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  • 1
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    Ocean temperature and salinity inverted from combined hydrographic and seismic data (2010)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 37 (4). L04601.
    Details
    Publication Date: 2017-06-20
    Description: Recently seismic reflection methods have been successfully applied to oceanographic issues. Here, we present a new approach, combining XBT and CTD surveys with seismic observations, to visualize long sections with a resolution down to a few meters. The challenge to a full investigation of mixing processes has been the tremendous span of spatial scales ranging from hundreds of kilometers to centimeters. Traditional hydrographic observations could only resolve the large scale effects by measuring temperature and salinity profiles at discrete locations typically several kilometers apart, whereas dedicated localized measurements allowed investigation of the ocean fine structure at the other end of the spatial spectrum. The intermediate scales have in contrast been difficult to observe systematically. Here we present temperature and salinity data inverted from seismic observations that cover the intermediate scales and provide a new approach to image mesoscale processes and allow the investigation of their dynamics at unprecedented resolution.
    Type: Article , PeerReviewed
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  • 2
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    Estimating internal wave spectra using constrained models of the dynamic ocean (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L00D07.
    Details
    Publication Date: 2017-10-13
    Description: Multi-Channel Seismic method (MCS), with its ability to image events down to a lateral resolution of 10 m has been successfully applied to address questions in physical oceanography. However, to date, these analyses have overlooked an important detail; the imaged boundaries are dynamic and move on a timescale that can be resolved by the MCS method. An important step in understanding the effect of the movement is calibration against constrained models. We demonstrate in this paper that it is possible using careful interpolation to take high resolution models of dynamic water (160 m x 2 m spatial resolution and 15 min temporal resolution) and generate models for synthetic seismic simulations (20 m x 4 m spatial resolution and 20 sec temporal resolution). We show that moving water, when ignored, will distort analyses of wavenumber spectra estimated from seismic data since the relative movement of water masses and the seismic acquisition vessel will change the apparent slope of spectra. Citation: Vsemirnova, E., R. Hobbs, N. Serra, D. Klaeschen, and E. Quentel (2009), Estimating internal wave spectra using constrained models of the dynamic ocean, Geophys. Res. Lett., 36, L00D07, doi: 10.1029/2009GL039598.
    Type: Article , PeerReviewed
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  • 3
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    Estimating movement of reflectors in the water column using seismic oceanography (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L00D03.
    Details
    Publication Date: 2017-07-27
    Description: The observation of spatial and temporal dynamics of the ocean is fundamental to understand global and regional aspects of water mixing. Physical oceanography has traditionally observed ocean structures with in situ measurements, often limited in temporal and/or spatial resolution. In exploration seismology a set of techniques has been developed over the last decades to image and characterize the physical properties of sub-seafloor structures by inversion methods at high horizontal resolution. The two different fields have made contact in seismic oceanography where the well developed methods of marine reflection seismology have been applied to the dynamic ocean. However, one aspect, so far ignored in seismic oceanography, is the dynamical, temporally varying nature of water structures. Here we show that it is possible to estimate temporal variations of reflectors in water structures as an inversion parameter. The new dynamic property reflector movement velocity gives an additional parameter to characterize ocean water dynamics.
    Type: Article , PeerReviewed
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  • 4
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    Joint inversion in hydrocarbon exploration (2016)
    AGU (American Geophysical Union) | Wiley
    In:  In: Integrated Imaging of the Earth: theory and applications. , ed. by Moorkamp, M., Lelievre, P. G., Linde, N. and Khan, A. Geophysical Monograph Series, 218 . AGU (American Geophysical Union), Wiley, Washington, DC, pp. 167-190. ISBN 978-1-118-92905-6
    Details
    Publication Date: 2017-01-04
    Description: This chapter investigates the particular challenges for joint inversion in the context of hydrocarbon exploration. It reviews the current literature and introduces interesting approaches that have been developed in the context of hydrocarbon exploration and could potentially be used in other application areas as well. Joint inversion methods incorporating petro physical models of the reservoir can directly yield quantities of interest such as porosity and permeability, but have to be carefully tuned to the area under investigation. The chapter presents two detailed joint inversion case studies, one for subsalt imaging and one for sub basalt imaging. It also covers emulation of the forward calculation, a concept that can be applied generally in joint inversion, but has only been applied in hydrocarbon exploration. For a successful joint inversion, it is necessary to invert each dataset, construct different coupling approaches, and evaluate the impact on the final results.
