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Remote Sensing Techniques for Ocean Dynamics: State of the Art, Present and Future Applications

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

Deadline for manuscript submissions: 30 April 2024 | Viewed by 8492

Special Issue Editors


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Guest Editor
National Institute of Oceanography and Applied Geophysics – OGS, 34010 Sgonico, TS, Italy
Interests: physical oceanography; ocean currents; vortex dynamics; autonomous technologies for ocean observations; remote sensing
Special Issues, Collections and Topics in MDPI journals

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Guest Editor
Consiglio Nazionale delle Ricerche, Istituto di Scienze Marine, 00133 Rome, Italy
Interests: physical oceanography; ocean currents; vortex dynamics; satellite oceanography; remote sensing

Special Issue Information

Dear Colleagues,

Ocean dynamics modulates natural and anthropogenic processes at several different space and time scales, from global climate change to the local dispersal of tracers and pollutants, with relevant impacts on marine ecosystems and maritime activities. Depending on the technique/instrument, remote sensing provides a unique opportunity to monitor ocean dynamics, ranging from sub-mesoscale to mesoscale, for regional/coastal areas up to global ocean contexts. Since the early 1990s, satellite altimetry has provided a unique opportunity to monitor the global ocean mesoscale dynamics from space, while radar platforms make it possible to resolve sub-mesoscale features in coastal areas. Scientific and socio-economic applications require observations with increasingly high spatial-temporal resolution and accuracy, thus fostering the development of new methodologies to improve present-day remote observations.

This Special Issue aims to publish studies covering different uses of remote sensing by describing and understanding the dynamical causes and mechanisms of ocean variability on different spatial (from local to global) and temporal (hourly to multi-decadal) scales. We welcome studies relying on single- to multi-variable approaches, combining in situ and remotely sensed data, capitalizing on recent advances in data-driven algorithms, and aiming at identifying the critical processes that need to be deepened and included in climate models. Papers with an interdisciplinary character that combine physical oceanography with other fields, ranging from atmosphere to biogeochemistry, from fisheries to ecology, from hazards to forecasting, are highly encouraged.

Articles may address, but are not limited to, the following topics:

  • Radar altimetry;
  • Doppler remote sensing techniques;
  • Future satellite missions for monitoring ocean dynamics;
  • Coastal HF-radar applications;
  • Extraction of ocean dynamics information from independent observations;
  • Data-driven and/or multi-variate monitoring techniques;
  • Operational oceanography;
  • Ocean state and monitoring;
  • Oil spill/debris monitoring.

Dr. Milena Menna
Dr. Daniele Ciani
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

  • ocean monitoring
  • remote sensing applications
  • ocean surface and interior dynamics
  • (sub)mesoscale processes
  • earth observation data integration

Published Papers (7 papers)

