NEC modeling to determine the effects on the fields radiated by a vertical
monopole when siting it near a salt-water coastline can be highly misleading
if the surface wave field is not considered.
For example, the plots linked below show that for average earth conductivity
the E-field at 5 degrees elevation is about 2.44 times greater in the
surface wave plot than in the far-field plot, at the same horizontal
distance from the radiator. Their difference is infinite in the horizontal
plane.
But if this radiator was sited 1 km from the ocean, then the fields at 1 km
shown in the surface wave plot would decay at nearly a 1/r rate as they
propagated further on that bearing, along and over the ocean surface.
This is a much different conclusion than reached when considering only the
NEC far-field analysis.
Comment/discussion is invited.
R. Fry
http://s24.postimg.org/6nchfpt1h/NEC_FF_vs_NF_Calcs.jpg
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