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A special issue of Remote Sensing (ISSN 2072-4292). This special issue belongs to the section "Ocean Remote Sensing".

Deadline for manuscript submissions: closed (20 May 2023) | Viewed by 18883

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Dr. Angelo Perilli

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Consiglio Nazionale delle Ricerche, Istituto per lo Studio Degli Impatti Antropici e Sostenibilità in Ambiente Marino, 09170 Oristano, Italy
Interests: mesoscale oceanic eddy; ocean circulation; water masses properties; mesoscale ocean dynamics and its interactions with marine ecosystem; in situ observations; satellite oceanography; operational oceanography
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Dr. Mariona Claret

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Institute of Marine Sciences, ICM-CSIC, Pg. Marítim Barceloneta, 37-49, 08003 Barcelona, Spain
Interests: physical-biological interactions at submeso- and mesoscales; near-inertial wave dynamics; large-scale currents and ocean biogeochemistry; ocean modeling
Special Issues, Collections and Topics in MDPI journals

Dr. Alexandre Stegner

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Laboratoire de Météorologie Dynamique, IPLS-CNRS, Ecole Polytechnique, Palaiseau, France
Interests: oceanography; geophysical fluid dynamics; oceanic eddies; remote sensing; IA

Special Issue Information

Mesoscale eddies are energetic coherent structures that play a crucial role in the ocean. They have typical horizontal scales ranging from 10-100 km and lifetimes from months to sometimes years. They can connect the coastal and the open ocean, generate a downscale energy cascade, trap and transport heat, salt, pollutants and biogeochemical tracers at long distances. They can also modulate the mixed layer depth, regulate air-sea heat and gas fluxes and influence local winds, clouds and rainfall. As a result, they have a profound impact on the ocean-atmosphere-biosphere system. However, the myriad mechanisms that control or impact all the above-mentioned components of the ocean are not yet fully explored.

Major breakthroughs in remote sensing have paved the way for a global understanding of the oceanic circulation. Automatic eddy detection and tracking algorithms, applied to low resolution altimetric, are efficient tools to study the dynamics of mesoscale eddies. To complete these standard technics, new methods such as Deep Learning have been developed to analyse visible images (SST, Ocean Colour) that contain higher spatial resolution eddy signature but can be corrupted by cloud coverage. These recent advances, combined with in-situ data (Argo floats, gliders, surface drifter, oceanographic cruises, etc.) and eddy resolving models, provide invaluable information on surface dynamics and the three-dimensional nature of eddies.

The aim of this Special Issue is to advance our understanding of complex mesoscale eddy activity. Therefore, this SI welcomes manuscripts dealing with eddy dynamics, eddy properties variability, transport, or impact on ocean circulations and on marine ecosystems We accept contributions based on standard and new methods that can permit the improvement of the mesoscale eddy identification and knowledge. We also strongly encourage works that combine these remote sensing techniques with theory, in-situ observations data and/or modelling output to explore complex physical-biological interactions driven by mesoscale eddies or to unveil the vertical structure of surface imprints of eddies detected by satellites.

Dr. Angelo Perilli
Dr. Mariona Claret
Dr. Alexandre Stegner
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Remote Sensing is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Mesoscale ocean dynamics
Satellite remote sensing
Ocean in-situ monitoring
Ocean circulation
Eddy resolving ocean models
Eddy detection and tracking algorithms
AI applied to oceanic remote sensing analysis
Marine ecosystems
Physical-biological interactions

Related Special Issue

Recent Advances on Oceanic Mesoscale Eddies II in Remote Sensing (1 article)

Published Papers (10 papers)

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18 pages, 10041 KiB

Open AccessArticle

Imprint of Mesoscale Eddies on Air-Sea Interaction in the Tropical Atlantic Ocean

by Habib Micaël A. Aguedjou, Alexis Chaigneau, Isabelle Dadou, Yves Morel, Ezinvi Baloïtcha and Casimir Y. Da-Allada

Remote Sens. 2023, 15(12), 3087; https://doi.org/10.3390/rs15123087 - 13 Jun 2023

