Implementing an Advanced Algorithm for Monitoring the Surface Circulation in the
Northern Gulf of Mexico
Co-PIs: Dmitri Nechaev; Max Yaremchuk (NRL)
Institution: The University of Southern Mississippi, Department of Marine Science
Duration: January 1st – June 30th, 2011 (6 months); Budget: $50,000
Introduction
This is a companion proposal of the project “Coastal Observation Platforms in Support of
Characterization of Oil Extent and Transport” (PI: S.Howden), which will provide support to keep
the CODAR stations for the Central Gulf of Mexico Ocean Observing System (CenGOOS)
operational. We propose to improve the accuracy of the surface velocity maps retrieved from the
radial velocity data of the CODAR stations and thus provide a tool for an extended analysis of the
surface circulation and pollutant/nutrient transports in the region.
Conventional CODAR data processing algorithms employ optimal interpolation technique for
retrieving the velocity fields from HRF observations. The results of optimal interpolation are
subject to uncertainties in specification of the background error covariance, become unreliable in
the presence of significant gaps in observations, and cannot be tuned for accurate retrieval of the
divergence of the surface currents.
We propose to implement a variational algorithm (Yaremchuk and Sentchev, 2009) for
processing the CODAR radial velocity data. Comparison of this algorithm with the conventional
optimal interpolation and more recent Open boundary Modal Analysis (Kaplan and Lekien, 2007)
have shown a significantly improved performance of the variational approach in coping with
gappy data and in accurately retrieving the divergent component of the surface flow.
The variational algorithm will be used to perform reanalysis of the CenGOOS CODAR data.
Improving the confidence limits of the circulation maps, and obtaining a reliable estimate of the
flow divergence in particular, will contribute to better understanding of the oil transport in the
Mississippi Bight and the transport of nutrient rich waters from the Mississippi River. It is expected
that accurate estimation of the surface flow divergence will greatly improve the reliability of
trajectories of water parcels retrieved from the CODAR observations, and thus will contribute to
the collaborative project “Oil spill hydrocarbons enhancing microbial respiration and summer
hypoxia in the Mississippi Bight (PI: K. Gundersen).
Methodology
The variational technique is a flexible approach to interpolation of the CODAR observation
onto a regular grid capable of
 Taking into account kinematic boundary conditions on a realistic coastline in a
multiply-connected domains (including islands);
 Selective tuning to account for physical properties of the flow (e.g. tidal, winddominated, and/or topographically controlled currents);
 Effective interpolation within the gaps using radial velocity data statistics;
 Variable spatial resolution depending on the density of the CODAR radial velocity
data.
The technique was already developed and validated in the regions of the Bodega Bay
(Yaremchuk and Sentchev, 2009), Bay of Biscay (Sentchev et al., 2010) and La Manche
(Yaremchuk and Sentchev, 2010).
Implementing the variational method to the Mississippi Bight region involves the following
tasks:
 Design of the regular interpolation grid based on the spatial distribution of the
CODAR radial velocity data and on the configuration of the NCOM model in the Gulf
of Mexico (NRL);
 Preprocessing, quality control, and reformatting the CODAR observations to be used
in the variational procedure;


Design of the cost function based on the statistical analysis of the CODAR radial
data;
Configuring the variational interpolation software and visualization software.
Preliminary Results
Figure 1 illustrates the advantage of the variational technique in retrieving the realistic
divergence of the flow field from CODAR observations. The mean relative error of the recovered
divergence field is two times smaller using the variational method as compared to the results of
the Open boundary Modal Analysis technique.
Fig 1. Velocity and divergence fields retrieved from simulated CODAR data in the Bodega
Bay by the variational method (upper panels) and by Open boundary Modal Analysis. Mean
relative interpolation errors e are shown in the upper right corners.
Collaborators & complimentary, ongoing, funded programs
As mentioned above, the products of this project will help support the analyses of the data collected
as part of the NGI project Monitoring and Assessment of Coastal and Marine Ecosystems in the Northern
Gulf (PI: S. Howden). Collaboration with the proposed project Oil spill hydrocarbons enhancing microbial
respiration and summer hypoxia in the Mississippi Bight (PI: K. Gundersen) is also planned with the
trajectory analyses providing a context for the sampling stations. The trajectories will be evaluated
alongside with the trajectories developed by the NRL from their NCOM modeling of northern Gulf.
Milestones: Identifiable accomplishments by month.
January
February
March
April
May
Design of the regular interpolation grid;
Preprocessing, quality control and reformatting the CODAR observations;
Design of the cost function based on the statistical analysis of the CODAR data;
Configuring the variational interpolation software and visualization software;
Conducting the variational analysis and visualization of the results;
June
Conducting the variational analysis and visualization of the results. Preparation of the
final report (due on July 15, 2011).
Deliverables: Monthly status reports will be provided by teleconference (Project Lead or
designee of record must participate). Final Project report will be due on July 15, 2011. Copies of
or links to project-related publications will be included.
Education and Outreach:
Graduate student support and a partial support for a postdoctoral fellow are planned in this
project.
References:
Kaplan, D., and F. Lekien (2007). Spatial interpolation of surface current data based on openboundary modal analysis. J. Geophys. Res. 112, C12007 (doi: 10.1029/ 2006JC003984).
Yaremchuk, M. and A. Sentchev (2009). Mapping radar-derived sea surface currents with a
variational model, Cont. Shelf Res. 29, 1711-1722.
Yaremchuk, M. and A. Sentchev (2010). Combining EOF and variational analysis for
interpolation of HFR data, Cont. Shelf Res. (under review).
Sentchev, A., P. Forget, Y. Barbin, M. Yaremchuk, and L. Marie (2010). Surface circulation in
the Iroise Sea (W. Brittany) from high resolution HF radar mapping, J. of Marine Systems
(submitted).