the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 Oct 2025
OceanTracker 0.5: Fast Adaptable Lagrangian Particle Tracking in Structured and Unstructured Grids
Abstract. Particle tracking is frequently used to compute particle movements within hydrodynamic ocean models; however, modelling millions of particles is computationally challenging. OceanTracker is designed to reduce the time required to obtain results from particle tracking. Firstly, by being computationally efficient, it enables users to simulate large numbers of particles in complex costal environments, enabling improved statistics or exploring a wider range of cases within acceptable run times. Secondly, OceanTracker can calculate multiple particle statistics during the computational run, eliminating the need to record and post-process large volumes of particle trajectories. The adaptability of OceanTracker’s modular computational pipeline allows users to add and modify components which govern particle physics, behaviour, and statistics. The computational pipeline is entirely assembled from user-provided parameters, supplied as a text file or built using helper methods. Coders can easily modify existing components through code inheritance. Currently, OceanTracker supports hydrodynamic model output for unstructured grids (SCHISM, FVCOM, DELFT3D-FM) and structured grids (ROMS, NEMO/GLORYS). Computing the trajectories for more than a million particles with OceanTracker on a single computer core is more than ten times faster than the OpenDrift code and twice as fast as the Ocean Parcels code, despite treating structured grids as unstructured. In addition to its single-core performance, OceanTracker can run computations in parallel across available cores. This can further increase speed by up to an order of magnitude on currently available multicore desktop processors.
Status: open (until 22 Dec 2025)
- RC1: 'Comment on egusphere-2025-4545', Erik van Sebille, 15 Nov 2025 reply
-
RC2: 'Comment on egusphere-2025-4545', Anonymous Referee #2, 24 Nov 2025
reply
The manuscript presents the new capabilities of the particle-tracking model OceanTracker and compares its performance with two other models, OpenDrift and Parcels. It also explains the design choices behind the model’s structure and features and illustrates these through examples.
General comments:
- The introduction should more clearly and concisely introduce the previous version of OceanTracker (including the hydrodynamic models it supported, as stated in the abstract) and explicitly state that this manuscript presents and evaluates the new version of the model.
- The manuscript would benefit from additional references throughout. A few specific places where references are needed are noted below, but this is a broader recommendation for the entire text.
- A thorough proofread is recommended, as there are numerous typos. I have listed the ones I noticed below, but I might have missed some.
Specific comments:
- line 62: Although fewer particle tracking tools exist for structured grids, a few are available. For example PyLag (https://pylag.readthedocs.io/en/latest/)
- Figure 1: Please add colorbars for panels 1b, 1c, and 1d. Also specify the time elapsed before the snapshots were taken. Clarify the meaning of the crosses shown on the maps.
- section 1.1: It would help to include a brief description of the particle tracking setup used in Figure 1 (e.g., study area location, simulation duration).
- line 96-97: Clarify whether this value refers to the average number of particles per cell over the full simulation period.
- line 100: Rewrite as "some of the new Ocean Tracker 0.5 features" to explicitly refer to the new version.
- line 132-133: specify "vertical dispersion" and remove "3D" in "vertical turbulent viscosity". Also clarify whether vertical dispersion is an addition to horizontal dispersion already available in earlier versions of OceanTracker.
- line 140-142: Add appropriate references.
- line 154: Correct the phrase “adding addition.”
- line 177: Correct "example"
- paragraph lines 180-189: Incorrect figure is cited; please revise.
- line 188: Clarify how users are expected to know which classes must be explicitly provided.
- Figure 3: The separation of dispersion and RK advection appears inconsistent with lines 136–137, which state that the random walk is applied to each RK sub-step rather than as a separate displacement.
- Caption of Figure 4: YAML configuration files are not mentioned anywhere in the text; a brief explanation should be added.
- Line 207: Correct “their a new location”
- Line 219: Fix spacing.
- Line 239: Correct “manages they appropriately.”
- Line 246: Correct “can different types.”
- Line 248: Fix punctuation.
- Line 250-260: Consider reversing the order of the “custom particle properties” and “core particle properties” paragraphs. The current order feels confusing because the text returns to custom properties afterward.
- Line 288: Explain why 24 hydrodynamic model time steps were chosen.
- Line 294-295: This information should be introduced earlier in the introduction.
- Line 303-304: The sentence is unclear; please rewrite and add a reference describing the method.
- Line 378-385: Is there no downside to this method?
- Line 402: Fix spacing.
