Line of sight propagation or Space wave propagation:-
Explanation:- Space wave propagation of electromagnetic energy includes radiated energy that travels in the lower few miles of Earth’s atmosphere. Space waves include direct and ground – reflected waves. Direct waves travel essentially in a straight line between the transmit and receive antennas. Space wave propagation with direct waves is commonly called line-of sight (LOS) transmission. Therefore, direct space wave propagation is limited by the curvature of the Earth. Ground reflected waves are waves reflected by Earth’s surface as they propagate between the transmit and receive antennas.