Abstract
This article describes the design and validation of deployable low-power probes and sensors to investigate the influence of the ionosphere and the Earth’s magnetic field on radio wave propagation below the plasma frequency of the ionosphere, known as Near Vertical Incidence Skywave (NVIS) propagation. The propagation of waves that are bent downward by the ionosphere is dominated by a bi-refractive mechanism called ‘magneto-ionic propagation’. The polarization of both downward waves depends on the spatial angle between the Earth’s magnetic field and the direction of propagation of the radio wave. The probes and sensors described in this article are needed to simultaneously investigate signal fading and polarization dynamics on six radio wave propagation paths. The 1-Watt probes realize a 57 dB signal-to-noise ratio. The probe polarization is controlled using direct digital synthesis and the cross-polarization is 25–35 dB. The intermodulation-free dynamic range of the sensor exceeds 100 dB. Measurement speed is 3000 samples/second. This publication covers design, practical realization and deployment issues. Research performed with these devices will be shared in subsequent publications.
Highlights
When a natural disaster occurs, relief work is severely hampered by telecommunication infrastructure damage
Precise measurements of the authors showed that the isolation of the characteristic waves in the ionosphere is at least 25–35 dB [25] and they described the ‘Happy Hour’ propagation phenomenon for the first time
Appleton and Builder showed that radio waves entering the ionosphere, under the influence of the Earth’s magnetic field, are split in two circularly polarized characteristic waves in opposite rotational directions, the ordinary and the extraordinary wave [8]
Summary
When a natural disaster occurs, relief work is severely hampered by telecommunication infrastructure damage. This is best illustrated with the landfall of Hurricane Katrina and the subsequent flooding of New Orleans in 2005 [1]. The roads into the disaster were flooded, which left the entire disaster zone, an area of 200 km × 200 km, without access and telecommunications. In such circumstances, as an alternative, Sensors 2019, 19, 2616; doi:10.3390/s19112616 www.mdpi.com/journal/sensors.
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