kinematics of shot geophone migration recent analysis and synthetic examples have shown that many prestack depth migration methods produce nonflat image gathers containing spurious events even when provided with a kinematically correct migration velocity field if this velocityfieldishighlyrefractive thispathologyoccursinall migration methods that produce partial images as independent migrations of data bins shot geophone prestack depth migration is an exception to this pattern each point in the prestack image volume depends explicitly on all traces within the migration aperture using a ray theoretical analysis we have found that shot geophone migration produces focusedsubsurface offsetdomainorflatscattering angledomain image gathers provided there is a curvilinear coordinate system defining pseudodepth with respect to which the rays carrying significant energy do not turn and that the acquisitioncoverageissufficienttodetermineallsuchrays although the analysis is theoretical and idealized a synthetic example suggests that its implications remain valid for practical implementations and that shot geophone prestack depth migration could be a particularly appropriate tool for velocityanalysisinacomplexstructure

sensitivity of prestack depth migration to the velocity model to get a correct earth image from seismic data acquired over complex structures it is essential to use prestack depth migration a necessary condition for obtaining a correct image is that the prestack depth migration is done with an accurate velocity model in cases where we need to use prestack depth migration determination of such a model using conventional methods does not give satisfactory results thus new iterative methods for velocity model determination have been developed the convergence of these methods can be accelerated by defining constraints on the model in such a way that the method only looks for those components of the true earth velocity field that influence the migrated image in order to determine these components the sensitivity of the prestack depth migration result to the velocity model is examined using a complex synthetic data set the marmousi data set for which the exact model is known the images obtained with increasingly smoothed versions of the true model are compared

wavefield tomography using reverse time migration backscattering abstractreverse time migration backscattering contains kinematic information that can be used to constrain velocity models the backscattering results from the correlation between forward scattered and backscattered wavefields from sharp interfaces i e sediment salt interfaces the synchronization between these wavefields depends on the velocity of the sediment section and the correct interpretation of the sharp boundary we have developed an optimization workflow in which the sediment velocity and the sharp boundary are updated iteratively the presence of sharp boundaries in the model lead to high and low wavenumber components in the objective function gradient the high wavenumber components correspond to the correlation of wavefields traveling in opposite directions whereas the low wavenumber components correspond to the correlation of wavefields traveling in the same direction this behavior is similar to reverse time migration in which the high wavenumber components represent the reflectors th

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

upper ocean temperature structure inertial currents and richardson numbers observed during strong meteorological forcing abstract upper ocean currents and temperature in the northeastern pacific were measured during a 14 day period in november 1980 as part of strex velocities in the upper ocean are dominated by near inertial frequency oscillations thew oscillations are modified by wind stress variations associated with the passage of a strong cold front the change in the inertial currents both in the mixed layer and below is qualitatively consistent with linear internal wave dynamics if turbulent stresses during the storm are assumed to extend 10 20 m below the mixed layer the ratio of mean squared buoyancy frequency n2 and mean squared shear s2 computed over a 10 m interval defines an average richardson number r0 n2 s2 r0 is approximately 2 5 except in regions of high inertial shear in particular values as low as 0 7 are obtained in a 20 m thick region immediately below the base of the mixed layer the data are consistent with a model of the oecanic shear field consisting of a background shear corresponding to a va

inversion of reflection seismograms by differential semblance analysis algorithm structure and synthetic examples1 seismograms predicted from acoustic or elastic earth models depend very non linearly on the long wavelength components of velocity this sensitive dependence demands the use of special variational principles in waveform based inversion algorithms the differential semblance variational principle is well suited to velocity inversion by gradient methods since its objective function is smooth and convex over a large range of velocity models an extension of the adjoint state technique yields an accurate estimate of the differential semblance gradient non linear conjugate gradient iteration is quite successful in locating the global differential semblance minimum which is near the ordinary least squares global minimum when coherent data noise is small several examples based on the 2d primaries only acoustic model illustrate features of the method and its performance

a note on the attenuation of surface gravity waves by rainfall rainfall has long been associated with damping of short surface gravity waves a theory is presented which uses a thin rain induced turbulent surface layer to explain the enhanced attenuation in the presence of a thin turbulent surface layer the e folding attenuation time for the 30 cm wavelength surface gravity waves needed for remote sensing of the ocean surface using synthetic aperture radar sar is reduced from several minutes to several seconds this explains the observation of low sar radar return from regions of high rainfall longer wavelengths are also affected depending on the strength of the mixing and the thickness of the turbulent layer

