1998 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

IEEE Transactions on Antennas and Propagation
Volume 46 Number 1, January 1998

Directional Characteristics of Sea-Wave Scattering Observed at Low-Grazing Angles

Page 41.

Abstract:

The mathematical and statistical description of waves on the sea surface has evolved over more than two centuries starting with Laplace (1776), Gerstner (1802), Airy (1845), Stokes (1847), Kelvin (1887), and Helmholtz (1888). Most of the major developments in this century are summarized by Apel [1] who has derived an improved model for the ocean surface wave vector spectrum of equilibrium sea states. Part of the motivation for this paper is Apel's observation that "\ldots in spite of the incorporation of an anisotropic angular distribution of wave energy, the observed azimuthal variation of radar scatter is not captured \ldots" The data set analysis summarized in this paper show that wave group processes are responsible for directionally organized sea surface radar back scattering patterns, which are long lived and consequently extend over large areas. This includes crosswind traveling wave systems. A property of wave group process structure is the steepening of waves as they pass through the center of the group. The mid-group sharpening of the waves, which can include crest spilling or breaking, significantly increases the radar scattering cross section observable with low-grazing-angle radars, usually most noticeable with horizontal (HH) polarization. Therefore, low grazing angle (LGA) radar provides a vastly improved means of seeing wavegroup phenomena over conventional oceanographic methods.

References

1. J. R. Apel, "An improved model of the ocean surface wave spectrum and its effects on radar backscatter," J. Geophys. Res., vol. 99, no. C8, pp. 16269-16291, Aug. 1994.
2. R. Manasse, "Pencil beam radar selectivity of ocean wave spectra," Lawrence Livermore Nat. Lab. Tech. Rep. UCRL-ID-118533, Aug. 1994.
3. B. O. Werle, "Sea backscatter spikes and wave group observations at low grazing angles," in Proc. IEEE Int. Radar Conf., Alexandria, VA, May 1995, pp. 187-194.
4. M. A. Sletten, D. B. Trizna, and J. P. Hansen, "Ultrawide-band radar observations of multipath propagation over the sea surface" IEEE Trans. Antennas Propagat., vol. 44, pp. 646-651, May 1996.
5. P. H. Y. Lee, J. D. Barter, K. L. Beach, C. L. Hindman, B. M. Lake, H. Rungaldier, J. C. Shelton, A. B. Williams, R. Yee, and H. C. Yuen, "X-band microwave backscatter from ocean waves," J. Geophys. Res., vol. 100, no. C2, pp. 2591-2611, Feb. 1995.
6. S. J. Frasier, Y. Liu, D. Moller, R. E. McIntosh and C. Long, "Directional ocean wave measurements in a coastal setting using a focused array imaging radar," IEEE Trans. Geosci. Remote Sensing, vol. 33, pp. 428-440, Mar. 1995.
7. K. D. Ward, "Low grazing angle radar measurements of ship generated internal waves in Scotland 1989-1991," Malvern, Worc., U.K., Defense Res. Agency, Memo. 4589, Mar. 1992.
8. S. K. Lehman, B. Johnston, R. Twogood, M. Wieting, T. Yorkey, H. Robey, D. Whelan, and R. Nagele, "Selected results from LLNL-Hughes RAR for west coast Scotland experiment 1991," UCRL-ID-112755, Lawrence Livermore Nat. Lab., Livermore, CA, Jan. 1993.
9. --, "Selected results from LLNL-Hughes RAR for west coast Scotland experiment 1992," UCRL-ID-112756, Lawrence Livermore Nat. Lab., Livermore, CA, Jan. 1993.
10. S. K. Lehman, C. J. Mullenhoff, H. E. Jones, G. Berry, M. J. Newman, T. Lamont-Smith, P. Hirst, and K. Ward, "Radar imagery from the 1994 Loch Linnhe trials," UCRL-ID-119071, Lawrence Livermore Nat. Lab., Livermore, CA, Oct. 1994.
11. M. P. Tulin, "Breaking of ocean waves and downshifting," in Waves and Nonlinear Processes in Hydrodynamics, J. Grue, B. Gjevik, and J. E. Weber, Eds.Norwell, MA: Kluwer, 1996, pp. 177-190.
12. D. E. Barrick, J. M. Headrick, R. W. Bogle, and D. D. Crombie, "Sea backscatter at HF: Interpretation and utilization of the echo," Proc. IEEE, vol. 62, pp. 673-680, June 1974.
13. S. R. Shurman, "Radar characterization of ship wake signatures and ambient ocean clutter features," in Proc. IEEE Nat. Radar Conf., Dallas, TX, Mar. 1989, pp. 182-187.
14. A. V. Ivanov and V. E. Gershenzon, "Sea surface investigation with a stationary pulse doppler radar," R&D Ctr. SCAN, Moscow, Russia, 1993.
15. M. J. Smith, E. M. Poulter, and J. A. McGregor, "Doppler radar measurements of wave groups and breaking waves," J. Geophys. Res., vol. 101, no. C6, pp. 14269-14282, Jun. 1996.
16. T. Lamont-Smith, "The estimation of ocean current from w-k analysis of radar data," Int. Geosci. Remote Sensing Symp. Conf. Record, Lincoln, NE, May 1996, vol. 3, pp. 1724-1744.
17. J. Fuchs, M. P. Tulin, S. Welch, and T. Waseda, "Inside the sea-spike: Low grazing angle radar imaging of laboratory waves repeatedly breaking in wave groups," in Int. Geosci. Remote Sensing Symp. Conf. Record, Singapore, Aug. 1997, pp. 714-718.
18. M. W. Long, Radar Reflectivity of Land and Sea, 2nd ed.Norwood, MA: Artech, 1983.