Oceanography The Official Magazine of
The Oceanography Society
Volume 22 Issue 01

View Issue TOC
Volume 22, No. 1
Pages 192 - 205

OpenAccess

Water Column Seismic Images as Maps of Temperature Gradient

Barry RuddickHaibin Song Chongzhi DongLuis Pinheiro
Article Abstract

Multichannel seismic imaging of ocean water column features is a new interdisciplinary study that may become an accepted oceanographic tool in coming years. We now know that reflectors are associated with water column thermohaline fine structures such as internal waves and intrusions (on a scale of ~ 10–50 m) associated with ocean mixing, and also that the images outline larger-scale oceanographic features such as currents, water-mass boundaries, eddies, meddies, and fronts. The synopticity and detail showing the relationships between mesoscale and fine-scale features promises improved insight into the processes that cascade energy from mesoscales to mixing scales.

In order to trust a new tool, oceanographers require a quantitative understanding of how the new tool acts upon physical properties to yield a final result. We explain the basic principles of multichannel seismics, and show that the imaging process can be viewed as a filtering operation acting on the acoustic impedance field, which, on the scales that matter, is primarily (but not completely) associated with temperature variations. Synthetic seismic images show the derivative of acoustic impedance, averaged over the resolution scale of the acoustic source wavelet—they are, aside from side-lobe effects, essentially smoothed maps of temperature gradient. We use a conductivity-temperature-depth (CTD) trace from the periphery of a meddy to estimate the contribution of thermal (83%) and saline (17%) anomalies to a synthetic seismic trace, and then use multiple CTD traces from the same data set to construct a synthetic seismic image. This synthetic image compares favorably to a real seismic image of a different meddy with important differences that can be ascribed to the higher lateral resolution of the seismic technique.

Citation

Ruddick, B., H. Song, C. Dong, and L. Pinheiro. 2009. Water column seismic images as maps of temperature gradient. Oceanography 22(1):192–205, https://doi.org/10.5670/oceanog.2009.19.

References

Armi, L., D. Hebert, N. Oakey, J. Price, P. Richardson, T. Rossby, and B. Ruddick. 1989. Two years in the life of a Mediterranean salt lens. Journal of Physical Oceanography 19:354–370.

Biescas, B., V. Sallares, J.L. Pelegrı, F. Machın, R. Carbonell, G. Buffett, and J.J. Danobeitia. 2008. Imaging meddy finestructure using multichannel seismic data. Geophysical Research Letters 35, L11609, doi:10.1029/2008GL033971.

Bracewell, R.N. 1978. The Fourier Transform and its Application. Second edition, McGraw-Hill Book Co., New York, 616 pp.

Brown, G.L., and A. Roshko. 1974. On the density effects and large structure in turbulent mixing layers. Journal of Fluid Mechanics 64:775–816.

Chen, C.T., and F.J. Millero. 1977. Speed of sound in seawater at high pressures. Journal of the Acoustical Society of America 62(5):1,129–1,135.

Fofonoff, N. P. 1985. Physical properties of seawater: A new salinity scale and equation of state of seawater. Journal of Geophysical Research 90(C2):3,332–3,342.

Géli, L., B. Savoye, X. Carton, and M. Stéphan. 2005. Seismic imaging of the ocean internal structure: A new tool in physical oceanography. Eos, Transactions of the American Geophysical Union 86(2):15.

Greenan, B., M. Nedimovic, K. Louden, R. Mirshak, B. Ruddick, and J. Shimeld. 2008. ROSE – Reflection Ocean Seismic Experiment. Bulletin of the Canadian Meteorological and Oceanographic Society 36(2):43–50.

Hardy, R. 2001. Basic Seismic Processing for Interpreters (Revised August 2008). http://www.xsgeo.com/course/contents.htm (accessed January 10, 2009).

Hebert, D., N. Oakey, B. Ruddick, L. Armi, J. Price, P.L. Richardson, and T. Rossby. 1988. CTD data collected during the survey of a Mediterranean salt lens. Canadian Data Report of Hydrography and Ocean Sciences No. 61, Fisheries and Oceans Canada, Ottawa, 379 pp.

Hobbs, R. 2007. PROJECT: GO–Geophysical Oceanography: A new tool to understand the thermal structure and dynamics of oceans. European Region Newsletter 2:7. Available online at: http://www.aapg.org/europe/newsletters/2007/06jun/
06jun07europe.pdf (accessed January 15, 2009).

Holbrook, W.S., P. Paramo, S. Pearse, and R.W. Schmitt. 2003. Thermohaline fine structure in an oceanographic front from seismic reflection profiling. Science 301:821–824.

Holbrook, W.S., and I. Fer. 2005. Ocean internal wave spectra inferred from seismic reflection transects. Geophysical Research Letters 32, L15604, doi:10.1029/2005GL023733.

Jackett, D.R., and T.J. McDougall. 1997. A neutral density variable for the world’s oceans. Journal of Physical Oceanography 27: 237–263.

