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An ability to reliably measure the first five Fourier coefficients of the directional distribution of ocean wave energy is becoming an international requirement for any directional wave measurement device. HF radar systems are now commonly used for surface current measurement in the coastal ocean but robust wave measurements are more difficult to achieve. A number of HF radar deployments have demonstrated an ability to measure the directional spectrum, and in this paper, an evaluation of the Fourier coefficients derived from these spectra is presented. It is shown that, when data quality is good, good quality spectra and Fourier coefficients result. Recommendations for addressing some of the radar data quality issues that do arise are presented.

Surface velocity data from two WERA high-frequency (HF) ocean radar systems, deployed as part of the Australian Integrated Marine Observing System (IMOS), are compared with near-surface currents obtained from drifters and acoustic Doppler current profilers (ADCPs). We evaluate data from two contrasting locations in the first detailed evaluation of the IMOS HF radar surface velocities. HF radar measurements are generally robust but demand quality-control procedures to eliminate obvious errors and outliers that appear temporarily or systematically in the data. A number of different quality control procedures and filters are applied and assessed including Taylor diagrams and Hampel and Savitzky–Golay filters. In addition, the need for and effect of averaging are discussed. The radar measurements of surface current agreed better with the near-surface drifter currents than with the subsurface ADCP currents. Nonetheless, the ADCP comparisons are consistent with those previously reported in other regions. The value of the Taylor diagram for comparing different surface current data sets and processing approaches is demonstrated. Noise levels in the radar current spectra are used to estimate the error in the measurements and in some cases, these errors were found to approach the precision of the radar estimates. Our results give guidance on the most useful temporal sampling resolution. In particular we show that at these sites and these operating frequencies, using 10-min sampling without further averaging does not provide additional information because the higher frequencies are dominated by noise. Averaging the radials over 30 min may be sufficient for many applications.

Scatterometer winds are increasingly being used by Meteorological Services to validate and assimilate into their forecast models and reanalyses. In this paper, ASCAT wind directions obtained in coa...

In recent decades, high-spatial resolution ocean radar and satellite imagery measurements have revealed a complex tangle of submesoscale filaments and eddies, in the surface velocity, temperature, and chlorophyll a fields. We use a suite of high-resolution data to characterize two counter-rotating, short-lived eddies formed at the front between the warm East Australian Current (EAC) and temperate coastal waters (30°S, Eastern Australia). In this region, submesoscale filaments and short-lived eddies are dynamically generated and decay at time scales of hours to days. Dominant cyclonic filaments of O(1) Rossby number formed along frontal jets and eddy boundaries, generating localized ageostrophic circulations at the submesoscale. Measurements of over-ocean wind direction and surface currents from high-frequency radars reveal the influence of the short-term, small-scale wind forcing on the surface circulation, enhancement of the horizontal shear, frontal jet destabilization, and the generation and decay of the cyclonic eddy. By contrast, the anticyclonic eddy formation was most likely associated with EAC mesoscale instability and anticyclonic vorticity. Lagrangian tracks show that surface particles can be temporarily trapped in the eddies and frontal convergent zones, limiting their transport. Mixing between EAC-derived and coastal waters was increased along the frontal regions, and particles starting at the divergent regions around the eddies experienced significant dispersion at submesoscales. The cyclonic cold-core eddy entrained high chlorophyll a shelf waters on its convergent side, suggesting spiral eddy cyclogenesis.\ud

HF radar surface current measurement is now a well-accepted technology and part of many operational oceanography systems. Although the UK was involved from the early stages in this technology there has not been the take-up seen elsewhere in the world most notably in the US and, more recently, in the Far East where such data are being routinely used for model evaluation and other applications. In addition to surface currents, simultaneous measurement of waves and winds has also been demonstrated although these are still often regarded as experimental and unreliable. This is in part because good quality wave measurement requires much higher quality radar data which is not always available so some published results are rather noisy. This paper will review the current state of the art in all these measurements and highlight some new developments which have the potential to increase their availability, accuracy and scope. The original wave measurement work in the UK was carried out using the Pisces HF radar system which was designed specifically for this application. New measurements using a modification of this radar, which exploits the fact that different radar operating frequencies have different responses to wave conditions, will be presented. Software developments to increase the robustness of HF radar metocean measurements will be discussed.

