Definition of D layer in English:

D layer

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.