Evaporation duct effects on sea clutter

Existing sea clutter models are in general agreement on the trends and magnitudes of sea reflectivity at low (1°-10°) grazing angles. However, at extremely low grazing angles (<1°), models, theory, and measurements show considerable differences. The effects of the oceanic evaporation duct on grazing angle are investigated. Significant changes in grazing angle due to the evaporation duct are found and the illumination of the sea surface by the radar is shown to extend well beyond the standard (4/3 earth) radar horizon range. A series of sea clutter model comparisons shows that much of the difference between models can be attributed to evaporation duct effects