequency broadband acoustic propagation in a shallow continental sea low frequency 6 3 630 hz acoustic broadband propagation loss data collected in areas of a shallow continental sea where the seabed is composed of hard substrates covered by thin less than 40 m deposits of unconsolidated sediment are presented data are shown to exhibit characteristics consistent with loss due to coupling to interface waves at the sediment substrate interface k e hawker j acoust soc am 65 682 686 1979 in instances of a physically thin sediment cover loss is also attributed to coupling to guided elastic waves in the sediment s j hughes et al j acoust soc am 88 283 397 1990 interpretations are supported by numerical modeling of propagation loss using a recently developed wave number integration code for horizontally layered fluid solid media and geoacoustic models consistent with geophysical data from the sites of acoustic experiments

seismic and hydroacoustic effects of the may 29 2010 submarine south sarigan volcanic explosion energy release and interpretation abstract the may 2010 submarine volcanic crisis of the shallow south sarigan seamount marianas arc ended on may 29 by a violent explosion that emitted a 12 km high atmospheric plume and created a crater 350 m in diameter the application of the multiphase localization method to the pg p t phases of this explosion allows us to refine considerably mainly based on the intense and impulsive t phases the location of their source that fits the position of the newly formed south sarigan crater we highlight the numerous similarities of this final explosion with artificial underwater explosions conventional or nuclear tests of known energy especially the explosive nature of the source in the volcanic basement is confirmed by the similarity of the p phases with those of underground nuclear tests and the application of discriminating criteria ms mb the explosive nature of the source in the water is also confirmedby the application of the identification criteria for hydroacoustic sources and the t phases exceptionally impulsive and of short durations these similarities allow us to provide a rough evaluation of the energy released by the south sarigan final explosion using the methods commonly applied to man generated explosions we estimate a minimal released energy of 1 kt 4 2 1012 j for the seismic effects of the shock and ca 1 t of equivalent tnt i e 4 2 109 j for the hydroacoustic effects of the explosive source in the water the processes leading to this final explosion are discussed on the basis of the sequence of the earlier seismic and eruptive events within the comprehensive nuclear test ban treaty framework this explosion that affected concomitantly the solid liquid and subaerial media is the first well documented one having generated intense waves p hydroacoustic t acoustic infrasounds and tsunamis

three dimensional numerical modeling of geoacoustic scattering from seafloor topography a three dimensional 3 d second order finite difference method was used to create synthetic seismograms for wave propagation in heterogeneous media in order to investigate the scattering of elastic and acoustic energy due to topography on the seafloor the method uses a fully staggered grid in cartesian coordinates as developed by virieux geophysics 51 889 901 1986 numerical results were generated for two models a linear fault scarp on the seafloor and a flat seafloor containing a rectangular channel wave front snapshots allow the scattering and focusing of different wave modes with direction to be visualized compressional and shear wave backscattering from the sides of the features can be seen together with the trapped compressional wave energy propagating inside the channel the results illustrate the effects of out of the plane scattering due to simple seafloor topographic features

acoustic signals of underwater explosions near surfaces underwater explosions are conventionally identified and characterized by their seismic and or acoustic signature based on spherical models of explosion bubbles these models can be misleading in cases where the bubble is distorted by proximity to the free surface the bottom or to a solid object an experimental and numerical study of the effects of various nearby surfaces on the bubble s acoustic signature is presented measurements from high speed movie visualizations and acoustic signals are presented which show that the effect of proximity to a rigid surface is to increase the first period weaken the first bubble pulse and affect significantly the second period resulting in a peak value at standoffs of the same order as the maximum bubble radius these results are compared to results under a free surface over a bed of sand and over a cavity in a rigid surface in all cases the first period is increasingly lengthened or shortened as the motion of fluid around the bubble is increasingly or decrea

shot and angle domain wave equation traveltime inversion of reflection data synthetic and field data examples abstractfull waveform inversion requires the accurate simulation of the dynamics and kinematics of wave propagation this is difficult in practice because the amplitudes cannot be precisely reproduced for seismic waves in the earth wave equation reflection traveltime tomography wt is proposed to avoid this problem by directly inverting the reflection traveltime residuals without the use of the high frequency approximation we inverted synthetic traces and recorded seismic data for the velocity model by wt our results demonstrated that the wave equation solution overcame the high frequency approximation of ray based tomography was largely insensitive to the accurate modeling of amplitudes and mitigated problems with ambiguous event identification the synthetic examples illustrated the effectiveness of the wt method in providing a highly resolved estimate of the velocity model a real data example from the gulf of mexico demonstrated these benefits of wt but also found the limitations in traveltime