Kelley, D.E., H.J.S. Fernando, A.E. Gargett, J. Tanny, and E. Ozsoy. 2003. The diffusive regime of double-diffusive convection. Progress in Oceanography 56:461–481.

Kunze, E., A.J. Williams III, and R.W. Schmitt. 1987. Optical microstructure in the thermohaline staircase east of Barbados. Deep-Sea Research Part A 34:1,697–1,704.

Lavery, A., R.W. Schmitt, and T.K. Stanton. 2003. High-frequency acoustic scattering from turbulent oceanic microstructure: The importance of density fluctuations. Journal of the Acoustical Society of America 114(5):2,685–2,697.

Lazear, G.D. 1993. Mixed-phase wavelet estimation using fourth-order cumulants. Geophysics 58:1,042–1,051.

MacKenzie, K.V. 1981. Nine-term equation for sound speed in the ocean. Journal of the Acoustical Society of America 70:807–812.

May, B.D., and D.E. Kelley. 1997. Effect of baroclinicity on double-diffusive interleaving. Journal of Physical Oceanography 27:1,997–2,008.

May, B.D., and D.E. Kelley. 2002. Contrasting the interleaving in two baroclinic ocean fronts. Dynamics of Atmospheres and Oceans 36:23–42.

McEwan, A.D. 1993. The kinematics of stratified mixing through internal wavebreaking. Journal of Fluid Mechanics 128:47–57.

McKean, R.S. 1974. Internal wave measurements in the presence of fine-structure. Journal of Physical Oceanography 94: 200–213.

Mowbray, D.E., and B.S.H. Rarity. 1967. A theoretical and experimental investigation of the phase configuration of internal waves of small amplitude in a density stratified liquid. Journal of Fluid Mechanics 28:1–16.

Nakamura, Y., T. Noguchi, T. Tsuji, S. Itoh, H. Niino, and T. Matsuoka. 2006. Simultaneous seismic reflection and physical oceanographic observations of oceanic fine structure in the Kuroshio extension front. Geophysical Research Letters 33, L23605, doi:10.1029/2006GL027437.

Nandi, P., W.S. Holbrook, S. Pearse, P. Paramo, and R.W. Schmitt. 2004. Seismic reflection imaging of water mass boundaries in the Norwegian Sea. Geophysical Research Letters 31, L23311, doi:10.1029/2004GL02135.

Ruddick, B.R. 1992. Intrusive mixing in a Mediterranean salt lens: Intrusion slopes and dynamical mechanisms. Journal of Physical Oceanography 22(11):1,274–1,285.

Ruddick, B.R., and D. Hebert. 1988. The mixing of Meddy “Sharon.” Pp. 249–262 in Small-Scale Turbulence and Mixing in the Ocean, J.C.J. Nihoul and B.M. Jamart, eds, Elsevier Science.

Ruddick, B., and D. Walsh. 1995. Observations of the density perturbations which drive thermohaline intrusions. Pp. 329–334 in Double-Diffusive Convection, A. Brandt and H.J.S. Fernando, eds, American Geophysical Union, Washington, DC.

Schmitt, R.W. 1994. Double diffusion in oceanography. Annual Review of Fluid Mechanics 26:255–285.

Sheriff, R.E., and L. P. Geldart. 1995. Exploration Seismology, 2nd ed. Cambridge University Press, 592 pp.

Tsuji, T., T. Noguchi, H. Niino, T. Matsuoka, Y. Nakamura, H. Tokuyama, S. Kuramoto, and N. Bangs. 2005. Two-dimensional mapping of fine structures in the Kuroshio Current using seismic reflection data. Geophysical Research Letters 32, L14609, doi:10.1029/2005GL023095.

Williams, A. J. 1974. Salt fingers observed in the Mediterranean outflow. Science 185:941–943.

Wood, W.T., S. Holbrook, M.K. Sen, and P.L. Stoffa, 2008. Full waveform inversion of reflection seismic data for ocean temperature profiles. Geophysical Research Letters 35, L04608, doi:10.1029/2007GL032359.

Yilmaz, O. 2001. Seismic Data Analysis: Processing, Inversion, and Interpretation of Seismic Data, vol. 2, 2nd ed. Investigations in Geophysics No. 10, Society for Exploration Geophysics, Tulsa, OK, 2,027 pp.

Copyright & Usage

This is an open access article made available under the terms of the Creative Commons Attribution 4.0 International License (https://creativecommons.org/licenses/by/4.0/), which permits use, sharing, adaptation, distribution, and reproduction in any medium or format as long as users cite the materials appropriately, provide a link to the Creative Commons license, and indicate the changes that were made to the original content. Images, animations, videos, or other third-party material used in articles are included in the Creative Commons license unless indicated otherwise in a credit line to the material. If the material is not included in the article’s Creative Commons license, users will need to obtain permission directly from the license holder to reproduce the material.