Academic, government, and private organizations from around the globe have established High Frequency radar (hereinafter, HFR) networks at regional or national levels. Partnerships have been established to coordinate and collaborate on a single global HFR network (http://global-hfradar.org/ ). These partnerships were established in 2012 as part of the Group on Earth Observations (GEO) to promote HFR technology and increase data sharing among operators and users. The main product of HFR networks are continuous maps of ocean surface currents within 200 km of the coast at high spatial (1-6 km) and temporal resolution (hourly or higher). Cutting-edge remote sensing technologies are becoming a standard component for ocean observing systems, contributing to the paradigm shift towards ocean monitoring. In 2017 the Global HFR Network was recognized by the Joint Technical WMO-IOC Commission for Oceanography and Marine Meteorology (JCOMM) as an observing network of the Global Ocean Observing System (GOOS). In this paper we will discuss the development of the network as well as establishing goals for the future. The U.S. High Frequency Radar Network (HFRNet) has been in operation for over thirteen years, with radar data being ingested from 31 organizations including measurements from Canada and Mexico. HFRNet currently holds a collection from over 150 radar installations totaling millions of records of surface ocean velocity measurements. During the past 10 years in Europe, HFR networks have been showing steady growth with over 60 stations currently deployed and many in the planning stage. In Asia and Oceania countries, more than 110 radar stations are in operation. HFR technology can be found in a wide range of applications: for marine safety, oil spill response, tsunami warning, pollution assessment, coastal zone management, tracking environmental change, numerical model simulation of 3-dimensional circulation, and research to generate new understanding of coastal ocean dynamics, depending mainly on each country's coastal sea characteristics. These radar networks are examples of national inter-agency and inter-institutional partnerships for improving oceanographic research and operations. As global partnerships grow, these collaborations and improved data sharing enhances our ability to respond to regional, national, and global environmental and management issues.

The IMOS HF-Radar array in South Australia provides observations of the ocean waters south of Spencer Gulf. In addition to ocean surface currents, the data from this array can be processed to provide near-real time observations of wave statistics and wind direction. The Australian Bureau of Meteorology requires access to these observations for forecast modelling but currently only have a single Waverider buoy operating in South Australian waters at Cape du Couedic, south of Kangaroo Island, which provides no directional information. The HF-Radar array could potentially be used to augment the current operational observation systems used by the Bureau. In this paper we evaluate the performance of the HF-Radar system against observations from the Waverider buoy and an automatic weather station at Neptune Island and also compare the HF-Radar observations to a wave model based on the eSA-Marine forecast grid. The results suggest that upgrading the HF-Radar to provide near-real time wave and wind data would provide a new, independent source of environmental observations for the Bureau.

A review is given of the impact that HF radars are having on the management of coastal hazards. Maps of surface currents can be produced every 10–20 minutes which, in real time, improve navigation safety in restricted areas commonly found near ports and harbours. The time sequence of surface current maps enables Lagrangian tracking of small parcels of surface water, which enables hazard mitigation in managing suspended sediments in dredging, in emergency situations where flotsam and other drifting items need to be found, and in pollution control. The surface current measurement capability is used to assist tsunami warnings as shown by the phased-array data from Chile following the Great Tohoku Earthquake in 2011. The newly launched Tsunami Warning Center in Oman includes a network of phased-array HF radars to provide real-time tsunami monitoring. Wind direction maps can be used to locate the position of cold fronts in the open ocean and to monitor the timing and strength of sea-breeze fronts in key locations.

It is well established that HF radar systems located on the coast can measure surface currents from close to the coast to more than 100km offshore. They can also be used to simultaneously measure the ocean wave directional spectrum. Thus current and wave power and other parameters relevant to the development of marine renewables can be measured. Wave measurements in the Celtic Sea using a Pisces HF radar system in 2003–2005 are presented. Good agreement with buoy data is demonstrated. The data are used to show that the wave power resource is variable in season, location and in direction with higher powers observed in Autumn but more directional variability in Winter.

