Upwind-Downwind Ratio of Radar Return Calculated from Facet Size Statistics of a Wind-Disturbed Water Surface

A wind tunnel with water as a lower surface has been used to obtain experimental data on the statistical distributions of facet size in relationship to wind velocity, facet slope, and flatness tolerance. Flatness tolerance is defined as one-tenth of the radar wavelength. Using the above experimental data, calculations are presented which, for the first time, relate the upwind-to-downwind ratio of radar return with radar beam depression angle for various wind velocities and radar wavelengths. Comparison with available sea-clutter measurements are made. It is concluded that the concept of facet size in relationship to flatness tolerance and slope distribution is useful for describing a rough surface from which radar waves are reflected.