SYNTHETIC APERTURE RADAR DETECTION OF SURFACE SHIP WAKES 
James D. Lyden, David R. Lyzenga and Robert A. Shuchman 
Radar Science Laboratory 
Environmental Research Institute of Michigan (ERIM) 
Ann Arbor, MI 48107 
ABSTRACT 
Synthetic Aperture Radar (SAR) images of moving ships often exhibit 
characteristic patterns associated with various wake components. 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 detection is given. 
1. INTRODUCTION 
Ship wake patterns exhibiting a wide diversity of appearance have been 
noted on SAR images collected with various SAR systems under a broad range 
of environmental conditions. As a result of a careful examination of the 
available data and a cataloging of these observations, in addition to 
several recent theoretical analyses, it appears that the wake structures 
within the existing body of observational data can be classified into three 
general categories of phenomena including: (1) surface waves generated 
directly by the ship, (2) turbulent wakes or vortices containing relatively 
persistent but non-propagating currents, which are visible by SAR through 
the interaction of ambient waves with these surface currents, and 
(3) internal waves generated by the ship, which again are visible because 
of their interactions with short surface waves. 
Although these are all fairly well-known phenomena, there are large 
theoretical uncertainties as well as voids in the experimental data associ- 
ated with each of these categories. There are also a number of observa- 
tions which are difficult to categorize or which seem to fall on the 
boundaries between these categories. Therefore, a large amount of effort 
remains to verify and expand the conclusions stated in this paper. The 
following is intended as a framework for this continuing effort rather than 
as a summary of a completed effort. 
2. SHIP-GENERATED SURFACE WAVES 
This category of SAR-observed ship wakes consists of two subcategories. 
0ne includes the short (centimeter-scale) waves which are directly observed 
by SAR through the Bragg scattering mechanism. The second includes the 
longer (decameter-scale) waves which form the classical Kelvin wake system. 
Although there is considerable controversy about the former sub-category, 
there is evidence that many observed wakes fall within this classification 
and are explainable by the simple heuristic model discussed in the follow- 
ing paragraph. The second sub-category is relatively non-controversial and 
fairly well-understood, although there are still some unresolved issues 
regarding the SAR imaging of the long gravity waves which form the Kelvin 
wake system. This set of phenomena is also discussed below. 
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