    Type: Book chapter , NonPeerReviewed
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  • 5
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    High resolution seismic imaging of the ocean structure using small volume airgun source array in the Gulf of Cadiz (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L00D09.
    Details
    Publication Date: 2017-10-12
    Description: A small volume (117 cu-inch) seismic source producing signal predominantly in the 150–200 Hz frequency window was used during the GO calibration experiment in the Gulf of Cadiz (April–May 2007). The data show the small scale (〈10 m in the z direction) internal structure of the ocean. High-resolution images display seismic reflectors that often appear as distinct, horizontal, short (∼a few hundred meters to a few km long) segments, lying at different depths, while low-resolution (∼20 to 30 Hz) display long, horizontal reflectors (∼a few tens of km), sometimes linked by short, apparently “dipping” segments. The present data suggest that this apparent dipping effect is due to the insufficient separation power (∼λ/4) of the low resolution data. Improving high resolution acquisition systems hence appears to be a critical challenge to understand the seismic response of the ocean.
    Type: Article , PeerReviewed
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  • 6
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    Effect of bandwidth on seismic imaging of rotating stratified turbulence surrounding an anticyclonic eddy from field data and numerical simulations (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L00D05.
    Details
    Publication Date: 2017-10-12
    Description: The fine resolution of long geoseismic sections should permit the characterization of oceanic turbulence properties over several decades of horizontal scales. The range of horizontal scales actually probed by three different acoustic sources is found to be directly linked to their frequency content. The horizontal inertial range with a spectral slope of k(h)(-5/3) extend up to 3 km wavelength for the most intense acoustic reflectors which surround strong anticyclonic eddies. The in situ data analysis is confirmed by high resolution numerical simulations of oceanic anticyclonic vortices, in a rotating temperature-stratified fluid (no salt), which show the spontaneous emergence of a concentration of acoustic reflectors above and below the eddy. These show an anisotropy and a spectral slope consistent with the framework of stratified turbulence, which differs from that of Garret and Munk for internal waves. The implications are that a direct energy cascade to smaller spatial scales is occurring at the boundaries of energetic oceanic vortices and may provide a mechanism to drive mixing in the ocean interior
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  • 7
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    Verification of velocity-resistivity relationships derived from structural joint inversion with borehole data (2013)
    AGU (American Geophysical Union) | Wiley
    In:  Geophysical Research Letters, 40 (14). pp. 3596-3601.
    Details
    Publication Date: 2017-06-20
    Description: We present results of three-dimensional joint inversion of seismic, magnetotelluric, and gravity data over a marine salt dome. Such structures are difficult to image with a single method, and our results demonstrate how combining different techniques can yield improved results. More importantly, we examine the reliability of velocity-conductivity relationships derived from structure-coupled joint inversion approaches. Comparison with a seismic reflection section shows that our models match the upper limit of the salt. Furthermore, velocity and resistivity logs from a borehole drilled into the salt dome's flank match, within error, those recovered by the inversion. The good match suggests that the difference in length scale does not have a significant effect in this case. This provides a strong incentive to incorporate borehole data into the joint inversion in the future and substantiates approaches that use the relationships derived from joint inversion models for lithological classification.
    Type: Article , PeerReviewed
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  • 8
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    Effect of seismic source bandwidth on reflection sections to image water structure (2009)
    AGU (American Geophysical Union)
    In:  Geophysical Research Letters, 36 . L00D08.
    Details
    Publication Date: 2017-10-12
    Description: The seismic reflection profile is the convolution of the seismic acquisition impulse response and the target impedance contrasts. In the ocean, these contrasts are mainly determined by the widths and gradients of the temperature transitions between the different water masses. Hence seismic oceanography profiles are sensitive to the frequency bandwidth of the seismic acquisition system. We tested a novel seismic source that allowed us to simultaneously profile the ocean with differing impulse responses. We show that frequencies ∼20 Hz are best to delineate large impedance contrasts that occur over a vertical scale of several tens of meters whereas frequencies ∼80 Hz image the boundaries of layers of around 10 m. We demonstrate a towed acquisition system that can operate from a research vessel to give a bandwidth from 10 to 120 Hz that could, if required, be modified to provide frequencies up to 200 Hz.
    Type: Article , PeerReviewed
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