International audience; High Frequency Radar (HFR) is a land-based remote sensing instrument offering a unique insight to coastal ocean variability, by providing synoptic, high frequency and high resolution data at the ocean atmosphere interface. HFRs have become invaluable tools in the field of operational oceanography for measuring surface currents, waves and winds, with direct applications in different sectors and an unprecedented potential for the integrated management of the coastal zone. In Europe, the number of HFR networks has been showing a significant growth over the past 10 years, with over 50 HFRs currently deployed and a number in the planning stage. There is also a growing literature concerning the use of this technology in research and operational oceanography. A big effort is made in Europe toward a coordinated development of coastal HFR technology and its products within the framework of different European and international initiatives. One recent initiative has been to make an up-to-date inventory of the existing HFR operational systems in Europe, describing the characteristics of the systems, their operational products and applications. This paper offers a comprehensive review on the present status of European HFR network, and discusses the next steps toward the integration of HFR platforms as operational components of the European Ocean Observing System, designed to align and integrate Europe’s ocean observing capacity for a truly integrated end-to-end observing system for the European coasts.

High frequency (HF) surface wave radar (HFSWR) has been demonstrated, in many experiments and papers, to be a powerful tool for sea-state detection. However, the availability and accuracy of the HFSWR measurements are limited by various unwanted clutter and interferences (collectively called ‘noise’) that contaminate the radar received signals, especially for wave estimation. This study extends the image recognition, segmentation and subspace projection method for removing the radio frequency interference developed in the previous study, to the mitigation of more general types of noise. Applications of this generalised method are presented. The results show that the noise can be largely removed regardless of their correlation in Doppler or range, their size in the range-Doppler domain and whether they are homogeneous or inhomogeneous. The effectiveness of all these approaches is validated by using data obtained with the Pisces HF radar, which is a high-performance radar developed for long-range wave measurement, operating in the lower half of the HF band (5–10-MHz).

In this study the assimilation of HF radar data into a high resolution, coastal Wavewatch III model is investigated. An optimal interpolation scheme is used to assimilate the data and the design of a background error covariance matrix which reflects the local conditions and difficulties associated with a coastal domain is discussed. Two assimilation schemes are trialled; a scheme which assimilates mean parameters from the HF radar data and a scheme which assimilates partitioned spectral HF radar data. This study demonstrates the feasibility of assimilating partitioned wave data into a coastal domain. The results show that the assimilation schemes provide satisfactory improvements to significant wave heights but more mixed results for mean periods. The best improvements are seen during a stormy period with turning winds. During this period the model is deficient at capturing the change in wave directions and the peak in the waveheights, while the high sea state ensures good quality HF radar data for assimilation. The study also suggests that there are both physical and practical advantages to assimilating partitioned wave data compared to assimilating mean parameters for the whole spectrum.

HF radar data are often collected for time periods that are optimized for current measurement applications where, in many cases, very high temporal resolution is needed. Previous work has demonstrated that this does not provide sufficient averaging for robust wave measurements to be made. It was shown that improvements could be made by averaging the radar data for longer time periods. HF radar provides measurements over space as well as in time, so there is also the possibility to average in space. However, the radar data are correlated in space because of the range and azimuth processing. The implications of this are discussed and estimates of the impact on the reduction in variance in the radar Doppler spectral estimates are obtained. Spatial inhomogeneities and temporal nonstationarity in the ocean wave field itself also need to be taken into account. It is suggested that temporal averaging over periods of up to one hour and spatial averaging over 9–25 nearest neighbors may be suitable, and these will be explored in later work.

More than 110 radar stations are in operation at the present time in Asia and Oceania countries, which is nearly half of all the existing radar stations in the world, for purposes related to marine safety, oil spill response, tsunami warning, coastal zone management and understanding of ocean current dynamics, depending mainly on each country’s coastal sea characteristics. This paper introduces the oceanographic radar networks of Australia, China, Japan, Korea and Taiwan, presented at the 1st Ocean Radar Conference for Asia (ORCA) held in May 2012, Seoul, Korea, to share information about the radar network developments and operations, knowledge and experiences of data management, and research activity and application of the radar-derived data of neighbouring countries. We hope this overview paper may contribute as the first step to promotion of regional collaborations in the radar observations and data usages and applications in order to efficiently monitor the coastal and marginal sea waters along the western Pacific Ocean periphery.