an objective method for computing advective surface velocities from sequential infrared satellite images using cross correlations between sequential infrared satellite images an objective technique is developed to compute advective sea surface velocities cross correlations are computed in 32 x 32 pixel search second image and 22 x 22 template first image windows from gradients of sea surface temperature computed from the satellite images velocity vectors computed from sequential images of the british columbia coastal ocean generally appear coherent and consistent with the seasonal surface current in the region during periods of strong wind forcing as indicated by maps of sea level pressure the image advective velocities are stronger and more coherent spatially and appear to cross surface temperature gradients when winds are weaker the advective velocities correspond better with the infrared temperature patterns suggesting the increased contribution of the geostrophic current to the surface flow velocities determined from coincident near surface drogued 5 10 m buoys positioned every half hour by internal loran c units in mid june show excellent agreement with the image advective velocities in addition conductivity temperature and depth ctd measurements taken during the buoy tracking confirm the homogeneity of the upper 10 m and ctd derived geostrophic currents are consistent with

high resolution near surface velocity model building using full waveform inversion a case study from southwest sweden full waveform inversion fwi is an iterative optimization technique that provides high resolution models of subsurface properties frequency domain acoustic fwi was applied to seismic data acquired over a known quick clay landslide scar in southwest sweden we inverted data from three 2 d seismic profiles 261 572 m long two of them shot with small charges of dynamite and one with a sledgehammer to our best knowledge this is the first published application of fwi to sledgehammer data both sources provided data suitable for waveform inversion the sledgehammer data containing even wider frequency spectrum inversion was performed for frequency groups between 27 5 and 43 1 hz for the explosive data and 27 5 51 0 hz for the sledgehammer the lowest inverted frequency was limited by the resonance frequency of the standard 28 hz geophones used in the survey high velocity granitic bedrock in the area is undulated and very shallow 15 100 m below the surface and exhibits a large p wave velocity contrast to the overlying normally consolidated sediments in order to mitigate the non linearity of the inverse problem we designed a multiscale layer stripping inversion strategy obtained p wave velocity models allowed to delineate the top of the bedrock and revealed distinct layers within the overlying sediments of clays and coarse grained materials models were verified in an extensive set of validating procedures and used for pre stack depth migration which confirmed their robustness

laboratory experiments simulating a coastal river inflow the dynamics of buoyant water entering a rotating basin are studied using a series of laboratory experiments designed to elucidate the alongshore transport mechanisms in river plumes inflowing water which is discharged perpendicular to the tank wall is observed to form a growing anticyclonic bulge and a coastal current downstream of the bulge detailed simultaneous measurements of the velocity and buoyancy fields in the plume confirm that the bulge momentum is in a gradient wind balance and the coastal current is geostrophic the growth of the bulge and accumulation of fluid within it coincides with a reduction in coastal current transport to approximately 50 of the inflow discharge the bulge is characterized by a depth scale h w hich is proportional to the geostrophic depth hg and two time dependent horizontal length scales yc the displacement of the bulge centre from the wall and rb the effective radius of the bulge these two length scales are proportional to the inertial radius

retrieving lateral variations from surface wave dispersion curves surface wave analysis is usually applied as a 1d tool to estimate v s profiles here we evaluate the potential of surface wave analysis for the case of lateral variations lateral variations can be characterized by exploiting the data redundancy of the ground roll contained in multifold seismic data first an automatic processing procedure is applied that allows stacking dispersion curves obtained from different records and which retrieves experimental uncertainties this is carried out by sliding a window along a seismic line to obtain an ensemble of dispersion curves associated to a series of spatial coordinates then a laterally constrained inversion algorithm is adopted to handle 2d effects although a 1d model has been assumed for the forward problem solution we have conducted different tests on three synthetic data sets to evaluate the effects of the processing parameters and of the constraints on the inversion results the same procedure applied to the synthetic data was then tested on a field case both the synthetic and field data show that the proposed approach allows smooth lateral variations to be properly retrieved and that the introduction of lateral constraints improves the final result compared to individual inversions

