Coastal high-frequency radars in the Mediterranean ??? Part 2: Applications in support of science priorities and societal needs

International audienceThe Mediterranean Sea is a prominent climate-change hot spot, with many socioeconomically vital coastal areas being the most vulnerable targets for maritime safety, diverse met-ocean hazards and marine pollution. Providing an unprecedented spatial and temporal resolution at wide coastal areas, high-frequency radars (HFRs) have been steadily gaining recognition as an effective land-based remote sensing technology for continuous monitoring of the surface circulation, increasingly waves and occasionally winds. HFR measurements have boosted the thorough scientific knowledge of coastal processes, also fostering a broad range of applications, which has promoted their integration in coastal ocean observing systems worldwide, with more than half of the European sites located in the Mediterranean coastal areas. In this work, we present a review of existing HFR data multidisciplinary science-based applications in the Mediterranean Sea, primarily focused on meeting end-user and science-driven requirements, addressing regional challenges in three main topics: (i) maritime safety, (ii) extreme hazards and (iii) environmental transport process. Additionally, the HFR observing and monitoring regional capabilities in the Mediterranean coastal areas required to underpin the underlying science and the further development of applications are also analyzed. The outcome of this assessment has allowed us to provide a set of recommendations for future improvement prospects to maximize the contribution to extending science-based HFR products into societally relevant downstream services to support blue growth in the Mediterranean coastal areas, helping to meet the UN's Decade of Ocean Science for Sustainable Development and the EU's Green Deal goals

Coastal high-frequency radars in the Mediterranean ??? Part 1: Status of operations and a framework for future development

Due to the semi-enclosed nature of the Mediterranean Sea, natural disasters and anthropogenic activities impose stronger pressures on its coastal ecosystems than in any other sea of the world.With the aim of responding adequately to science priorities and societal challenges, littoral waters must be effectively monitored with high-frequency radar (HFR) systems. This land-based remote sensing technology can provide, in near-real time, fine-resolution maps of the surface circulation over broad coastal areas, along with reliable directional wave and wind information. The main goal of this work is to showcase the current status of the Mediterranean HFR network and the future roadmap for orchestrated actions. Ongoing collaborative efforts and recent progress of this regional alliance are not only described but also connected with other European initiatives and global frameworks, highlighting the advantages of this cost-effective instrument for the multi-parameter monitoring of the sea state. Coordinated endeavors between HFR operators from different multi-disciplinary institutions are mandatory to reach a mature stage at both national and regional levels, striving to do the following: (i) harmonize deployment and maintenance practices; (ii) standardize data, metadata, and quality control procedures; (iii) centralize data management, visualization, and access platforms; and (iv) develop practical applications of societal benefit that can be used for strategic planning and informed decision-making in the Mediterranean marine environment. Such fit-for-purpose applications can serve for search and rescue operations, safe vessel navigation, tracking of marine pollutants, the monitoring of extreme events, the investigation of transport processes, and the connectivity between offshore waters and coastal ecosystems. Finally, future prospects within the Mediterranean framework are discussed along with a wealth of socioeconomic, technical, and scientific challenges to be faced during the implementatio

Correspondence Between Perceived Pubertal Development and Hormone Levels in 9-10 Year-Olds From the Adolescent Brain Cognitive Development Study.

