  The dynamics of coherent structures present in real-world environmental data
is analyzed. The method developed in this Paper combines the power of the
Proper Orthogonal Decomposition (POD) technique to identify these coherent
structures in experimental data sets, and its optimality in providing Galerkin
basis for projecting and reducing complex dynamical models. The POD basis used
is the one obtained from the experimental data. We apply the procedure to
analyze coherent structures in an oceanic setting, the ones arising from
instabilities of the Algerian current, in the western Mediterranean Sea. Data
are from satellite altimetry providing Sea Surface Height, and the model is a
two-layer quasigeostrophic system. A four-dimensional dynamical system is
obtained that correctly describe the observed coherent structures (moving
eddies). Finally, a bifurcation analysis is performed on the reduced model.