the ideal response of a gulf of mexico estuary plume to wind forcing its connection with salt flux and a lagrangian view 1 the plume structure of perdido bay estuary pbe a typical bay on the florida alabama coast along the gulf of mexico was simulated using an existing calibrated model to better understand plume dynamics in the pbe and similar bay systems idealized sensitivity experiments were conducted to examine the influence of wind stress on the 3 d plume signature the results indicate that wind speed and direction significantly influence plume orientation area width length and depth the plume size was reduced under the effect of wind and increased wind forcing among wind forced cases the plume is largest for northerly offshore winds and smallest for southerly onshore winds bay shelf salt flux and water flux were also investigated since they are important for the formation of a 3 d plume structure model simulations show that water outflow to the coastal ocean is strongest under northerly winds and can be stopped by southerly winds for moderately strong winds the outflow and plume size are larger for easterly downwelling favorable winds than for westerly upwelling favorable winds the opposite is true for outflow and plume size for these two wind directions under stronger winds for all wind directions the ratio of salt flux and water flux at the bay mouth increases with wind speed this ratio trend is consistent with higher outflow salinities and this decreased buoyancy signature along with more energetic vertical mixing reduces plume size a detailed understanding of this water and salt flux is essential to the plume dynamics studied here and for other plumes additional particle transport analysis using variable wind forcing was conducted to determine the influence of the plume on particle movement the results showed a consistency between the surface plume salt flux and particle transport and illustrate the strong effects that winds have on particle fate and dispersion

convergence and downwelling at a river plume front abstract the small scale structure of the circulation and hydrography at the frontal boundary of the connecticut river plume in long island sound has been resolved using a novel combination of instruments a towed acoustic doppler current profiler adcp and a rigid array of current meters and conductivity temperature sensors observations were made during the latter half of the eastward ebb tide when the river plume was well established and the front was moving to the west at approximately 0 3 m s 1 two across front transects revealed a horizontal convergence rate in the across front velocity components at 0 6 m of 0 05 0 1 s 1 this was associated with a salt induced horizontal density gradient of 10 2 kg m4 observations obtained during a period in which the towed adcp was caught in the zone of maximum surface convergence showed significant downwelling with a near surface maximum of 0 2 m s 1 vertical velocities of this magnitude are consistent with observed magnitudes of the convergence rate at 0 6

source levels for shallow underwater sound charges this paper presents a simple method for removing the surface reflected component from the explosion waveform of signal underwater sound sus charges detonated at shallow depths in order to obtain accurate estimates of the source levels the method is based on the repeated subtraction of time shifted segments of portions of the source waveform that are uncontaminated by the surface reflection the technique provides a method for an accurate estimation of the source levels for charges detonated at depths shallower than 90 m the method is evaluated by comparing the source levels from the processed waveforms with results obtained by scaling source levels for deeper charges to depths of 58 and 18 3 m

effects of variability associated with the antarctic circumpolar current on sound propagation in the ocean a series of small depth charges was detonated along a transect from new zealand to antarctica over a period of three days in late december of 2006 signals were recorded by hydrophones deployed near the source and at a sparse network of permanent hydrophone stations operated by the international monitoring system ims at distances up to 9 600 km our purpose was to determine how well signal characteristics could be predicted by the world ocean atlas 2005 woa05 climatological database for sources within the antarctic circumpolar current acc where recorded signal to noise ratios are high travel times and signal dispersion are predicted to within two seconds under the assumption that propagation is adiabatic and follows a geodesic path the deflection of the transmission path by abrupt spatial variations in sound speed at the northern acc boundary is predicted to decrease travel times to the ims stations by several seconds depending on the path the accuracy of source locations estimates based only on travel times depends on the monthly or seasonal database used to predict velocities and on whether we account for path deflection the configuration of the ims hydrophones limits source location accuracy within the acc comparison of signal spectra for recordings near the source and at distance show that transmission loss is nearly uniform as a function of frequency

