The line of sight is the line that connectsthe observer with the observed object. This expression is often used withmeasurements of Doppler velocity and magnetic field in magnetograms, whereonly the c
omponent of the vector field directed along the line of sight ismeasured.
Line-of-sight propagation refers to electromagnetic radiation or electromagnetic waves travelling in a straight line. The rays or waves are deviated or reflected by obstructions and cannot travel over
the horizon or behind obstacles. Beyond that, material disperses the rays respectively the energy of the waves.