An Observation of the Directional Wave Spectrum Evolution from Shoreline to Fully Developed

Walsh, Edward J.; Hancock, D. W.; Hines, D. E.; Swift, Robert N.; Scott, J. F.

doi:10.1175/1520-0485(1989)019<0670:aootdw>2.0.co;2

Cited by 70 publications

(48 citation statements)

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“…The SRA (and its predecessor, the surface contour radar (SCR), as well as the ATM (and its predecessor, the airborne oceanographic lidar (AOL)) use a direct ranging technique. By measuring the time of flight of the return signal from the air-water interface, the elevation topography of the ocean surface can be derived [Kenney et al, 1979; Hoge and Krabill, 1984;Walsh et al, 1985Walsh et al, , 1987Walsh et al, , 1989Parsons and Walsh, 1989].…”

Section: Remote Sensing By Radio and Optical Rangingsupporting

confidence: 67%

Airborne remote sensing applications to coastal wave research

Hwang¹,

Walsh²,

Krabill³

et al. 1998

J. Geophys. Res.

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Abstract. Airborne sensors provide effective coverage of a broad region and are suitable for large-scale experiments. In this paper, two scanning sensors that use the direct ranging technique to measure surface wave displacement are described. On a NASA P-3 aircraft the sensors can complete one run across a 100-km continental shelf in 17 min. A case study is presented using radar-measured, two-dimensional surface topography to derive wave damping due to bottom friction. The results are in good agreement with an analytical model based on a quadratic formulation of bottom shear stress. This study demonstrates that remote sensing measurements can be used for rapid characterization of surface waves on the continental shelf and in coastal regions. Examples illustrated in this paper include the derivation of wavenumber spectra and estimation of the dissipation rate of shoaling ocean swell. IntroductionOcean wave research has placed emphasis either on the deep ocean to develop global wave modeling techniques or on the coastal waters to study wave effects on processes such as nearshore circulation and beach erosion. In terms of comprehensive and nearly simultaneous in situ measurements at a sufficient number of locations the continental shelf between deep water and the surf zone has been largely left out so that a critical gap obviously exists. For studying waves in the littoral environment the area of coverage reaches from the edge of the continental slope to the coastline. Because of the large expanse of the continental shelf (the shelf width along the East Coast of the United States is of the order of 100 km) the application of remote sensing for studying wave propagation on the continental shelf is an attractive option. With an airspeed of the order of 100 m/s, airborne sensors can provide very efficient two-dimensional surface wave measurements over a large oceanic area. For example, a NASA P-3 aircraft can cross the continental shelf's 100-km width near Duck, North Carolina, within 1000 s. Such broad-range coverage is impossible to achieve with in situ sensors. In this paper, the application of airborne remote sensing using scanning radar and scanning lidar is discussed. Section 2 describes the measurement principles of these remote sensing techniques and the relevant resolution issues. Section 3 presents examples of applications using spatial remote sensing data to study wave propagation and related phenomena in the coastal region. The spatial remote sensing data from the scanning radar are used to derive Remote Sensing by Radio and Optical RangingThe data analyzed in this paper were collected from a NASA P-3 aircraft using a scanning radar altimeter (SRA) and an airborne topographic mapper (ATM, a scanning lidar system).

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Section: Remote Sensing By Radio and Optical Rangingsupporting

confidence: 67%

Airborne remote sensing applications to coastal wave research

Hwang¹,

Walsh²,

Krabill³

et al. 1998

J. Geophys. Res.

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“…The present case covers a large range of wave conditions, with 470 Ͻ X* Ͻ 8700, that complements the more developed waves 1100 Ͻ X* Ͻ 24 000 observed by Walsh et al (1989). Evolution of E* and f * p with X* (Fig.…”

Section: April 2007mentioning

confidence: 99%

“…Motivated by the analyses of Kahma and Calkoen (1992) and Walsh et al (1989), a first series of tests was performed to investigate the potential effect of wind direction errors and evaluate air-sea stability parameterizations. The WW3 model was thus run with uniform and steady wind fields with U 10 ϭ 9.43 m s Ϫ1 and three wind directions ( * u ϭ 0°, which is offshore, 20°, and 30°).…”

Section: Model Hindcasts a Preliminary Test Of Air-sea Stability Andmentioning

confidence: 99%

“…Yet, the balance of processes that lead to the observed spectral shapes is still poorly understood. Walsh et al (1989) also discussed wave growth in a slanting fetch using spectra obtained from a surface contour radar. They showed that the slanting fetch effect contributed to the scatter in previous wave growth observations that include shore-oblique wind angles as large as 20°(e.g., Kahma 1981) or 30° (Hasselmann et al 1973).…”

