Ultrawide-band radar observations of multipath propagation over the sea surface

An ultrawide-band radar system centered at 10 GHz has been developed for sea-scatter research and was recently deployed on a research pier in the North Atlantic. The radar is based on a time-domain reflectometer module for a sampling oscilloscope. Using transient excitation of a traveling wave-tube amplifier, the system generates 200-ps wide pulses with a 10-GHz center frequency and a peak power of approximately 1 KW. The resulting range resolution is approximately 3 cm. The system was used to investigate low-grazing angle, multipath effects in the ocean environment using a trihedral corner reflector, mounted 45 cm above the water surface. The ultrahigh-range resolution of the system allows spatial separation of the direct and indirect echoes from the trihedral. In addition, a comparison of the indirect vertically- (VV) and horizontally- (HH) polarized echoes illustrates the effects of Brewster angle damping. The implications of these effects for sea-clutter statistics are briefly discussed.