Synthetic aperture radar (SAR) images of moving ships often exhibit characteristic patterns associated with various wake phenomena. These features can be classified into three general categories which include (1) surface waves generated by the ship, (2) turbulent or vortex wakes, and (3) internal waves. In this paper an overview of the present status of SAR ship wake imaging is presented.

Synthetic aperture radar (SAR) images collected over the Arctic marginal ice zone show gravity wave patterns in both the open water and the ice. Diffuse wave patterns are visible in the water at near range (small incidence angles), while more distinct wave patterns are visible in the ice across the entire swath. The wave patterns in the ice appear as bright lines rather than sinusoidal intensity variations. Additionally, the images show a periodic displacement of the ice/water boundary, apparently due to Doppler shift effects associated with the gravity wave orbital motions. These observations are interpreted as evidence for the velocity bunching effect and also illustrate the effects of random Scatterer motions in the open water.

During the SAXON-FPN exueriment reduct7on of the normaIized r d a r cross in Nov. 1990 the section (NRCS) by two monomolecular surface films floating on the sea surface was measured by radars operating at different frequencies. The radars included the 5-frequency scatterometer (L-? S-, C-, Xand Ku-band) of the University of Hamburg flown on a BO 105 helicopter, the L-, Cand X-band SAR system flown on the US NADC P3 aircraft and the Cband SAR flown on the DO 228 aircraft of the DLR, Germany. It is shown that the reduction of the NRCS exhibits a charateristic deuendence on Bragg wavenumber, which can be explained 6y Marangoni ;&e theory. Based on the preliminary results of this investigation we conjecture that it is possible to measure visco-elastic properties of surface films by multi-frequency radars. As a consequence, it should be feasible to'discriminate between mineral oil films and natural surface films floating on the sea surface by using multi-frequency radars provided that the visco-elastic characteristics of the natural slicks are sufficiently different from known characteristics of mineral oil films.

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