The accuracy of wave direction and spreading at the Bragg-matched wavelength measured with HF radar over a wide range of HF operating frequencies is demonstrated by comparison with buoy data. The agreement for shortwave direction is better than that obtained for wind direction, which has been the more common application of this measurement, because these waves are not always aligned with the wind direction, particularly in short fetch and low wind speed situations. The method assumes a model of shortwave directionality and the validity of this is explored by using the buoy Fourier coefficients, with inconclusive results. The radar measurements do not use the linear dispersion relationship, but the comparison with buoy data does, and the implications of this are discussed.

HF radar wave measurements are presented focussing on theoretical limitations, and thus radar operating parameters, and quality control requirements to ensure robust measurements across a range of sea states. Data from three radar deployments, off the west coast of Norway, Celtic Sea and Liverpool Bay using two different radar systems, WERA and Pisces, and different radio frequency ranges, are used to demonstrate the wave measurement capability of HF radar and to illustrate the points made. Aspects of the measurements that require further improvements are identified. These include modifications to the underlying theory particularly in high sea states, identification and removal of ships and interference from the radar signals before wave processing and/or intelligent partitioning to remove these from the wave spectrum. The need to match the radio frequency to the expected wave peak frequency and waveheight range, with lower radio frequencies performing better at higher waveheights and lower peak frequencies and vice versa, is demonstrated. For operations across a wide range of oceanographic conditions a radar able to operate at more than one frequency is recommended for robust wave measurement. Careful quality control is needed to ensure accurate wave measurements. (C) 2010 Elsevier B.V. All rights reserved.

Data assimilation is a method used for optimally combining information to improve forecasting and model parameters. Three data assimilation algorithms are investigated and used for assimilating HF radar data into the SWAN wave model. The schemes under consideration are the Ensemble Kalman Filter, Ensemble Optimal Interpolation and a Three-Dimensional Variational scheme. Two approaches for updating the ocean wave spectrum are considered which consist of describing the spectrum using integral wave parameters of the whole spectrum and wave parameters within various frequency bands. The results show improvement in the wave parameters at the buoy location for the 3DVAR and ENS-OI scheme. The EnKF only shows good performance in one of the considered runs which leads to a conclusion that the methods used for calculating the errors for the EnKF scheme need further analysis.

Averaging is required for the measurement of ocean surface wave spectra and parameters with any measurement system in order to reduce the variance in the estimates. Sampling theory for buoy measurements is well known. The same theory can be applied to the impact of sampling on the estimation of high-frequency (HF) radar power spectra from which wave measurements are derived. Some work on the impacts on the HF radar wave measurements themselves is reviewed and applied to datasets obtained with three different radar systems, operating at different radio frequencies in different geographical locations. Comparisons with collocated buoy measurements are presented showing qualitative agreement with the sampling impact predictions but indicating that there are more sources of differences than can be explained by sampling. Increased averaging is applied to two of these datasets to demonstrate the improvement in data quality and quantity that can be obtained.

The high-quality backscattered spectra provided by the WERA HF radar systems in the Wave Hub area are used to estimate different wave parameters at the location of a wave buoy. The HF radar estimations are done using three different wave estimation algorithms: the standard WERA software, the software provided by Actimar and the software provided by Seaview Sensing. The data obtained with each methodology is validated against the data measured from an in situ instrument followed by a discussion to compare results obtained from each methodology and identify strengths and limitations. In general, all three methodologies provided good estimations of wave parameters. Differences between methods are found mostly in the data availability which is attributed to the type of method and to the quality criterion thresholds. From all wave parameters compared, estimation of significant wave height provides the best combination of data quality and availability.

HF radar current measurements systems are in widespread use around the world providing very useful data sets for many applications. Data quality is generally good although sometimes the data are noisy especially at the edges of the spatial coverage. New approaches to the quality control of these measurements to remove noisy results or replace them with more reliable estimates, for both direction-finding and phased-array systems, are discussed here and some encouraging results are presented.

