Airborne Measurements of the Wavenumber Spectra of Ocean Surface Waves. Part II: Directional Distribution*

An airborne scanning lidar system acquires three-dimensional (3D) spatial topography of ocean surface waves. From the spatial data, wavenumber spectra are computed directly. The spectral properties in terms of the spectral slope and dimensionless spectral coefficient have been verified to be in very good agreement with existing data. One of the unique features of the 3D spatial data is its exceptional directional resolution. Directional properties such as the wavenumber dependence of the directional spreading function and the evolution of bimodal development are investigated with these high-resolution, phase-resolving spatial measurements. Equations for the spreading parameters, the lobe angle, and the lobe ratio are established from the airborne scanning lidar datasets. Fourier decomposition of the measured directional distribution is presented. The directional parameters can be represented by a small number (4) of the Fourier components. The measured directional distributions are compared with numerical experiments of nonlinear wave simulations to explore the functional form of the dissipation source term.

[1]  Kevin Ewans,et al.  Observations of the Directional Spectrum of Fetch-Limited Waves , 1998 .

[2]  Joseph Chase,et al.  The Directional Spectrum of a Wind Generated sea as Determined From Data Obtained by the Stereo Wave Observation Project , 2015 .

[3]  I. Young,et al.  A review of the central role of nonlinear interactions in wind—wave evolution , 1993, Philosophical Transactions of the Royal Society of London. Series A: Physical and Engineering Sciences.

[4]  Kenneth C. Jezek,et al.  Greenland ice sheet thickness changes measured by laser altimetry , 1994 .

[5]  Lucy R. Wyatt.  The Effect of Fetch on the Directional Spectrum of Celtic Sea Storm Waves , 1995 .

[6]  M. Donelan,et al.  Directional spectra of wind-generated ocean waves , 1985, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[7]  Harald E. Krogstad,et al.  Maximum Entropy Estimation of the Directional Distribution in Ocean Wave Spectra , 1986 .

[8]  L. H. Holthuijsen,et al.  Observations of the Directional Distribution of Ocean-Wave Energy in Fetch-Limited Conditions , 1983 .

[9]  Fukuzo Tasai,et al.  Observations of the Directional Spectrum of Ocean WavesUsing a Cloverleaf Buoy , 1975 .

[10]  C. Peng,et al.  A comparison of in situ and airborne radar observations of ocean wave directionality , 1985 .

[11]  Robert N. Swift,et al.  Airborne Measurements of the Wavenumber Spectra of Ocean Surface Waves. Part I: Spectral Slope and Dimensionless Spectral Coefficient* , 2000 .

[12]  J. Ewing,et al.  Directional Wave Spectra Observed during JONSWAP 1973 , 1980 .

[13]  M. Banner,et al.  Modeling Spectral Dissipation in the Evolution of Wind Waves. Part I: Assessment of Existing Model Performance , 1994 .

[14]  Joan Oltman-Shay,et al.  A Data-Adaptive Ocean Wave Directional-Spectrum Estimator for Pitch and Roll Type Measurements , 1984 .

[15]  M. Banner.  Equilibrium Spectra of Wind Waves , 1990 .

[16]  Robert N. Swift,et al.  Accuracy of airborne laser altimetry over the Greenland ice sheet , 1995 .

[17]  M. Banner,et al.  A note on the bimodal directional spreading of fetch‐limited wind waves , 1995 .

[18]  I. Young,et al.  On the measurement of directional wave spectra , 1994 .

[19]  W. Krabill,et al.  Airborne remote sensing applications to coastal wave research , 1998 .

[20]  K. Hasselmann,et al.  On the Existence of a Fully Developed Wind-Sea Spectrum , 1984 .