High-frequency Radar Measurements Research Articles

Determination of Mesoscale Surface Currents in Shallow-Water Regions According to the Data of High-Frequency Radar Measurements

We propose a new method for the evaluation of the velocities of surface currents according to the data of measurements carried out by using high-frequency land-based radars. The method is based on the representation of the velocity fields via two scalar potentials, expansion of these potentials in series in basis functions, and determination of the coefficients of expansion according to the data of radar measurements as solutions of the corresponding variational problems. The errors of the procedure of determination of the coefficients of expansion are removed by using a special regularization procedure based on information theory. The proposed method enables one to fill gaps in the space and time series of radar measurements. We illustrate the method by an example of numerical analysis of mesoscale and submesoscale (10–50 km) surface currents in the Monterey Bay (California, USA) performed on the basis of the data of radar measurements carried out in August 1994.

Validation and intercomparisons of wave measurements and models during the EuroROSE experiments

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.

Maximum-Likelihood Estimation of the Directional Distribution of 0.53-Hz Ocean Waves

Abstract 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.

Mapping Surface Currents in Monterey Bay With CODAR-Type HF Radar

HIGH-FREQUENCY (HF) radar measurements have been employed around Monterey Bay, CA, to measure ocean surface currents since February 1992. The first array consisted of two older-generation CODAR instruments located at sites near Monterey in the south and Moss Landing, halfway around the bay to the north (Front Cover: Fig. 1). In 1994, the southern site was replaced with a newer-generation SeaSonde system at Pt. Pinos and a similar unit was installed near Santa Cruz on the northern shore of Monterey Bay. Finally, in 1996, the CODAR system in Moss Landing was replaced by a modern SeaSonde unit. Several months time series of two-dimensional surface currents have been collected for Monterey Bay since the first CODAR units were installed. These data represent the most extensive measurements collected to date from compact, directionfinding HF radar systems (Barrick and Lipa, 1997: Paduan and Graber, 1997). Indeed, Monterey Bay is the only location where continuous HF radar measurements are underway. The geometry of the bay (a curving coastline with a radius of -20 km) is ideal for a multisite HF radar network. The overwater distance is close to the typical radar range and, when three or more shore locations are utilized, the entire region can be observed without lost coverage along the baseline between radar sites. This geometry also makes Monterey Bay well suited for validation and development of the algorithms for currents, waves, and wind direction because a large ocean region is oversampled. Not only can in situ measurements within this region be compared with the remotely sensed estimates, but self-consistency (or lack thereof) in the HF radar measurements can be used to characterize errors in the radar data (Melton, 1995).

Significant waveheight measurement with h.f. radar

Abstract High frequency radar measurements of significant waveheight during two experiments in the Celtic Sea are discussed. A new algorithm has been developed which can be used to provide measurements of significant waveheight with accuracies of about 12 per cent relative to wave-buoy measurements. A dual-radar system is required for this measurement. For use with a single-radar system, some additional information on the directional properties of the wave spectrum are required.

High frequency radar measurements of tidal currents flowing through San Pablo Strait, San Francisco Bay1

High frequency (HF) radar measurements of the surface current averaged over the upper 0.5 m in San Pablo Strait were compared with current meter measurements of the subsurface current made at 9.4 m below mean lower low water (MLLW) over two 12.4‐h tidal cycles. After averaging the radar and current meter data over two tidal cycles, a southerly (ebbing direction) surface current of 32 cm·s−1 was deduced from the radar measurements and a northerly (flooding direction) subsurface current of 7 cm·s−1 from the current meter measurements. This nontidal flow is maintained by freshwater discharge from the Sacramento–San Joaquin Rivers into Suisun and San Pablo Bays. The radar measurement technique provides quantitative estimates of the surface currents that previously were determined only from surface drifter studies.