The Australian Coastal Ocean Radar Network (ACORN) is a facility of the Australian Integrated Marine Observing System (IMOS). It is one of a number of HF radar networks being developed worldwide for coastal ocean monitoring. HF radars can measure surface currents, waves, and winds, and the methods involved are summarized in this chapter. ACORN is described, and examples of the data products are presented together with some comments on their accuracy and availability. At the time of writing, only surface current data are provided through the IMOS portal in the form of files and maps that are used for scientific research, operational modeling, fisheries, and other applications. Wave measurements will also soon be available via the portal and are already being used for modeling applications.

This paper presents results of a trial of a Pisces HF radar system aimed at assessing its use as a component of a wave-monitoring network being installed around the coasts of England and Wales. The radar system has been operating since December 2003 and the trial continued to June 2005. The data have been processed in near-real time and displayed on a website. Radar measurements of the directional spectrum and derived parameters are compared with those measured with a directional waverider and with products from the Met Office, United Kingdom, operational wave model. Radar measurements of currents and winds are also compared with Met Office model products and, in the case of winds, with the QuikSCAT scatterometer. Statistics on data availability and accuracy are presented. The results demonstrate that useful availability and accuracy in wave and wind parameters are obtained above a waveheight threshold of 2 m and at ranges up to 120 km at the radar operating frequencies (7-10 MHz) used. Waveheight measurements above about 1 m can be made with reasonable accuracy (e.g., mean difference of 2.5% during January-February 2004). Period and direction parameters in low seas are often contaminated by noise in the radar signal. The comparisons provide some evidence of wave model limitations in offshore wind and swell conditions

High-frequency (HF) radar systems are remote sensing tools that can be used to measure oceanographic parameters. Problems can occur when using the conventional periodogram (PG) method for computing power spectral estimates from backscattered radar signals. Temporal and spatial inhomogeneities within the radar measurement region can cause distortion in the spectra. This paper describes an instantaneous-frequency (IF) filtering technique that has been developed to measure the first-order modulation contained within the radar signal. Successful removal of this modulation is shown to yield an increased quality and quantity of ocean measurements

The Barrick–Weber equations describe the interaction of radar signals with the dynamic ocean surface, and so provide a mathematical basis for oceanic remote sensing. This report considers the inversion of these equations with several of the row-action methods commonly used to solve large linear systems with unstructured sparsity. It is found that the performance of the methods in inverting both synthetic and measured Doppler spectral data is comparable, with the method of Chahine–Twomey–Wyatt offering a slight advantage in the reliability of the recovery of the full directional wave spectrum and of parameters derived from its integration. Some remarks and open questions on the ill-posedness of the inversion problem conclude the paper.

Ocean Surface Current Radar (OSCR) HF radar measurements of ocean waves and currents were made during the Shoaling Waves Experiment (SHOWEX) in the fall of 1999. During some periods, at some locations, good quality wave measurements were obtained. Limitations in the wave measurement capability due to OSCR hardware, deployment configuration, signal-to-noise ratio, and antenna sidelobes are identified and discussed. A short period of large currents in the presence of antenna pattern distortion is identified as the source of the main errors in the wave measurements.

A Bayesian method for estimating directional wave spectra from the Doppler spectra obtained by HF radar is examined using data acquired during the SCAWVEX project. Applicability, validity and accur...

This article suggests a linear functional relationship model for comparing two sets of circular data subject to unobservable errors. Unlike the corresponding and relatively well-studied model for linear data, maximum likelihood estimation for this model is very complicated and no explicit solutions are possible. Using a numerical approximation, we are able to solve the likelihood equations approximately, and to obtain good approximations to the likelihood estimates of the parameters. The quality of our estimates and the feasibility of the estimation method are illustrated via simulation. By establishing a parallel with the model for linear data, we are able to explain the various problems occurring in the process of estimation and to substantiate our numerical results. The interest in the model arose in connection with the study of ocean wave data; an application to such data is also given.

