Measurement and Interpretation of North Atlantic Ocean Marine Radar Sea Scatter

Results are presented for experiments conducted with a noncoherent, high-resolution marine navigation radar aboard the NOAA ship Researcher in the North Atlantic Ocean. High-resolution radar backscatter data were collected under wind-wave equilibrium conditions, i.e., both fetch and time requirements for fully developed seas were satisfied for the wind speeds reported. Cumulative distributions of normalized radar cross section NRCS of the sea surface are calculated and found to follow two Weibull distributions. Based on their characteristics, the distributions may be ascribed to two different scattering mechanisms one due to scatterers evenly distributed over the surface, such as Bragg scatter one due to localized scattering features, such as wave crests. The percentage occurrence of the localized scattering events often called sea spikes behaves with wind speed in a manner much like that found for whitecaps. Other characteristics of the two distributions also appear to correlate with wind speed, with a weak dependence on air-sea surface temperature difference. For very low grazing angles, many of these characteristics vary sharply near the 2 deg. depression angle, which is a critical angle in several scattering models. An additional scattering model is proposed here to explain this behavior.