Measured changes in ocean surface roughness due to atmospheric boundary layer rolls

Vandemark, D.; Pd, Mourad; Bailey, Sa; Crawford, Timothy L.; Vogel, Christoph; Sun, Jielun; Chapron, Bertrand

doi:10.1029/1999jc000051

Cited by 29 publications

(34 citation statements)

References 23 publications

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“…It is well known that these areas are also characterized by strong boundary currents (Gulf Stream, Kuroshio, Agulhas ...) with warm waters that is generally conducive to wave amplification and faster wind-wave growth (e.g. Vandemark et al 2001). Neither effect is included in the present calculation because the accuracy of both modelled surface currents and air-sea stability parameterizations are likely to be insufficient (Collard et al 2008;Ardhuin et al 2007).…”

Section: A Global Scale Resultsmentioning

confidence: 99%

Semiempirical Dissipation Source Functions for Ocean Waves. Part I: Definition, Calibration, and Validation

Ardhuin

Rogers

Babanin

et al. 2010

Journal of Physical Oceanography

781

681

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New parameterizations for the spectral dissipation of wind-generated waves are proposed. The rates of dissipation have no predetermined spectral shapes and are functions of the wave spectrum, in a way consistent with observation of wave breaking and swell dissipation properties. Namely, swell dissipation is nonlinear and proportional to the swell steepness, and wave breaking only affects spectral components such that the non-dimensional spectrum exceeds the threshold at which waves are observed to start breaking. An additional source of short wave dissipation due to long wave breaking is introduced, together with a reduction of wind-wave generation term for short waves, otherwise taken from Janssen (J. Phys. Oceanogr. 1991). These parameterizations are combined and calibrated with the Discrete Interaction Approximation of Hasselmann et al. (J. Phys. Oceangr. 1985) for the nonlinear interactions. Parameters are adjusted to reproduce observed shapes of directional wave spectra, and the variability of spectral moments with wind speed and wave height. The wave energy balance is verified in a wide range of conditions and scales, from the global ocean to coastal settings. Wave height, peak and mean periods, and spectral data are validated using in situ and remote sensing data. Some systematic defects are still present, but the parameterizations probably yield the most accurate overall estimate of wave parameters to date. Perspectives for further improvement are also given.

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Section: A Global Scale Resultsmentioning

confidence: 99%

Semiempirical Dissipation Source Functions for Ocean Waves. Part I: Definition, Calibration, and Validation

Ardhuin

Rogers

Babanin

et al. 2010

Journal of Physical Oceanography

781

681

View full text Add to dashboard Cite

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“…Figure 5 shows the locations of three contiguous segments of processed Q240 data blocks, and two contiguous segments of processed Q560 data blocks, located in the surf zone adjacent to the mouth of the Murray River. Because of the dihedral angle of the wings, there is not complete overlap of the Q240 and Q560 footprints, as seen in Figure 5 (segments [3][4][5]. In this Section, we show a comparison of sea surface topography and wave profiles obtained from Q240 and Q560 data.…”

Section: Mouth Of Murray River Regionmentioning

confidence: 99%

Demonstration of Two Portable Scanning LiDAR Systems Flown at Low-Altitude for Investigating Coastal Sea Surface Topography