head wave data inversion for geoacoustic parameters of the ocean bottom off vancouver island head wave signals from small explosive charges have been analyzed to determine a geoacoustic profile for a shallow water site off the west coast of vancouver island the experimental design contained a vertical aperture provided by a vertical line array and a synthetic horizontal aperture from shots at different ranges from the vertical line array the simultaneous use of travel time and amplitude data for both apertures provided improved accuracy and vertical resolution of the estimated geoacoustic profile travel time vs range data from head waves from three distinct sub bottom interfaces were used to measure compressional speeds in the layers below the interfaces and estimate the layers thicknesses spatial filtering of the vertical line array data was necessary to resolve the head wave arrival from the shallowest layers analysis of the interference structure of the head wave power spectra at the vertical line array provided the means to measure the travel time of the head wave from the deepest layer in addition the head wave power spectra were used to estimate the compressional wave attenuation using a method based on the variation with range of the logarithmic derivative with respect to frequency of the head wave spectrum

characterizing storm water dispersion and dilution from small coastal streams characterizing the dispersion and dilution of storm water from small coastal creeks is important for understanding the importance of land derived subsidies to nearby ecosystems and the management of anthropogenic pollutants in southern california creek runoff is episodic intense and short lived while the plumes are buoyant all of which make the field sampling of freshwater plumes challenging numerical modeling offers a viable way to characterize these systems the dilution and dispersion of freshwater from two creeks that discharge into the santa barbara channel california is investigated using regional ocean modeling system roms simulations with a horizontal resolution of 100 m tight coupling is found among precipitation hydrologic discharge wind forcing and submesoscale flow structures which all contribute to plume evolution during flooding plumes are narrow and attached to the coast due to downwelling onshore wind forcing and intense vorticity filaments lying parallel to the shelf as the storm passes the winds typically shift to offshore upwelling favorable conditions and the plume is advected offshore which enhances its dilution plumes reach the bottom nearshore while they form thin layers a few meters thick offshore dilution field of passive tracers released with the runoff is strongly anisotropic with stronger cross shelf gradients than along shelf dispersion analysis of statistical moments of the passive tracer distribution results in scale dependent diffusivities consistent with the particle pair analysis of romero et al 2013 model validation the roles of submesoscale processes and wind forcing on plume evolution and application to ecological issues and marine resource management are discussed

coastal river plumes collisions and coalescence abstract plumes of buoyant river water spread in the ocean from river mouths and these plumes influence water quality sediment dispersal primary productivity and circulation along the world s coasts most investigations of river plumes have focused on large rivers in a coastal region for which the physical spreading of the plume is assumed to be independent from the influence of other buoyant plumes here we provide new understanding of the spreading patterns of multiple plumes interacting along simplified coastal settings by investigating i the relative likelihood of plume to plume interactions at different settings using geophysical scaling ii the diversity of plume frontal collision types and the effects of these collisions on spreading patterns of plume waters using a two dimensional hydrodynamic model and iii the fundamental differences in plume spreading patterns between coasts with single and multiple rivers using a three dimensional hydrodynamic model geophysical scaling suggests that coastal margins with numerous small rivers watershed areas 2 such as found along most active geologic coastal margins were much more likely to have river plumes that collide and interact than coastal settings with large rivers watershed areas 100 000 km 2 when two plume fronts meet several types of collision attributes were found including refection subduction and occlusion we found that the relative differences in pre collision plume densities and thicknesses strongly influenced the resulting collision types the three dimensional spreading of buoyant plumes was found to be influenced by the presence of additional rivers for all modeled scenarios including those with and without coriolis and wind combined these results suggest that plume to plume interactions are common phenomena for coastal regions offshore of the world s smaller rivers and for coastal settings with multiple river mouths in close proximity and that the spreading and fate of river waters in these settings will be strongly influenced by these interactions we conclude that new investigations are needed to characterize how plumes interact offshore of river mouths to better understand the transport and fate of terrestrial sources of pollution nutrients and other materials in the ocean

wave equation traveltime inversion this paper presents a new traveltime inversion method based on the wave equation in this new method designated as wave equation traveltime inversion wt seismograms are computed by any full wave forward modeling method we use a finite difference method the velocity model is perturbed until the traveltimes from the synthetic seismograms are best fitted to the observed traveltimes in a least squares sense a gradient optimization method is used and the formula for the frechet derivative perturbation of traveltimes with respect to velocity is derived directly from the wave equation no traveltime picking or ray tracing is necessary and there are no high frequency assumptions about the data body wave diffraction reflection and head wave traveltimes can be incorporated into the inversion in the high frequency limit wt inversion reduces to ray based traveltime tomography it can also be shown that wt inversion is approximately equivalent to full wave inversion when the starting velocity model is

