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2. Phase-Difference Radiotomography of the Ionosphere;Andreeva;Geomagn. Aeronom.,1992
3. Signal of long retardation;Appleton;Nature,1928
4. Asymptotic integration of ray equations in three-dimensional quasylayered environment;Baranov,1980
5. The Influence main ionospherc trough on distant propagation of HF radio wave;Beley,1987