2011

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Abstract:We demonstrate the efficacy of a commercial portable 2D laser scanner (operating at a wavelength close to 1,000 nm) deployed from a fixed-wing aircraft for measuring the sea surface topography and wave profiles over coastal waters. The LiDAR instrumentation enabled simultaneous measurements of the 2D laser scanner with two independent inertial navigation units, and also simultaneous measurements with a more advanced 2D laser scanner (operating at a wavelength near 1,500 nm). The latter scanner is used routinely for accurately measuring terrestrial topography and was used as a benchmark in this study. We present examples of sea surface topography and wave profiles based on low altitude surveys (< ~300 m) over coastal waters in the vicinity of Cape de Couedic, Kangaroo Island, South Australia and over the surf zone adjacent to the mouth of the Murray River, South Australia. Relative wave heights in the former survey are shown to be consistent with relative wave heights observed from a waverider buoy located near Cape de Couedic during the LiDAR survey. The sea surface topography of waves in the surf zone was successfully mapped with both laser scanners resolving relative wave height variations and fine structure of the sea surface to within approximately 10 cm. A topographic map of the sea surface referenced to the airborne sensor frame transforms to an accurate altimetry map which may be used with airborne electromagnetic instrumentation to provide an averaged altimetry covering a portion of the larger electromagnetic footprint. This averaged altimetry is deemed to be significantly more reliable as a measurement of OPEN ACCESS Remote Sens. 2011, 3 1984 altimetry than spot measurements using a nadir-looking laser altimeter and would therefore improve upon the use of airborne electromagnetic methods for bathymetric mapping in surf-zone waters. The aperture range of the scanner does not necessarily determine the swath. We observed that instead, the maximum swath at a given altitude was limited by the angle of incidence of the laser at the water surface.

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“…The LongEZ is a small pusher propeller aircraft specially instrumented for researching atmospheric turbulence and surface characteristics (French et al 2000;Crescenti et al 2002). The LongEZ participated in numerous field experiments, including air-sea and air-land exchange experiments (Crawford et al 1993;Dobosy et al 1997;Brooks et al 1997;Vogel and Crawford 1999;Crescenti et al 1999;Mourad et al 2000;Vandemark et al 2001;Sun et al 2001). Its ability to measure atmospheric turbulence has been tested in various field experiments in comparison with other flux aircraft (Crawford and Dobosy 1992;Dobosy et al 1997;Hacker and Crawford 1999;MacPherson et al 1999).…”

Section: Directional Wave Spectra From Field Measurements a Laser Inmentioning

confidence: 99%

“…If all 38 or 13 laser pulses fail to pass the threshold, the reflected laser power strength collected from the photodiode receiver is zero. The three lasers on board the LongEZ were tested by Hall et al (2000) and Vandemark et al (2001) in a laboratory. They found that each laser beam intersects the sea surface with a surface area of about 0.035 m (along-flight track) ϫ 0.06 m (cross-flight track) when the aircraft flies at a height of 12.5 m. They also found that the probability of obtaining a laser return over a smooth surface is small since it depends on the chance of having a surface within the small footprint of the laser beam to be oriented perpendicular to the laser beam.…”

Section: Directional Wave Spectra From Field Measurements a Laser Inmentioning

confidence: 99%

“…The National Oceanic and Atmospheric Administration (NOAA) LongEZ research aircraft Crescenti et al 2002) was equipped with three laser altimeters for measurements of surface elevation, in addition to its traditional atmospheric turbulence measurements during the Shoaling Waves Experiment (SHOWEX) and the Coupled Boundary Layer Air-Sea Transfer experiment under weak winds (CBLAST-Low). The data from the three laser altimeters on the LongEZ have been utilized to calculate mean square slopes of long waves in Sun et al (2001) and Vandemark et al (2001). The ability to simultaneously measure atmospheric turbulence and surface waves demonstrated by the LongEZ during SHOWEX provides a desirable platform to investigate air-sea interactions over large areas, especially with spatially varying wave fields.…”

Section: Introductionmentioning

confidence: 99%

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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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Measured changes in ocean surface roughness due to atmospheric boundary layer rolls

Cited by 29 publications

References 23 publications

Semiempirical Dissipation Source Functions for Ocean Waves. Part I: Definition, Calibration, and Validation

Semiempirical Dissipation Source Functions for Ocean Waves. Part I: Definition, Calibration, and Validation

Demonstration of Two Portable Scanning LiDAR Systems Flown at Low-Altitude for Investigating Coastal Sea Surface Topography

Measurement of Directional Wave Spectra Using Aircraft Laser Altimeters

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