デッカ空間波伝搬特性の解析と応用

概要

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At Hiroshima and Kagoshima, the measurements of field strength of Decca frequencies (mainly 71kHz and 85kHz) were carried out for 48 hours every month during 1972-73. The reason why is that the selection of both sites for studying geomagnetic effect depends upon the direction of propagation from transimitter. The study performed at the N-S path (Kagoshima) and the E-W path (Hiroshima). Since the variation of total field strength showed 8dB at Hiroshima and 2dB at Kagoshima in maximum, this difference might be due to the effect above. Moreover, the significant features of the variation pattern of total field strength were observed during sunrise transition, being decreased from the nocturnal mean strength about one hour before ground sunrise. Successively the marked minimum was occured at the time when the solar zenith angle about χ=98°was at the midpoint of path. It would be suggested that the skywave was much attenuated by the daytime ionosphere formed in the morning sunlight. Through the observation, this minimum occure regularly, despite of short propagation distance such as 300km. The diagram showing seasonal change in transition period of Decca system in western Japan was illustrated based on the two year's observation.
社団法人日本航海学会の論文
1974-07-31