Multi-directional wave spectra from marine X-band radar

Lund, Björn; Collins, Clarence O.; Tamura, Hitoshi; Graber, Hans C.

doi:10.1007/s10236-016-0961-z

Cited by 22 publications

(20 citation statements)

References 48 publications

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“…The vast majority of MR current retrieval studies in the literature performs a single current fit across all available ocean wave numbers, which is equivalent to assuming that the upper ocean current is constant with depth or that upper ocean vertical shear is negligible (e.g., Bell et al, 2012;Gangeskar, 2018;Hessner et al, 2019;Ludeno et al, 2016). In recent years, however, the wave number-dependent variability of the Doppler term in equation (1) has been recognized as a valuable proxy for upper ocean vertical current shear (e.g., Campana et al, 2016Campana et al, , 2017Lund et al, , 2016.…”

Section: Novel Approach: Narrow Wave Number Bandsmentioning

confidence: 99%

Marine X‐Band Radar Currents and Bathymetry: An Argument for a Wave Number‐Dependent Retrieval Method

et al. 2020

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This study evaluates shipboard marine X‐band radar (MR) near‐surface current and bathymetry measurements under shallow water conditions. The retrieval algorithm is based on the surface wave signal within three‐dimensional wave number frequency MR backscatter intensity variance spectra. The MR data were collected during a research cruise that investigated submesoscale processes and their impact on oil spill transport in the Louisiana Bight. The MR currents and bathymetry are validated using measurements from 500 GPS‐equipped surface drifters, a shipboard acoustic Doppler current profiler, and a shipboard single‐beam echo sounder. Earlier results from the same experiment but using a different set of sensors indicate strong upper ocean vertical current shear over a 3.5 hr period, despite only mild wind forcing. Here, the MR currents are derived as a function of wave number, providing a measure of vertical shear for the full duration of the cruise. Strong vertical shear is frequently observed, with a maximum difference of 0.42 m/s between the MR high (effective depth of ∼0.9 m) and low ( ∼2.4 m) wave number bins. Treating the drifter and echo sounder measurements as truth, the accuracies of the MR near‐surface currents and bathymetry are 0.04–0.07 m/s and 1.2 m (or 7% of the mean water depth). However, it is shown that ∼50% of the MR high wave number and drifter current differences is due to vertical shear. The shallow water MR near‐surface current accuracy thus matches findings from a previous deep water validation where vertical shear was much weaker.

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Section: Novel Approach: Narrow Wave Number Bandsmentioning

confidence: 99%

Marine X‐Band Radar Currents and Bathymetry: An Argument for a Wave Number‐Dependent Retrieval Method

et al. 2020

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“…In other words, we need to determine the frequency-wavenumber spectrum using spatiotemporal wave measurements. Such data can be extracted from, for example, marine radars (e.g., Lund et al, 2016) or stereo video footage (e.g., Leckler et al, 2015), and the latter technique has in later years led to studies of the directional frequency-wavenumber spectrum (Leckler et al, 2015;Peureux et al, 2018). Spatial and temporal wave data can also be acquired simultaneously using a large amount of wave staffs (Donelan et al, 1985).…”

Section: Introductionmentioning

confidence: 99%

A New Inverse Phase Speed Spectrum of Nonlinear Gravity Wind Waves

et al. 2019

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The rear face of the wave spectrum is described by an equilibrium and a saturation subrange. Although accurate information about these ranges are highly relevant for wave modeling and many practical applications, there have been inconsistencies between results originating from temporal and spatial measurements. These discrepancies have been explained by the Doppler shift and the harmonics of nonlinear waves. We present high‐frequency wave measurements from the Baltic Sea gathered with R/V Aranda using a wave staff array, which provided directional frequency‐wavenumber data. In addition to the traditional wavenumber and frequency spectra, F(k) and S(ω), we also define a new spectrum that is a function of the inverse phase speed. We denote this spectrum Q(ν), where ν=kω−1. The properties of this Q‐spectrum were studied using data from four different sites. A strongly forced fetch‐limited case showed an equilibrium‐to‐saturation transition in the Q‐spectrum, with less variations in the equilibrium constants compared to the frequency spectra. The transition to a saturation regime happened around Uν=3 in all spectra where an equilibrium range was identified. Most duration‐limited spectra had no equilibrium range in the inverse phase speed domain. The absence of an equilibrium range was consistent with the wavenumber domain, but the frequency spectra still showed an apparent equilibrium subrange extending to ωU/g=5. The consistency of the saturation ranges between the Q‐spectrum and the wavenumber spectrum indicate a weak Doppler shift effect. We deduced that the main factor distorting the frequency spectra was wave nonlinearities.

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“…In 2013, an effective method was proposed by Francesco et al to mitigate the aliasing problem in X-band marine data [22]. In 2016, Lund used WAVEWATCH-III (WW3) wave modeling results to help increase the strength of marine radar [23,24]. An advanced wave retrieval technique that accurately measured the multidirectional wave spectrum was introduced.…”

Section: Introductionmentioning

confidence: 99%

Wave Height and Wave Period Derived from a Shipboard Coherent S-Band Wave Radar in the South China Sea

Chen

Zhao

et al. 2019

Remote Sensing

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To expand the scope of ocean wave observations, a shipboard coherent S-band wave radar system was developed recently. The radar directly measures the wave orbital velocity from the Doppler shift of the received radar signal. The sources of this Doppler shift are analyzed. After removing the Doppler shifts caused by the ocean current and platform, the radial velocities of water particles of the surface gravity waves are retrieved. Subsequently, the wavenumber spectrum can be obtained based on linear wave theory. Later, the significant wave height and wave periods (including mean wave period and peak wave period) can be calculated from the wavenumber spectrum. This radar provides a calibration-free way to measure wave parameters and is a novel underway coherent microwave wave radar. From 9 September to 11 September, 2018, an experiment involving radar-derived and buoy-measured wave measurements was conducted in the South China Sea. The Doppler spectra obtained when the ship was in the state of navigation or mooring indicated that the quality of the radar echo was fairly good. The significant wave heights and wave periods measured using the radar are compared with those obtained from the wave buoy. The correlation coefficients of wave heights and mean wave periods between these two instruments both exceed 0.9 while the root mean square differences are respectively less than 0.15 m and 0.25 s, regardless of the state of motion of the ship. These results indicate that this radar has the capability to accurately measure ocean wave heights and wave periods.

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Multi-directional wave spectra from marine X-band radar

Cited by 22 publications

References 48 publications

Marine X‐Band Radar Currents and Bathymetry: An Argument for a Wave Number‐Dependent Retrieval Method

Marine X‐Band Radar Currents and Bathymetry: An Argument for a Wave Number‐Dependent Retrieval Method

A New Inverse Phase Speed Spectrum of Nonlinear Gravity Wind Waves

Wave Height and Wave Period Derived from a Shipboard Coherent S-Band Wave Radar in the South China Sea

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