The objective of the EuroROSE (European Radar Ocean Sensing) project was to combine area covering ground-based remote-sensed wave and current data with high-resolution numerical forecast models to provide nowcasts and forecasts for coastal marine operators. Two experiments to test and to demonstrate the system took place: one on the coast of Norway, north of Bergen in March 2000 and the second on the north coast of Spain at Gijon in October–November 2000. Qualitative and quantitative intercomparisons of the wave measurements and wave model products from these experiments are presented. These include measurements using the Wellen Radar (WERA) high-frequency (HF) radar, the WaMoS (Wave Monitoring System) X-band radar, a directional Waverider and output from the WAM wave model. Comparisons are made of the full directional spectra and of various derived parameters. This is the first-ever intercomparison between HF and X-band radar wave measurements and between either of these and WAM. It has provided a data set covering a much wider range of storm and swell conditions than had been available previously for radar wave-measurement validation purposes and has clarified a number of limitations of the radars as well as providing a lot of very useful radar wave data for future model-validation applications. The intercomparison has led to improvements in the data quality control procedures of both WaMoS and WERA. The two radar sytems measured significant wave height with mean biases of 3% and 6%, respectively, and mean direction differences of less than 2° in both cases. Limitations in the WAM model implementation are also discussed.

The interpretation of high-frequency (HF) radar backscatter from the sea surface to provide measurements of waves, winds, and currents has been developing over the last 30 years. Dual radar systems are usually used because it is then possible to resolve direction and amplitude ambiguities in wave and wind measurement and provide full vector surface currents. In this paper the accuracy and limitations of wave measurements with single radar systems are explored using data sets obtained in a number of experiments using dual radar systems. It is shown that single radar estimates of significant wave height, mean wave period, and wind (or short wave) direction provide two alternative estimates, neither of which is as accurate as a dual radar estimate. Furthermore, there appears to be no way of selecting which of the single radar estimates is correct without bringing in additional information not provided by the radar itself. It is suggested that single radar systems could be used through assimilation of the dat...

This paper presents a first look at directional wave spectra measurements, and derived parameters, obtained using the Australian Coastal Ocean Radar Network WERA HF radar systems and the Seaview Sensing software package. Selected examples show that such measurements can be made and include bimodal and swell-dominated cases. Some issues limiting their availability and accuracy are discussed.

High-frequency (HF) radar systems are currently used to collect wave and current data. By applying the fast Fourier transform (FFT) method to the radar backscatter from the ocean surface, the Doppler spectrum is calculated, and from this the directional wave spectrum and wave parameter measurements are obtained. Because of the random nature of the ocean surface, spectral measurements are subject to random variability. To obtain stable estimates, each spectrum is calculated by averaging a number of FFT estimates. This method requires long data series, and problems may arise particularly in rapidly varying sea conditions. We consider the use of an alternative technique, the modified-covariance method, which can provide stable spectral estimates from short data sets. We show that the modified-covariance method with smaller data sets gives satisfactory results, comparable to those of the FFT method as usually applied, while the FFT method with smaller data sets performs poorly. Accurate wave parameter measurements are still obtained when the amount of data is reduced by a factor of four. The work suggests that an autoregressive model order of 30 and the use of 1500 data samples is sufficient for the accurate measurement of significant waveheight, mean period and wind direction.

The power spectrum of backscatter from the ocean surface at HF radio frequencies is characterized by two large peaks called the first-order Bragg peaks. These are surrounded by a continuum due to second-order effects. The power spectrum can be described in low to moderate sea states by a nonlinear integral equation relating it to the ocean wave directional spectrum. Inverting this equation provides an estimate of the directional spectrum. A number of inversion methods have been published. In this paper, the Wyatt method is discussed. This method uses the part of the backscatter power spectrum that surrounds the larger Bragg peak. An extension of the method to include the spectrum around the weaker peak is discussed, and some improvements in the solution are demonstrated. Until recently, all published work in this area concerned solutions to a linearized version of the equation. The second extension presented here tackles the nonlinear problem but points out the limitations of the approach and sho...

