How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus soil?
Why The far field of a vertical depends on ground reflection out to many wavelengths from the antenna. Seawater is a very good conductor, so it reflects the wave nearly perfectly and the direct and reflected waves add in phase at low takeoff angles; ordinary soil is lossy and absorbs much of the energy striking it at grazing angles. The result is that a vertical over saltwater shows noticeably stronger low-angle radiation, which is why shoreline and shipboard verticals are prized for DX.
Watch out The choices about extra lobes or lobes merging describe what happens when you change antenna height or stack elements in wavelengths, not what changes when you swap the ground constants under a vertical.
Saltwater is the world's best ground screen: verticals on the beach get a low-angle DX boost.