gulf stream surface convergence imaged by synthetic aperture radar on july 20 1990 the north edge of the gulf stream 36 7 n 72 0 w was sampled by the r v cape henlopen and simultaneously imaged by the jet propulsion laboratory s airborne synthetic aperture radar sar hydrographic measurements show an abrupt surface front separating warm salty gulf stream water in the south from a filament of cool fresh 33 practical salinity unit psu water to the north the filament lies within the stream and is likely water entrained from the continental shelf the southern boundary of the filament is marked by increased surface wave breaking in a 100 to 200 m wide zone accumulations of sargassum and an orthogonal velocity change of 20 cm s the front is manifested in a sequence of sar images as a narrow line having returns 1 2 db higher than background a second transient sar line occurs near the northern filament boundary the observations are compared with model calculations of the surface wave hydrodynamics and radar scattering the ocean waves are driven by southwesterly 8 m s winds and interact with the front to produce primarily an enhancement of 2 to 3 m waves over a 200 m wide region centered downwind of the front using a composite scattering radar model along with measured breaking wave statistics we show that the observed modulations in the radar backscatter can be accounted for through breaking wave and tilted bragg wave scattering effects these results further show that sar images of the ocean surface can be exploited for detailed study of particular ocean processes

kinematic artifacts in prestack depth migration strong refraction of waves in the migration velocity model introduces kinematic artifacts coherent events not corresponding to actual reflectors into the image volumes produced by prestack depth migration applied to individual data bins because individual bins are migrated independently the migration has no access to the bin component of slowness this loss of slowness information permits events to migrate along multiple incident reflected ray pairs thus introducing spurious coherent events into the image volume this pathology occurs for all common binning strategies including common source common offset and common scattering angle since the artifacts move out with bin parameter their effect on the final stacked image is minimal provided that the migration velocity model is kinematically correct however common image gathers may exhibit energetic primary events with substantial residual moveout even with the kinematically accurate migration velocity model

measurement of surface currents using sequential synthetic aperture radar images of slick patterns near the edge of the gulf stream two dimensional surface currents are estimated over an area of 100 km2 near the inshore edge of the gulf stream by correlating the surface slick patterns observed on two synthetic aperture radar sar images collected about 20 min apart the currents obtained from this analysis are found to agree well with shipboard acoustic doppler current profiler adcp measurements at 10 to 20 m depths the orientations of the long linear slicks observed in this region differ from the mean current direction by about 16 but coincide with the direction of maximum radial deformation or strain as calculated from the observed current field the calculated current gradients indicate a mean surface convergence of about 2 10 5 s 1 and a cyclonic vorticity of about 1 10 4 s 1 values which fall within the range of previous estimates in the study area these results suggest that slick patterns may be used to infer surface current magnitude and direction from a time sequence of sar images but that care must be exercised in inferring current directions from the orientations of slick patterns within a single image

seismic wave equation demigration migration reverse time migration is a well known method based on a single scattering approximation it is designed to obtain seismic images in the case of a complex subsurface it can however be a very time consuming task because the number of computations is directly proportional to the number of processed sources in the context of velocity model building iterative approaches require that one derives a series of migrated sections for different velocity models we propose to replace the summation over sources by a summation over depth offsets or time delays defined in the subsurface for that we have developed a new relationship between two migrated sections obtained for two different velocity models starting from one of the two images we obtain a second section correctly and efficiently for each time delay we compute a generalized source term by extending the concept of exploding reflector to nonzero offset we obtain the final migrated section by solving the same wave equation in the perturbed model with the modified source term our work included testing the methodology on 2d synthetic data sets particularly when the initial and perturbed velocity models differ greatly

solving the paradox of the end of the little ice age in the alps 1 the causes and timing of the little ice age fifteenth to nineteenth centuries are still unclear crowley 2000 bond et al 2001 shindell et al 2001 during the last part of this event 1760 1830 the advance of glaciers in the alps conflicts with the summer temperature signal intergovernmental panel on climate change 2001 this paper attempts to solve this paradox from glacier fluctuations and monthly temperature data we show that mean winter precipitation was higher by at least 25 during this final phase compared to the twentieth century average and that glacier recession after 1830 clearly resulted from a winter precipitation decrease and not a temperature increase conversely since the beginning of the twentieth century glacier changes have been driven mainly by temperature change