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Research

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29 pages, 32345 KiB  
Article
Using a Combination of High-Frequency Coastal Radar Dataset and Satellite Imagery to Study the Patterns Involved in the Coastal Countercurrent Events in the Gulf of Cadiz
by Claudia Fanelli, Juan Jesús Gomiz Pascual, Miguel Bruno-Mejías and Gabriel Navarro
Remote Sens. 2024, 16(4), 687; https://doi.org/10.3390/rs16040687 - 15 Feb 2024
Viewed by 662
Abstract
This study exploits the combination of High-Frequency Coastal Radar (HFR) information with satellite-derived observations to characterize the patterns involved in the coastal countercurrents (CCCs) events in the Gulf of Cadiz (GoC), which is situated in the SW of the Iberian Peninsula. The westward [...] Read more.
This study exploits the combination of High-Frequency Coastal Radar (HFR) information with satellite-derived observations to characterize the patterns involved in the coastal countercurrents (CCCs) events in the Gulf of Cadiz (GoC), which is situated in the SW of the Iberian Peninsula. The westward alongshore currents are observed throughout the year, but the main drivers necessary to develop this flow and its extension in both parts of the basin are not fully clear. In order to identify the main physical processes (both local and remote) that induce the development of these countercurrents and to evaluate the connection of the circulation patterns between the eastern and the western part of the GoC, we make use of several data sources available for the region. First of all, a land-based system of HFR antennas located at four different sites of the GoC provides the velocity field of the surface circulation of the basin. To achieve a significant characterization of the CCCs in the Gulf, the dataset analyzed is processed by means of a series of operations, including the Empirical Orthogonal Functions (EOFs) analysis used to identify spatial and temporal variability of the flow, a low-pass filter used to isolate the sub-inertial signal of the current and temporal interpolation to fill in the missing values. Secondly, given the known importance of the zonal component of the local winds combined with the variations in the mean pressure at sea level over the Western Mediterranean during these events, time series of meteorological data are processed and correlated with the current velocity series via a statistical analysis. Finally, sea surface temperature fields and chlorophyll-a distribution patterns are used as tracers to obtain information on the extension of the countercurrents where HFR data are missing in four cases studied during the year 2017. The conducted analysis revealed the consistent occurrence of westward coastal currents throughout the year, driven in the most intense cases by a combination of the zonal component of the local wind and atmospheric pressure fluctuations over the Western Mediterranean Sea. During those events, CCCs reached the Portuguese side of the Gulf and facilitated the advection of biological material and warmer waters. Full article
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19 pages, 6244 KiB  
Article
Integrating Hydrography Observations and Geodetic Data for Enhanced Dynamic Topography Estimation
by Mahmoud Pirooznia, Behzad Voosoghi, Davod Poreh and Arash Amini
Remote Sens. 2024, 16(3), 527; https://doi.org/10.3390/rs16030527 - 30 Jan 2024
Viewed by 644
Abstract
Dynamic topography (DT) refers to the time-varying component of the sea surface height influenced by factors like ocean currents, temperature, and salinity gradients. Accurate estimation of DT is crucial for comprehending oceanic circulation patterns and their impact on climate. This study introduces two [...] Read more.
Dynamic topography (DT) refers to the time-varying component of the sea surface height influenced by factors like ocean currents, temperature, and salinity gradients. Accurate estimation of DT is crucial for comprehending oceanic circulation patterns and their impact on climate. This study introduces two approaches to estimating DT: (1) utilizing satellite altimetry to directly observe sea surface height and (2) considering the steric and non-steric components of sea level anomalies. The steric term is calculated using salinity and temperature data obtained from local buoy data, Argo observations, and the World Ocean Atlas model. The non-steric term is calculated using GRACE Satellite gravimetry data. To estimate the assimilated DT, four methods are utilized, including variance component estimation (VCE), Bayesian theory, Kalman filter, and 3D variational (3DVAR). These methods assimilate the two aforementioned schemes. The validity of the estimated DT is assessed by comparing the calculated sea surface current, derived from the obtained DT, with observations from local current meter stations. The results indicate that the VCE method outperforms other methods in determining the final DT. Furthermore, incorporating the steric and non-steric terms of sea level in determining DT in coastal areas enhances the accuracy of estimating sea surface currents. Full article
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20 pages, 12782 KiB  
Article
The CNES CLS 2022 Mean Sea Surface: Short Wavelength Improvements from CryoSat-2 and SARAL/AltiKa High-Sampled Altimeter Data
by Philippe Schaeffer, Marie-Isabelle Pujol, Pierre Veillard, Yannice Faugere, Quentin Dagneaux, Gérald Dibarboure and Nicolas Picot
Remote Sens. 2023, 15(11), 2910; https://doi.org/10.3390/rs15112910 - 02 Jun 2023
Cited by 2 | Viewed by 1354
Abstract
A new mean sea surface (MSS) was determined by focusing on the accuracy provided by exact-repeat altimetric missions (ERM) and the high spatial coverage of geodetic (or drifting) missions. The goal was to obtain a high-resolution MSS that would provide centimeter-level precision. Particular [...] Read more.
