Broadband observations of propagation anomaly of VHF waves transmitted from oversea broadcasting stations

Takano, Toshiaki; Sakai, Kurt; Nagashima, I.; Nakata, Hiroyuki; Akaike, H.; Ujigawa, Satoshi; Higasa, Han; Shimakura, S.

doi:10.1109/aprasc.2004.1422486

Cited by 3 publications

(2 citation statements)

References 4 publications

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“…In the two cases presented here, it is seen that the distance between the transmitter and receiving station is beyond the LOS range but is less than 300 km and the signal were received only in horizontal polarization mode of the antenna. It is also noted from the reported results of many workers [Sakai et al 2003, Takano et al 2004] that mode of propagation of frequencies of wave length m > 4-6 m, is generally through ionospheric F layer or by sporadic E layer, but for m < 4 m as in the present case, the reflection through ionosphere is not expected. This aspect can be further substantiated on computing the maximum possible frequency (f max ) that can be reflected by the ionosphere in the context of signal transmitted by the Chukha transmitter.…”

Section: Possible Mode Of Propagation Of Over Horizon Signalsupporting

confidence: 70%

“…Therefore, except for some special situations, a VHF signal is not reflected by the ionosphere but escapes into the space. But ionospheric propagations of signals in the VHF range prior to an EQ are also possible as presented by many workers [Gokhberg et al 1984, Kushida and Kushida 2002, Sakai et al 2003, Takano et al 2004, Yasuda et al 2009, Moriya et al 2010.…”

Section: Introductionmentioning

confidence: 99%

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Orographic role in anomalous VHF propagation on the background of impending earthquakes (EQ)

Devi

Medhi

Barbara

et al. 2015

Annals of Geophysics

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<p>The role of orographic factors in modifying atmospheric dynamics on the background of an impending earthquake (EQ) that might lead to propagation of a signal beyond the Line Of Sight (LOS) is examined in the paper. The analysis is based on the data of anomalous reception of VHF FM-signal at Gauhati University (GU, 26.15°N, 91.66°E), a station located in the sub Himalayan terrain. The signal reception records show that their anomalous appearance are associated closely with earthquake events of M >5.0, a phenomenon identified as EQ precursor. To identify sources of such reception, the paper presents some analytical approaches involving the terrain factors, impending EQ and atmospheric variabilities. Finally, the contribution of location/topography of the transmitter, receiver and epicenter in modifying the EQ induced atmospheric factors, is brought in to the ambit of analysis for explaining the observed over horizon VHF signal propagation. A special reference is made on the EQ time drop in temperature, increase in humidity and hence modification in Radio Refractive Index (RRI) gradient, in favoring such reception. A model in support of the observation on EQ time lithosphere-atmosphere coupling relevant to widening of radio horizon limit is also proposed.</p>

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Section: Possible Mode Of Propagation Of Over Horizon Signalsupporting

confidence: 70%