Wind Speed Dependence of Single-Site Wave-Height Retrievals from High-Frequency Radars

Haus, Brian K.; Shay, Lynn K.; Work, Paul A.; Voulgaris, George; Ramos, Roberto; Martinez-Pedraja, Jorge

doi:10.1175/2010jtecho730.1

Cited by 14 publications

(6 citation statements)

References 53 publications

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“…Also Wyatt (1986) and Wyatt et al (2006) have presented a method to invert Barrick et al's (1974) integral equation for the second-order cross section; it uses the measured second-order Doppler spectrum to estimate the ocean directional wave spectrum. More recently, Haus et al (2010) suggested a method to correct the bias in ocean wave height estimates from a single radar site introduced by the angle between the radio beam and wave direction.…”

Section: Wind Speed and Direction Estimation From Hf Radarsmentioning

confidence: 99%

“…HF radars can deliver real-time data at relatively high spatial resolutions (300-1500 m) and can be installed, operated, and maintained in all weather conditions at a reduced cost compared with satellite or in situ sensor technology. HF radars are used routinely to measure ocean surface currents (e.g., Barrick 1977b;Wyatt et al 2006;Parks et al 2009) , ocean wave spectra (e.g., Barrick 1977a, c;Wyatt 1986;Gurgel et al 2006;Haus et al 2010), and even wind direction (e.g., Heron and Rose 1986;Harlan and Georges 1994;Wyatt et al 2006). However, the measurement of wind speed still poses a challenge.…”

Section: Introductionmentioning

confidence: 99%

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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: 99%

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

et al. 2011

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“…Conventional validation studies of HF radar-derived waves are mainly based on comparison with fixed-point observations. This is because in situ devices have high precision and thus the evaluation results are generally reliable (Wyatt et al 1999(Wyatt et al , 2006Haus et al 2010;Long et al 2011;Lipa et al 2014;Atan et al 2016;Lorente et al 2018). However, an obvious limitation of this approach is that the comparison results are limited to only a few points (mostly in the sector of highprecision coverage) and they do not reflect the full spatial distribution of the accuracy of HF radarderived waves.…”

Section: Introductionmentioning

confidence: 99%

Assessment of Significant Wave Height in the Taiwan Strait Measured by a Single HF Radar System

Cai

Shang

Wei

et al. 2019

Journal of Atmospheric and Oceanic Technology

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Dual high-frequency (HF) radar systems are often used to provide measurements of waves, winds, and currents. In this study, the accuracy of wave measurements using a single HF radar system (OS081H-A) was explored using datasets obtained during 5–27 January 2014 in the southwestern Taiwan Strait. We selected the study region as an area with >90% coverage (i.e., the range was <100 km). Qualitative and quantitative intercomparison of wave measurements (by the radar and five buoys) and wave model products [from the Simulating Wave Nearshore (SWAN) model] were conducted. Intercomparison of the modeled and in situ significant wave height Hs showed that the model-predicted Hs could be considered to be acceptable for use as “sea truth” to evaluate the radar-derived Hs, with mean bias from −0.45 to −0.16 m, mean absolute error (MAE) of 0.24–0.45 m, and root-mean-square error of 0.31–0.54 m. It was found that the MAE of radar-derived Hs was ≤ 1 m for 86% of the sector (except at the edge of sector) when the model-predicted Hs was ≥ 1.5 m. In particular, the MAE was less than 0.6 m for 63% of the sector, which was mainly distributed in the area with a bearing from −50° to +70° and a range of 20–70 km. The results are promising, but more work is needed. We employed a spatial distribution function for the MAE of the radar-derived Hs over the sample duration based on range, bearing, and mean radar-derived Hs.

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“…20c) where again sites N5 and N6 indicate a high broadening of the spectrum. It has been shown that the second-order spectra at large radar beam directions (.458) from the boresight, can be inaccurate due to signal contamination by sidelobe interference (Haus et al 2010). The calibration sites N4 and O2 have the lowest radial beam angles (,408), while all other sites are expected to be more susceptible to sidelobe interference.…”

Section: B Inverted Bulk Wave Parametersmentioning

confidence: 99%

Swell and Wind Wave Inversion Using a Single Very High Frequency (VHF) Radar

Alattabi

Cahl

Voulgaris

2019

Journal of Atmospheric and Oceanic Technology

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A hybrid, empirical radar wave inversion technique that treats swell and wind waves separately is presented and evaluated using a single 48-MHz radar unit and in situ wave measurements. This hybrid approach greatly reduces errors in radar wave inversion during swell seas. Our analysis suggests that, prior to the inversion, the second-order spectrum should be normalized using Barrick’s weighting function because this process removes harmonic and corner reflection peaks from the inversion and improves the results. In addition, the resulting calibration constants for the wind wave component are not wave-frequency dependent and are similar in magnitude to those found in previous studies using different operating-frequency radars. This result suggests radar frequency independence, although additional experimental verification is required. The swell component of the model presented here ignores the effect of swell’s propagation direction on the radar signal. Although this approach has several limitations and may only be useful near the coast (where swell propagates close to perpendicular to the coastline), the resulting wave inversion is accurate even when swell is propagating close to perpendicular to the radar beam direction. RMS differences relative to in situ wave height measurements range from 0.16 to 0.25 m as the radar beam angle increases from 22° to 56°.

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Wind Speed Dependence of Single-Site Wave-Height Retrievals from High-Frequency Radars

Cited by 14 publications

References 53 publications

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

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

Assessment of Significant Wave Height in the Taiwan Strait Measured by a Single HF Radar System

Swell and Wind Wave Inversion Using a Single Very High Frequency (VHF) Radar

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