A new mean sea surface (MSS) was determined by focusing on the accuracy provided by exact-repeat altimetric missions (ERM) and the high spatial coverage of geodetic (or drifting) missions. The goal was to obtain a high-resolution MSS that would provide centimeter-level precision. Particular attention was paid to the homogeneity of the oceanic content of this MSS, and specific processing was also carried out, particularly on the data from the geodetic missions. For instance, CryoSat-2 and SARAL/AltiKa data sampled at high frequencies were enhanced using a dedicated filtering process and corrected from oceanic variability using the results of the objective analysis of sea-level anomalies provided by DUACS multi-missions gridded sea-level anomalies fields (MSLA). Particular attention was also paid to the Arctic area by combining traditional sea-surface height (SSH) with the sea levels estimated within fractures in the ice (leads). The MSS was determined using a local least-squares collocation technique, which provided an estimation of the calibrated error. Furthermore, our technique takes into account altimetric noises, ocean-variability-correlated noises, and along-track biases, which are determined independently for each observation. Moreover, variable cross-covariance models were fitted locally for a more precise determination of the shortest wavelengths, which were shorter than 30 km. The validations performed on this new MSS showed an improvement in the finest topographic structures, with amplitudes exceeding several cm, while also continuing to refine the correction of the oceanic variability. Overall, the analysis of the precision of this new CNES_CLS 2022 MSS revealed an improvement of 40% compared to the previous model, from 2015. Full article
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29 pages, 45930 KiB  
Article
Surface and Interior Dynamics of Arctic Seas Using Surface Quasi-Geostrophic Approach
by Marta Umbert, Eva De-Andrés, Rafael Gonçalves-Araujo, Marina Gutiérrez, Roshin Raj, Laurent Bertino, Carolina Gabarró and Jordi Isern-Fontanet
Remote Sens. 2023, 15(7), 1722; https://doi.org/10.3390/rs15071722 - 23 Mar 2023
Viewed by 1420
Abstract
This study assesses the capability of Surface Quasi-Geostrophy (SQG) to reconstruct the three-dimensional (3D) dynamics in four critical areas of the Arctic Ocean: the Nordic, Barents, East Siberian, and Beaufort Seas. We first reconstruct the upper ocean dynamics from TOPAZ4 reanalysis of sea [...] Read more.
This study assesses the capability of Surface Quasi-Geostrophy (SQG) to reconstruct the three-dimensional (3D) dynamics in four critical areas of the Arctic Ocean: the Nordic, Barents, East Siberian, and Beaufort Seas. We first reconstruct the upper ocean dynamics from TOPAZ4 reanalysis of sea surface height (SSH), surface buoyancy (SSB), and surface velocities (SSV) and validate the results with the geostrophic and total TOPAZ4 velocities. The reconstruction of upper ocean dynamics using SSH fields is in high agreement with the geostrophic velocities, with correlation coefficients greater than 0.8 for the upper 400 m. SSH reconstructions outperform surface buoyancy reconstructions, even in places near freshwater inputs from river discharges, melting sea ice, and glaciers. Surface buoyancy fails due to the uncorrelation of SSB and subsurface potential vorticity (PV). Reconstruction from surface currents correlates to the total TOPAZ4 velocities with correlation coefficients greater than 0.6 up to 200 m. In the second part, we apply the SQG approach validated with the reanalysis outputs to satellite-derived sea level anomalies and validate the results against in-situ measurements. Due to lower water column stratification, the SQG approach’s performance is better in fall and winter than in spring and summer. Our results demonstrate that using surface information from SSH or surface velocities, combined with information on the stratification of the water column, it is possible to effectively reconstruct the upper ocean dynamics in the Arctic and Subarctic Seas up to 400 m. Future remote sensing missions in the Arctic Ocean, such as SWOT, Seastar, WaCM, CIMR, and CRISTAL, will produce enhanced SSH and surface velocity observations, allowing SQG schemes to characterize upper ocean 3D mesoscale dynamics up to 400 m with higher resolutions and lower uncertainties. Full article
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30 pages, 6524 KiB  
Article
Refining the Resolution of DUACS Along-Track Level-3 Sea Level Altimetry Products
by Marie-Isabelle Pujol, Stéphanie Dupuy, Oscar Vergara, Antonio Sánchez Román, Yannice Faugère, Pierre Prandi, Mei-Ling Dabat, Quentin Dagneaux, Marine Lievin, Emeline Cadier, Gérald Dibarboure and Nicolas Picot
Remote Sens. 2023, 15(3), 793; https://doi.org/10.3390/rs15030793 - 30 Jan 2023
Cited by 7 | Viewed by 1731
Abstract
This paper describes the demonstration of a regional high-resolution level-3 (L3) altimeter data unification and altimeter combination system (DUACS) developed with support from the French space agency (CNES). Deduced from full-rate (20 Hz to 40 Hz) level-2 (L2) altimeter measurements, this product provides [...] Read more.
