High Resolution Ocean Radar Observations in Ports and Harbours

Observations are shown from an ocean radar system which operates in the VHF frequency band (100-180 MHz) and produce surface current measurements on grid scales of 50-200m over ranges up to 6-10 km. This is a scale of operation that is well suited to measurement tasks in Ports, harbours and coastal zones. Ocean radars commonly used for mapping surface currents in coastal zones operate in the HF frequency band and measure currents on grid scales of 3-6 km over distances of 100-200km. The VHF ocean radar system consists of two stations which look at the same patch of ocean from different directions. Each station measures the radial component of the surface current at each grid point, and by combining data from both stations it is possible to produce maps of surface current vectors. Each station can cover a 60-degree sector of azimuth, and for wider coverage it is possible to use multiplexed receive antennas to double the size of the sector. The time to make the basic 60-degree sector for two stations is 10 minutes, and becomes 20 minutes for the wider 120 degree coverage. Results are shown for sheltered coastal waters and for open coast line where there are breaking waves. This methodology is particularly appropriate for monitoring currents in congested port areas where fixed moorings may be compromised

Evaluation of a new airborne microwave remote sensing radiometer by measuring the salinity gradients across the shelf of the Great Barrier Reef lagoon

Over the last ten years, some operational airborne remote sensing systems have become available for mapping surface salinity over large areas in near real time. A new dual-polarized Polarimetric L-band Multibeam Radiometer (PLMR) has been developed to improve accuracy and precision when compared with previous instrument generations. This paper reports on the first field evaluation of the performance of the PLMR by measuring salinity gradients in the central Great Barrier Reef. Before calibration, the raw salinity values of the PLMR and conductivity-temperature-depth (CTD) differed by 3-6 psu. The calibration, which uses in situ salinity data to remove long-term drifts in the PLMR as well as environmental effects such as surface roughness and radiation from the sky and atmosphere, was carried out by equating the means of the PLMR and CTD salinity data over a subsection of the transect, after which 85% of the salinity values between the PLMR and CTD are within 0.1 psu along the complete transect. From offshore to inshore across the shelf, the PLMR shows an average cross-shelf salinity increase of about 0.4 psu and a decrease of 2 psu over the inshore 20 km at -19deg S (around Townsville) and -18deg S (around Lucinda), respectively. The average cross-shelf salinity increase was 0.3 psu for the offshore 100 km over all transects. These results are consistent with the in situ CTD results. This survey shows that PLMR provided an effective method of rapidly measuring the surface salinity in near real time when a calibration could be made

Ocean surface radar current measurements in the surf break zone at Coffs Harbour

Ocean surface radars are being used routinely to map surface currents over tens of kilometres at resolutions typically around 3 km. At higher frequencies, in the VHF band, the Bragg wavelength for backscatter is reduced so that at 152.2 MHz the dominant scatter is from a wave with a wavelength just shorter than 1 m, compared with 5 m at 30 MHz. At this wavelength, the Bragg waves are heavily modulated by underlying wind waves and swell which produce significant broadening of the first-order Bragg peaks. The broadening of the peaks does not significantly impair our ability to locate the frequency of the peak and hence\ud to derive surface current measurements. An upward-looking acoustic current profiler was used for inter-comparison with the surface currents measured by the radar. The deployment at Coffs Harbour was relatively short, but included calm conditions as well as a period of strong winds where the breaker zone extended well out from the shore. Although both the acoustic current meter measurements and the radar surface current data were affected by the presence of swell, it is clear that the VHF radar has potential to monitor rip currents and coastal vortices under surf break conditions when conventional techniques become limited

Wave height and wind direction from the HF coastal ocean surface radar

The biggest difficulty in extracting wind direction from high-frequency (HF) backscatter ground-wave radar data is in not knowing the fundamental shape of the directional spreading function at the Bragg wavelength for the sea-surface gravity waves. In this paper we present data from a deployment of the HF coastal ocean surface radar (COSRAD) which samples the same patch of water from a range of different angles, allowing us to determine the shape of the spectral spreading function for the Bragg resonant gravity waves. The resulting evaluation of wind direction compares favourably with wind-vane measurements in the vicinity. A routine method for extracting root mean square (rms) wave heights from HF backscatter ground-wave radar spectra has been developed based on the theoretical work of D.E. Barrick. This method is reviewed in the paper and a "best practice" procedure is described for routine production of rms wave heights. Results are shown for a recent deployment of the COSRAD HF radar near Cairns in the Great Barrier Reef Region of northeast Australia. The observed rms wave heights agree reasonably well with those given by the JONSWAP model over the same range of wind speeds. A method for obtaining a measure of the spreading of the directional wave spectrum has been developed. Over the period of observation, the wind speeds varied between 2 and 11 m/s, and the S values for the M.S. Longuet-Higgins et al. spreading function were in the range 1.94 ± 0.62. These S values are less than those given by the JONSWAP model, especially at low wind speeds. A sensitivity study was carried out on the spread of wind directions which would arise from this variability in the wave directional spreading function. For single measurements, the error in wind direction is ±25°, but with spectral averaging over time and space the HF radar errors in wind directions are reduced to about ±10°