target oriented joint least squares migration inversion of time lapse seismic data sets two related formulations are proposed for target oriented joint least squares migration inversion of time lapse seismic data sets time lapse seismic images can be degraded when reservoir overburden is complex or when acquisition geometries significantly differ because the migration operator does not compensate for the resulting amplitude and phase distortions under these circumstances time lapse amplitudes are poor indicators of production related changes in reservoir properties to correct for such image degradation time lapse imaging is posed as joint inverse problems that utilize concatenations of target oriented approximations to the linear least squares imaging hessian in both formulations spatial and temporal constraints ensure inversion stability and geologically consistent time lapse images using two numerical time lapse data sets we confirmed that these formulations can attenuate illumination artifacts caused by complex overburden or geometry differences and that they yield better quality images than obtainable with migration

high resolution measurements made across a tidal intrusion front high spatial resolution current and hydrographic measurements have been made across a tidal intrusion front in the james river estuary virginia during the first few hours of flood the current measurements were made with a surface towed acoustic doppler current profiler which was used in both profile and side scan configurations the profile data show a 30 50 cm s 1 inflow of water from the chesapeake bay a time evolving across front density gradient and downward velocity beneath the front of about 15 cm s 1 the side scan observations directly measure the across front change in current and provide a view of the three dimensional character of the frontal interface the near surface horizontal strain rate a critical parameter for understanding the modulation of surface waves across the front is estimated to be about 0 04 s 1 using phillips 1984 theory as a guide fronts with such large strain rates as these should be discernible in imagery from the ers 1 c band synthetic aperture radar for wind speeds of 4 m s 1

polarization based wave equation migration velocity analysis in acoustic media abstractthe source extrapolation step in wave equation prestack reverse time migration gives wavefield polarization information which can be used to generate angle domain common image gathers adcigs from seismic reflection data from acoustic media concatenation of p wave polarization segments gives wavefield propagation paths wavepaths which are similar to the raypaths in ray based velocity tomography the adcigs provide residual depth moveout rmo information from which a system of linear equations is constructed for tomography to solve for the velocity ratio used for velocity updating an empirical relation between the rmo data and the velocity ratio updates reduces the amount of computation and is stabilized by the feedback provided by the iterative loop through prestack migration to rmo to velocity update to prestack migration correcting the rmos to flatten the adgigs is the convergence condition synthetic data for a layered model with a fault successfully illustrates the method

ocean surface features and currents measured with synthetic aperture radar interferometry and hf radar this paper describes the results of the first quantitative comparison between high resolution ocean surface current fields extracted from interferometric synthetic aperture radar insar measurements and those from a high frequency hf ocean surface current radar oscr system data from each of these radar systems along with supporting measurements from shipboard and buoy mounted sensors were collected during the high resolution remote sensing experiment high res on june 20 1993 on the continental shelf off the coast of cape hatteras north carolina both components of the surface current were obtained from the insar system at roughly 10 m resolution from two orthogonal flight legs over the region separated in time by about 30 min the oscr system measured two dimensional surface current vectors at about 1 km resolution over this same region while the usns bartlett was collecting hydrographic samples and near surface current measurements two dimensional wave spectra as well as meteorological and additional current measurements were collected at two buoys within the experimental area we discuss in the paper two techniques for eliminating the effect of surface wave motion on the insar current estimates one method relies on some knowledge of the local wind and wave field and the use of a microwave scattering model the other method makes use of a few in situ current measurements spaced at different range locations across the insar image using either of these techniques we find that the agreement between the insar and oscr current estimates is generally very good furthermore the insar current and magnitude imagery show the presence of undulating surface features where abrupt changes in the current speed and direction occurred the ship surveys indicate that these features were caused by the collision of water masses of different density we show for the first time in this paper a high resolution area extensive vector surface current map derived from the insar of the two dimensional flow in the vicinity of these features our results demonstrate convincingly that high resolution oceanic surface current vectors can be derived from insar current measurements and that these measurements may be very beneficial for detailed studies of the dynamics of small scale surface features in regions of strong current divergences or shears