This paper describes the demonstration of a regional high-resolution level-3 (L3) altimeter data unification and altimeter combination system (DUACS) developed with support from the French space agency (CNES). Deduced from full-rate (20 Hz to 40 Hz) level-2 (L2) altimeter measurements, this product provides sea level anomalies (SLA) and other essential physical variables at a spatial resolution of one sample every ~1 km over the North Atlantic Ocean. This allows us to resolve wavelengths from ~35 km to ~55 km depending on the altimeter considered. This was made possible by recent advances in radar altimeter processing for both synthetic aperture radar (SAR) and low-resolution-mode (LRM) measurements, as well as improvements made to different stages of the DUACS processing chain. Firstly, the new adaptive and low-resolution with range migration correction (LR-RMC) processing techniques were considered for Jason and Sentinel-3 (S3A), respectively. They significantly reduce errors at short wavelengths, and the adaptive processing also reduces possible land contamination near the coast. Next, up-to-date geophysical and environmental corrections were selected for this production. This includes specific corrections intended to reduce the measurement noise on LRM measurements and thus enhance the observability at short wavelengths. Compared with the 1 Hz product, the observable wavelengths reached with the demonstration high-resolution product are reduced by up to one third, or up to half in the northeast Atlantic region. The residual noises were optimally filtered from full-rate measurements, taking into consideration the different observing capabilities of the altimeters processed. A specific data recovery strategy was applied, significantly optimizing the data availability, both in the coastal and open ocean areas. This demonstration L3 product is thus better resolved than the conventional 1 Hz product, especially near the coast, where it is defined up to ~5 km against ~10 km for the 1 Hz version. Multi-mission cross-calibration processing was also optimized with an improved long-wavelength error (LWE) correction, leading to a better consistency between tracks, with a 9–15% reduction in SLA variance at cross-overs. The new L3 product improves the overall consistency with tide gauge measurements, with a reduction in SLA differences variance by 5 and 17% compared with the 1 Hz product from the S3A and Jason-3 (J3) measurements, respectively. Primarily intended for regional applications, this product can significantly contribute to improving high-resolution numerical model output via data assimilation. It also opens new perspectives for a better understanding of regional sea-surface dynamics, with an improved representation of the coastal currents and a refined spectral content revealing the unbalanced signal. Full article
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15 pages, 4351 KiB  
Technical Note
Improved Surface Currents from Altimeter-Derived and Sea Surface Temperature Observations: Application to the North Atlantic Ocean
by Daniele Ciani, Sarah Asdar and Bruno Buongiorno Nardelli
Remote Sens. 2024, 16(4), 640; https://doi.org/10.3390/rs16040640 - 08 Feb 2024
Viewed by 769
Abstract
We present a study on the ocean surface currents reconstruction by merging Level-4 (L4, gap-free) altimeter-derived geostrophic currents and satellite sea surface temperature. Building upon past studies on the multi-variate reconstruction of geostrophic currents from satellite observations, we regionalized and optimized an algorithm [...] Read more.
We present a study on the ocean surface currents reconstruction by merging Level-4 (L4, gap-free) altimeter-derived geostrophic currents and satellite sea surface temperature. Building upon past studies on the multi-variate reconstruction of geostrophic currents from satellite observations, we regionalized and optimized an algorithm to improve the altimeter-derived surface circulation estimates in the North Atlantic Ocean. A ten-year-long time series (2010–2019) is presented and validated by means of in situ observations. The newly optimized algorithm allowed us to improve the currents estimate along the main axis of the Gulf Stream and in correspondence of well-known upwelling areas in the North Eastern Atlantic, with percentage improvements of around 15% compared to standard operational altimetry products. Full article
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14 pages, 15239 KiB  
Technical Note
Aerial Drone Imaging in Alongshore Marine Ecosystems: Small-Scale Detection of a Coastal Spring System in the North-Eastern Adriatic Sea
by Gilda Savonitto, Paolo Paganini, Alessandro Pavan, Martina Busetti, Michela Giustiniani, Michela Dal Cin, Cinzia Comici, Stefano Küchler and Riccardo Gerin
Remote Sens. 2023, 15(19), 4864; https://doi.org/10.3390/rs15194864 - 07 Oct 2023
Cited by 1 | Viewed by 1066
Abstract
The eastern coastline of the Gulf of Trieste (north-eastern Adriatic Sea, Italy) is characterized by the occurrence of coastal and submarine freshwater springs of karstic origin. In one of these areas, we performed a survey with a drone with a thermal camera installed, [...] Read more.
The eastern coastline of the Gulf of Trieste (north-eastern Adriatic Sea, Italy) is characterized by the occurrence of coastal and submarine freshwater springs of karstic origin. In one of these areas, we performed a survey with a drone with a thermal camera installed, in tandem with in situ oceanographic sampling with a CTD. Drone images revealed a small time-space scale (i.e., up to a few meters) phenomenon of freshwater plumes floating over seawater. Comparing sea surface temperature data with those acquired in situ revealed that the phenomenon was not clearly detectable by the classical oceanographic monitoring, this surface spring freshwater layer being too thin. Instead, the drone’s thermal camera detected these dynamics with great accuracy, indicating that aerial drones can be efficiently used for studying fine-scale events involving surface waters (e.g., spills/pollution). The experience gained allowed us to discuss some of the advantages and disadvantages of using drone thermal imaging for monitoring alongshore areas. Full article
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