early arrival waveform tomography on near surface refraction data we develop a waveform tomography method for estimating the velocity distribution that minimizes the waveform misfit between the predicted and observed early arrivals in space time seismograms by fitting the waveforms of early arrivals early arrival waveform tomographyewt naturally takes into account more general wave propagation effects compared to the high frequency method of traveltime tomography meaning that ewt can estimate a wider range of slowness wavenumbers another benefit of ewt is more reliable convergence compared to full waveform tomography because an early arrival misfit function contains fewer local minima synthetic test results verify that the waveform tomogram is much more accurate than the traveltime tomogram and that this algorithm has good convergence properties for marine data from the gulf of mexico the statics problem caused by shallow gassy muds was attacked by using ewt to obtain a more accurate velocity model using the waveform tomogram to correct for statics the stacked section was significantly improved compared to using the normal moveout nmo velocity and moderately improved compared to using the traveltime tomogram inverting high resolution land data from mapleton utah showed an ewt velocity tomogram that was more consistent with the ground truth trench log than the traveltime tomogram our results suggest that ewt can provide supplemental shorter wavelength information compared to the traveltime tomogram for both shallow and moderately deep seismic data

horizontal resolution of multichannel analysis of surface waves abstractthe multichannel analysis of surface wave masw method has been effectively and widely used to determine near surface shear wave velocity horizontal resolution of the masw method represents the minimum horizontal length of recognizable geologic anomalous bodies on a pseudo 2d s wave velocity vs section accurately assessing the achievable lateral resolution is one of the main issues in lateral variation reconstruction using the masw method it is difficult to quantitatively estimate the horizontal resolution of the masw method because of the many influencing factors such as parameters of the observation system the depth of an anomalous body and the velocity contrast between the anomalous body and the surrounding rocks we first analyzed the horizontal resolution of the masw method based on numerical simulation experiments according to different influencing factors of the horizontal resolution we established different laterally heterogeneous models and observation systems and then simulated

spreading dynamics of small river plumes off the northeastern coast of the black sea observed by landsat 8 and sentinel 2 abstract we use near simultaneous ocean color satellite imagery from nasa s landsat 8 and esa s sentinel 2 missions to reconstruct surface currents along the northeastern shore of the black sea and study the spread of a small river plume formed in this area several times a year landsat 8 and sentinel 2 satellites both pass over the study area within a time interval of

traveltime information based wave equation inversion we propose a new wave equation inversion method that mainly depends on the traveltime information of the recorded seismic data unlike the conventional method we first apply a p transform to the seismic data to form the delayed shot seismic record back propagate the transformed data and then invert the velocity model by maximizing the wavefield energy around the shooting time at the source locations data fitting is not enforced during the inversion so the optimized velocity model is obtained by best focusing the source energy after a back propagation therefore inversion accuracy depends only on the traveltime information embedded in the seismic data this method may overcome some practical issues of waveform inversion in particular it relaxes the dependency of the seismic data amplitudes and the source wavelet

a simple theory for the fate of buoyant coastal discharges abstract a simple theory that predicts the vertical structure and offshore spreading of a localized buoyant inflow onto a continental shelf is formulated the theory is based on two competing mechanisms that move the buoyant fluid offshore 1 the radial spread of the lighter water over the ambient water being deflected by the coriolis force and producing an anticyclonic cyclostrophic plume and 2 offshore transport of buoyant water in the frictional bottom boundary layer that moves the entire plume offshore while maintaining contact with the bottom the surface expression of the cyclostrophic plume moves offshore a distance ys 2 3g h0 2i 2g h0 2i 1 2f where g is reduced gravity based on the inflow density anomaly h0 is the inflow depth i is the inflow velocity and f is the coriolis parameter the plume remains attached to the bottom to a depth given by hb 2l ih0f g 1 2 where l is the inflow width both scales are based solely on parameters of the buoyant inflow at its source there