Cited by 2 | Viewed by 1312

Abstract

This study investigates the effect of mesoscale eddies on air–sea heat and fresh water exchange in the tropical Atlantic Ocean (TAO) using 8 years of satellite altimetry data, combined with sea surface temperature (SST), latent and sensible heat fluxes (LHF and SHF), infrared fluxes (IRF) and precipitation (PR) data. Results indicate that approximately ∼40% of cyclonic eddies contribute to warm SST anomalies, and ∼40% of anticyclonic eddies contribute to cold SST anomalies. Eddies were found to play a role in the variability in LHF, SHF and IRF, contributing 10–35% of their total variability, with the largest contributions observed beneath the intertropical convergence zone (ITCZ) and frontal SST areas. Composite analysis of SST and heat flux anomalies over eddies suggested that the anomalies created through horizontal advection processes may not significantly impact the overall LHF, SHF and IRF over eddies, contrary to vertical processes. Despite a lack of clear correlation between heat flux and PR anomalies over eddies in the TAO, significant correlations were found beneath the ITCZ, suggesting that eddies may impact both heat fluxes and PR in the ITCZ region. This study provides an original contribution to the understanding of the impact of ocean mesoscale eddies on the atmosphere in the TAO. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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10 pages, 64576 KiB

Open AccessCommunication

Eddy Detection in the Marginal Ice Zone with Sentinel-1 Data Using YOLOv5

by Eduard Khachatrian, Nikita Sandalyuk and Pigi Lozou

Remote Sens. 2023, 15(9), 2244; https://doi.org/10.3390/rs15092244 - 24 Apr 2023

Cited by 3 | Viewed by 1911

Abstract

The automatic detection and analysis of ocean eddies in the marginal ice zone via remote sensing is a very challenging task but of critical importance for scientific applications and anthropogenic activities. Therefore, as one of the first steps toward the automation of the eddy detection process, we investigated the potential of applying YOLOv5, a deep convolutional neural network architecture, to specifically collected and labeled high-resolution synthetic aperture radar data for a very dynamic area over the Fram Strait. Our approach involved fine-tuning pre-trained YOLOv5 models on a sparse dataset and achieved accurate results with minimal training data. The performances of the models were evaluated using several metrics, and the best model was selected by visual examination. The experimental results obtained from the validation and test datasets consistently demonstrated the robustness and effectiveness of the chosen model to identify submesoscale and mesoscale eddies with different structures. Moreover, our work provides a foundation for automated eddy detection in the marginal ice zone using synthetic aperture radar imagery and contributes to advancing oceanography research. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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32 pages, 29332 KiB

Open AccessArticle

Combining an Eddy Detection Algorithm with In-Situ Measurements to Study North Brazil Current Rings

by Corentin Subirade, Pierre L’Hégaret, Sabrina Speich, Rémi Laxenaire, Johannes Karstensen and Xavier Carton

Remote Sens. 2023, 15(7), 1897; https://doi.org/10.3390/rs15071897 - 31 Mar 2023

Cited by 2 | Viewed by 1422

Abstract

North Brazil Current (NBC) rings are believed to play a key role in the Atlantic Ocean circulation and climate. Here, we use a new collection of high-resolution in-situ observations acquired during the EUREC

^{4}

A-OA field experiment together with satellite altimetry to define, [...] Read more.

^{4}

A-OA field experiment together with satellite altimetry to define, with unprecedented detail, the structure and evolution of these eddies. In-situ observations reveal a more complex structure than previously documented. In particular, we highlight a measurable impact of the Amazon outflow in creating a barrier layer over a large portion of the eddies. We show that this unprecedented data set allows us to estimate the accuracy of satellite altimetry gridded fields. The geostrophic velocities derived from satellite altimetry turn out to be considerably lower (up to 50% in amplitude) than the values measured by current meters. However, eddy properties as detected by TOEddies, a newly developed algorithm show to be relatively precise. For example, the eddy center and maximum azimuthal velocity contour fall within 25 ± 5 km and 16 ± 9 km, respectively, from the in-situ observed values. We apply TOEddies to 27 years of satellite altimetry to investigate the generic NBC rings behavior. We found a mean generation rate of 4.5 ± 1.1 rings per year, and a strong seasonal cycle in all eddy properties. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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18 pages, 7167 KiB

Open AccessArticle

Oceanic Eddy Detection and Analysis from Satellite-Derived SSH and SST Fields in the Kuroshio Extension

by Wei Cui, Jungang Yang, Yongjun Jia and Jie Zhang

Remote Sens. 2022, 14(22), 5776; https://doi.org/10.3390/rs14225776 - 16 Nov 2022