Aim: To examine individual variability between perceived physical features and hormones of pubertal maturation in 9-10-year-old children as a function of sociodemographic characteristics. Methods: Cross-sectional metrics of puberty were utilized from the baseline assessment of the Adolescent Brain Cognitive Development (ABCD) Study—a multi-site sample of 9–10 year-olds (n = 11,875)—and included perceived physical features via the pubertal development scale (PDS) and child salivary hormone levels (dehydroepiandrosterone and testosterone in all, and estradiol in females). Multi-level models examined the relationships among sociodemographic measures, physical features, and hormone levels. A group factor analysis (GFA) was implemented to extract latent variables of pubertal maturation that integrated both measures of perceived physical features and hormone levels. Results: PDS summary scores indicated more males (70%) than females (31%) were prepubertal. Perceived physical features and hormone levels were significantly associated with child\u27s weight status and income, such that more mature scores were observed among children that were overweight/obese or from households with low-income. Results from the GFA identified two latent factors that described individual differences in pubertal maturation among both females and males, with factor 1 driven by higher hormone levels, and factor 2 driven by perceived physical maturation. The correspondence between latent factor 1 scores (hormones) and latent factor 2 scores (perceived physical maturation) revealed synchronous and asynchronous relationships between hormones and concomitant physical features in this large young adolescent sample. Conclusions: Sociodemographic measures were associated with both objective hormone and self-report physical measures of pubertal maturation in a large, diverse sample of 9-10 year-olds. The latent variables of pubertal maturation described a complex interplay between perceived physical changes and hormone levels that hallmark sexual maturation, which future studies can examine in relation to trajectories of brain maturation, risk/resilience to substance use, and other mental health outcomes

Nouvelles techniques de traitement du signal en radio-océanographie

The measurement of sea surface currents by HF radar raises several issues in terms of radar calibration, spatial resolution and parasite signals. Conventional azimuth scanning processing called beam forming has limited angular resolution for most phased array radar and high angular resolution processing methods called direction finding generally produce lacunary maps. In this thesis we propose : a) a high angular resolution processing technique based on direction finding algorithm allowing to obtain full and low-noise maps ; b) an automatic antenna calibration method ; c) other methods to removing artifacts related to radio frequency interference and clutter echoes. These methods, initially planned for phased array radars, have been adapted to compact radars called CODAR where the main difficulty is the calibration due to the nature of the antennas. The measurements obtained with these new techniques have been validated with in situ campaigns with errors in the low range of the scientific literature.La mesure des courants marins de surface par radar HF soulève plusieurs problématiques au niveau de la calibration des radars, de la résolution spatiale et des signaux parasites. Le traitement conventionnel fonctionnant par balayage azimutal appelé formation de voie a une résolution angulaire limitée pour la plupart des radars à réseau de phase et les méthodes de traitement à haute résolution pour la recherche des directions d'arrivées produisent généralement des cartes lacunaires. Dans cette thèse nous proposons : a) une technique de traitement à haute résolution angulaire permettant d'obtenir des cartes pleines et peu bruitées ; b) une méthode de calibration automatique des antennes ; c) des méthodes de suppression des artefacts liés aux interférences radio et aux échos parasites. Ces méthodes, initialement prévues pour les radars à réseau de phase, ont été adaptées aux radars compacts CODAR dont la principale difficulté est la calibration en raison de la nature des antennes. Les mesures de courant obtenues avec ces nouvelles techniques ont été validées par des campagnes in situ avec des erreurs dans la fourchette basse de la littérature scientifique

Nouvelles techniques de traitement du signal en radio-océanographie

The measurement of sea surface currents by HF radar raises several issues in terms of radar calibration, spatial resolution and parasite signals. Conventional azimuth scanning processing called beam forming has limited angular resolution for most phased array radar and high angular resolution processing methods called direction finding generally produce lacunary maps. In this thesis we propose : a) a high angular resolution processing technique based on direction finding algorithm allowing to obtain full and low-noise maps ; b) an automatic antenna calibration method ; c) other methods to removing artifacts related to radio frequency interference and clutter echoes. These methods, initially planned for phased array radars, have been adapted to compact radars called CODAR where the main difficulty is the calibration due to the nature of the antennas. The measurements obtained with these new techniques have been validated with in situ campaigns with errors in the low range of the scientific literature.La mesure des courants marins de surface par radar HF soulève plusieurs problématiques au niveau de la calibration des radars, de la résolution spatiale et des signaux parasites. Le traitement conventionnel fonctionnant par balayage azimutal appelé formation de voie a une résolution angulaire limitée pour la plupart des radars à réseau de phase et les méthodes de traitement à haute résolution pour la recherche des directions d'arrivées produisent généralement des cartes lacunaires. Dans cette thèse nous proposons : a) une technique de traitement à haute résolution angulaire permettant d'obtenir des cartes pleines et peu bruitées ; b) une méthode de calibration automatique des antennes ; c) des méthodes de suppression des artefacts liés aux interférences radio et aux échos parasites. Ces méthodes, initialement prévues pour les radars à réseau de phase, ont été adaptées aux radars compacts CODAR dont la principale difficulté est la calibration en raison de la nature des antennes. Les mesures de courant obtenues avec ces nouvelles techniques ont été validées par des campagnes in situ avec des erreurs dans la fourchette basse de la littérature scientifique