the influence of the marine atmospheric boundary layer on ers 1 synthetic aperture radar imagery of the gulf stream in september 1991 the ers 1 synthetic aperture radar sar collected a set of four colocated images over the western gulf stream gs the sar images were supplemented by satellite infrared imagery and measurements of the marine atmospheric boundary layer mabl from both a pair of surface buoys and a suite of instrument on the ukrainian research vessel r v vernadsky which between september 15 and 19 made six transects across the gs northern boundary within the sar swaths the influence of wind variations within the mabl was evident in each of the four sar images evidence for thermal wind effects is seen in the changing character of the imagery as the mean wind across the sea surface temperature boundary changed direction from pass to pass both in situ data and analytical models suggest that much of the day to day sar image variability was the result of changes in the character of the mabl especially evident near the northern gs boundary where the sign of the atmospheric stability fluctuated over short spatial scales because many of the governing parameters of the mabl rapidly decorrelate significant changes in the sar imagery occurred during the 3 days between passes nevertheless at least some manifestation of the gs was evident in the sar imagery on each of the four passes

improving the gradient of the image domain objective function using quantitative migration for a more robust migration velocity analysis migration velocity analysis aims at determining the background velocity model classical artefacts such as migration smiles are observed on subsurface offset common image gathers due to spatial and frequency data limitations we analyse their impact on the differential semblance functional and on its gradient with respect to the model in particular the differential semblance functional is not necessarily minimum at the expected value tapers are classically applied on common image gathers to partly reduce these artefacts here we first observe that the migrated image can be defined as the first gradient of an objective function formulated in the data domain for an automatic and more robust formulation we introduce a weight in the original data domain objective function the weight is determined such that the hessian resembles a dirac function in that way we extend quantitative migration to the subsurface offset domain this is an automatic way to compensate for illumination we analyse the modified scheme on a very simple 2d case and on a more complex velocity model to show how migration velocity analysis becomes more robust

image domain velocity inversion and event location for microseismic monitoring abstractmicroseismic event locations obtained from seismic monitoring data sets are often a primary means of determining the success of fluid injection programs such as hydraulic fracturing for oil and gas extraction geothermal projects and wastewater injection event locations help the decision makers to evaluate whether operations conform to expectations or parameters need to be changed and may be used to help assess and reduce the risk of induced seismicity however obtaining accurate event location estimates requires an accurate velocity model which is not available at most injection sites common velocity updating techniques require picking arrivals on individual seismograms this can be problematic in microseismic monitoring particularly for surface acquisition due to the low signal to noise ratio of the arrivals we have developed a full wavefield adjoint state method for locating seismic events while inverting for p and s wave velocity models that optimally focus multiple complementary ima

a new interpretation of multifrequency multipolarization radar signatures of the gulf stream front radar signatures which are observed on sir c x sar multifrequency multipolarization synthetic aperture radar images of the gulf stream off the u s east coast are compared with results of simulations with a numerical radar imaging model based on in situ data current and wind variations are included into the model as well as a variation of the thermal stability of the marine atmospheric boundary layer across the gulf stream front according to our model predictions all of these parameter variations can cause radar signatures of similar shape and modulation depth but due to specific dependencies of radar signatures on variations of surface currents and winds we show that it is possible to distinguish between radar signatures of oceanic and atmospheric origin in multifrequency multipolarization images and to estimate the corresponding current and wind variations independently for one set of radar images we derive a most likely scenario of oceanic and atmospheric parameters during the time of the image acquisition for which good overall agreement between observed and simulated radar signatures is obtained at most radar channels

radar backscatter from breaking waves in gulf stream current convergence fronts bright linear features have been observed in radar imagery taken near the gulf stream gs boundary on two separate occasions in each case these have been observed directly over strong current convergences progress has been made in understanding the origin of these signatures through simulations that incorporate environmental forcing from the winds and currents these simulations significantly underestimate the backscatter unless wave breaking wb effects are included at least approximately using a new quasistatistical procedure that generalizes and quantifies earlier procedures for including wb effects the authors have been able to successfully simulate the magnitude and behavior of these signatures the approach combines the statistically based composite model of radar backscatter with a deterministic feature model that relates backscatter from breaking waves to a particular geometrical model of a spilling breaker this is accomplished using localized criteria defined by local wave crest acceleration to determine the probability of breaking and by extending the feature model so that its unknown parameters may be evaluated directly from wave current interaction calculations the new approach provides an estimate of the critical crest acceleration of a potentially breaking wave as a function of wind speed that agrees with independent measurements