Viewed by 1673

Abstract

Vigorous mesoscale eddies are broadly distributed in the Kuroshio Extension and can generally be identified from sea surface height (SSH) and sea surface temperature (SST) fields. Nevertheless, the changes in SSH and SST caused by mesoscale eddies and their seasonal correlation in the Kuroshio Extension are not clear, as well as the difference between identified eddy results from the two data. Combining in situ Argo float profiles data, the correlation between SSH anomaly (SSHA) and SST anomaly (SSTA) signals in mesoscale eddies are analyzed. The result shows that SSTA–SSHA signals inside eddies are generally more correlated in winter than in summer. Argo subsurface temperature anomalies θ′ and SSHA signals inside eddies show a high correlation, with a regression coefficient θ′/SSHA of about 7 °C·m⁻¹, while correlations of Argo θ′–SSTA inside eddies are low. Generally, the lifetime and propagation distance of SSTA-based eddies are shorter and smaller than those of SSHA-based eddies, which may be related to the rapid changes in SSTA field and the interference of small-scale oceanic signal in the SST field. Comparing with SSHA-based eddies, which exist primarily around the region of the Kuroshio mainstream (33°–36°N), SSTA-based eddies are concentrated in the Oyashio Extension (39°–42°N), where SST gradient is large, and changes in SST fields caused by mesoscale eddies are more obvious and more likely to be captured by satellites there. In addition, the geographical distributions of SSHA- and SSTA-based eddy amplitudes are consistent with the absolute dynamic topography and SST gradient. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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23 pages, 5073 KiB

Open AccessArticle

Oceanic Mesoscale Eddies Identification Using B-Spline Surface Fitting Model Based on Along-Track SLA Data

by Luochuan Xu, Miao Gao, Yaorong Zhang, Junting Guo, Xianqing Lv and Anmin Zhang

Remote Sens. 2022, 14(22), 5713; https://doi.org/10.3390/rs14225713 - 11 Nov 2022

Cited by 1 | Viewed by 1655

Abstract

Gridded reanalysis data has been widely used in oceanic mesoscale eddy identification. However, there is little research on identifying oceanic mesoscale eddies based on along-track data. In this paper, the B-spline surface fitting model is established for oceanic mesoscale eddy identification. This innovative model can embody along-track data’s advantages in accuracy, universality, and instantaneity, and directly identify oceanic mesoscale eddies solely based on along-track data. We start with ideal experiments using simulated data to explore the error sources of B-spline surface fitting for one oceanic mesoscale eddy, followed by practical experiments with measured data to analyze the effect of the B-spline surface fitting and the fitting errors further. Compared with eddies obtained from gridded reanalysis data, results show that the B-spline surface fitting model based on along-track data has an ideal effect in identifying oceanic mesoscale eddies; little difference exists between the fitting result and measured data. The model proposes a new technological means to deal with along-track data, which contributes to oceanic mesoscale eddy identification and marine element data analysis. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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29 pages, 14573 KiB

Open AccessArticle

Eddy Induced Cross-Shelf Exchanges in the Black Sea

by Anıl Akpınar, Ehsan Sadighrad, Bettina A. Fach and Sinan Arkın

Remote Sens. 2022, 14(19), 4881; https://doi.org/10.3390/rs14194881 - 30 Sep 2022

Cited by 6 | Viewed by 1413

Abstract

Cross-shelf exchanges in the Black Sea were investigated using remote sensing data and an ocean circulation model to which an eddy-tracking algorithm and Lagrangian particle tracking model was applied. An anticyclonic eddy in 1998 and a cyclonic eddy in 2000 were investigated in detail. Eddy-induced cross-shelf transport of low salinity and high Chl-a waters reached a maximum in the presence of filaments associated with these eddies. The daily mean volume transport by the eddies was comparable with the previously documented transport by eddies of similar size in the north-western shelf region. Lagrangian particle tracking results showed that 59% of particles initially released over the shelf were transported offshore within 30 days by the 1998 anticyclone and 27% by the 2000 cyclone. The net volume transport across the Black Sea shelf-break reached the maxima in winter, coinciding with the increase in wind stress curl and mean kinetic energy that is a measure of the intensity of the boundary current. Ekman transport directly influences the cross-shelf exchanges in the surface layer. The south-eastern Black Sea is presented as an important area for cross-shelf transport. The total cross-shelf transport can be divided into its “large-scale” and “eddy-induced” components. Eddy-induced transport was 34% and 37% of the total cross-shelf transport (1998–2014) in the Black Sea in the off-shelf and on-shelf directions, respectively, but these values ranged between 25% and 65% depending on the eddy activity over time. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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23 pages, 33051 KiB

