Radio measurements of oceanic winds at long ranges: An evaluation

Stewart, Robert H.; Barnum, J.

doi:10.1029/rs010i010p00853

Cited by 92 publications

(27 citation statements)

References 5 publications

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“…Except for an early approach by Stewart and Barnum (1975) and the multi-frequency method by Vesecky et al (2005), wind speed derivation techniques to date are based on the analysis of the second-order sidebands. Dexter and Theodorides (1982) provided a method using wave height (H s ) and peak frequency (f p ) to estimate wind speed by relating these parameters to wind speeds required to generate waves with similar characteristics.…”

Section: Wind Speed and Direction Estimation From Hf Radarsmentioning

confidence: 99%

“…However, the use of the second-order signal suffers from reduced range coverage (when compared with the first-order signal) and also there might be parts of the ocean spectrum contributing to the second-order signal that are not related to local wind conditions (e.g., swell). Stewart and Barnum (1975) suggested wind speed derivation from the widening of the first-order Bragg peaks, but their approach using sky-wave HF radar data was found to be limited (cf. Green et al 2009).…”

Section: Introductionmentioning

confidence: 98%

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Wind-speed inversion from HF radar first-order backscatter signal

et al. 2011

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Land-based high-frequency (HF) radars have the unique capability of continuously monitoring ocean surface environments at ranges up to 200 km off the coast. They provide reliable data on ocean surface currents and under slightly stricter conditions can also give information on ocean waves. Although extraction of wind direction is possible, estimation of wind speed poses a challenge. Existing methods estimate wind speed indirectly from the radar derived ocean wave spectrum, which is estimated from the second-order sidebands of the radar Doppler spectrum. The latter is extracted at shorter ranges compared with the first-order signal, thus limiting the method to short distances. Given this limitation, we explore the possibility of deriving wind speed from radar first-order backscatter signal. Two new methods are developed and presented that explore the relationship between wind speed and wave generation at the Bragg frequency matching that of the radar. One of the methods utilizes the absolute energy level of the radar first-order peaks while the second method uses the directional spreading of the wind generated waves at the Bragg frequency. For both methods, artificial neural network analysis is performed to derive the interdependence of the relevant parameters with wind speed. The first method is suitable for application only at single locations where in situ data are available and the network has been trained for while the second method can also be used outside of the training location on any point within the radar coverage area. Both methods require two or more radar sites and information on the radio beam direction. The methods are verified with data collected in Fedje, Norway, and the Ligurian Sea, Italy using beam forming HF WEllen RAdar (WERA) systems operated at 27.68 and 12.5 MHz, respectively. The results show that application of either method requires wind speeds above a minimum value (lower limit). This limit is radar frequency dependent and is 2.5 and 4.0 m/s for 27.68 and 12.5 MHz, respectively. In addition, an upper limit is identified which is caused by wave energy saturation at the Bragg wave frequency. Estimation of this limit took place through an evaluation of a year long database of ocean spectra generated by a numerical model (third generation WAM). It was found to be at 9.0 and 11.0 m/s for 27.68 and 12.5 MHz, respectively. Above this saturation limit, conventional second-order methods have to be applied, which at this range of wind speed no longer suffer from low signal-to-noise ratios. For use in operational systems, a hybrid of first- and second-order methods is recommended

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Section: Wind Speed and Direction Estimation From Hf Radarsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 98%

Wind-speed inversion from HF radar first-order backscatter signal

et al. 2011

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“…The transmitted electromagnetic signal propagates along the conductive sea surface and is backscattered by the resonant ocean's surface gravity waves with exactly half the wavelength transmitted (Crombie 1955). Furthermore, a modulation of the signals scattered by ocean waves in response to the wind has been used to estimate wind direction and, in some cases, wind speed near the ocean surface (Long and Trizna 1973;Stewart and Barnum 1975;Shearman and Wyatt 1982;Shen et al 2012). These first-order Bragg lines are Doppler shifted (a fraction of a hertz above and below the transmitted signal) by Bragg resonant surface gravity waves and ocean currents propagating radially toward or away from the radar.…”

Section: Introductionmentioning

confidence: 99%

High-Frequency Radars: Beamforming Calibrations Using Ships as Reflectors*

Flores-Vidal

Flament

Durazo

et al. 2013

Journal of Atmospheric and Oceanic Technology

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Linear array antennas and beamforming techniques offer some advantages compared to direction finding using squared arrays. The azimuthal resolution depends on the number of antenna elements and their spacing. Assuming an ideal beam pattern and no amplitude taper across the aperture, 16 antennas in a linear array spaced at half the electromagnetic wavelength theoretically provide a beam resolution of 3.58 normal to the array, and up to twice that when the beam is steered within an azimuthal range of 608 from the direction normal to the array. However, miscalibrated phases among antenna elements, cables, and receivers (e.g., caused by service activities without recalibration) can cause errors in the beam-steering direction and distortions of the beam pattern, resulting in unreliable ocean surface current and wave estimations. The present work uses opportunistic ship echoes randomly received by oceanographic highfrequency radars to correct an unusual case of severe phase differences between receiver channels, leading to a dramatic improvement of the surface current patterns. The method proposed allows for simplified calibrations of phases to account for hardware-related changes without the need to conduct the regular calibration procedure and can be applied during postprocessing of datasets acquired with insufficient calibration.

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“…Long and Trizna (1973) used radar at Chesapeake Bay to map winds in the North Atlantic, and Stewart and Barnum (1975) evaluated the accuracy of that technique. Shearman and Wyatt (1982) describe the results of mapping winds during the JASIN experiment.…”

Section: Wind Measurementsmentioning

confidence: 99%

“…Phased-array radars have also been used to measure currents. Stewart and Joy (1974) used a multifrequency radar on San Clemente Island to measure the vertical current shear at two bearings. Ha (1979) used the multifrequency Stanford radar with a highly directional transmitting antenna to measure currents along its boresight and compared his measurements with drifting spar buoys.…”

Section: Current Measurementsmentioning

confidence: 99%