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  • OCEANOGRAPHY  (13)
  • 1
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    A case study of wave-current interaction near an oceanic front (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: High resolution directional wave spectrum data were obtained from two NASA airborne radars during the Frontal Air-Sea Interaction Experiment in February 1986. The observations show a significant change in the wave number spectrum across the front. On the basis of surveys from a towed sensor and on satellite imagery, the front location and current field are estimated. A numerical model is developed for the wave-current interaction and is used to model the wave refraction across the frontal current. A parametric study is performed to demonstrate the effects of current meandering. The main consequence of meandering is the formation of caustics and shadow zone regions in which the wave energy is significantly enhanced or reduced. Spectral simulation along the aircraft track reveals a reduction of more that 60 percent in wave energy in the shadow zone; this is consistent with the observations.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 94; 16189-16
    Format: text
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  • 2
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    Aircraft and satellite measurement of ocean wave directional spectra using scanning-beam microwave radars (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A microwave radar technique for remotely measuring the vector wave number spectrum of the ocean surface is described. The technique which employs short-pulse, noncoherent radars in a conical scan mode near vertical incidence, is shown to be suitable for both aircraft and satellite application, the technique was validated at 10 km aircraft altitude, where we have found excellent agreement between buoy and radar-inferred absolute wave height spectra.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 987-1004
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  • 3
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    A comparison of SIR-B directional ocean wave spectra with aircraft scanning radar spectra (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Directional ocean wave spectra derived from Shuttle Imaging Radar-B (SIR-B) L-band imagery collected off the coast of Southern Chile on 11 and 12 October 1984 were compared with independent spectral estimates from two airborne scanning radars. In sea states with significant wave heights ranging from 3 to 5 meters, the SIR-B-derived sspectra at 18 deg and 25 deg off nadir yielded reasonable estimates of wavelengths, directions, and spectral shapes for all wave systems encountered, including a purely azimuth-traveling system. A SIR-B image intensity variance spectrum containing predominantly range-traveling waves closely resembles an independent aircraft estimate of the slope variance spectrum. The prediction of a U.S. Navy global spectral ocean wave model on 11 October 1984 exhibited no significant bias in dominant wave number but contained a directional bias of about 30 deg with respect to the mean of the aircraft and spacecraft estimates.
    Keywords: OCEANOGRAPHY
    Type: Science (ISSN 0036-8075); 232; 1531-153
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  • 4
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    ROWS estimates of wave height, wind speed, and directional wave spectra for SIR-B underflights off Chile, October 11 and 12, 1984 (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An account is given of the successful operation of the Goddard Ku-band Radar Ocean Wave Spectrometer (ROWS) on four out of five of the NASA Wallops' P-3 underflights of the Shuttle Imaging Radar-B (SIR-B) off the coast of southern Chile during the period of October 7-12, 1984. ROWS provided surface wind speed, wave height, and directional wave height spectrum estimates from the instrument's nadir altimeter mode and off-nadir spectrometer mode. ROWS estimates of the directional spectra of 300-400-m wavelength swell-dominated 3-5 m seas on October 11 and 12 are presented and compared to SCR (Surface Contour Radar), SIR-B, and Navy GSOWM spectra. Good agreement is found with SCR height spectra for the 12th (when the SCR was operable). Also, surprisingly good agreement is found between ROWS slope spectra and SIR-B image spectra for both the 11th and 12th for both swell and local wind-sea components. ROWS altimeter mode estimates of maximum winds of about 10 m/s on the 11th and 12th are seen to be consistent with the ROWS spectrometer mode observed local wind-sea peak frequencies of about 0.12-0.14 Hz.