Application of VHF high resolution radar to evaluating circulation around a seawater intake facility

The Australian Institute of Marine Science operates a research aquarium at Cape Ferguson in North Queensland which requires a high volume circulation of ocean water from the adjacent bay. Turbidity and water quality are significant issues which govern the location of the seawater intakes. A VHF high resolution ocean radar was deployed at the site of the sea water intakes in order to evaluate the circulation in an area of approximately 2 km 2 km with spatial resolution of about 100 m. The short deployment showed that there are complex flow patterns at this scale, and identified three bodies of water which may affect the quality of water that enters the intakes

High Resolution Ocean Radar Observations\ud in Ports and Harbours

Observations are shown from an ocean radar system which operates in the VHF frequency band (100-180 MHz) and produce surface current measurements on grid scales of 50-200m over ranges up to 6-10 km. This is a scale of operation that is well suited to measurement tasks in Ports, harbours and coastal zones. Ocean radars commonly used for mapping surface currents in coastal zones operate in the HF frequency band and measure currents on grid scales of 3-6 km over distances of 100-200km.\ud The VHF ocean radar system consists of two stations which look at the same patch of ocean from different directions. Each station measures the radial component of the surface current at each grid point, and by combining data from both stations it is possible to produce maps of surface current vectors. Each station can cover a 60-degree sector of azimuth, and for wider coverage it is possible to use multiplexed receive antennas to double the size of the sector. The time to make the basic 60-degree sector for two stations is 10 minutes, and becomes 20 minutes for the wider 120 degree coverage.\ud Results are shown for sheltered coastal waters and for open coast line where there are breaking waves. This methodology is particularly appropriate for monitoring currents in congested port areas where fixed moorings may be compromised

The Australian coastal ocean radar network: lessons learned in the establishment phase

HF ocean radar is a leading technology for measuring parameters of the ocean's surface in coastal waters. The technical and logistical advantage of shore-based measurements of the coastal ocean is a significant improvement over in situ measurements, and the cost per data point is low. The ability of HF radars to make 2D maps of surface currents and other parameters over quite large coastal areas is powerful and when establishment decisions were being made for the Integrated Marine Observing System (IMOS) in Australia a plan was adopted to establish the Australian Coastal Ocean Radar Network (ACORN). At the time of establishment we knew that HF coastal ocean radar was dominated by two genres of technology, and a planning decision was made to include elements of each of the phased array and crossed-loop genres into the new network. Because these are new technologies some of the applications and issues around quality control are still being developed and the inclusion of both genres allows ACORN staff and users of the archived data to fairly compare the genres. This paper addresses issues of process in setting up radar stations and establishing a data archive of good quality and easy access

Operational requirements for oceanographic ground-wave HF radars: experiences from the Australian Coastal Ocean Radar Network

The Australian Coastal Ocean Radar Network, ACORN, comprises 12 radars located in pairs to provide surface current, wave and wind measurements at 6 locations around the Australian Coast. It is part of the Federally-funded Integrated Marine Observing System, IMOS. WERA phased-array radars have been installed at 4 of these locations and SeaSonde direction-finding radars at the other two. In this paper the performance of these systems, in terms of radar and metocean data availability and quality will be discussed. Some of the issues that impact on performance will be identified and possible solutions discussed with a view to developing a clear recommendation for future operational systems to augment the existing network

The Australian Coastal Ocean Radar Network data availability and quality

This paper presents an overview of the Australian Coastal Ocean Radar Network (ACORN), part of the Australian Integrated Marine Observing System (IMOS. ACORN currently operates 12 radars in 6 dual radar pairs at sites around the coast of Australia. Some of the issues associated with operating multiple radar systems with different technical requirements, often sited in remote areas, are discussed. The availability of data depends on the robustness of the radar systems, the level of external interference and the ability to respond quickly to hardware and software issues that may arise. Some validations of the data obtained will be presented

Structure and influence of tropical river plumes in the Great Barrier Reef: Application and performance of an airborne sea surface salinity mapper

360 PARK AVE SOUTH, NEW YORK, NY, 10010-171