estimation of seismic velocities of upper oceanic crust from ocean bottom reflection loss data this paper describes a bayesian inversion of acoustic reflection loss versus angle measurements to estimate the compressional and shear wave velocities in young uppermost oceanic crust layer 2a the data were obtained in an experiment on the thinly sedimented western flank of the endeavor segment of the juan de fuca ridge using a towed horizontal hydrophone array and small explosive charges as sound sources measurements were made at three sites at increasing distance from the ridge spreading center to determine the effect of age of the crust on seismic velocities the inversion used reflection loss data in a 1 3 octave band centered at 16 hz the compressional and shear wave velocities of the basalt were highly sensitive parameters in the inversion the compressional wave velocity increased from 2547 30 to 2710 18 m s over an age span of 1 4 million years ma from the spreading center an increase of 4 5 1 0 ma the basalt shear wave velocity increased by nearly a factor of 2 from 725 to 1320 m s o

automatic velocity analysis via shot profile migration we described an implementation of differential semblance velocity analysis based on shot profile migration and illustrated its ability to estimate complex strongly refracting velocity fields the differential semblance approach to velocity analysis uses waveform data directly it does not require any sort of traveltime picking the objective function minimized by the differential semblance algorithm can measure either focusing of the image in offset or flatness of the image in scattering angle we showed that the offset variant of differential semblance yields somewhat more reliable migration velocity estimates than does the scattering angle variant and we explain why this is so we observed that inconsistency with the underlying model born scattering about a transparent background can lead to degraded velocity estimates from differential semblance and we showed how to augment the objective function with stack power to enhance ultimate accuracy a 2d marine survey over a target obscured by the lensing effects of a gas chimney provides an opportunity for direct comparison of differential semblance with reflection tomography the differential semblance estimate yields a more data consistent model flatter angle gathers than does reflection tomography in this application resulting in a more interpretable image below the gas cloud

structure of the buoyant plume formed by ob and yenisei river discharge in the southern part of the kara sea during summer and autumn this article focuses on the interaction between the ob and yenisei dominated parts of the large ob yenisei buoyant plume formed in the southern part of the kara sea during ice free periods it was shown that certain wind forcing and river discharge conditions cause the formation of a specific structure of the ob yenisei plume with significantly different properties of the ob and yenisei dominated water masses under these conditions the yenisei runoff generates a narrow coastal current propagating northward from the yenisei gulf along the taymyr peninsula which is isolated by the ob dominated water mass from ambient sea water as a result the low salinity yenisei dominated water mass occupies a relatively small area while more saline ob dominated water mass spreads over a wide area between the gulf of ob and the taymyr peninsula the formation of the isolation configuration of the ob yenisei plume described above is presumed to be caused by the eastward ekman transport and the resulting downwelling flow of the ob dominated waters under the low saline and warm yenisei dominated waters along the taymyr peninsula based on satellite imagery wind reanalysis and river discharge data collected and derived for the period of 2005 2011 it was estimated that the isolation configuration is regularly formed during late summer and autumn when the ob discharge to the kara sea exceeds the yenisei discharge and the local atmospheric circulation is dominated by the northerly wind regime assessment of the frequency and duration of the occurrence of the isolation configuration showed their synoptic time scale and significant inter annual variability

modeling explosion generated scholte waves in sandy sediments with power law dependent shear wave speed experimental measurements of scholte waves from underwater explosions collected off the coast of virginia beach va in shallow water are presented it is shown here that the dispersion of these explosion generated scholte waves traveling in the sandy seabed can be modeled using a power law dependent shear wave speed profile and an empirical source model that determines the pressure time series at 1 m from the source as a function of tnt equivalent charge weight