- Line 403: Fix spacing.
- Line 454: Fix spacing.
- Line 497: Add a reference.
Citation: https://doi.org/10.5194/egusphere-2025-4545-RC2 -
RC3: 'Comment on egusphere-2025-4545', Willi Rath, 27 Nov 2025
reply
The manuscript _OceanTracker 0.5: Fast Adaptable Lagrangian Particle Tracking in Structured and Unstructured Grids_ by _Ross Vennell et al._ describes the software OceanTracker 0.5. I don't consider this paper publishable in its current form. Based on the scientific and formal quality of the manuscript alone, I'd tend to recommend a rejection. But the design choices made in the software are novel and the reported (though partially only claimed) performance and versatility of the tool are impressive. Hence I recommend _major_ revisions.
I include an annotated copy of the manuscript with detailed comments. Please refer to these comments for detailed and granular remarks and suggestions. Throughout the annotation, I tried adhering to the following color scheme: Green is for positive aspects. Blue highlights wording, grammar, or typographic issues. Orange requests clarification of numerical, physical or software engineering details which I feel are necessary to support otherwise poorly substantiated and often unclear claims of greatness of the described tool which I highlighted in red. Many of the highlighted lines have notes attached to them.
Major concerns:
- Form and language: The manuscript appears to be sloppily prepared. There's misalignment and artefacts in schematics, there's informal and un-precise language, there's typos and typographical issues all over the text.
- Especially the first part of the manuscript is full of rather un-specific and bold claims of greatness which often remain completely obscure. Examples:
- Before it's even clear what OceanTracker does exactly aim to do, its speed is pointed out.
- Later, it claims to achieve "full configurability and adaptability" by users not knowing how to code only to state in the very next sentence that there's a coding-based mechanism supporting more complex simulations. But how can both be true?
- The notion of "speed" and "acceptable time" from a user perspective are not defined. And "millions of particles" is used as a placeholder for a large and challenging task without any relation to requirements like statistical significance of derived statistics, variability of the underlying currents, experiment time frames etc.
- Many of the paragraphs use a cyclic argument. For example, the claim that modularity leads to adaptability is made in L42, followed by details of the modular structure, which in turn are followed by a rephrased repetition of the initial claim. However, adaptability of software is usually not hampered by lack of modularity (while modularity can be _one_ strategy to achieve better adaptability) but by hidden complexity, leaky abstractions etc. How do the authors ensure their modular structure actually _is_ easy to reconfigure or adapt?
- Most of the major technical achievements which would warrant the publication of this manuscript in the first place are only hinted at. For example, multi threading and multi processing are conflated. And internal design decisions such as what exactly the data structures holding particle properties look like are described in different and contradicting ways. As a consequence, even a reader familiar with the challenges of developing similar scientific software, is left with hardly an idea about how (and why?) specific design decisions were made, let alone being enabled to validate or falsify specific claims or learn from what's presented for similar software.
- The performance analyses lack specifics which in my experience are crucial for understanding performance of scientific software especially on HPC systems which is where any serious general circulation model output would be available and where substantial Lagrangian simulations would hence be performed.Positive aspects:
- The argument for using uniform sigma grids (around L380) is properly substantiated: It identifies a problem, and then describes the solution implemented in OceanTracker in a way that a reader from a background similar to the authors could directly implement themselves.
- The paragraphs around L470 has an almost perfect structure: Clearly identify a challenge, describe a range of solutions, indicate which solution was picked, and be transparent about tradeoffs and downsides.
Viewed
Since the preprint corresponding to this journal article was posted outside of Copernicus Publications, the preprint-related metrics are limited to HTML views.
| HTML | XML | Total | BibTeX | EndNote | |
|---|---|---|---|---|---|
| 173 | 0 | 6 | 179 | 0 | 0 |
- HTML: 173
- PDF: 0
- XML: 6
- Total: 179
- BibTeX: 0
- EndNote: 0
Viewed (geographical distribution)
Since the preprint corresponding to this journal article was posted outside of Copernicus Publications, the preprint-related metrics are limited to HTML views.
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
Review of “OceanTracker 0.5: Fast Adaptable Lagrangian Particle Tracking in Structured and Unstructured Grids” by Vennell et al
In this manuscript, the authors showcase the OceanTracker software and describe its features and design decisions. They compare its performance in some realistic cases to the OpenDrift and Parcels frameworks.
My main comments are
Minor comments
Erik van Sebille