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

the effect of rain in calming the sea abstract the effect of rain in damping surface waves appears to be significant in the estimation of wind speed from the backscatter of radar signal from the sea surface the radar backscatter depends on the small scale roughness of the sea surface this is modified by the generation of capillary and gravity capillary ripples by raindrops and by the increased damping of the wavelengths of 10 cm scale the phenomenon is also important in wave generation and wave breaking since in both cases the short wavelengths play a key role a laboratory experiment has been performed to investigate the damping of water waves by rain in the absence of wind rain of intensity of 300 mm h 1 falls on mechanically generated progressive waves the wave amplitude is measured before the wave enters and after it exits the rain section of a tank 2 35 m long on the assumption of exponential damping it is found that the effect of rain can be described by an eddy viscosity e 0 3 cm2 s 1 the major part of the damping is attrib

3 d shallow water seismic survey evaluation and design using the focal beam method a case study offshore abu dhabi for 3 d shallow water seismic surveys offshore abu dhabi imaging the target reflectors requires high resolution characterization and monitoring of hydrocarbon reservoirs by seismic amplitude versus offset techniques demands high pre stack amplitude fidelity in this region however it still was not clear how the survey parameters should be chosen to satisfy the required data quality to answer this question we applied the focal beam method to survey evaluation and design this subsurfaceand target oriented approach enables quantitative analysis of attributes such as the best achievable resolution and pre stack amplitude fidelity at a fixed grid point in the subsurface for a given acquisition geometry at the surface this method offers an efficient way to optimize the acquisition geometry for maximum resolution and minimum amplitude versus offset imprint we applied it to several acquisition geometries in order to understand the effects of survey parameters such as the four spatial sampling intervals and apertures of the template geometry the results led to a good understanding of the relationship between the survey parameters and the resulting data quality and identification of the survey parameters for reflection imaging and amplitude versus offset applications

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

seismic envelope inversion reduction of local minima and noise resistance waveform inversion met severe challenge in retrieving long wavelength background structure we have proposed to use envelope inversion to recover the large scale component of the model using the large scale background recovered by envelope inversion as new starting model we can get much better result than the conventional full waveform inversion by comparing the configurations of the misfit functional between the envelope inversion and the conventional waveform inversion we show that envelope inversion can greatly reduce the local minimum problem the combination of envelope inversion and waveform inversion can deliver more faithful and accurate final result with almost no extra computation cost compared to the conventional full waveform inversion we also tested the noise resistance ability of envelope inversion to gaussian noise and seismic interference noise the results showed that envelope inversion is insensitive to gaussian noise and to a certain extent insensitive to seismic interference noise this indicates the robustness of this method and its potential use for noisy data

study of gulf stream features with a multifrequency polarimetric sar from the space shuttle using simulations of radar cross section rcs based on wave current interaction calculations the authors investigate the origin of a prominent enhancement in l band from signals that were transmitted and received respectively with horizontal h and vertical v polarization radar return this was observed in imagery of the northern boundary of the gulf stream gs during the first shuttle radar laboratory srl 1 mission the calculations of surface roughness are based on a one dimensional 1d surface current model that closely resembles a current shear that was observed in in situ current measurements taken at both sides of the gs at the time srl 1 imaged the gs boundary in agreement with trends observed in the imagery significant enhancements in l band hv polarization cross section occur in the neighborhood of the gs thermal boundary relative to comparable vertical polarization vv cross section signatures at x c and l band the authors also find reasonably good agreement between the simulated and observed magnitudes of the gs signatures based on calculations of wave action using two different radar imaging models and they provide an overview of a number of additional submesoscale features associated with the gs that were present in the image of the gs boundary

insar imagery of surface currents wave fields and fronts the authors demonstrate the ability of interferometric radar imagery to determine both relative and absolute surface velocities in the open ocean absolute phase calibration is accomplished by noting the azimuthal displacement of range travelling targets demonstrating for the first time that under favourable circumstances phase calibration can be achieved in open ocean in the absence of ground truth the high resolution of radar imagery permits observation of sharp velocity discontinuities e g the gulf stream boundary and the wave field the recent sir c x sar shuttle missions dramatically emphasize the experimental and observational aspects of space based radar the combination of absolute velocities high spatial resolution and wide area coverage suggest that interferometric radar imagery can provide a unique and powerful aid both for studies of global circulation patterns and detailed analysis of slope shelf water interactions with ocean currents in particular the authors employ this measurement of the surface currents and wave field near a velocity front to help refine and bound results of their modeling of calculated radar images of the front the results of this paper are compared with available ground truth

