Microwave radio reflection from ground and water surfaces

Reflection of microwaves from ground and water surfaces for a number of wavelengths between 0.86 and 26.5 centimeters have been measured over paths of a few thousand feet and grazing angles of the reflected ray up to 5 degrees. Antennas with comparable patterns large enough to illuminate a large surface area were used. A variety of surface conditions including bare ground and smooth and choppy water were studied. For the particular overland path used, the ground appeared smooth at 26.5 and 9 centimeters wavelength, evidenced considerable roughness to 3.2 centimeters and appeared very rough to 0.86 centimeters. The mean reflection coefficient decreased with decreasing wavelength. For the overwater paths, the reflection for all wavelengths was that associated with a smooth surface when the conditions were calm. For a choppy surface, the millimeter signal showed large time variations and its apparent reflection coefficient decreased.