  While more rigorous and sophisticated methods for identifying Lagrangian
based coherent structures exist, the finite-time Lyapunov exponent (FTLE) field
remains a straightforward and popular method for gaining some insight into
transport by complex, time-dependent two-dimensional flows. In light of its
enduring appeal, and in support of good practice, we begin by investigating the
effects of discretization and noise on two numerical approaches for calculating
the FTLE field. A practical method to extract and refine FTLE ridges in
two-dimensional flows, which builds on previous methods, is then presented.
Seeking to better ascertain the role of an FTLE ridge in flow transport, we
adapt an existing classification scheme and provide a thorough treatment of the
challenges of classifying the types of deformation represented by an FTLE
ridge. As a practical demonstration, the methods are applied to an ocean
surface velocity field data set generated by a numerical model.
