2 research outputs found
Quasi-Objective Eddy Visualization from Sparse Drifter Data
We employ a recently developed single-trajectory Lagrangian diagnostic tool,
the trajectory rotation average , to visualize
oceanic vortices (or eddies) from sparse drifter data. We apply the to two drifter data sets that cover various
oceanographic scales: the Grand Lagrangian Deployment (GLAD) and the Global
Drifter Program (GDP). Based on the , we develop a
general algorithm that extracts approximate eddy boundaries. We find that the outperforms other available single-trajectory-based
eddy detection methodologies on sparse drifter data and identifies eddies on
scales that are unresolved by satellite-altimetry
Relative Fluid Stretching and Rotation for Sparse Trajectory Observations
As most mathematically justifiable Lagrangian coherent structure detection
methods rely on spatial derivatives, their applicability to sparse trajectory
data has been limited. For experimental fluid dynamicists and natural
scientists working with Lagrangian trajectory data via passive tracers in
unsteady flows (e.g. Lagrangian particle tracking or ocean buoys), obtaining
material measures of fluid rotation or stretching is currently only possible
for trajectory concentrations that are often out-of-reach. To facilitate
frame-indifferent investigations in unsteady and sparsely sampled flows, we
present a novel approach to quantify fluid stretching and rotation via relative
Lagrangian velocities. This technique provides a formal objective extension of
quasi-objective metrics to unsteady flows by accounting for mean flow behavior.
For extremely sparse experimental data, fluid structures may be significantly
undersampled, and the mean flow behavior becomes difficult to quantify. We
provide a means to maintain the accuracy of our novel sparse flow diagnostics
in extremely sparse sampling scenarios, such as ocean buoy data and Lagrangian
particle tracking. We use data from multiple numerical and experimental flows
to show that our methods can identify structures beyond existing limits of
sparse, frame-indifferent diagnostics, and exhibit improved interpretability
over common frame-dependent diagnostics