impact of variable inflow on the dynamics of a coastal buoyant plume the impact of buoyant discharge variations on the dynamics of coastal buoyancy driven currents is studied using a primitive equation numerical model spem5 first variable discharge is introduced as harmonic fluctuations of the inflow velocity at the tidal period 12 hours and subinertial period 10 days frequencies tidal fluctuations produce only minor effects on the buoyant plume compared to the case of constant inflow while subinertial fluctuations substantially modify the anticyclonic bulge a partially detached anticyclonic plume forms when discharge subsides after reaching its peak value such a plume has maximum offshore extension some distance downstream of the mouth with the lightest water separated from the coast a secondary bulge forms during the low runoff interval when high discharge resumes this secondary bulge is shifted offshore and enhanced for some time an individual high discharge event is next considered where both the net transport of the inflow and the absolute value of its density anomaly increase and then return to their initial background values over 5 and 10 day time intervals this event also generates a partially detached plume especially with the 10 day duration in this case the lightest water occupies the downstream part of the bulge and is separated not only from the coast but also from the mouth the effect of variable discharge is more dramatic with a uniform downstream current of 0 1 m s under such conditions constant buoyant discharge does not form a well pronounced anticyclonic bulge in contrast variable discharge produces an almost circular anticyclone during the high runoff interval as runoff decreases this anticyclone separates from the source and either continues to propagate downstream as an individual eddy or is modified by the next cycle of increasing discharge observational evidence for both the partially detached bulge near the mouth and the anticyclone propagating downstream from its source is presented in this study one feature was observed at the mouth of the columbia river estuary the second feature was observed off the southern new jersey coast 150 km south of its source the hudson estuary

mid frequency shallow water fine grained sediment attenuation measurements attenuation is perhaps the most difficult sediment acoustic property to measure but arguably one of the most important for predicting passive and active sonar performance measurement techniques can be separated into direct measurements e g via sediment probes sediment cores and laboratory studies on ideal sediments which are typically at high frequencies o 104 105 hz and indirect measurements where attenuation is inferred from long range propagation or reflection data generally o 102 103 hz a frequency gap in measurements exists in the 600 4000 hz band and also a general acknowledgement that much of the historical measurements on fine grained sediments have been biased due to a non negligible silt and sand component a shallow water measurement technique using long range reverberation is critically explored an approximate solution derived using energy flux theory shows that the reverberation is very sensitive to depth integrated attenuation in a fine grained sediment layer and separab

ctbto s data and analysis pertaining to the search for the missing argentine submarine ara san juan the argentine submarine ara armada de la republica argentina san juan went missing on november 15th 2017 with its last confirmed contact location around 600 kilometres east of comodoro rivadavia chubut argentina in the days following the initiation of the multi national search and rescue mission the comprehensive nuclear test ban treaty organization ctbto analysed data recorded by its international monitoring system ims sensor network for any signals that could support this effort two of the ims hydrophone stations ha10 in the central atlantic ocean and ha04 in the southern indian ocean were found to have recorded an unusual hydroacoustic signal of unknown nature a hydroacoustic anomaly which originated from the vicinity of the last known location of the ara san juan on december 1st 2017 confirmation of the detection and localization capability of the ims network was made possible by a calibration test involving a depth charge deployed by the argentine navy also this signal was detected by the two ims hydrophone stations and its origin located to within 39 km of the announced deployment location after extended search operations on november 17th 2018 the ara san juan was found on the seabed at approximately 900 metres depth less than 20 km from the location of the hydroacoustic anomaly provided by ctbto this paper presents the methodologies applied by ctbto within months after the loss of the submarine aimed at detecting locating and characterizing the november 15th signal of unknown origin and the december 1st calibration explosion

refraction tomography over a buried waste disposal site determining the depth and geometry of a landfill s lower boundary is a difficult task potential field methods generally lack the necessary depth resolution and seismic reflection data are usually contaminated by source generated noise in the time range of interest 50 ms to address this problem we have developed a surface 2 d tomographic refraction scheme that is based on a fast finite difference eikonal solver and an inversion method that incorporates appropriate damping and smoothing constraints this new scheme has been applied to a first arrival traveltime data set collected across adjacent landfills in northern switzerland high quality seismic data were collected along five profiles that crossed the landfills and two that sampled undisturbed natural sediments seismic waves generated from multiple shots were recorded on large numbers of closely spaced receivers during quiet evening periods reliability of the resultant velocity tomograms was estimated on the basis of 1 ray diagrams 2 plot

