Very low grazing angle radar backscatter from the ocean surface

A very low grazing angle (<0.2 degrees ) sea clutter measurements program was conducted with the L- and S-band TRADEX and C-band ALCOR radars on Roi Namur, Marshall Islands. Clutter returns were observed to the maximum measurement range of 60 km. L-band data could be explained by diffraction over a spherical Earth, but at the higher frequencies ducting was in clear evidence. The average high-amplitude return, associated with sea spikes, persisted on the order of 3 s. The probability density function followed a lognormal, rather than Weibull, distribution. The fact that coherent spectral analyses could be made to a 60 km range, well beyond the horizon, supports a coherent duct model.<>