Open AccessArticle

Why Do Inverse Eddy Surface Temperature Anomalies Emerge? The Case of the Mediterranean Sea

by Evangelos Moschos, Alexandre Barboni and Alexandre Stegner

Remote Sens. 2022, 14(15), 3807; https://doi.org/10.3390/rs14153807 - 07 Aug 2022

Cited by 10 | Viewed by 1957

Abstract

It is widely accepted that the signature of anticyclonic (cyclonic) eddies on the sea surface temperature corresponds to a warm (cold) core anomaly. Nevertheless, this statement has been put to question by recent regional studies showing the existence of inverse eddy SST anomalies: Cold Core anticyclones and, respectively, Warm Core cyclones. This study shows that the emergence of these inverse anomalies is a seasonal phenomenon that affects the life cycle of mesoscale eddies in the Mediterranean Sea. We use remote sensing observations and in situ data to analyse the eddy-induced SST anomaly over a 3-year period (2016–2018). We build an eddy core SST anomaly index to quantify the amount of Cold Core anticyclones and Warm Core cyclones all over the year and especially during the spring re-stratification period. We find that

70 %

of eddy anomalies are inverse in May and June both for cyclones and anticyclones. Regular temperature anomalies could reach

1.5

°C, while inverse ones are only present in the first 50 m of the oceanic layer and hardly exceed

1

°C. In order to understand the underlying dynamical processes, we construct a simple vertical column model to study the impact of the seasonal air–sea fluxes on the surface stratification inside and outside eddies. It is only by taking into account a differential diapycnal eddy mixing—increased in anticyclones and reduced in cyclones—that we reproduce correctly, in agreement with the observations, the surface temperature inversion in the eddy core. This simplified model suggests that vertical mixing modulation by mesoscale eddies might be the key mechanism that leads to the eddy–SSTA seasonal inversion in the ocean. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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20 pages, 4506 KiB

Open AccessArticle

The Response and Feedback of Ocean Mesoscale Eddies to Four Sequential Typhoons in 2014 Based on Multiple Satellite Observations and Argo Floats

by Jiagen Li, Han Zhang, Shanshan Liu, Xiuting Wang and Liang Sun

Remote Sens. 2021, 13(19), 3805; https://doi.org/10.3390/rs13193805 - 23 Sep 2021

Cited by 4 | Viewed by 2230

Abstract

Four sequential tropical cyclones generated and developed in the Northwest Pacific Ocean (NWP) in 2014, which had significant impacts on the oceanic environment and coastal regions. Based on a substantial dataset of multiple-satellite observations, Argo profiles, and reanalysis data, we comprehensively investigated the interactions between the oceanic environment and sequential tropical cyclones. Super typhoon Neoguri (2014) was the first typhoon-passing studied area, with the maximum sustained wind speed of 140 kts, causing strong cold wake along the track. The location of the strongest cold wake was consistent with the pre-existing cyclonic eddy (CE), in which the average sea surface temperature (SST) cooling exceeded −5 °C. Subsequently, three tropical cyclones passed the ocean environment left by Neoguri, namely, the category 2 typhoon Matmo (2014), the tropical cyclone Nakri (2014) and the category 5 typhoon Halong (2014), which caused completely different subsequent responses. In the CE, due to the fact that the ocean stratification was strongly destroyed by Neoguri and difficult to recover, even the weak Nakri could cause a secondary response, but the secondary SST cooling would be overridden by the first response and thus could cause no more serious ocean disasters. If the subsequent typhoon was super typhoon Halong, it could cause an extreme secondary SST cooling, exceeding −8 °C, due to the deep upwelling, exceeding 700 m, surpassing the record of the maximum cooling caused by the first typhoon. In the anti-cyclonic eddy (AE), since the first typhoon Neoguri caused strong seawater mixing, it was difficult for the subsequent weak typhoons to mix the deeper, colder and saltier water into the surface, thus inhibiting secondary SST cooling, and even the super typhoon Halong would only cause as much SST cooling as the first typhoon. Therefore, the ocean responses to sequential typhoons depended on not only TCs intensity, but also TCs track order and ocean mesoscale eddies. In turn, the cold wake caused by the first typhoon, Neoguri, induced different feedback effects on different subsequent typhoons. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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19 pages, 4688 KiB

