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Integrated Marine Observing System (IMOS)

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    The Newcastle (NEWC) HF ocean radar system covers an area of the Central Coast, New South Wales, an area subject to the variability of the East Australian Current (EAC) and its coupling with coastal winds, tides, and waves. In this area the EAC separates from the coast and generates several eddies which control the larval species and the higher marine species and ecosystems in which they forage. The NEWC HF ocean radar system consists of two SeaSonde crossed loop direction finding stations located at Sea Rocks (32.441575 S 152.539022 E) and Red Head (33.010245 S 151.727059 E). These radars operate at a frequency of 5.2625 MHz, with a bandwidth of 25 KHz, a maximum range of 200 Km and a range resolution of 6 Km. Within the HF radar coverage area surface currents are measured.

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    Radial data files contain radial components of sea surface parameters measured by HF ocean radars operated by Australian Coastal Ocean Radar Network (ACORN), a facility of Integrated Marine Observing System (IMOS). Regardless of the radar system (WERA or SeaSonde), the primary product is the radial component of the sea surface current along a line between the radar station and a point on the sea surface. By combining radials measured at two stations surface current vectors can be constructed. These surface current vectors can then be used to study tides, wind-driven currents and perform lagrangian particle tracking. Raw data collected at each radar site are re-processed by ACORN in order to assign quality control flags to data points. This is not possible in real-time because real-time data are produced by proprietary manufacturer software without quality control flags and it is not feasible to transfer the raw data to ACORN in real-time. Each radial file contains a set of standard metadata fields, such as radar system type, operating frequency and bandwidth. Other metadata fields describe radar system type-specific parameters. Radial file metadata fields are described in a separate ACORN data document. In addition, for WERA radar systems, ACORN provides quality controlled heights of left and right bragg peaks, from which the wind direction can be inferred.

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    The Red Head (RHED) HF ocean radar site (33.010245 S 151.727059 E) is one of two HF ocean radars covering the Newcastle area, New South Wales. The other HF ocean radar station is at Seal Rocks. The HF ocean radar coverage is from the coast to beyond the edge of the continental shelf. The RHED HF ocean radar is a SeaSonde crossed-loop direction finding array. This radar operates at a frequency of 5.2625 MHz, with a bandwidth of 25 KHz, a maximum range of 200 Km and a range resolution of 6 Km. Within the HF radar coverage area surface current radials are measured.

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    The Turquoise Coast (TURQ) HF ocean radar system covers the area of shelf between Seabird and Jurien Bay and is the logical continuation of major research efforts to understand the role of the Leeuwin Current System (Leeuwin Current, the Leeuwin Undercurrent and Capes Current) in controlling not only the physical system but also its links to both pelagic and benthic ecosystems. In contrast to eastern ocean basins, which are highly productive, Western Australia experiences an oligotrophic environment. The Leeuwin Current is a shallow (<300 m deep), narrow band (< 100 km wide) of warm, lower salinity, nutrient depleted water of tropical origin that flows poleward from Exmouth to Cape Leeuwin and into the Great Australian Bight. The Current plays a dominant role in controlling the marine life and climate of the region. Questions which may be addressed by using the HF ocean radar data from TURQ (and ROT) include the variability of the Leeuwin current and its response to the ENSO cycle; Leeuwin Current eddies and their interaction with the shelf waters; and the interaction between the Leeuwin Current, the Capes Current and coastal current during the summer. This is an important region for Western Rock lobster recruitment, and the meanders of the warm Leeuwin Current influence the ecology. This is a region with low tidal range and with a coastline subject to strong sea breezes and intense winter storms. Coastally trapped waves may be generated by the winter weather systems and by tropical cyclones in the summer. The TURQ HF ocean radar system consists of two SeaSonde crossed loop direction finding stations located at Seabird (31.281 S 115.444 E) and Cervantes (30.506 S 115.060E). From 2012-12-15T11:00:00 the Cervantes station has been replaced by the Green Head station (30.073 S 114.967E) and from 2013-03-19T00:00:00 the Seabird station has been replaced by the Lancelin station (31.027 S 115.328 E). These radars operate at a frequency of 5.211 MHz, with a bandwidth of 50 KHz, a maximum range of 200 Km and a range resolution of 3 Km. Within the HF radar coverage area surface currents are measured. The TURQ area of coverage has a small overlap of commonly observed ocean with the Rottnest Shelf (ROT) WERA HF ocean radar system on its south side. Together, the TURQ and ROT systems provide continuous monitoring of the shelf from Fremantle to Jurien Bay.