The spatial coverage, temporal availability and spectral and parameter accuracy of wave measurements using radars operating at the upper end of the high frequency (HF) radio band are discussed. The two radars used are the Ocean Surface Current Radar (OSCR) developed in the UK and the Wellen Radar (WERA) developed in Germany. The measurements show that useful accuracy is obtainable with very good potential for operational coastal monitoring. Direction biases over most of the frequency range are less than 15°. The relative bias in significant waveheight estimation in high sea-states is within ±5%. Although there is some deterioration in spectral performance in high sea-states, this is primarily confined to amplitudes at the higher ocean wave frequencies where a modelling approach could be adopted. Gaps in spatial and temporal coverage and some reduction in accuracy in mean direction estimation are due to surface current variability or antenna sidelobes.

The paper reviews methods for quality assessment and intercomparison of ocean wave data. The sampling variability for conventional time series recordings is summarized and compared to less common area measuring measurements. The sampling variability affects the scatter seen in simultaneous observations, and variability in excess of the sampling variability signifies real differences between the instruments. Various means of intercomparing wave parameters and spectra are discussed and two somewhat unconventional ways of deriving regression and calibration relationships are also shown. The methods are illustrated using data from SCAWVEX, focusing mainly on wave data from the HF radars and Directional Waveriders.

Recent developments in the measurement of directional wave spectra using high-frequency (HF) radar have shown its ability to resolve multimodal wave spectra. Such spectra contain information about the different swell and wind–sea systems contributing to the ocean wave field. This paper presents the results of work to automatically segment multimodal wave spectra into the individual modes present. It describes how this is achieved by using sampled wave spectra and simple set theoretic transforms from mathematical morphology. By concentrating upon these simple transforms for regular sampling sets, the authors show that the same approach can be taken for wave spectra sampled with a nonuniformly distributed sampling set. This is particularly useful for spectra measured using HF radar since the inversion method used in their extraction yield spectra sampled onto a nonuniform sampling set. Results of this analysis are presented.

The maximum-likelihood method is used to extract parameters of two-parameter models of the directional spreading of short wind waves from the power spectrum of high-frequency (HF) radar backscatter. The wind waves have a wavelength of half the radio wavelength that, for the data presented here, is at a frequency of 0.53 Hz. The parameters are short-wave direction, which at this frequency can be identified with wind direction, and the directional spread angle, the parameterization of which is model dependent. For the data presented here, the results suggest that the Donelan directional spreading model provides a better description of directional spreading than the coss model. The HF radar and wave buoy measurements are compared and show good agreement. Measurements are presented that show the temporal and spatial structure of the short-wave field responding to the passage of a frontal system.

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.

This paper presents a comparison of radial currents measured using a SeaSonde and a WERA HF radar on the West Coast of Australia. These radars are part of the Australian Coastal Ocean Radar Network which is a facility of the Australian Integrated Marine Observing system. Radial currents are the component of current along the radar look direction which is the measurement obtainable from an individual radar system. The two radars are sited 7km apart and the assumption is made that the radial currents from the two radars should be similar far enough away from these sites. The results, although preliminary, show that there is reasonable agreement at these distances. In addition the radial currents from both radars agree well with ADCP measurements at one of the ADCP sites. There is less agreement at the second ADCP site which is attributed to the more complex topography at that site.

OSCR is an HF radar system that has been developed for high spatial resolution coastal surface current measurement. This paper describes preliminary results that demonstrate that wave measurement can be successfully obtained from suitably processed OSCR data. Comparisons with data from a WAVEC directional buoy are presented and show encouraging agreement. Some of the limitations to the measurement process are discussed and indicate a maximum range of about 20 km. Surface current variability on short time scales presents the most serious obstacle to wave measurement. This appears to be more of a problem when the mean currents are large, in that in these circumstances the data fail initial quality control criteria. However, in lower mean currents, the effect is often still present and leads to errors in long wave measurement.

This paper describes measurements of the directional spectrum of storm waves obtained using the PISCES high-frequency radar. The storm occurred during the Netherlands UK Radar Wavebuoy Experimental Comparison 2 experiment in March 1987. Wind direction changes from southerly to northwesterly over a period of five hours led to a rapid change in short-wave direction but did not lead to changes in the mean direction of the long energetic wind waves. Wind waves generated in the changed wind direction are shown to be fetch limited, and the spectrum is shown to be dominated by long-fetch wind waves generated by the component of wind blowing from the southwest.

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.