No abstract

No abstract

Recent observations of microwave backscatter from breaking gravity waves indicate that the cross-polarized signals (HV and VH) are much larger than expected from thcoretical predictions derived using perturbative imethods. Experiments have been conducted to specifically exalmine the depolarization effects of scattering from breaking waves which give rise to such large cross-polarized signals. A simple model is constructed to provide the scattering mechanism which can explain the scattering results.

Grant # N00014-00-1-0075 http://nt-waves.apl.washington.edu LONG-TERM GOALS Our long-range objective is to detect and understand sea surface signatures produced by a variety of natural and man-made causes. SCIENTIFIC OBJECTIVES The scientific objectives of this research are to investigate the generation and propagation of bound waves and turbulent breaking regions and to understand their role in microwave backscatter from the ocean. Bound waves and turbulent breaking regions are types of small-scale surface roughness that are carried along by longer waves. They are distinct from the much-studied short wind waves that produce most microwave backscatter from the ocean but propagate at their intrinsic phase speed, which is significantly slower than the speed of longer waves. APPROACH Our approach is to carry out field and laboratory measurements combined with modeling to attempt to define the origin and characteristics of bound waves and turbulent breaking regions and to determine their effect on microwave backscatter from wind-roughened water surfaces. Comparison of microwave and infrared measurements is also carried out in order to determine the relationship between bound waves and microscale breaking as defined by IR detection of skin layer disruption. WORK COMPLETED The first of our field experiments was carried out on the CIRPAS Twin Otter airplane during ONR's Shoaling Waves Experiment in November 1999. Some results from that experiment were shown in last year's report. The second experiment was carried out on FLIP in September and October 2000. It consisted of simultaneously observing the same sea surface spot with low-incidence-angle IR and high-incidence-angle microwaves to determine the relationship between bound waves and microscale breaking. An initial survey of the data collected has now been carried out and indicate that the data will probably be sufficient to meet our objectives. We have also spent considerable time this year analyzing laboratory data collected in 1996 in the wind wave tank at the Canada Centre for Inland Waters. These data have yielded definitive information on 1

No abstract