retrieval of sea surface range velocities from envisat asar doppler centroid measurements the processing steps and error corrections needed to retrieve estimates of sea surface range doppler velocities from envisat advanced synthetic aperture radar wide swath medium resolution image products are presented retrieval accuracies based on examination of the corrected doppler shift measurements are assessed the root mean square errors of the doppler shift after bias corrections are found to be 4 7 and 3 9 hz in vv and hh polarizations respectively at 35 incidence angle this corresponds to horizontal doppler velocities of 23 and 19 cm s

radar scattering behavior of estuarine outflow plumes we present results of dual polarized radar scattering measurements of the chesapeake bay outflow plume near unity polarization ratios ratios of horizontally polarized radar echoes over vertically polarized ones are observed in large incidence angle 60 spl deg to 80 spl deg radar echoes from the outflow plume and its frontal boundary normally referred to as a front under strong surface current convergence 0 008 0 02 s sup 1 suggesting the existence of steepened and breaking waves in the regions cumulative distribution functions of the horizontally polarized radar returns from the front show approximately 90 of the radar echoes are from steepened and breaking waves vertically polarized echoes do not show this effect these experimental results substantiate early modeling investigators speculation of featured scattering contributing to horizontally polarized radar signatures of oceanic fronts our results also suggest that horizontal radar polarization can be used to remotely sense additional hydrodynamic processes such as wave trapping blocking and breaking near oceanic fronts better than what is possible with only vertical polarization

microseismic image domain velocity inversion marcellus shale case study abstractseismic monitoring at injection wells relies on generating accurate location estimates of detected micro seismicity event location estimates assist in optimizing well and stage spacings assessing potential hazards and establishing causation of larger events the largest impediment to generating accurate location estimates is an accurate velocity model for surface based monitoring the model should capture 3d velocity variation yet rarely is the laterally heterogeneous nature of the velocity field captured another complication for surface monitoring is that the data often suffer from low signal to noise levels making velocity updating with established techniques difficult due to uncertainties in the arrival picks we use surface monitored field data to demonstrate that a new method requiring no arrival picking can improve microseismic locations by jointly locating events and updating 3d p and s wave velocity models through image domain adjoint state tomography this approach creates a co

imaging mesoscale upper ocean dynamics using synthetic aperture radar and optical data a synergetic approach for quantitative analysis of high resolution ocean synthetic aperture radar sar and imaging spectrometer data including the infrared ir channels is suggested this approach first clearly demonstrates that sea surface roughness anomalies derived from sun glitter imagery compare very well to sar roughness anomalies as further revealed using these fine resolution similar to 1 km observations the derived roughness anomaly fields are spatially correlated with sharp gradients of the sea surface temperature sst field to quantitatively interpret sar and optical in visible and ir ranges images equations are derived to relate the surface roughness signatures to the upper ocean flow characteristics as developed a direct link between surface observations and divergence of the sea surface current field is anticipated from these satellite observations intense cross frontal dynamics and vertical motions are then found to occur near sharp horizontal gradients of the sst field as a plausible mechanism it is suggested that interactions of the wind driven upper layer with the quasi geostrophic current field via ekman advective and mixing mechanisms result in the generation of secondary ageostrophic circulation producing convergence and divergence of the surface currents the proposed synergetic approach combining sst sun glitter brightness and radar backscatter anomalies possibly augmented by other satellite data e g altimetry scatterometry ocean color can thus provide consistent and quantitative determination of the location and intensity of the surface current convergence divergence upwelling downwelling this in turn establishes an important step toward advances in the quantitative interpretation of the upper ocean dynamics from their two dimensional satellite surface expressions

benthic observations on the madeira abyssal plain fronts abstract analysis of data from a mooring with five vector averaging current meters between 10 and 70 m above the bed of the madeira abyssal plain reveals the existence of narrow regions with relatively large gradients of potential temperature or fronts the orientation and structure of the fronts is examined by combining the temperature and current data and plotting contours of equal potential temperature on the progressive vector diagrams a procedure justified because of the known horizontal coherence of the currents and the relatively long time scales of evolution of the benthic boundary layer sections through the fronts show that they are typically 300 m in width they extend horizontally for at least 8 km the temperature differences across the observed fronts are only 2 4 mdeg c the frontal surfaces are tilted at 10 deg to the horizontal the observed cold fronts being steeper and with isotherms more closely compacted in the lower levels than warm fronts these features possibly result from