单词	D-layer
释义	D-layer /ˈdiːleɪə / noun The lowest layer of the ionosphere, able to reflect low-frequency radio waves.They will penetrate to the D-layer and increase the ionisation process and the electron density.... The ionospheric D-layer is a narrow bandwidth radar target often with a very small scattering cross section. Simply due to the height difference of the ‘responsible’ layer, troposcatter is useful up to distances of 700 Km, whereas D-layer is at best in the 600/1300 Km range. Origin 1930s: from an arbitrary use of the letter D.
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