Open AccessArticle

The Impact of the Mesoscale Ocean Variability on the Estimation of Tidal Harmonic Constants Based on Satellite Altimeter Data in the South China Sea

by Qian Yu, Haidong Pan, Yanqiu Gao and Xianqing Lv

Remote Sens. 2021, 13(14), 2736; https://doi.org/10.3390/rs13142736 - 12 Jul 2021

Cited by 9 | Viewed by 1826

Abstract

The estimation accuracy of tidal harmonic constants is of great significance to maritime traffic and port construction. However, due to the long sampling period of satellite altimeters, tidal signals alias the mesoscale ocean frequencies. As a result, the harmonic analysis is affected by mesoscale environmental noise. In this study, the influence of the mesoscale ocean variability (MOV) on the estimation of tidal harmonic constants was quantified by analyzing 25 years of altimeter data from the Topex/Poseidon (T/P) and Jason satellites in the South China Sea (SCS). The results indicated that the absolute amplitude differences (AADs) of the eight major tidal constituents before and after the mesoscale variability correction (MVC) were generally within 10 mm, and most were within 6 mm. For the relative impact, M₂, O₁, and K₁ were not obviously affected by the MOV because of their large amplitudes, and the AADs generally accounted for less than ±10% of the amplitudes. As a tidal constituent with amplitude less than 2 cm in the SCS, the amplitude of K₂ was significantly affected by the MOV, with the ratios of the AADs to its own amplitudes ranging from −64.79% to 95.99% in space. In terms of phase, the K₂ tide was most affected by the MOV: 63% of the data points before and after correction were over ±5°, and the maximum and minimum values were 86.46° and −176.27°, respectively. The absolute phase differences of other tidal constituents before and after the MVC were generally concentrated within ±5°. The impact of the MOV on the evolution of tidal amplitudes in the SCS was also explored. It was found that the MOV can cause pseudo-rapid temporal variations of tidal amplitudes in some regions of the SCS. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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14 pages, 7703 KiB

Open AccessTechnical Note

Divergence Observation in a Mesoscale Eddy during Chla Bloom Revealed in Submesoscale Satellite Currents

by Tran Thi My Hong, Young-Gyu Park and Jun Myoung Choi

Remote Sens. 2023, 15(4), 995; https://doi.org/10.3390/rs15040995 - 10 Feb 2023

Cited by 3 | Viewed by 1510

Abstract

Oceanic mesoscale eddies continuously regulate the horizontal and vertical transport of mass, heat, salt, carbon, and nutrients throughout the ocean system owing to their ubiquity, three-dimensionality, and long-term persistence. Although satellites have been the main platforms used to observe mesoscale eddies and chlorophyll-a (Chla) distributions, they cannot support submesoscale physical–biological interactions. Contemporary satellite observations of Eulerian velocity fields are unable to resolve submesoscale processes that govern vertical migration and mixing, which are crucial for controlling the nutrients and light for phytoplankton in the surface layer. We explored the physical–biological interaction between the anticyclonic mesoscale eddy and the Chla secondary bloom that occurred after the spring bloom in the East/Japan Sea using the Geostationary Ocean Color Imager (GOCI). The GOCI currents were generated using GOCI Chla data and were used to map streamlines, vorticity, and divergence to characterize the surface current near the eddy. In the early spring bloom period, the eddy interior showed Chla depletion as the eddy was trapped externally. We found that the second bloom period coincided with a higher divergence or upwelling period in the eddy core, and a sharp Chla peak was observed when wind-induced Ekman suction was pronounced. This study describes the first satellite observation of surface layer divergence inside an anticyclonic mesoscale eddy with internal Chla blooms, utilizing a submesoscale-permitting GOCI-based surface current. Full article

(This article belongs to the Special Issue Recent Advances on Oceanic Mesoscale Eddies)

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