Nouvelles techniques de traitement du signal en radio-océanographie

The measurement of sea surface currents by HF radar raises several issues in terms of radar calibration, spatial resolution and parasite signals. Conventional azimuth scanning processing called beam forming has limited angular resolution for most phased array radar and high angular resolution processing methods called direction finding generally produce lacunary maps. In this thesis we propose : a) a high angular resolution processing technique based on direction finding algorithm allowing to obtain full and low-noise maps ; b) an automatic antenna calibration method ; c) other methods to removing artifacts related to radio frequency interference and clutter echoes. These methods, initially planned for phased array radars, have been adapted to compact radars called CODAR where the main difficulty is the calibration due to the nature of the antennas. The measurements obtained with these new techniques have been validated with in situ campaigns with errors in the low range of the scientific literature.La mesure des courants marins de surface par radar HF soulève plusieurs problématiques au niveau de la calibration des radars, de la résolution spatiale et des signaux parasites. Le traitement conventionnel fonctionnant par balayage azimutal appelé formation de voie a une résolution angulaire limitée pour la plupart des radars à réseau de phase et les méthodes de traitement à haute résolution pour la recherche des directions d'arrivées produisent généralement des cartes lacunaires. Dans cette thèse nous proposons : a) une technique de traitement à haute résolution angulaire permettant d'obtenir des cartes pleines et peu bruitées ; b) une méthode de calibration automatique des antennes ; c) des méthodes de suppression des artefacts liés aux interférences radio et aux échos parasites. Ces méthodes, initialement prévues pour les radars à réseau de phase, ont été adaptées aux radars compacts CODAR dont la principale difficulté est la calibration en raison de la nature des antennes. Les mesures de courant obtenues avec ces nouvelles techniques ont été validées par des campagnes in situ avec des erreurs dans la fourchette basse de la littérature scientifique

Nouvelles techniques de traitement du signal en radio-océanographie

The measurement of sea surface currents by HF radar raises several issues in terms of radar calibration, spatial resolution and parasite signals. Conventional azimuth scanning processing called beam forming has limited angular resolution for most phased array radar and high angular resolution processing methods called direction finding generally produce lacunary maps. In this thesis we propose : a) a high angular resolution processing technique based on direction finding algorithm allowing to obtain full and low-noise maps ; b) an automatic antenna calibration method ; c) other methods to removing artifacts related to radio frequency interference and clutter echoes. These methods, initially planned for phased array radars, have been adapted to compact radars called CODAR where the main difficulty is the calibration due to the nature of the antennas. The measurements obtained with these new techniques have been validated with in situ campaigns with errors in the low range of the scientific literature.La mesure des courants marins de surface par radar HF soulève plusieurs problématiques au niveau de la calibration des radars, de la résolution spatiale et des signaux parasites. Le traitement conventionnel fonctionnant par balayage azimutal appelé formation de voie a une résolution angulaire limitée pour la plupart des radars à réseau de phase et les méthodes de traitement à haute résolution pour la recherche des directions d'arrivées produisent généralement des cartes lacunaires. Dans cette thèse nous proposons : a) une technique de traitement à haute résolution angulaire permettant d'obtenir des cartes pleines et peu bruitées ; b) une méthode de calibration automatique des antennes ; c) des méthodes de suppression des artefacts liés aux interférences radio et aux échos parasites. Ces méthodes, initialement prévues pour les radars à réseau de phase, ont été adaptées aux radars compacts CODAR dont la principale difficulté est la calibration en raison de la nature des antennes. Les mesures de courant obtenues avec ces nouvelles techniques ont été validées par des campagnes in situ avec des erreurs dans la fourchette basse de la littérature scientifique

