Sea-Surface Backscattering and the Soliton Mechanism
Abstract
Sonar and radar measurements both indicate that there are fundamental problems with the present wind-wave models of the sea surface at higher wavenumbers; i.e., backscattering strengths at high frequencies and small grazing angles are much greater than predicted and the Doppler spectra show no evidence of the dispersion expected in the gravity-capillary regime. Quasi-linear wave theories do not account for these effects. Laboratory wind-wave flume measurements also support this conclusion. Photographs reveal that wavefronts of ripples tend to steepen with increasing fetch. Spectra of wave-gauge data also show a corresponding growth of coherent harmonics. Nonlinear amplitude effects can account for the non-dispersive behavior of waves in this regime. With further increase in fetch, the wave-gauge data also show the growth of subharmonics followed by rapid degeneration to a continuous spectrum. This suggests that a second mechanism is involved in sea-state development; namely, chaotic behavior arising from surface-instability and wave-wind interaction. The proposed program could have far-reaching implications. The primary goal is to predict sonar and radar scattering phenomena in total detail from knowledge of surface-wave statistics; however, the study reveals a potential "chaotic" mechanism for wave generation that could be crucial to developing a more comprehensive predictive model of sea-state development.
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 21, 1986
- Accession Number
- ADA637906
Entities
People
- D. Middleton
- J. W. Fitzgerald
- R. H. Mellen