Measurements and Characterizations of Air-to-Ground Channel Over Sea Surface at C-Band With Low Airborne Altitudes

This paper presents an experimental study of air-to-ground channels over sea surface at the C-band (5.7 GHz) with low airborne altitudes (0.37-1.83 km) through wideband channel measurements. In this paper, the multipath statistics and the propagation loss at different airborne altitudes are estimated and analyzed. It is observed that about 95% (86%) of the measured channel responses can be represented by the 3-ray (2-ray) multipath model. As the airborne altitude decreases, there is a higher probability for the appearance of multipath components. Moreover, it is found that the evaporation duct and elevated duct over the sea surface are the two important factors that can significantly affect the over-water air-to-ground communication link. These ducts can also decrease the rate of radio-wave attenuation, i.e., a decrease in path-loss exponent n in the log-distance path-loss models.