Ten years ago, de Loor and co-workers at TNO, The Netherlands, were the
first to report bottom topography patterns in real aperture radar (RAR)
images of the southern North Sea. At that time, this was a real puzzle.
The skin depth of microwaves for sea water is only of the order of
centimeters while the sea bottom is about 20 meters below the surface.
Electromagnetic radiation therefore cannot probe the bottom directly.
Similar phenomena were found in radar imagery from SEASAT and SIR-AlB
synthetic aperture radars (SAR's) of Nantucket Shoals, the English
Channel and many other coastal areas. Since then theory and ocean field
experiments (Le., Phelps Bank, Georgia Straits, SARSEX, TOWARD, FASINEX,
etc.) have advanced our understanding considerably. We now know that
these surface signatures are the results of surface currents, perturbed
by the bottom topography, which refract the propagation and modulate the
energy of (short) surface waves so as to cause microwave backscatter
power variations. Hence, any large scale ocean features containing
nonuniform surface currents (i.e. internal waves, eddies, fronts, etc.)
will cause similar manifestations in the radar imagery by means of
current-wave-microwave interactions. Observations confirm this.