OceanEddies

A collection of algorithms to autonomously identify and track mesoscale ocean eddies in sea surface height (SSH) satellite data

Eddyscan

An eddy identification algorithm that utilizes thresholding to detect eddies in SSH data.

Requirements

• Matlab

Usage

There are two scripts which can be used to call eddyscan: scan_single.m and scan_ssh_subset.m. The second script is can be used to scan many timesteps at once. Below is an example for using scan_single.m:

% Find all anticyclonic eddies
ssh_slice = ncread('ssh_data.nc', 'Grid_0001');
landval = max(ssh_slice(:));
ssh_slice(ssh_slice == landval) = NaN;
lat = ncread('ssh_data.nc', 'NbLatitudes');
lon = ncread('ssh_data.nc', 'NbLongitudes');
lon(lon >= 180) = lon(lon >= 180)-360;
eddies = scan_single(ssh_slice, lat, lon, 'anticyc', 'v2');

LNN

A tracking algorithm (surpassed by MHA) for eddies.

Requirements

• Matlab

Usage

See track_lnn.m.

MHA

A tracking algorithm that maintains multiple hypothesis and does n-scan pruning. MHA can allow eddies to disappear for one timestep from the data to avoid breaking tracks.

Requirements

• Python
• Cython
• Scipy
• Numpy

Build

To build MHA, run python setup.py build_ext -b mht in mha/.

Example Usage

MHA can be called from within MATLAB, the command line, or python. See track_mha.m and track_mha.py for running from MATLAB or the command line respectively. Below is an example for using MHA in python:

import mht

eddies_path = '/path/to/eddyscan/out'

roots = mht.build_mht(mht.list_eddies(eddies_path, 'eddies'), do_lookahead=True)
mht.write_tracks(roots, 'cyclonic_tracks.mat', mht.list_dates(eddies_path, 'eddies'))

Eddy track viewer

This eddy viewer will display eddy tracks with the bodies borders layed on top of the ssh data. It allows moving back and forth, and requires you to subset the data for performance (the subset could consist of the entire world, but that would not give any performance boost).

Requirements

• Matlab

Example Usage

% Must have loaded ssh data, expects ssh, lat, lon, dates
% ssh should use NaNs for land

mk_global_data; % Need to modify script according to your setup
mk_all_subsets; % May need to modify. Which subsets are generated are in this file
load_and_plot('subsets/swpacific');