VELOCITY PROJECTION: METHODS FOR SURFACE-TO-SUBSURFACE CURRENTS   Colin Y. Shen, Thomas E. Evans, George O. Marmorino, and Gloria J. Lindemann Code 7250, Naval Research Laboratory, Washington, D.C. 20375

This is the poster presented at the Operational Oceanography Symposium, Oceanology International in London, March 5, 2002. Additional animation of the sea surface height field derived from velocity projection is inserted in section 4 for the Cape Henry site and in section 5 for the Mississippi Sound site.

This poster presents practical methods, referred to as velocity projection, that obtain profiles of subsurface currents from surface current and wind data derivable from radar remote sensing, drifters, or ocean feature tracking. The methods use hydrodynamic equations and surface data as constraints to project the surface current directly downward to obtain the profiles, thereby obviating the need for first-guess subsurface initialization. This downward projection has made the methods practical – for example, calculation of 400 profiles from given surface data can be done in a matter a few seconds on the latest desktop PC. Application of velocity projection to three coastal sites is shown, where the surface current data are obtained with shore-based HF radars. In addition to current profiles, velocity projection obtains dynamically consistent estimates of sea surface slope and eddy viscosity as part of the solution procedure. The velocity projection results are shown to be consistent (within the limits of measurement uncertainty) with in situ ADCP current profiles and and sea surface slope measured with bottom pressrue sensors.

View the entire POSTER, or individual sections:

1. Introduction
2. Velocity Projection Algorithm
3. Cape Hatteras Site
4. Cape Henry Site
5. Mississippi Sound Site
6. Test of Deeper Water Method
7. Summary and Opportunities

Acknowledgements:

This work is supported by the "Optimal 3D Currents From Remote Scene Sequences" project at the Naval Research Laboratory, sponsored by the Office of Naval Research. We are grateful for the contributions by the following people: ADCP data from Clifford Trump of NRL, OSCR data from Lynn Shay and Hans Graber of University of Miami, and ADCP and bottom pressure data from Zack Hallock of NRL for the NRL/ONR High Resolution and Coastal Remote Sensing and experiments; CODAR data from Arne-R. Diercks of Ocean Technologies, L.L.C, ADCP data from Craig Cumbee and Carl Szczechowski of NAVO, and helpful data access provided by Suzanne Carroll of Planning System Inc. for the NAVO/EPA NGLI experiment.

Papers referenced in the poster:

1. Shen, C. Y. and T. E. Evans. 2001. "Surface-to -subsurface velocity projection for shallow water currents". J. Geophys. Res. (Oceans), 106, 6973-6984.
2. Shen, C. Y. and T. E. Evans. 2002. "Dynamically constrained projection for subsurface current Velocity". J. Geophys. Res. (Oceans), submitted.
3. Marmorino, G. O., C. Y. Shen, G. J. Lindemann, T. E. Evans, Z. R. Hallock. 2002. "Use of ‘velocity projection’ to infer sea-level slope over the inner shelf", in preparation.
4. Davies, A. M. and J. Xing. 2001. "The influence of eddy viscosity parameterization and turbulence energy closure scheme upon the coupling of tidal and wind induced currents". Estuarine, Coastal and Shelf Sciences, 53, 415-436.
5. Csanady, G.T. 1997. "The slip law of the free surface". J. Oceanography, 53, 67-80
6. Asper, V., J.P. Blaha, C. Szczechowski, C. Cumbee, R. Willems, S. Lohrenz, D. Redalje, and A-R. Diercks. 2001. "The Northern Gulf Of Mexico Littoral Initiative (NGLI): A Collaborative Modeling, Monitoring, And Research Effort" J. Miss. Acad. Sci. Vol 46(1), 60.
7. Shen, C. Y. 2002. "A note on the ‘observability’ condition". J. Phys. Oceanogr., submitted.

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This page is maintained by: Gloria Lindemann
It was last modified on March 28, 2002.