Characteristics of the Doppler frequency shift of NWC (22.3kHz) signals observed by Jikiken (EXOS-B) satellite are described. Among 46 experimental passes of the spacecraft, the NWC signals were detected on 26 passes. From the characteristics of the detected Doppler shift, it was found that in three passes the signals had reached the spacecraft via nonducted propagation in the geomagnetic meridian planes; in five passes, the signals had propagated in ionozation ducts; and in six passes the signals had propagated in the offmeridian nonducted mode. The last case took place when the spacecraft was located in the dusk region, where a longitudinal electron density gradient was present, probably causing this type of propagation. This interpretation was confirmed by three dimensional ray tracing.
JIKIKEN (EXOS-B) による NWC 局 VLF 信号のドップラーシフトの測定
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