matched field evaluation of acoustic scattering from arctic ice this paper investigates the three dimensional acoustic scatter from large scale features under the arctic ice cover using field data collected during the cearex experiments in april 1989 the analysis involves the identification and isolation of the features under the ice canopy and the simultaneous evaluation of their spatial scattering characteristics a two step matched field processing mfp algorithm is used to solve this complex multiparameter estimation problem using one large 1200 m and four short 300 m vertical line arrays and a crossed horizontal hydrophone array in a matched field processing scheme beamforming under the ice sheet was performed to obtain an approximate map of the rough interface between ice and water this analysis yields estimates for scattering strengths for frequencies ranging between 25 and 105 hz it is shown that scatter from the elastic ice surface is a frequency selective phenomenon this beamformed map is then used to isolate a single discrete scatterer and s

reflection seismic waveform tomography 1 in seismic waveform tomography if using reflection data with limited source receiver offsets it is difficult to reconstruct the deep part of the subsurface velocity model we present two approaches to tackle this problem layer stripping and weighted updating in a layer stripping procedure we replace the top portion of seismic data with synthetics generated from the previous layer inversion and make the current inversion focus on the minimization of the data misfit corresponding to the deep part of the model to improve efficiency we use only sparsely sampled frequency data in the deeper layer inversions unlike the first layer inversion where we use densely sampled frequency data as usual the sparsely sampled frequencies together have the full wave number coverage for effective imaging combined use of dense and sparse sampling in frequency is a compromise between resolution and efficiency as it reduces the number of iterations needed in layer stripping inversion while still producing a good image in the second scheme we apply depth dependent weights to model updates in order to improve the convergence in an iterative solution the weighting is inversely proportional to the ray density variation along the depth and is mathematically equivalent to the application of an inverse hessian matrix which sharpens the gradient vector for model updating for real seismic data we transfer point source shot records to line source records by partial amplitude compensation and phase adjusting before inputting it to the waveform tomography we perform traveltime inversion to generate a reliable layered velocity model and then waveform tomography to produce a high resolution image of the subsurface model through frequency domain iteration

long range acoustic scattering from a shallow water mud volcano cluster analysis of reverberation measurements in the straits of sicily shows high intensity discrete scattered returns 10 20db above background reverberation these returns are due to scattering from mud volcanoes the reverberation from the mud volcanoes at ranges of 15 22km is reasonably consistent over these spatial scales i e kilometers and temporal scales of several hours measurements separated by 4years are also similar statistical characterization indicates that the reverberation associated with a mud volcano cluster is strongly non rayleigh and that the reverberation can be characterized by a single shape parameter roughly independent of frequency the non rayleigh statistics with a concomitant increase in the probability of false alarm indicate that mud volcanoes are a likely source of clutter mean target strengths were estimated at 1 11db over 160 1400hz and are consistent with target strengths measured during a different year at short direct path ranges accumulated evidence points to

evidence for a common scale o 0 1 m that controls seabed scattering and reverberation in shallow water analysis of the spectral content of long range reverberation yields two observations first there is a remarkably similar scale o 0 1 m between three diverse continental shelf regions this is surprising given the complexity and diversity of geologic processes second there is strong evidence that the scale is associated with heterogeneities within the sediment thus sediment volume scattering not interface scattering controls long range reverberation from a few hundred hertz to several kilohertz this is also unexpected given that at long ranges the vertical grazing angles are less than the critical angle and hence the penetration of the acoustic field into the sub bottom is expected to be modest the consistency of the scale o 0 1 m suggests an underlying feature or mechanism that is consistent across many ostensibly diverse geological settings neither the feature nor mechanism is known at this time

velocity observations of the california current derived from satellite imagery 1 this research examines the potential of ocean velocity observations generated from the maximum cross correlation technique mcc applied to thermal infrared imagery to capture the total current at a high sampling rate especially in the nearshore region allowing for a novel view of the california current comparison of 12 years of weekly ocean velocity fields derived from the mcc method with velocity observations from drifting buoys reveals strong correspondence between the data sets the mcc method however is able to produce over 10 times the number of observations comparison of mcc velocities with geostrophic velocities from altimetry demonstrates differences that suggest ageostrophic currents in the mcc observations that are likely wind driven the time averaged mean velocity field from mcc observations reveals strong offshore jet like features that extend off of coastline promontories eddy statistics from the mcc velocity observations indicate dramatically different dynamics in the nearshore and offshore regions differences in spatial statistics derived from the mcc observations compared to previous studies of the region are attributed to wind driven currents in the observations that can dominate the variability of the current in the nearshore region