Gap filling of the CALYPSO HF radar sea surface current data through past measurements and satellite wind observations

High frequency (HF) radar installations are becoming essential components of operational real-time marine monitoring systems. The underlying technology is being further enhanced to fully exploit the potential of mapping sea surface currents and wave fields over wide areas with high spatial and temporal resolution, even in adverse meteo-marine conditions. Data applications are opening to many different sectors, reaching out beyond research and monitoring, targeting downstream services in support to key national and regional stakeholders. In the CALYPSO project, the HF radar system composed of CODAR SeaSonde stations installed in the Malta Channel is specifically serving to assist in the response against marine oil spills and to support search and rescue at sea. One key drawback concerns the sporadic inconsistency in the spatial coverage of radar data which is dictated by the sea state as well as by interference from unknown sources that may be competing with transmissions in the same frequency band. This work investigates the use of Machine Learning techniques to fill in missing data in a high resolution grid. Past radar data and wind vectors obtained from satellites are used to predict missing information and provide a more consistent dataset.peer-reviewe

Oil spill risk assessment on the Maltese coastal areas

A significant percentage of the global oil transport goes through the Mediterranean sea. Most of the maritime traffic carrying oil and other dangerous liquid substances travels across the Malta Channel. The risk of marine spillages within the stretch of sea between Malta and Sicily is very high and beaching on the Maltese shores can cause irreversible environmental damage at the detriment of important economic resources. The aim of this work is to determine the probability and volume percentage of oil that would reach the coast in case of an accident in the proximity of the Maltese Islands. Various spill scenarios are considered to get a realistic estimate as much as possible.peer-reviewe

Development of a novel tool to predict different water quality scenarios within a Marine Protected Area (MPA) in the Maltese Islands : the 2D SHYFEM-BFM model

Effective operational marine conservation and management is thwarted by a lack of financial and human resources. A coupled 2D hydrodynamic (SHYFEM) and ecological (BFM) model was developed in the current study as a Decision Support System (DSS) to spearhead good governance of a Marine Protected Area (MPA) in Dwejra (Maltese Islands) in the Central Mediterranean. Two scenarios were considered – one with the current levels of nutrient runoff from land and one in which such levels are increased as a result of a greater human activity within the area. Although the developed numerical modeling platform needs to be refined and to be run for a longer time -frame, its output suggests that it is a promising tool to assist in the operational management of an MPA.peer-reviewe

Assessing the offshore wave energy potential for the Maltese islands

Direct wave observations using a Datawell buoy deployed to the west of Gozo, and a numerical wave modeling exercise targeted to map the spatial and temporal signatures of the wave fields around the Maltese Islands over a span of five years (1st January 2007 to 31st December 2011) have been conducted within the BLUE OCEAN ENERGY® project. This has provided a detailed characterization of local wave climates and an estimation of the available wave energy potentials in the coastal and offshore areas of the Maltese Islands. This data is essential to assess the overall feasibility of constructing wave energy production farms based on WECs, to test the most adequate devices to harvest wave energy, as well as to identify the best candidate sites for an optimal and most economically practical extraction. The study reveals that the best sites in the Maltese waters would be those located at the western approaches to the islands, given that these are more exposed to the prevailing North-Westerly winds. At these sites, maximum significant wave heights can exceed 7 m in winter, even in close proximity to the coast, and with a seasonal mean of 1.92 m as determined from direct measurements. The mean wave power transport during the winter season is estimated at 15 kW m-1; the wave resource is more than halved in spring and even weaker in autumn; it is under 2 kW m-1 during summer. Stronger wave fields occur at a few kilometres to the South West of Filfla Island where the modelled mean wave power reaches values of 13 kW m-1 in the winter months, but at less accessible sites and greater distances from shore.Alternative Technologies Ltd., Energy Investment Ltd, JMV Vibro Blocks Ltd., Solar Engineering Ltd. and Solar Solutions Ltd.peer-reviewe

A first attempt at testing correlation between MODIS ocean colour data and in situ chlorophyll-a measurements within Maltese coastal waters

The study of spatio-temporal trends for key water quality parameters in the Maltese coastal waters is hindered by the lack of systematic observations spanning over the full domain and for sufficiently long time periods. Satellite data offers an alternative source of information, but requires ground truthing against in situ measurements. The aim of this study is to attempt the statistical comparison of MODIS ocean colour data, for a near-shore marine area off the north-east coastline of Malta, with in situ surface chlorophyll-a measurements, and to extract a twelve-month ocean colour data series for the same marine area. Peaks in surface chlorophyll-a concentration occurred in the January-February period, with lowest values being recorded during the early spring period. Log bias values indicate that the MODIS dataset under-estimates the surface chlorophyll-a values, whilst RMSD and r2 values suggest that the match-up between satellite and in situ values is only partly consistent.peer-reviewe

