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The part of the earth's outer atmosphere where free electrons, arising from ionization, are normally present in quantities sufficient to modify the propagation characteristics of radio waves traversing it.

Note: For purposes of reference, the ionosphere is divided into three regions whose boundaries are approximately spherical and concentric with the surface of the earth.

Reference: B.S.

Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)


Centre of buoyancy


International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM