skip to primary navigationskip to content
 

E324: Four-Dimensional Seismic Oceanography of Faroe-Shetland Trough (Lead Supervisor: Nicky White, Earth Sciences)

Supervisors: Nicky White (Earth Sciences), Michael Keaveny (PGS) and Richard Lamb (PGS)

Importance of the area of research:

Recently, it has been shown that seismic reflection profiling yields spectacular and well-resolved acoustic images of different water masses in the oceans. These images have already provided new and exciting insights into important oceanographic phenomena (e.g. structure and evolution of thermohaline fronts, internal eddy formation, diapycnal mixing). Just as satellite imagery revolutionized our understanding of the physical, chemical and biological evolution of the sea surface, the nascent discipline of `seismic oceanography' is likely to have an equally profound impact upon our quantitative understanding of four-dimensional (4D) oceanic circulation.

Project summary:

It is well known within the seismic industry that the acoustic velocity of the water column changes rapidly through time and space in certain locations (e.g. Faroe-Shetland Channel, Gulf of Mexico). The resultant static and amplitude shifts are often abrupt and they can have important and deleterious effects upon 3D and 4D seismic images. As exploration and production move into ultra-deep waters (³ 1.5 km), these effects will be more dramatic for at least two reasons. First, significant internal tides break along the continental shelf in water depths of ³ 1 km. Secondly, deep-water masses flow along, and interact in a complex manner at, continental shelves. Automatic methods for correcting water static shifts are carried out direct picking of acoustic velocity at the sea bed and little attempt has been made to develop a general understanding of the changing acoustic velocity structure

What the student will do:

This PhD project will address the general problem of 3D acoustic imaging of the water column and its implications for time-lapse imaging. It is divided into four stages. First, the student will generate acoustic images by developing and applying a novel processing strategy to 3D datasets from oceanographically significant deep-water locations where we already know that excellent images of the water column can be obtained. Secondly, these images will be interpreted and calibrated with the aid of extensive legacy hydrographic measurements, notably temperature and salinity. Thirdly, existing 1D and 2D seismic tomographic imaging algorithms will be adapted to generate accurate acoustic velocity models. Fourthly, when converted to temperature, these models will form the basis of a fluid dynamical understanding of important phenomena such as diapycnal mixing. They will also be used to develop strategies for correcting static and amplitude shifts along and across repeat sail lines.

Please contact the lead supervisor directly for further information relating to what the successful applicant will be expected to do, training to be provided, and any specific educational background requirements.

References:

Sheen, K., White, N., Caulfield, C., & Hobbs, R.W., 2012. Seismic imaging of a large horizontal vortex at abyssal depths beneath the Sub-Antarctic Front. Nature Geosciences, 5, 542{546, doi:10.1038/NGEO1502.

Sheen, K., White, N., Caulfield, C. & Hobbs, R.W., 2011. Estimating Geostrophic Velocity Fields from Seismic Images of Oceanic Structure. J. Atmos. Ocean. Tech., doi: 10.1175/JTECH-D-10-05012.1.

Sheen, K.L. & White, N., & Hobbs, R., 2009. Estimating mixing rates from seismic images of oceanic structure. Geophys. Res. Letts., 36, L00D04.

Follow this link to find out about applying for this project

Other projects involving the supervisor(s) listed can be viewed here:

Filed under: