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HF Radar Monitoring System and Response

against Marine Oil Spills in the Malta Channel

Aldo Drago (Project Leader)and

Adam Gauci

University of MaltaPhysical Oceanography Unit

HF RHF RADARADAR NNETWORKETWORK

ONON THETHE MMALTAALTA CCOASTOAST

CALYPSO Radar Network

• The CALYPSO project envisages the installation of two HF-Radars on the MalteseIslands and one HF-Radar on the Southern Coast of Sicily to measure two-dimensional sea surface currents and waves in the Malta Channel.

• The main target of the project is to obtain high quality real time maps of the surface currents in the stretch of sea between Malta and Sicily.

• On the Maltese coast , radars will be set up at:

• Ta’ Barkat, Xghajra, Malta

• Sopu Tower Area, Nadur, Gozo

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CALYPSO Radar Network

• In Phase 1, two antennas will be installed on the Maltese coast with the central server that acts as data combining station.

• In Phase 2, the third radar on the Sicilian coast will be install and linked to a mirror data collecting server in Sicily.

• The area of interest is between 80 and 100km wide .

Phase 1 expected beam coverage Phase 2 expected beam coverage

CALYPSO Radar Network

• Data close to the coast is especially required on the Malta side since the Grand Harbour is within the overlapping region of the beam patterns.

Ta’ Ta’ BarkatBarkat, MALTA, MALTAphase 1phase 1

Ta’ Ta’ SopuSopu Area, GOZOArea, GOZOphase 1phase 1

SICILYSICILYphase 2phase 2

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CALYPSO Radar Network

• Deliverables of the HF radar monitoring project are:

• real time polar surface currents map with a range of up to approximately 75 km subject to environmental conditions such as noise in the operating band and final antenna placement.

• real time 2D vector currents maps in the overlap region of the three radar stations.

• Output is user-selectable at regularly scheduled intervals (e.g. every 30 minutes or every hour). The recommended setting is of one hour.

• Estimates of significant wave height and other wave parameters (such as direction and period in annular crowns around the radar site).

Typical HF Radar output for Ria de Vigo

Radar Technology

• HF Radars rely on Bragg Scattering of electromagnetic radio waves from gravity waves travelling along the sea surface.

• The radars transmit a vertically polarised signal which propagates onto the water in a radial path away from the mast. When the radar signal hits ocean waves, the radar signal is scattered in many directions.

• By Bragg’s principle, the radar signal produces an echo returning directly to its source only when the signal scatters off a sea wave with a wavelength that is exactly half the wavelength of the transmitted radio signal, and when the sea wave is travelling in a radial path either directly away from or towards the radar.

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Radar Technology

• The scattered radar electromagnetic waves add coherently resulting in a strong return ofenergy at two sharp peaks in the Doppler Spectrum.

• Due to the underlying ocean currents, the detected peak does not have a constantDoppler shift. Once the theoretical wave speed is computed from the dispersion relation,and subtracted from the Doppler frequency shift, the radial velocity component of thesurface current can be found.

• By installing more than one radar at different locations with an overlapping beampattern, the same patch of water can be viewed from different angles, and the surfacecurrent radial velocity components can be summed to determine the total surfacecurrent velocity vector.

• Each HF Radar station measures radialvelocities at five degrees angularresolution at several distances . Radial datafrom two or more than two stations can befinally combined to produce hourly maps ofcurrent vectors within a regular grid .

• The range-cell spacing and total rangedepends on the transmit signal centrefrequency and the bandwidth.

Radar Technology

• A second derived measurement from each radarstation is the significant wave height and the wavedirection , which are extracted from the secondorder Doppler Spectrum.

• Existing wave climatologies confirm that the mostcommon waves in this region have a period of about3 seconds .

• In order to have a consistent data flow, thefrequency range close to13MHz was consideredto be the most appropriate.

• Lower radar operating frequency favours greaterrange of measurement, but requires longer oceanwaves to be present.

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Radar Technology

• Ocean observing HF radar stations can be set in either a monostatic or a bistatic/multistatic configuration.

• In a monostatic radar configuration, the transmitter and receiver are co-locatedtogether.

• In a bistatic configuration, the transmitter is positioned away from the receiver by tens ofkilometres.

• The quality of a 2D current vector map depends on the number of vectors produced ateach point on the grid.

• Two 1D radial velocity vectors produced by a monostatic system on a polar coordinategrid can be combined to create a 2D vector map. The 1D vectors must be of goodquality and have an angle of intersection greater than 2- degrees.

• If the radars in Ta’ Barkat, Malta and in Ragusa, Sicily are equipped with simultaneousmonostatic and multistatic scatter processing capabilities, higher quality 2D vectors canbe computed.

Radar Technology

• In phase 1, the radars installed at Ta’ Barkat (Malta) and Ta’ Sopu (Gozo) will have monostatic capabilities i.e. a transmitter and receiver will be installed at both stations.

• In the blue area, monostatic backscatter from the two radars will produce good quality 1D radial velocity vectors that can be combined into a 2D vector map.

• In the orange region (close to the coast), the angle of incidence formed by the two monostatic 1D vectors is less than 20o. In this area, the 1D vectors will be looking at the same radial velocity component which is not ideal for computing the 2D vector map. The two nearly parallel components will be used and a fitting technique will be incorporated. This will reduce uncertainty in the data.

Monostatic

Monostatic

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Radar Technology

• Current mappings close to the coast can be enhanced by installing the radars in Sicily and Ta’ Barkat with simultaneous monostatic and multistatic scatter processing capabilities.

• Ta’ Barkat would be able to process not only its own monostatic signal but also two other HF signals transmitted by the other two radars.

• In the blue area, we will be able to compute a total vector made up of three individual vectors thus increasing the quality of the final 2D vector map.

• In the orange area, we will be able to generate an additional set of measurements based on the transmitted signal from Sicily which is reflected towards Ta’ Barkat. The angle that is formed is greater than 20o and good quality 2D vectors can be computed.

signal from Sicily

Monostatic

MonostaticMultistatic

Requirements on the Malta side

• All radiating elements should be mounted on a single mast and must not occupy morethan 4m2.

• Environmental impact of the systems needs to be kept to an absolute minimum.

• The transmitted power should have no influence on human health and must be limitedto 40 watts as identified by the ITU.

• The measured azimuthal angles for polar currents maps shall only be limited by theexisting coastline.

• The Malta radar network must allow for future expansion ideally for the full Straitbetween Sicily and Tunisia.

• The three HF radars that are being set up in this project should use a synchronizationtechnology that will allow up to a total of 10 sites to operate at the same frequency atthe same time within the assigned bandwidth without interfering. For Malta, theoperating band will be at 13 ± 1 MHz range.

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Requirements on the Malta side

• All electronic components associated to the remote radars shall be mounted inside anenvironmental enclosure housing. Temperatures in the shelter may rise to up to 40oC insummer time.

• The continuous power requirement of one radar unit is 500 watts. Communication linkadds 100 watts. All electronics including climate control requires a total of 1500 wattsfor each radar site.

• A high-speed communication link needs to be installed at each radar site. This link isfor transmission of radar data to the server and most importantly, for remote monitoringand manipulation of the equipment. The minimum required bandwidth is of 128kbps forupload and download.

• To operate the HF radar technology, you need to have a radio-electric bandwidthlicense .

Site Locations: Ta’ Barkat, Xghajra, Malta

• In Malta, the radar will be installed at Ta’ Barkat, limits of Xghajra.

• The location was chosen after taking into account safety, and energy access.

• Permission was obtained to place the equipment within the premises of the Water Services Corporation wastewater treatment plant. A small room is to be built.

• The antenna is to be erected on the plant’s outflow very close to the coastline approximately 70m away from where the equipment will be housed.

• The mast will be raised by about 4m to achieved alongshore coverage and to avoid surrounding terrain.

• Trenching works are required to pass the cable from the antenna to the electronics.

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Site Locations: Ta’ Barkat, Xghajra, Malta

Site Locations: Ta’ Barkat, Xghajra, Malta

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Site Locations: Ta’ Sopu, Nadur, Gozo

• A site recognition field trip was done along the whole northern coast of Gozo.

• The optimal place for the antenna is about 80m west from Sopu Tower at Ta’ Barkat, limits of Nadur.

• The mast will have unobstructed sea views and will be fixed to existing rock avoiding the use of any construction or concrete.

• The electronics rack will be placed within the Armed Forces of Malta barracks (PP4) about 330m away from the mast.

• A corrugated conduit with diameter of about 60mm will be used through the rocky area from the antenna to the electronics.

• Use of Sopu Tower for antenna installation and equipment housing was discouraged due to permit and electricity issues. The tower is also not very spacious.

Site Locations: Ta’ Sopu, Nadur, Gozo

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Tender

• Tender published on the 6th December 2011 .

• Advert published on the Malta Government Gazette on the 6th December 2011 .

• Closed on 31st January 2011 at 10am .

• Two day information and question session held on the 4 th and 5 th of January 2012 .

• Only CODAR submitted proposal.

• Evaluation committee members will assess this submission.

Tender

• Minimum requirements in the proposal for HF Radar System and Accessories

1

SSRS-100 SR SeaSonde HF Radar station operating at 11.4-14.0 MHz delivering real time surfacecurrents maps with a range of up to 75 km, a radial resolution of 2.0 km based on a frequencybandwidth assignation of 90 kHz, with an azimuthal resolution that is starting at 1 degree and isconfigurable among the system software options.

2

SHARE (Spectrum Harmonizing Acquisition RADAR Enhancement) technology for usinguniversally available timing signals from the Global Positioning System (GPS) to discipline thetiming of a rubidium clock standard and this way allow the synchronization of multiple radars sothey can operate simultaneously within the same frequency band based on the use of the gatedFMCW waveform and the relative timing of its modulation.

3

Remote site enclosure, electronic stainless steel enclosure for indoor/outdoor mounting anddimensions 950 x 600 x 800 mm, with 50 kg of weight. Electronic transmit and receive units as wellas MAC computer, uninterrupted power supply unit for the receiver and transmit chassis (UPS1500 VA), communication modem and connection is located in it. Power supply line protectionunits and field cables protections are included.

4Uninterrupted power supply 1500 VA/10 min unit keeping the transmit and receive chassisoperation, including remote power down and power up software, system support and diagnosticssoftware.

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Tender

• Minimum requirements in the proposal for HF Radar System and Accessories

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Communication modem for wireless 5GHz unlicensed band operating bridging solution, allowingfor communication between two computers for a distance of several km (maximum range dependsof antenna, environmental and geographic conditions, it can reach up to 20 km). Compact solutionusing two antennas for each communication link that need to have direct visibility among them.

6Antenna cable, the Tx unit and the Rx antenna need a total of three special low attenuation cableswith a maximum length of 300 m. In case the distance between Rx and electronic unit is less than100m RG8 cable can be used instead of RG8.

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SSDP-100 PowerMAC G5 and PORTUS software for the management of a network of up to sixremote HF radar stations generating two dimensional currents vector maps and wave parametersas well as diagnostics variables, having applications for the remote monitoring of the system forthe reliable management of operation, realtime data export software in ASCII format.

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SSDA-ES100 Special software package for enhanced multistatic data processing of sea echoscoming from a series of SeaSonde transmitters simultaneously with the remote station ownmonostatic backscatter.

Project Timeline

Jan 1

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Closing of tender, information meetingand collection of submissions

Construction of trench and preparation of data communication service at Ta’ Sopu Gozo

Construction of shed and preparation of data communication service at Ta’ Barkat Malta

Adjudication and signing of contract

Contract start, revision of contract scope and time plan

Confirmation of frequency, obtain permits and other preparatory work by IOI-MOC

Equipment production

Transportation of equipment to Malta

Inspection of equipment by IOI-MOC

Inspection of state of preparatory works

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Project Timeline

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System installation and commissioning

As built documentation

Partial provisional acceptance by IOI-MOC

System calibration and optimisation by IOI-MOC and support of CNR

Training courses at IOI-MOC

Full provisional acceptance by IOI-MOC

System operation and maintenance by IOI-MOC with support of provider and CNR