    Keywords: OCEANOGRAPHY
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  • 5
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    A comparison of in situ and airborne radar observations of ocean wave directionality (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The directional spectrum of a fully arisen, about 3 m sea as measured by an experimental airborne radar, the NASA K(u)-band radar ocean wave spectrometer (ROWS), is compared to reference pitch-roll buoy data and to the classical SWOP (stereo wave observations project) spectrum for fully developed conditions. The ROWS spectrum, inferred indirectly from backscattered power measurements at 5-km altitude, is shown to be in excellent agreement with the buoy spectrum. Specifically, excellent agreement is found between the two nondirectional height spectra, and mean wave directions and directional spreads as functions of frequency. A comparison of the ROWS and SWOP spectra shows the two spectra to be very similar, in detailed shape as well as in terms of the gross spreading characteristics. Both spectra are seen to exhibit bimodal structures which accord with the Phillips' (1958) resonance mechanism. This observation is thus seen to support Phillips' contention that the SWOP modes were indeed resonance modes, not statistical artifacts.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 1005-101
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  • 6
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    Microwave radar oceanographic investigations (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Radar Ocean Wave Spectrometer (ROWS) technique was developed and demonstrated for measuring ocean wave directional spectra from air and space platforms. The measurement technique was well demonstrated with data collected in a number of flight experiments involving wave spectral comparisons with wave buoys and the Surface Contour Radar (SCR). Recent missions include the SIR-B underflight experiment (1984), FASINEX (1986), and LEWEX (1987). ROWS related activity is presently concentrating on using the aircraft instrument for wave-processes investigations and obtaining the necessary support (consensus) for a satellite instrument development program. Prospective platforms include EOS and the Canadian RADARSAT.
    Keywords: OCEANOGRAPHY
    Type: Laboratory for Oceans; p 149-152
    Format: application/pdf
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  • 7
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    The reflection of impulses from a nonlinear random sea (1979)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: A model of the reflection of radar impulses from the sea at near-vertical incidence is used to account for non-Gaussian ocean waves statistics. The joint probability density function (pdf), of wave height and slope, is calculated according to the theory of Longuet-Higgins (1963) on the distribution of variables in a 'weakly nonlinear' random era. The long-crested approximation is made, a Phillips wave spectrum is assumed, and the Gram-Charlier series is truncated after skewness terms. It is found that the height and height-slope skewness coefficients bear the ratio 1:2 and that the derived impulse response and conditional cross section versus wave height are in excellent agreement with previous observations. Finally, it is suggested that the empirically determined and theoretically predicted sea state bias be corrected for in the routine processing of satellite radar altimeter data.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research; 84; Aug. 20
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  • 8
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    Frequency dependence of electromagnetic bias in radar altimeter sea surface range measurements (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Range measurements made by satellite radar altimeters experience a bias toward the troughs of ocean waves. A series of aircraft flights during February-April 1989 measured this electromagnetic (EM) bias at three radar frequencies and the UV under a variety of wind and wave conditions, and provided the first airborne open-ocean measurements at the 13.6-GHz and 5.3-GHz operating frequencies of the NASA altimeter on the TOPEX/Poseidon satellite. The data suggest that the mean EM bias decreases linearly with increasing radar frequency between 5.3 and 36 GHz, according to the expression: EM bias (percent of significant wave height) = (3.0-0.0617 F)(1 +/-0.5), where F is in gigahertz. EM bias is fairly constant over a mesoscale region on a given day but can fluctuate significantly from one day to another. It shows a strong increase at all radar frequencies with increasing wind speed, although other sea state conditions, such as the wind direction relative to the wave direction, are also factors.
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 96; 20
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  • 9
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    Comment on 'Imaging radar observations of directional properties of ocean waves' by William McLeish and Duncan B. Ross (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: OCEANOGRAPHY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 90; 7367-737
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  • 10
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    Some case studies of ocean wave physical processes utilizing the GSFC airborne radar ocean wave spectrometer (1984)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The NASA K sub u band Radar Ocean Wave Spectrometer (ROWS) is an experimental prototype of a possible future satellite instrument for low data rate global waves measurements. The ROWS technique, which utilizes short pulse radar altimeters in a conical scan mode near vertical incidence to map the directional slope spectrum in wave number and azimuth, is briefly described. The potential of the technique is illustrated by some specific case studies of wave physical processes utilizing the aircraft ROWS data. These include: (1) an evaluation of numerical hindcast model performance in storm sea conditions, (2) a study of fetch limited wave growth, and (3) a study of the fully developed sea state. Results of these studies, which are briefly summarized, show how directional wave spectral observations from a mobile platform can contribute enormously to our understanding of wave physical processes.
    Keywords: OCEANOGRAPHY
    Type: NASA. Marshall Space Flight Center Frontiers of Remote Sensing of the Oceans and Troposphere from Air and Space Platforms; p 233-245
    Format: application/pdf
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