Richard Clark wrote:
"The legendary characteristic of Sea Water is found in its far field
reflective characteristic which is remarkable due largely to its huge
SWR to fields---."

Yes, a wave striking the sea finds a high reflection coefficient and
ground waves do well too.

I am looking at a broadcast allocation book prepared by Cleveland
Institute of Radio Electronics in 1959. Many changes in stations and
coverage since then, but the book contains an estimated ground
conductivity map for the U.S.A. which probably has changed very little
since then.

Coastal Texas is almost as good as it gets when it comes to soil on the
map, 30 millimhos per meter. Seawater is not shown on the map but its
conductivity is given as 5,000 millimhos per meter or 167 times as good
as the best soil. Around New York City, conductivity is shown between
0.5 and 4 millimhos. Surface irregularities caused by structures make
additional attenuation.

The conductivities shown on the map are probably good averages as the
preparers had the propagation data of thousands of broadcast stations
which proved their performance to the FCC to work with.

Terman has a ground constant table on page 808 of his 1955 of his 1955
edition. Sea water is given a conductivity of 45,000 micromhos per cm,
or 45 millimhos per cm.

John Cunningham says in "The Complete Broadcast Antenna Handbook: on
page 309 that:
"The conductivity of the earth ranges from about 2 millimhos per meter
for dry sandy locations to as high as 5 mhos/m for sea water."

I think the figures given above are in reasonable agreement. I haven`t
researched the conductivity of carbon, but it is reasonably high being
used for motor brushes, battery electrodes, and vacuum tube plates.

Best regards, Richard Harrison, KB5WZI