CALYPSO an operational network of HF radars for the Malta-Sicily Channel

An HF radar observing system composed of three CODAR SeaSondes is providing real-time surface current pseudo-Eulerian maps every hour in the strip of sea dividing Malta and Sicily. This initiative forms part of the CALYPSO project that principally aims to support the efficient response against marine oil spills in this busy area of maritime transportation in the Mediterranean. In combination to numerical models, an operational chain of activities provides essential data to a spectrum of applications and addresses the needs of a number of responsible entities in Malta and Sicily, targeting the better control of the trans-boundary maritime space and greater efficiency for security and safety at sea. The usefulness of this effort is measured by the level of usage of the data provided by CALYPSO through dedicated web services with browsing, viewing, and user-defined download of data. The project comprised several validation and system performance tuning exercises through the matching of radar data with direct sea current measurements using drifters and ADCP deployments. The spatial coverage and high temporal resolution of the HF radar data collected since September 2012 is permitting a unique and detailed characterization of the surface circulation variability in the area at sub-to-mesoscale and seasonal scales. Substantial eddy field structures are evidenced; their origin, dynamics, evolution and linkages to biological processes and the location of fisheries is the subject of ongoing research.peer-reviewe

Validation of HF radar sea surface currents in the Malta-Sicily Channel

A network of High-Frequency radar (HFR) stations runs operationally in the Malta-Sicily Channel (MSC), Central Mediterranean Sea, providing sea surface current maps with high temporal (1 h) and spatial (3 × 3 km) resolutions since August 2012. Comparisons with surface drifter data and near-surface Acoustic Doppler Current Profiler (ADCP) observations, as well as radar site-to-site baseline analyses, provide quantitative assessments of HFR velocities accuracy. Twenty-two drifters were deployed within the HFR domain of coverage between December 2012 and October 2013. Additionally, six ADCP vertical current profiles were collected at selected positions during a dedicated field survey. External radio-frequency interferences lead to significant gaps in the HFR coverage, which were minimized by an interpolation technique applied to the surface current fields. The validation of HFR velocities was first performed for each individual station in the network, using data generated with both the ideal and the measured antenna patterns. The validation was then repeated with pairs of HFR stations using the site-to-site baseline error analysis. The analysis confirms that the baseline error estimations and the full validation metrics for this HFR frequency band are consistent, and in some aspects superior, when compared to results from similar studies in other regions. The validation with drifter tracks suggests that the adopted interpolation procedure does not in general impact on the comparison metrics, but may introduce biases when used to extrapolate currents in regions where radar geometrical constraints are suboptimal. The analysis of the percentage of contribution of individual HFR stations shown that the quality of HFR data is influenced by the network geometry

Structure and biodiversity of a Maltese maerl bed : new insight into the associated assemblage 24 years after the first investigation

Maerl beds are biogenic benthic habitats distributed worldwide and known to sustain high productivity and biodiversity levels. In the Mediterranean, the number of studies that have been carried out is limited, and little is known on its real distribution, mostly due to the difficulties of exploring such habitats — Due to the high transparency of Mediterranean waters, maerl can be found at depths of over 50 m making mandatory the use of benthic grabs and ROVs. The last published data from Maltese waters were taken two decades ago. In this present study, we provide new insights on this poorly known habitat, in particular regarding the north western bank, designated as a NATURA 2000 protected area, in which human activities are also carried out, such as blue fin tuna ranching. The objective of this work is to provide information regarding this delicate habitat, especially relevant for future management plans and authorities.peer-reviewe

New insights of the Sicily Channel and southern Tyrrhenian Sea variability

International audienceThe dynamics of the Sicily Channel and the southern Tyrrhenian Sea are highly influenced by the seasonal variability of the Mediterranean basin-wide circulation, by the interannual variability of the numerous mesoscale structures present in the Channel, and by the decadal variability of the adjacent Ionian Sea. In the present study, all these aspects are investigated using in-situ (Lagrangian drifter trajectories and Argo float profiles) and satellite data (Absolute Dynamic Topography, Sea Level Anomaly, Sea Surface Temperature, wind products) over the period from 1993 to 2018. The availability of long time series of data and high-resolution multi-sensor surface currents allow us to add new details on the circulation features and on their driving mechanisms and to detect new permanent eddies not yet described in literature. The structures prevailing in winter are mainly driven by wind, whereas those prevailing in summer are regulated by topographical forcing on surface currents. The strength of the surface structures located at the western entrance of the Ionian Sea and of the mesoscale activity along the northern Sicily coast is modulated by the large-scale internal variability. The vertical hydrological characteristics of these mesoscale eddies are delineated using the Argo float profiles inside these structure