New techniques of signal processing in radio-oceanography

La mesure des courants marins de surface par radar HF soulève plusieurs problématiques au niveau de la calibration des radars, de la résolution spatiale et des signaux parasites. Le traitement conventionnel fonctionnant par balayage azimutal appelé formation de voie a une résolution angulaire limitée pour la plupart des radars à réseau de phase et les méthodes de traitement à haute résolution pour la recherche des directions d'arrivées produisent généralement des cartes lacunaires. Dans cette thèse nous proposons : a) une technique de traitement à haute résolution angulaire permettant d'obtenir des cartes pleines et peu bruitées ; b) une méthode de calibration automatique des antennes ; c) des méthodes de suppression des artefacts liés aux interférences radio et aux échos parasites. Ces méthodes, initialement prévues pour les radars à réseau de phase, ont été adaptées aux radars compacts CODAR dont la principale difficulté est la calibration en raison de la nature des antennes. Les mesures de courant obtenues avec ces nouvelles techniques ont été validées par des campagnes in situ avec des erreurs dans la fourchette basse de la littérature scientifique.The measurement of sea surface currents by HF radar raises several issues in terms of radar calibration, spatial resolution and parasite signals. Conventional azimuth scanning processing called beam forming has limited angular resolution for most phased array radar and high angular resolution processing methods called direction finding generally produce lacunary maps. In this thesis we propose : a) a high angular resolution processing technique based on direction finding algorithm allowing to obtain full and low-noise maps ; b) an automatic antenna calibration method ; c) other methods to removing artifacts related to radio frequency interference and clutter echoes. These methods, initially planned for phased array radars, have been adapted to compact radars called CODAR where the main difficulty is the calibration due to the nature of the antennas. The measurements obtained with these new techniques have been validated with in situ campaigns with errors in the low range of the scientific literature

Self-calibration and antenna grouping for bistatic oceanographic High-Frequency Radars

16 pages, 11 figuresWe propose two concepts for the significant improvement of surface current mapping with bistatic oceanographic High-Frequency Radars. These ameliorations pertain to the azimuthal processing of radar data with linear or quasi-linear antenna arrays. The first idea is to take advantage of the remote transmitter to perform an automatic correction of the complex gains of the receiving antennas based on the analysis of the signal received in the direct path. This direct signal can be found at the zero-Doppler and minimal range cell in the Range-Doppler representation. We term this adjustment as "self-calibration" of the receiving array, as it can be performed in real-time without any specific action from the operator. The second idea consists in applying a Direction Finding technique (instead of traditional Beam Forming) not only to the full array of antenna but also to subarrays made of a smaller number of sequential antennas, a method which we refer to as "antenna grouping". The combination of self-calibration and antenna grouping makes it possible to obtain high-resolution maps with full coverage, thereby combining the respective merits of Direction Finding and Beam Forming techniques. In addition the method is found robust to missing antennas in the array. These techniques are applied to and illustrated with the multistatic High-Frequency Radar network in Toulon

New signal processing techniques for phased-array oceanographic radars: self-calibration, antenna grouping, and denoising

Abstract Original techniques are proposed for the improvement of surface current mapping with phased-array oceanographic high-frequency radars. The first idea, which works only in bistatic configuration, is to take advantage of a remote transmitter to perform an automatic correction of the receiving antennas based on the signal received in the direct path, an adjustment that is designated as “self-calibration.” The second idea, which applies to both mono- and bistatic systems, consists in applying a direction finding (DF) technique (instead of traditional beamforming), not only to the full antenna array but also to subarrays made of a smaller number of sequential antennas, a method that is referred to as “antenna grouping.” In doing this, the number of sources can also be varied, leading to an increased number of DF maps that can be averaged, an operation that is designated as “source stacking.” The combination of self-calibration, antenna grouping, and source stacking makes it possible to obtain high-resolution maps with increased coverage and is found robust to damaged antennas. The third improvement concerns the mitigation of noise in the antenna signal. These methods are illustrated with the multistatic high-frequency radar network in Toulon and their performances are assessed with drifters. The improved DF technique is found to significantly increase the accuracy of radar-based surface current when compared to the conventional beamforming technique