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    The Seal Rocks (SEAL) HF ocean radar site (32.441575 S 152.539022 E) is one of two HF ocean radars covering the Newcastle area, New South Wales. The other HF ocean radar station is at Red Head. The HF ocean radar coverage is from the coast to beyond the edge of the continental shelf. The SEAL HF ocean radar is a SeaSonde crossed-loop direction finding array. This radar operates at a frequency of 5.2625 MHz, with a bandwidth of 25 KHz, a maximum range of 200 Km and a range resolution of 6 Km. Within the HF radar coverage area surface current radials are measured.

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    The Nora Creina (NOCR) HF ocean radar site (37.329 S 139.850 E) is one of two HF ocean radars covering the Bonney Coast, South Australia. The other HF ocean radar station is at Blackfellows Cave. The HF ocean radar coverage is from the coast to beyond the edge of the continental shelf. The NOCR HF ocean radar is a SeaSonde crossed-loop direction finding array. This radar operates at a frequency of 5.211 MHz, with a bandwidth of 50 KHz, a maximum range of 200 Km and a range resolution of 3 Km. The antenna bearing is 255 deg true east of north (approximately west by south-west). Within the HF radar coverage area surface current radials are measured. This station was decommissioned in March 2017.

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    The Blackfellows Cave (BFCV) HF ocean radar site (37.940 S 140.457 E) is one of two HF ocean radars covering the Bonney Coast, South Australia. The other HF ocean radar station is at Nora Creina. The HF ocean radar coverage is from the coast to beyond the edge of the continental shelf. The BFCV HF ocean radar is a SeaSonde crossed-loop direction finding array. This radar operates at a frequency of 5.211 MHz, with a bandwidth of 50 KHz, a maximum range of 200 Km and a range resolution of 3 Km. The antenna bearing is 257 deg true east of north (approximately west by south-west). Within the HF radar coverage area surface current radials are measured. This station was decommissioned in March 2017.

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    The Bonney Coast (BONC) HF ocean radar system covers an area of the Bonney Coast, South Australia, which has a recurring annual upwelling feature near to the coast that significantly changes the ecosystem from one of warm water originating in Western Australia, to one dominated by cold upwelling water from off the continental shelf. The dynamics of this area and the relationship between ocean circulation, chemistry and sediments control the larval species and the higher marine species and ecosystems in which they forage. The data from this site provide linking observations between the Southern Ocean and NSW through processes that occur on weekly to El Nino time scales. The BONC HF ocean radar system consists of two SeaSonde crossed loop direction finding stations located at Nora Creina (37.329 S 139.850 E) and Blackfellows Cave (37.940 S 140.457 E). These radars operate at a frequency of 5.211 MHz, with a bandwidth of 50 KHz, a maximum range of 200 Km and a range resolution of 3 Km. Within the HF radar coverage area surface currents are measured. This site was decommissioned in March 2017.

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    The Green Head (GHED) HF ocean radar site (30.073 S 114.967E) is one of two HF ocean radars covering Rottnest Shelf and Perth Canyon on the Turquoise Coast north of Perth. The other HF ocean radar station is at Seabird, or Lancelin from 2013-03-19. The HF ocean radar coverage is from the coast to beyond the edge of the continental shelf. The GHED HF ocean radar is a SeaSonde crossed-loop direction finding array. This radar operates at a frequency of 5.211 MHz, with a bandwidth of 50 KHz, a maximum range of 200 Km and a range resolution of 3 Km. The antenna bearing is 288 deg true east of north (approximately west by north-west). Within the HF radar coverage area surface current radials are measured.

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    Coastal ocean surface radar is a land-based technique which uses scattering from the rough sea surface to obtain echoes which are Doppler shifted by the dynamics of the sea. It has been shown (Crombie, 1955) that the scatter is predominantly a Bragg interaction between the radio wave and the sea surface gravity wave that is propagating in the same direction and with half the wavelength of the radio wave. This Bragg interaction gives two strong first-order lines in the echo spectrum; one from the resonant gravity wave moving radially away from the station, and one from the resonant gravity wave moving towards the station. Direction-finding systems determine the azimuthal direction of a source point by comparing amplitude and phase signals on crossed loop receive antennas. The direction finding calculation is done on Doppler shift spectra for a specified range which includes return echoes from all azimuths. This means that the spectra are spread and second-order echoes from one direction are swamped by the first-order echoes from other directions. Consequently, parameter extraction using second-order echoes is not possible on a routine basis. Directional wave spectra at the location of each radar station are produced by analysing the full azimuthal spread of first-order echo amplitudes, and wind directions are derived across the grid points by taking the ratio of the positive and negative Bragg echoes. SeaSonde HF ocean radar stations are used on the Turquoise Coast (Seabird and Cervantes), Western Australia, and on the Bonney Coast (Nora Creina and Blackfellows Cave), South Australia.