Section: Introductionmentioning

confidence: 99%

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Swell and Slanting-Fetch Effects on Wind Wave Growth

Ardhuin

Herbers

Vledder

et al. 2007

Journal of Physical Oceanography

119

103

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Wind-sea generation was observed during two experiments off the coast of North Carolina. One event with offshore winds of 9-11 m s Ϫ1 directed 20°from shore normal was observed with eight directional stations recording simultaneously and spanning a fetch from 4 to 83 km. An opposing swell of 1-m height and 10-s period was also present. The wind-sea part of the wave spectrum conforms to established growth curves for significant wave height and peak period, except at inner-shelf stations where a large alongshore wind-sea component was observed. At these short fetches, the mean wave direction m was observed to change abruptly across the wind-sea spectral peak, from alongshore at lower frequencies to downwind at higher frequencies. Waves from another event with offshore winds of 6-14 m s Ϫ1 directed 20°-30°from shore normal were observed with two instrument arrays. A significant amount of low-frequency wave energy was observed to propagate alongshore from the region where the wind was strongest. These measurements are used to assess the performance of some widely used parameterizations in wave models. The modeled transition of m across the wind-sea spectrum is smoother than that in the observations and is reproduced very differently by different parameterizations, giving insights into the appropriate level of dissipation. Calculations with the full Boltzmann integral of quartet wave-wave interactions reveal that the discrete interaction approximation parameterization for these interactions is reasonably accurate at the peak of the wind sea but overpredicts the directional spread at high frequencies. This error is well compensated by parameterizations of the wind input source term that have a narrow directional distribution. Observations also highlight deficiencies in some parameterizations of wave dissipation processes in mixed swell-wind-sea conditions.

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“…Cox and Munk (1954) used sun glitter to observe oceanic wave patterns. With developments of radar, laser, and acoustic technology, directional wave spectra have been derived in various field experiments, which demonstrate the ability to map wave fields for an area (Beal et al 1986;Walsh et al 1985Walsh et al , 1989Krogstad et al 1988;Trevorrow and Booth 1995;Wyatt 1995;Hwang 1995;Frasier et al 1995;Hwang et al 2000a,b,c).…”

Section: Introductionmentioning

confidence: 99%

Measurement of Directional Wave Spectra Using Aircraft Laser Altimeters

Sun

Burns

Vandemark

et al. 2005

Journal of Atmospheric and Oceanic Technology

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A remote sensing method to measure directional oceanic surface waves by three laser altimeters on the NOAA LongEZ aircraft is investigated. To examine feasibility and sensitivity of the wavelet analysis method to various waves, aircraft motions, and aircraft flight directions relative to wave propagation directions, idealized surface waves are simulated from various idealized aircraft flights. In addition, the wavelet analysis method is also applied to two cases from field measurements, and the results are compared with traditional wave spectra from buoys. Since the wavelet analysis method relies on the "wave slopes" measured through phase differences between the time series of the laser distances between the aircraft and sea surface at spatially separated locations, the resolved directional wavenumber and wave propagation direction are not affected by aircraft motions if the resolved frequencies of the aircraft motion and the wave are not the same. However, the encounter wave frequency, which is directly resolved using the laser measurement from the moving aircraft, is affected by the Doppler shift due to aircraft motion relative to wave propagations. The wavelet analysis method could fail if the aircraft flies in the direction such that the aircraft speed along the wave propagation direction is the same as the wave phase speed (i.e., the aircraft flies along wave crests or troughs) or if two waves with different wavelengths and phase speed have the same encountered wavelength from the aircraft. In addition, the data noise due to laser measurement uncertainty or natural isotropic surface elevation perturbations can also affect the relative phase difference between the laser distance measurements, which in turn affects the accuracy of the resolved wavenumber and wave propagation direction. The smallest waves measured by the lasers depend on laser sampling rate and horizontal distances between the lasers (for the LongEZ this is 2 m). The resolved wave direction and wavenumber at the peak wave from the two field experiments compared well with on-site buoy observations. Overall, the study demonstrates that three spatially separated laser altimeters on moving platforms can be utilized to resolve two-dimensional wave spectra.

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An Observation of the Directional Wave Spectrum Evolution from Shoreline to Fully Developed

Cited by 70 publications

References 0 publications

Airborne remote sensing applications to coastal wave research

Airborne remote sensing applications to coastal wave research

Swell and Slanting-Fetch Effects on Wind Wave Growth

Measurement of Directional Wave Spectra Using Aircraft Laser Altimeters

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